- isa<>: -
- The isa<> operator works exactly like the Java
+
The isa<> operator works exactly like the Java "instanceof" operator. It returns true or false depending on whether a reference or pointer points to an instance of the specified class. This can - be very useful for constraint checking of various sorts (example below).
- cast<>: -
- The cast<> operator is a "checked cast" operation. It
- converts a pointer or reference from a base class to a derived cast, causing
+
The cast<> operator is a "checked cast" operation. It + converts a pointer or reference from a base class to a derived class, causing an assertion failure if it is not really an instance of the right type. This should be used in cases where you have some information that makes you believe that something is of the right type. An example of the isa<> - and cast<> template is: + and cast<> template is:
-- static bool isLoopInvariant(const Value *V, const Loop *L) { - if (isa<Constant>(V) || isa<Argument>(V) || isa<GlobalValue>(V)) - return true; +
++static bool isLoopInvariant(const Value *V, const Loop *L) { + if (isa<Constant>(V) || isa<Argument>(V) || isa<GlobalValue>(V)) + return true; - // Otherwise, it must be an instruction... + // Otherwise, it must be an instruction... return !L->contains(cast<Instruction>(V)->getParent()); -
+} + +Note that you should not use an isa<> test followed by a cast<>, for that use the dyn_cast<> @@ -303,57 +358,51 @@ file (note that you very rarely have to include this file directly).
- dyn_cast<>: -
- The dyn_cast<> operator is a "checking cast" operation. It
- checks to see if the operand is of the specified type, and if so, returns a
+
The dyn_cast<> operator is a "checking cast" operation. + It checks to see if the operand is of the specified type, and if so, returns a pointer to it (this operator does not work with references). If the operand is not of the correct type, a null pointer is returned. Thus, this works very - much like the dynamic_cast operator in C++, and should be used in the - same circumstances. Typically, the dyn_cast<> operator is used - in an if statement or some other flow control statement like this: - -
- if (AllocationInst *AI = dyn_cast<AllocationInst>(Val)) { - ... - } -
+ much like the dynamic_cast<> operator in C++, and should be + used in the same circumstances. Typically, the dyn_cast<> + operator is used in an if statement or some other flow control + statement like this: + ++-+if (AllocationInst *AI = dyn_cast<AllocationInst>(Val)) { + // ... +} +
+This form of the if statement effectively combines together a - call to isa<> and a call to cast<> into one - statement, which is very convenient.
+This form of the if statement effectively combines together a call + to isa<> and a call to cast<> into one + statement, which is very convenient.
-Another common example is:
+Note that the dyn_cast<> operator, like C++'s + dynamic_cast<> or Java's instanceof operator, can be + abused. In particular, you should not use big chained if/then/else + blocks to check for lots of different variants of classes. If you find + yourself wanting to do this, it is much cleaner and more efficient to use the + InstVisitor class to dispatch over the instruction type directly.
-- // Loop over all of the phi nodes in a basic block - BasicBlock::iterator BBI = BB->begin(); - for (; PHINode *PN = dyn_cast<PHINode>(BBI); ++BBI) - std::cerr << *PN; -
- -Note that the dyn_cast<> operator, like C++'s - dynamic_cast or Java's instanceof operator, can be abused. - In particular you should not use big chained if/then/else blocks to - check for lots of different variants of classes. If you find yourself - wanting to do this, it is much cleaner and more efficient to use the - InstVisitor class to dispatch over the instruction type directly.
- -
- - cast_or_null<>: - -
- The cast_or_null<> operator works just like the - cast<> operator, except that it allows for a null pointer as - an argument (which it then propagates). This can sometimes be useful, - allowing you to combine several null checks into one. +
- cast_or_null<>: + +
The cast_or_null<> operator works just like the + cast<> operator, except that it allows for a null pointer as an + argument (which it then propagates). This can sometimes be useful, allowing + you to combine several null checks into one.
- - dyn_cast_or_null<>: +
- dyn_cast_or_null<>: -
- The dyn_cast_or_null<> operator works just like the - dyn_cast<> operator, except that it allows for a null pointer - as an argument (which it then propagates). This can sometimes be useful, - allowing you to combine several null checks into one. +
The dyn_cast_or_null<> operator works just like the + dyn_cast<> operator, except that it allows for a null pointer + as an argument (which it then propagates). This can sometimes be useful, + allowing you to combine several null checks into one.
-
These five templates can be used with any classes, whether they have a v-table or not. To add support for these templates, you simply need to add @@ -365,31 +414,42 @@ are lots of examples in the LLVM source base.
Often when working on your pass you will put a bunch of debugging printouts and other code into your pass. After you get it working, you want to remove -it... but you may need it again in the future (to work out new bugs that you run +it, but you may need it again in the future (to work out new bugs that you run across).
Naturally, because of this, you don't want to delete the debug printouts, but you don't want them to always be noisy. A standard compromise is to comment them out, allowing you to enable them if you need them in the future.
-The "Support/Debug.h" +
The "llvm/Support/Debug.h" file provides a macro named DEBUG() that is a much nicer solution to this problem. Basically, you can put arbitrary code into the argument of the DEBUG macro, and it is only executed if 'opt' (or any other tool) is run with the '-debug' command line argument:
-...+
DEBUG(std::cerr << "I am here!\n");
...
+DOUT << "I am here!\n"; ++
Then you can run your pass like this:
-$ opt < a.bc > /dev/null -mypass+
<no output>
$ opt < a.bc > /dev/null -mypass -debug
I am here!
$
+$ opt < a.bc > /dev/null -mypass +<no output> +$ opt < a.bc > /dev/null -mypass -debug +I am here! ++
Using the DEBUG() macro instead of a home-brewed solution allows you to not have to create "yet another" command line option for the debug output for @@ -407,7 +467,7 @@ program hasn't been started yet, you can always just run it with
...+
DEBUG(std::cerr << "No debug type\n");
#undef DEBUG_TYPE
#define DEBUG_TYPE "foo"
DEBUG(std::cerr << "'foo' debug type\n");
#undef DEBUG_TYPE
#define DEBUG_TYPE "bar"
DEBUG(std::cerr << "'bar' debug type\n");
#undef DEBUG_TYPE
#define DEBUG_TYPE ""
DEBUG(std::cerr << "No debug type (2)\n");
...
+DOUT << "No debug type\n"; +#undef DEBUG_TYPE +#define DEBUG_TYPE "foo" +DOUT << "'foo' debug type\n"; +#undef DEBUG_TYPE +#define DEBUG_TYPE "bar" +DOUT << "'bar' debug type\n"; +#undef DEBUG_TYPE +#define DEBUG_TYPE "" +DOUT << "No debug type (2)\n"; ++
Then you can run your pass like this:
-$ opt < a.bc > /dev/null -mypass+
<no output>
$ opt < a.bc > /dev/null -mypass -debug
No debug type
'foo' debug type
'bar' debug type
No debug type (2)
$ opt < a.bc > /dev/null -mypass -debug-only=foo
'foo' debug type
$ opt < a.bc > /dev/null -mypass -debug-only=bar
'bar' debug type
$
+$ opt < a.bc > /dev/null -mypass +<no output> +$ opt < a.bc > /dev/null -mypass -debug +No debug type +'foo' debug type +'bar' debug type +No debug type (2) +$ opt < a.bc > /dev/null -mypass -debug-only=foo +'foo' debug type +$ opt < a.bc > /dev/null -mypass -debug-only=bar +'bar' debug type ++
Of course, in practice, you should only set DEBUG_TYPE at the top of a file, to specify the debug type for the entire module (if you do this before -you #include "Support/Debug.h", you don't have to insert the ugly +you #include "llvm/Support/Debug.h", you don't have to insert the ugly #undef's). Also, you should use names more meaningful than "foo" and "bar", because there is no system in place to ensure that names do not conflict. If two different modules use the same string, they will all be turned @@ -439,15 +526,15 @@ even if the source lives in multiple files.
The "Support/Statistic.h" file -provides a template named Statistic that is used as a unified way to +href="/doxygen/Statistic_8h-source.html">llvm/ADT/Statistic.h" file +provides a class named Statistic that is used as a unified way to keep track of what the LLVM compiler is doing and how effective various optimizations are. It is useful to see what optimizations are contributing to making a particular program run faster.
@@ -455,7 +542,7 @@ making a particular program run faster.Often you may run your pass on some big program, and you're interested to see how many times it makes a certain transformation. Although you can do this with hand inspection, or some ad-hoc method, this is a real pain and not very useful -for big programs. Using the Statistic template makes it very easy to +for big programs. Using the Statistic class makes it very easy to keep track of this information, and the calculated information is presented in a uniform manner with the rest of the passes being executed.
@@ -463,27 +550,73 @@ uniform manner with the rest of the passes being executed. it are as follows:-
-
- Define your statistic like this:
-
static Statistic<> NumXForms("mypassname", "The # of times I did stuff");+ Define your statistic like this:
+ ++-+#define DEBUG_TYPE "mypassname" // This goes before any #includes. +STATISTIC(NumXForms, "The # of times I did stuff"); +
+The Statistic template can emulate just about any data-type, - but if you do not specify a template argument, it defaults to acting like - an unsigned int counter (this is usually what you want).
+ Whenever you make a transformation, bump the counter:
+ ++-+++NumXForms; // I did stuff! +
+- Whenever you make a transformation, bump the counter:
-
++NumXForms; // I did stuff
The STATISTIC macro defines a static variable, whose name is + specified by the first argument. The pass name is taken from the DEBUG_TYPE + macro, and the description is taken from the second argument. The variable + defined ("NumXForms" in this case) acts like an unsigned integer.
+ +That's all you have to do. To get 'opt' to print out the statistics gathered, use the '-stats' option:
-$ opt -stats -mypassname < program.bc > /dev/null+
... statistic output ...
+$ opt -stats -mypassname < program.bc > /dev/null +... statistics output ... ++
When running gccas on a C file from the SPEC benchmark +
When running opt on a C file from the SPEC benchmark suite, it gives a report that looks like this:
-7646 bytecodewriter - Number of normal instructions+
725 bytecodewriter - Number of oversized instructions
129996 bytecodewriter - Number of bytecode bytes written
2817 raise - Number of insts DCEd or constprop'd
3213 raise - Number of cast-of-self removed
5046 raise - Number of expression trees converted
75 raise - Number of other getelementptr's formed
138 raise - Number of load/store peepholes
42 deadtypeelim - Number of unused typenames removed from symtab
392 funcresolve - Number of varargs functions resolved
27 globaldce - Number of global variables removed
2 adce - Number of basic blocks removed
134 cee - Number of branches revectored
49 cee - Number of setcc instruction eliminated
532 gcse - Number of loads removed
2919 gcse - Number of instructions removed
86 indvars - Number of canonical indvars added
87 indvars - Number of aux indvars removed
25 instcombine - Number of dead inst eliminate
434 instcombine - Number of insts combined
248 licm - Number of load insts hoisted
1298 licm - Number of insts hoisted to a loop pre-header
3 licm - Number of insts hoisted to multiple loop preds (bad, no loop pre-header)
75 mem2reg - Number of alloca's promoted
1444 cfgsimplify - Number of blocks simplified
+ 7646 bitcodewriter - Number of normal instructions + 725 bitcodewriter - Number of oversized instructions + 129996 bitcodewriter - Number of bitcode bytes written + 2817 raise - Number of insts DCEd or constprop'd + 3213 raise - Number of cast-of-self removed + 5046 raise - Number of expression trees converted + 75 raise - Number of other getelementptr's formed + 138 raise - Number of load/store peepholes + 42 deadtypeelim - Number of unused typenames removed from symtab + 392 funcresolve - Number of varargs functions resolved + 27 globaldce - Number of global variables removed + 2 adce - Number of basic blocks removed + 134 cee - Number of branches revectored + 49 cee - Number of setcc instruction eliminated + 532 gcse - Number of loads removed + 2919 gcse - Number of instructions removed + 86 indvars - Number of canonical indvars added + 87 indvars - Number of aux indvars removed + 25 instcombine - Number of dead inst eliminate + 434 instcombine - Number of insts combined + 248 licm - Number of load insts hoisted + 1298 licm - Number of insts hoisted to a loop pre-header + 3 licm - Number of insts hoisted to multiple loop preds (bad, no loop pre-header) + 75 mem2reg - Number of alloca's promoted + 1444 cfgsimplify - Number of blocks simplified ++
Obviously, with so many optimizations, having a unified framework for this stuff is very nice. Making your pass fit well into the framework makes it more @@ -491,471 +624,2135 @@ maintainable and useful.
Several of the important data structures in LLVM are graphs: for example +CFGs made out of LLVM BasicBlocks, CFGs made out of +LLVM MachineBasicBlocks, and +Instruction Selection +DAGs. In many cases, while debugging various parts of the compiler, it is +nice to instantly visualize these graphs.
+ +LLVM provides several callbacks that are available in a debug build to do +exactly that. If you call the Function::viewCFG() method, for example, +the current LLVM tool will pop up a window containing the CFG for the function +where each basic block is a node in the graph, and each node contains the +instructions in the block. Similarly, there also exists +Function::viewCFGOnly() (does not include the instructions), the +MachineFunction::viewCFG() and MachineFunction::viewCFGOnly(), +and the SelectionDAG::viewGraph() methods. Within GDB, for example, +you can usually use something like call DAG.viewGraph() to pop +up a window. Alternatively, you can sprinkle calls to these functions in your +code in places you want to debug.
+ +Getting this to work requires a small amount of configuration. On Unix +systems with X11, install the graphviz +toolkit, and make sure 'dot' and 'gv' are in your path. If you are running on +Mac OS/X, download and install the Mac OS/X Graphviz program, and add +/Applications/Graphviz.app/Contents/MacOS/ (or wherever you install +it) to your path. Once in your system and path are set up, rerun the LLVM +configure script and rebuild LLVM to enable this functionality.
+ +SelectionDAG has been extended to make it easier to locate +interesting nodes in large complex graphs. From gdb, if you +call DAG.setGraphColor(node, "color"), then the +next call DAG.viewGraph() would highlight the node in the +specified color (choices of colors can be found at colors.) More +complex node attributes can be provided with call +DAG.setGraphAttrs(node, "attributes") (choices can be +found at Graph +Attributes.) If you want to restart and clear all the current graph +attributes, then you can call DAG.clearGraphAttrs().
+ +This section describes how to perform some very simple transformations of -LLVM code. This is meant to give examples of common idioms used, showing the -practical side of LLVM transformations.
Because this is a "how-to" section, -you should also read about the main classes that you will be working with. The -Core LLVM Class Hierarchy Reference contains details -and descriptions of the main classes that you should know about.
+LLVM has a plethora of data structures in the llvm/ADT/ directory, + and we commonly use STL data structures. This section describes the trade-offs + you should consider when you pick one.
+ ++The first step is a choose your own adventure: do you want a sequential +container, a set-like container, or a map-like container? The most important +thing when choosing a container is the algorithmic properties of how you plan to +access the container. Based on that, you should use:
+ +-
+
- a map-like container if you need efficient look-up + of an value based on another value. Map-like containers also support + efficient queries for containment (whether a key is in the map). Map-like + containers generally do not support efficient reverse mapping (values to + keys). If you need that, use two maps. Some map-like containers also + support efficient iteration through the keys in sorted order. Map-like + containers are the most expensive sort, only use them if you need one of + these capabilities. + +
- a set-like container if you need to put a bunch of + stuff into a container that automatically eliminates duplicates. Some + set-like containers support efficient iteration through the elements in + sorted order. Set-like containers are more expensive than sequential + containers. + + +
- a sequential container provides + the most efficient way to add elements and keeps track of the order they are + added to the collection. They permit duplicates and support efficient + iteration, but do not support efficient look-up based on a key. + + +
- a bit container provides an efficient way to store and + perform set operations on sets of numeric id's, while automatically + eliminating duplicates. Bit containers require a maximum of 1 bit for each + identifier you want to store. + +
+Once the proper category of container is determined, you can fine tune the +memory use, constant factors, and cache behaviors of access by intelligently +picking a member of the category. Note that constant factors and cache behavior +can be a big deal. If you have a vector that usually only contains a few +elements (but could contain many), for example, it's much better to use +SmallVector than vector +. Doing so avoids (relatively) expensive malloc/free calls, which dwarf the +cost of adding the elements to the container.
The LLVM compiler infrastructure have many different data structures that may -be traversed. Following the example of the C++ standard template library, the -techniques used to traverse these various data structures are all basically the -same. For a enumerable sequence of values, the XXXbegin() function (or -method) returns an iterator to the start of the sequence, the XXXend() -function returns an iterator pointing to one past the last valid element of the -sequence, and there is some XXXiterator data type that is common -between the two operations.
+ + -Because the pattern for iteration is common across many different aspects of -the program representation, the standard template library algorithms may be used -on them, and it is easier to remember how to iterate. First we show a few common -examples of the data structures that need to be traversed. Other data -structures are traversed in very similar ways.
+Fixed size arrays are very simple and very fast. They are good if you know +exactly how many elements you have, or you have a (low) upper bound on how many +you have.
+Heap allocated arrays (new[] + delete[]) are also simple. They are good if +the number of elements is variable, if you know how many elements you will need +before the array is allocated, and if the array is usually large (if not, +consider a SmallVector). The cost of a heap +allocated array is the cost of the new/delete (aka malloc/free). Also note that +if you are allocating an array of a type with a constructor, the constructor and +destructors will be run for every element in the array (re-sizable vectors only +construct those elements actually used).
SmallVector<Type, N> is a simple class that looks and smells +just like vector<Type>: +it supports efficient iteration, lays out elements in memory order (so you can +do pointer arithmetic between elements), supports efficient push_back/pop_back +operations, supports efficient random access to its elements, etc.
-It's quite common to have a Function instance that you'd like to -transform in some way; in particular, you'd like to manipulate its -BasicBlocks. To facilitate this, you'll need to iterate over all of -the BasicBlocks that constitute the Function. The following is -an example that prints the name of a BasicBlock and the number of -Instructions it contains:
+The advantage of SmallVector is that it allocates space for +some number of elements (N) in the object itself. Because of this, if +the SmallVector is dynamically smaller than N, no malloc is performed. This can +be a big win in cases where the malloc/free call is far more expensive than the +code that fiddles around with the elements.
-// func is a pointer to a Function instance+
for (Function::iterator i = func->begin(), e = func->end(); i != e; ++i) {
// print out the name of the basic block if it has one, and then the
// number of instructions that it contains
cerr << "Basic block (name=" << i->getName() << ") has "
<< i->size() << " instructions.\n";
}
This is good for vectors that are "usually small" (e.g. the number of +predecessors/successors of a block is usually less than 8). On the other hand, +this makes the size of the SmallVector itself large, so you don't want to +allocate lots of them (doing so will waste a lot of space). As such, +SmallVectors are most useful when on the stack.
-Note that i can be used as if it were a pointer for the purposes of -invoking member functions of the Instruction class. This is -because the indirection operator is overloaded for the iterator -classes. In the above code, the expression i->size() is -exactly equivalent to (*i).size() just like you'd expect.
+SmallVector also provides a nice portable and efficient replacement for +alloca.
+std::vector is well loved and respected. It is useful when SmallVector isn't: +when the size of the vector is often large (thus the small optimization will +rarely be a benefit) or if you will be allocating many instances of the vector +itself (which would waste space for elements that aren't in the container). +vector is also useful when interfacing with code that expects vectors :). +
-Just like when dealing with BasicBlocks in Functions, it's -easy to iterate over the individual instructions that make up -BasicBlocks. Here's a code snippet that prints out each instruction in -a BasicBlock:
+One worthwhile note about std::vector: avoid code like this:
-// blk is a pointer to a BasicBlock instance+
for (BasicBlock::iterator i = blk->begin(), e = blk->end(); i != e; ++i)
// the next statement works since operator<<(ostream&,...)
// is overloaded for Instruction&
cerr << *i << "\n";
+for ( ... ) {
+ std::vector<foo> V;
+ use V;
+}
+
+However, this isn't really the best way to print out the contents of a -BasicBlock! Since the ostream operators are overloaded for virtually -anything you'll care about, you could have just invoked the print routine on the -basic block itself: cerr << *blk << "\n";.
+Instead, write this as:
-Note that currently operator<< is implemented for Value*, so -it will print out the contents of the pointer, instead of the pointer value you -might expect. This is a deprecated interface that will be removed in the -future, so it's best not to depend on it. To print out the pointer value for -now, you must cast to void*.
+
+std::vector<foo> V;
+for ( ... ) {
+ use V;
+ V.clear();
+}
+
+Doing so will save (at least) one heap allocation and free per iteration of +the loop.
std::deque is, in some senses, a generalized version of std::vector. Like +std::vector, it provides constant time random access and other similar +properties, but it also provides efficient access to the front of the list. It +does not guarantee continuity of elements within memory.
-If you're finding that you commonly iterate over a Function's -BasicBlocks and then that BasicBlock's Instructions, -InstIterator should be used instead. You'll need to include llvm/Support/InstIterator.h, -and then instantiate InstIterators explicitly in your code. Here's a -small example that shows how to dump all instructions in a function to the standard error stream:
+
In exchange for this extra flexibility, std::deque has significantly higher +constant factor costs than std::vector. If possible, use std::vector or +something cheaper.
+#include "llvm/Support/InstIterator.h"-Easy, isn't it? You can also use InstIterators to fill a -worklist with its initial contents. For example, if you wanted to -initialize a worklist to contain all instructions in a Function -F, all you would need to do is something like: -
...
// Suppose F is a ptr to a function
for (inst_iterator i = inst_begin(F), e = inst_end(F); i != e; ++i)
cerr << *i << "\n";
std::set<Instruction*> worklist;+ +
worklist.insert(inst_begin(F), inst_end(F));
The STL set worklist would now contain all instructions in the -Function pointed to by F.
+std::list is an extremely inefficient class that is rarely useful. +It performs a heap allocation for every element inserted into it, thus having an +extremely high constant factor, particularly for small data types. std::list +also only supports bidirectional iteration, not random access iteration.
+In exchange for this high cost, std::list supports efficient access to both +ends of the list (like std::deque, but unlike std::vector or SmallVector). In +addition, the iterator invalidation characteristics of std::list are stronger +than that of a vector class: inserting or removing an element into the list does +not invalidate iterator or pointers to other elements in the list.
ilist<T> implements an 'intrusive' doubly-linked list. It is +intrusive, because it requires the element to store and provide access to the +prev/next pointers for the list.
+ +ilist has the same drawbacks as std::list, and additionally +requires an ilist_traits implementation for the element type, but it +provides some novel characteristics. In particular, it can efficiently store +polymorphic objects, the traits class is informed when an element is inserted or +removed from the list, and ilists are guaranteed to support a +constant-time splice operation.
+ +These properties are exactly what we want for things like +Instructions and basic blocks, which is why these are implemented with +ilists.
+ +Related classes of interest are explained in the following subsections: +-
+
- ilist_traits +
- iplist +
- llvm/ADT/ilist_node.h +
Sometimes, it'll be useful to grab a reference (or pointer) to a class -instance when all you've got at hand is an iterator. Well, extracting -a reference or a pointer from an iterator is very straight-forward. -Assuming that i is a BasicBlock::iterator and j -is a BasicBlock::const_iterator:
- -Instruction& inst = *i; // grab reference to instruction reference+ +
Instruction* pinst = &*i; // grab pointer to instruction reference
const Instruction& inst = *j;
However, the iterators you'll be working with in the LLVM framework are -special: they will automatically convert to a ptr-to-instance type whenever they -need to. Instead of dereferencing the iterator and then taking the address of -the result, you can simply assign the iterator to the proper pointer type and -you get the dereference and address-of operation as a result of the assignment -(behind the scenes, this is a result of overloading casting mechanisms). Thus -the last line of the last example,
+ilist_traits<T> is ilist<T>'s customization +mechanism. iplist<T> (and consequently ilist<T>) +publicly derive from this traits class.
+Instruction* pinst = &*i;+ +
is semantically equivalent to
+iplist<T> is ilist<T>'s base and as such +supports a slightly narrower interface. Notably, inserters from +T& are absent.
-Instruction* pinst = i;+
ilist_traits<T> is a public base of this class and can be +used for a wide variety of customizations.
+It's also possible to turn a class pointer into the corresponding iterator, -and this is a constant time operation (very efficient). The following code -snippet illustrates use of the conversion constructors provided by LLVM -iterators. By using these, you can explicitly grab the iterator of something -without actually obtaining it via iteration over some structure:
+ + -void printNextInstruction(Instruction* inst) {
BasicBlock::iterator it(inst);
++it; // after this line, it refers to the instruction after *inst.
if (it != inst->getParent()->end()) cerr << *it << "\n";
}
+ilist_node<T> implements a the forward and backward links +that are expected by the ilist<T> (and analogous containers) +in the default manner.
+ilist_node<T>s are meant to be embedded in the node type +T, usually T publicly derives from +ilist_node<T>.
Other STL containers are available, such as std::string.
-Say that you're writing a FunctionPass and would like to count all the -locations in the entire module (that is, across every Function) where a -certain function (i.e., some Function*) is already in scope. As you'll -learn later, you may want to use an InstVisitor to accomplish this in a -much more straight-forward manner, but this example will allow us to explore how -you'd do it if you didn't have InstVisitor around. In pseudocode, this -is what we want to do:
+There are also various STL adapter classes such as std::queue, +std::priority_queue, std::stack, etc. These provide simplified access to an +underlying container but don't affect the cost of the container itself.
-initialize callCounter to zero+
for each Function f in the Module
for each BasicBlock b in f
for each Instruction i in b
if (i is a CallInst and calls the given function)
increment callCounter
And the actual code is (remember, since we're writing a -FunctionPass, our FunctionPass-derived class simply has to -override the runOnFunction method...):
-Function* targetFunc = ...;+ + + +
class OurFunctionPass : public FunctionPass {
public:
OurFunctionPass(): callCounter(0) { }
virtual runOnFunction(Function& F) {
for (Function::iterator b = F.begin(), be = F.end(); b != be; ++b) {
for (BasicBlock::iterator i = b->begin(); ie = b->end(); i != ie; ++i) {
if (CallInst* callInst = dyn_cast<CallInst>(&*i)) {
// we know we've encountered a call instruction, so we
// need to determine if it's a call to the
// function pointed to by m_func or not.
if (callInst->getCalledFunction() == targetFunc)
++callCounter;
}
}
}
private:
unsigned callCounter;
};
Set-like containers are useful when you need to canonicalize multiple values +into a single representation. There are several different choices for how to do +this, providing various trade-offs.
You may have noticed that the previous example was a bit oversimplified in -that it did not deal with call sites generated by 'invoke' instructions. In -this, and in other situations, you may find that you want to treat -CallInsts and InvokeInsts the same way, even though their -most-specific common base class is Instruction, which includes lots of -less closely-related things. For these cases, LLVM provides a handy wrapper -class called CallSite. -It is essentially a wrapper around an Instruction pointer, with some -methods that provide functionality common to CallInsts and -InvokeInsts.
+If you intend to insert a lot of elements, then do a lot of queries, a +great approach is to use a vector (or other sequential container) with +std::sort+std::unique to remove duplicates. This approach works really well if +your usage pattern has these two distinct phases (insert then query), and can be +coupled with a good choice of sequential container. +
-This class has "value semantics": it should be passed by value, not by -reference and it should not be dynamically allocated or deallocated using -operator new or operator delete. It is efficiently copyable, -assignable and constructable, with costs equivalents to that of a bare pointer. -If you look at its definition, it has only a single pointer member.
++This combination provides the several nice properties: the result data is +contiguous in memory (good for cache locality), has few allocations, is easy to +address (iterators in the final vector are just indices or pointers), and can be +efficiently queried with a standard binary or radix search.
Frequently, we might have an instance of the Value Class and we want to -determine which Users use the Value. The list of all -Users of a particular Value is called a def-use chain. -For example, let's say we have a Function* named F to a -particular function foo. Finding all of the instructions that -use foo is as simple as iterating over the def-use chain -of F:
+If you have a set-like data structure that is usually small and whose elements +are reasonably small, a SmallSet<Type, N> is a good choice. This set +has space for N elements in place (thus, if the set is dynamically smaller than +N, no malloc traffic is required) and accesses them with a simple linear search. +When the set grows beyond 'N' elements, it allocates a more expensive representation that +guarantees efficient access (for most types, it falls back to std::set, but for +pointers it uses something far better, SmallPtrSet).
-Function* F = ...;+
for (Value::use_iterator i = F->use_begin(), e = F->use_end(); i != e; ++i) {
if (Instruction *Inst = dyn_cast<Instruction>(*i)) {
cerr << "F is used in instruction:\n";
cerr << *Inst << "\n";
}
}
The magic of this class is that it handles small sets extremely efficiently, +but gracefully handles extremely large sets without loss of efficiency. The +drawback is that the interface is quite small: it supports insertion, queries +and erasing, but does not support iteration.
-Alternately, it's common to have an instance of the User Class and need to know what -Values are used by it. The list of all Values used by a -User is known as a use-def chain. Instances of class -Instruction are common Users, so we might want to iterate over -all of the values that a particular instruction uses (that is, the operands of -the particular Instruction):
+Instruction* pi = ...;+ + - +
for (User::op_iterator i = pi->op_begin(), e = pi->op_end(); i != e; ++i) {
Value* v = *i;
...
}
SmallPtrSet has all the advantages of SmallSet (and a SmallSet of pointers is +transparently implemented with a SmallPtrSet), but also supports iterators. If +more than 'N' insertions are performed, a single quadratically +probed hash table is allocated and grows as needed, providing extremely +efficient access (constant time insertion/deleting/queries with low constant +factors) and is very stingy with malloc traffic.
+ +Note that, unlike std::set, the iterators of SmallPtrSet are invalidated +whenever an insertion occurs. Also, the values visited by the iterators are not +visited in sorted order.
There are some primitive transformation operations present in the LLVM -infrastructure that are worth knowing about. When performing -transformations, it's fairly common to manipulate the contents of basic -blocks. This section describes some of the common methods for doing so -and gives example code.
++DenseSet is a simple quadratically probed hash table. It excels at supporting +small values: it uses a single allocation to hold all of the pairs that +are currently inserted in the set. DenseSet is a great way to unique small +values that are not simple pointers (use SmallPtrSet for pointers). Note that DenseSet has +the same requirements for the value type that DenseMap has. +
Instantiating Instructions
++FoldingSet is an aggregate class that is really good at uniquing +expensive-to-create or polymorphic objects. It is a combination of a chained +hash table with intrusive links (uniqued objects are required to inherit from +FoldingSetNode) that uses SmallVector as part of +its ID process.
+ +Consider a case where you want to implement a "getOrCreateFoo" method for +a complex object (for example, a node in the code generator). The client has a +description of *what* it wants to generate (it knows the opcode and all the +operands), but we don't want to 'new' a node, then try inserting it into a set +only to find out it already exists, at which point we would have to delete it +and return the node that already exists. +
+ +To support this style of client, FoldingSet perform a query with a +FoldingSetNodeID (which wraps SmallVector) that can be used to describe the +element that we want to query for. The query either returns the element +matching the ID or it returns an opaque ID that indicates where insertion should +take place. Construction of the ID usually does not require heap traffic.
+ +Because FoldingSet uses intrusive links, it can support polymorphic objects +in the set (for example, you can have SDNode instances mixed with LoadSDNodes). +Because the elements are individually allocated, pointers to the elements are +stable: inserting or removing elements does not invalidate any pointers to other +elements. +
-Creation of Instructions is straight-forward: simply call the -constructor for the kind of instruction to instantiate and provide the necessary -parameters. For example, an AllocaInst only requires a -(const-ptr-to) Type. Thus:
+AllocaInst* ai = new AllocaInst(Type::IntTy);+ +
will create an AllocaInst instance that represents the allocation of -one integer in the current stack frame, at runtime. Each Instruction +
std::set is a reasonable all-around set class, which is decent at +many things but great at nothing. std::set allocates memory for each element +inserted (thus it is very malloc intensive) and typically stores three pointers +per element in the set (thus adding a large amount of per-element space +overhead). It offers guaranteed log(n) performance, which is not particularly +fast from a complexity standpoint (particularly if the elements of the set are +expensive to compare, like strings), and has extremely high constant factors for +lookup, insertion and removal.
+ +The advantages of std::set are that its iterators are stable (deleting or +inserting an element from the set does not affect iterators or pointers to other +elements) and that iteration over the set is guaranteed to be in sorted order. +If the elements in the set are large, then the relative overhead of the pointers +and malloc traffic is not a big deal, but if the elements of the set are small, +std::set is almost never a good choice.
+ +LLVM's SetVector<Type> is an adapter class that combines your choice of +a set-like container along with a Sequential +Container. The important property +that this provides is efficient insertion with uniquing (duplicate elements are +ignored) with iteration support. It implements this by inserting elements into +both a set-like container and the sequential container, using the set-like +container for uniquing and the sequential container for iteration. +
+ +The difference between SetVector and other sets is that the order of +iteration is guaranteed to match the order of insertion into the SetVector. +This property is really important for things like sets of pointers. Because +pointer values are non-deterministic (e.g. vary across runs of the program on +different machines), iterating over the pointers in the set will +not be in a well-defined order.
+ ++The drawback of SetVector is that it requires twice as much space as a normal +set and has the sum of constant factors from the set-like container and the +sequential container that it uses. Use it *only* if you need to iterate over +the elements in a deterministic order. SetVector is also expensive to delete +elements out of (linear time), unless you use it's "pop_back" method, which is +faster. +
+ +SetVector is an adapter class that defaults to using std::vector and std::set +for the underlying containers, so it is quite expensive. However, +"llvm/ADT/SetVector.h" also provides a SmallSetVector class, which +defaults to using a SmallVector and SmallSet of a specified size. If you use +this, and if your sets are dynamically smaller than N, you will save a lot of +heap traffic.
+ ++UniqueVector is similar to SetVector, but it +retains a unique ID for each element inserted into the set. It internally +contains a map and a vector, and it assigns a unique ID for each value inserted +into the set.
+ +UniqueVector is very expensive: its cost is the sum of the cost of +maintaining both the map and vector, it has high complexity, high constant +factors, and produces a lot of malloc traffic. It should be avoided.
+ ++The STL provides several other options, such as std::multiset and the various +"hash_set" like containers (whether from C++ TR1 or from the SGI library). We +never use hash_set and unordered_set because they are generally very expensive +(each insertion requires a malloc) and very non-portable. +
+ +std::multiset is useful if you're not interested in elimination of +duplicates, but has all the drawbacks of std::set. A sorted vector (where you +don't delete duplicate entries) or some other approach is almost always +better.
+ ++If your usage pattern follows a strict insert-then-query approach, you can +trivially use the same approach as sorted vectors +for set-like containers. The only difference is that your query function +(which uses std::lower_bound to get efficient log(n) lookup) should only compare +the key, not both the key and value. This yields the same advantages as sorted +vectors for sets. +
++Strings are commonly used as keys in maps, and they are difficult to support +efficiently: they are variable length, inefficient to hash and compare when +long, expensive to copy, etc. StringMap is a specialized container designed to +cope with these issues. It supports mapping an arbitrary range of bytes to an +arbitrary other object.
+ +The StringMap implementation uses a quadratically-probed hash table, where +the buckets store a pointer to the heap allocated entries (and some other +stuff). The entries in the map must be heap allocated because the strings are +variable length. The string data (key) and the element object (value) are +stored in the same allocation with the string data immediately after the element +object. This container guarantees the "(char*)(&Value+1)" points +to the key string for a value.
+ +The StringMap is very fast for several reasons: quadratic probing is very +cache efficient for lookups, the hash value of strings in buckets is not +recomputed when lookup up an element, StringMap rarely has to touch the +memory for unrelated objects when looking up a value (even when hash collisions +happen), hash table growth does not recompute the hash values for strings +already in the table, and each pair in the map is store in a single allocation +(the string data is stored in the same allocation as the Value of a pair).
+ +StringMap also provides query methods that take byte ranges, so it only ever +copies a string if a value is inserted into the table.
++IndexedMap is a specialized container for mapping small dense integers (or +values that can be mapped to small dense integers) to some other type. It is +internally implemented as a vector with a mapping function that maps the keys to +the dense integer range. +
+ ++This is useful for cases like virtual registers in the LLVM code generator: they +have a dense mapping that is offset by a compile-time constant (the first +virtual register ID).
+ ++DenseMap is a simple quadratically probed hash table. It excels at supporting +small keys and values: it uses a single allocation to hold all of the pairs that +are currently inserted in the map. DenseMap is a great way to map pointers to +pointers, or map other small types to each other. +
+ ++There are several aspects of DenseMap that you should be aware of, however. The +iterators in a densemap are invalidated whenever an insertion occurs, unlike +map. Also, because DenseMap allocates space for a large number of key/value +pairs (it starts with 64 by default), it will waste a lot of space if your keys +or values are large. Finally, you must implement a partial specialization of +DenseMapInfo for the key that you want, if it isn't already supported. This +is required to tell DenseMap about two special marker values (which can never be +inserted into the map) that it needs internally.
+ ++std::map has similar characteristics to std::set: it uses +a single allocation per pair inserted into the map, it offers log(n) lookup with +an extremely large constant factor, imposes a space penalty of 3 pointers per +pair in the map, etc.
+ +std::map is most useful when your keys or values are very large, if you need +to iterate over the collection in sorted order, or if you need stable iterators +into the map (i.e. they don't get invalidated if an insertion or deletion of +another element takes place).
+ ++The STL provides several other options, such as std::multimap and the various +"hash_map" like containers (whether from C++ TR1 or from the SGI library). We +never use hash_set and unordered_set because they are generally very expensive +(each insertion requires a malloc) and very non-portable.
+ +std::multimap is useful if you want to map a key to multiple values, but has +all the drawbacks of std::map. A sorted vector or some other approach is almost +always better.
+ +Unlike the other containers, there are only two bit storage containers, and +choosing when to use each is relatively straightforward.
+ +One additional option is +std::vector<bool>: we discourage its use for two reasons 1) the +implementation in many common compilers (e.g. commonly available versions of +GCC) is extremely inefficient and 2) the C++ standards committee is likely to +deprecate this container and/or change it significantly somehow. In any case, +please don't use it.
+The BitVector container provides a fixed size set of bits for manipulation. +It supports individual bit setting/testing, as well as set operations. The set +operations take time O(size of bitvector), but operations are performed one word +at a time, instead of one bit at a time. This makes the BitVector very fast for +set operations compared to other containers. Use the BitVector when you expect +the number of set bits to be high (IE a dense set). +
+The SparseBitVector container is much like BitVector, with one major +difference: Only the bits that are set, are stored. This makes the +SparseBitVector much more space efficient than BitVector when the set is sparse, +as well as making set operations O(number of set bits) instead of O(size of +universe). The downside to the SparseBitVector is that setting and testing of random bits is O(N), and on large SparseBitVectors, this can be slower than BitVector. In our implementation, setting or testing bits in sorted order +(either forwards or reverse) is O(1) worst case. Testing and setting bits within 128 bits (depends on size) of the current bit is also O(1). As a general statement, testing/setting bits in a SparseBitVector is O(distance away from last set bit). +
+This section describes how to perform some very simple transformations of +LLVM code. This is meant to give examples of common idioms used, showing the +practical side of LLVM transformations.
Because this is a "how-to" section, +you should also read about the main classes that you will be working with. The +Core LLVM Class Hierarchy Reference contains details +and descriptions of the main classes that you should know about.
+ +The LLVM compiler infrastructure have many different data structures that may +be traversed. Following the example of the C++ standard template library, the +techniques used to traverse these various data structures are all basically the +same. For a enumerable sequence of values, the XXXbegin() function (or +method) returns an iterator to the start of the sequence, the XXXend() +function returns an iterator pointing to one past the last valid element of the +sequence, and there is some XXXiterator data type that is common +between the two operations.
+ +Because the pattern for iteration is common across many different aspects of +the program representation, the standard template library algorithms may be used +on them, and it is easier to remember how to iterate. First we show a few common +examples of the data structures that need to be traversed. Other data +structures are traversed in very similar ways.
+ +It's quite common to have a Function instance that you'd like to +transform in some way; in particular, you'd like to manipulate its +BasicBlocks. To facilitate this, you'll need to iterate over all of +the BasicBlocks that constitute the Function. The following is +an example that prints the name of a BasicBlock and the number of +Instructions it contains:
+ ++// func is a pointer to a Function instance +for (Function::iterator i = func->begin(), e = func->end(); i != e; ++i) + // Print out the name of the basic block if it has one, and then the + // number of instructions that it contains + llvm::cerr << "Basic block (name=" << i->getName() << ") has " + << i->size() << " instructions.\n"; ++
Note that i can be used as if it were a pointer for the purposes of +invoking member functions of the Instruction class. This is +because the indirection operator is overloaded for the iterator +classes. In the above code, the expression i->size() is +exactly equivalent to (*i).size() just like you'd expect.
+ +Just like when dealing with BasicBlocks in Functions, it's +easy to iterate over the individual instructions that make up +BasicBlocks. Here's a code snippet that prints out each instruction in +a BasicBlock:
+ ++// blk is a pointer to a BasicBlock instance +for (BasicBlock::iterator i = blk->begin(), e = blk->end(); i != e; ++i) + // The next statement works since operator<<(ostream&,...) + // is overloaded for Instruction& + llvm::cerr << *i << "\n"; ++
However, this isn't really the best way to print out the contents of a +BasicBlock! Since the ostream operators are overloaded for virtually +anything you'll care about, you could have just invoked the print routine on the +basic block itself: llvm::cerr << *blk << "\n";.
+ +If you're finding that you commonly iterate over a Function's +BasicBlocks and then that BasicBlock's Instructions, +InstIterator should be used instead. You'll need to include llvm/Support/InstIterator.h, +and then instantiate InstIterators explicitly in your code. Here's a +small example that shows how to dump all instructions in a function to the standard error stream:
+ +
+#include "llvm/Support/InstIterator.h" + +// F is a pointer to a Function instance +for (inst_iterator I = inst_begin(F), E = inst_end(F); I != E; ++I) + llvm::cerr << *I << "\n"; ++
Easy, isn't it? You can also use InstIterators to fill a +work list with its initial contents. For example, if you wanted to +initialize a work list to contain all instructions in a Function +F, all you would need to do is something like:
+ ++std::set<Instruction*> worklist; +// or better yet, SmallPtrSet<Instruction*, 64> worklist; + +for (inst_iterator I = inst_begin(F), E = inst_end(F); I != E; ++I) + worklist.insert(&*I); ++
The STL set worklist would now contain all instructions in the +Function pointed to by F.
+ +Sometimes, it'll be useful to grab a reference (or pointer) to a class +instance when all you've got at hand is an iterator. Well, extracting +a reference or a pointer from an iterator is very straight-forward. +Assuming that i is a BasicBlock::iterator and j +is a BasicBlock::const_iterator:
+ ++Instruction& inst = *i; // Grab reference to instruction reference +Instruction* pinst = &*i; // Grab pointer to instruction reference +const Instruction& inst = *j; ++
However, the iterators you'll be working with in the LLVM framework are +special: they will automatically convert to a ptr-to-instance type whenever they +need to. Instead of dereferencing the iterator and then taking the address of +the result, you can simply assign the iterator to the proper pointer type and +you get the dereference and address-of operation as a result of the assignment +(behind the scenes, this is a result of overloading casting mechanisms). Thus +the last line of the last example,
+ ++Instruction *pinst = &*i; ++
is semantically equivalent to
+ ++Instruction *pinst = i; ++
It's also possible to turn a class pointer into the corresponding iterator, +and this is a constant time operation (very efficient). The following code +snippet illustrates use of the conversion constructors provided by LLVM +iterators. By using these, you can explicitly grab the iterator of something +without actually obtaining it via iteration over some structure:
+ +
+void printNextInstruction(Instruction* inst) {
+ BasicBlock::iterator it(inst);
+ ++it; // After this line, it refers to the instruction after *inst
+ if (it != inst->getParent()->end()) llvm::cerr << *it << "\n";
+}
+
+Say that you're writing a FunctionPass and would like to count all the +locations in the entire module (that is, across every Function) where a +certain function (i.e., some Function*) is already in scope. As you'll +learn later, you may want to use an InstVisitor to accomplish this in a +much more straight-forward manner, but this example will allow us to explore how +you'd do it if you didn't have InstVisitor around. In pseudo-code, this +is what we want to do:
+ ++initialize callCounter to zero +for each Function f in the Module + for each BasicBlock b in f + for each Instruction i in b + if (i is a CallInst and calls the given function) + increment callCounter ++
And the actual code is (remember, because we're writing a +FunctionPass, our FunctionPass-derived class simply has to +override the runOnFunction method):
+ +
+Function* targetFunc = ...;
+
+class OurFunctionPass : public FunctionPass {
+ public:
+ OurFunctionPass(): callCounter(0) { }
+
+ virtual runOnFunction(Function& F) {
+ for (Function::iterator b = F.begin(), be = F.end(); b != be; ++b) {
+ for (BasicBlock::iterator i = b->begin(), ie = b->end(); i != ie; ++i) {
+ if (CallInst* callInst = dyn_cast<CallInst>(&*i)) {
+ // We know we've encountered a call instruction, so we
+ // need to determine if it's a call to the
+ // function pointed to by m_func or not.
+ if (callInst->getCalledFunction() == targetFunc)
+ ++callCounter;
+ }
+ }
+ }
+ }
+
+ private:
+ unsigned callCounter;
+};
+
+You may have noticed that the previous example was a bit oversimplified in +that it did not deal with call sites generated by 'invoke' instructions. In +this, and in other situations, you may find that you want to treat +CallInsts and InvokeInsts the same way, even though their +most-specific common base class is Instruction, which includes lots of +less closely-related things. For these cases, LLVM provides a handy wrapper +class called CallSite. +It is essentially a wrapper around an Instruction pointer, with some +methods that provide functionality common to CallInsts and +InvokeInsts.
+ +This class has "value semantics": it should be passed by value, not by +reference and it should not be dynamically allocated or deallocated using +operator new or operator delete. It is efficiently copyable, +assignable and constructable, with costs equivalents to that of a bare pointer. +If you look at its definition, it has only a single pointer member.
+ +Frequently, we might have an instance of the Value Class and we want to +determine which Users use the Value. The list of all +Users of a particular Value is called a def-use chain. +For example, let's say we have a Function* named F to a +particular function foo. Finding all of the instructions that +use foo is as simple as iterating over the def-use chain +of F:
+ +
+Function *F = ...;
+
+for (Value::use_iterator i = F->use_begin(), e = F->use_end(); i != e; ++i)
+ if (Instruction *Inst = dyn_cast<Instruction>(*i)) {
+ llvm::cerr << "F is used in instruction:\n";
+ llvm::cerr << *Inst << "\n";
+ }
+
+Alternately, it's common to have an instance of the User Class and need to know what +Values are used by it. The list of all Values used by a +User is known as a use-def chain. Instances of class +Instruction are common Users, so we might want to iterate over +all of the values that a particular instruction uses (that is, the operands of +the particular Instruction):
+ +
+Instruction *pi = ...;
+
+for (User::op_iterator i = pi->op_begin(), e = pi->op_end(); i != e; ++i) {
+ Value *v = *i;
+ // ...
+}
+
+Iterating over the predecessors and successors of a block is quite easy +with the routines defined in "llvm/Support/CFG.h". Just use code like +this to iterate over all predecessors of BB:
+ +
+#include "llvm/Support/CFG.h"
+BasicBlock *BB = ...;
+
+for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) {
+ BasicBlock *Pred = *PI;
+ // ...
+}
+
+Similarly, to iterate over successors use +succ_iterator/succ_begin/succ_end.
+ +There are some primitive transformation operations present in the LLVM +infrastructure that are worth knowing about. When performing +transformations, it's fairly common to manipulate the contents of basic +blocks. This section describes some of the common methods for doing so +and gives example code.
+ +Instantiating Instructions
+ +Creation of Instructions is straight-forward: simply call the +constructor for the kind of instruction to instantiate and provide the necessary +parameters. For example, an AllocaInst only requires a +(const-ptr-to) Type. Thus:
+ ++AllocaInst* ai = new AllocaInst(Type::Int32Ty); ++
will create an AllocaInst instance that represents the allocation of +one integer in the current stack frame, at run time. Each Instruction subclass is likely to have varying default parameters which change the semantics of the instruction, so refer to the doxygen documentation for the subclass of Instruction that you're interested in instantiating.
-Naming values
+Naming values
+ +It is very useful to name the values of instructions when you're able to, as +this facilitates the debugging of your transformations. If you end up looking +at generated LLVM machine code, you definitely want to have logical names +associated with the results of instructions! By supplying a value for the +Name (default) parameter of the Instruction constructor, you +associate a logical name with the result of the instruction's execution at +run time. For example, say that I'm writing a transformation that dynamically +allocates space for an integer on the stack, and that integer is going to be +used as some kind of index by some other code. To accomplish this, I place an +AllocaInst at the first point in the first BasicBlock of some +Function, and I'm intending to use it within the same +Function. I might do:
+ ++AllocaInst* pa = new AllocaInst(Type::Int32Ty, 0, "indexLoc"); ++
where indexLoc is now the logical name of the instruction's +execution value, which is a pointer to an integer on the run time stack.
+ +Inserting instructions
+ +There are essentially two ways to insert an Instruction +into an existing sequence of instructions that form a BasicBlock:
+ +-
+
- Insertion into an explicit instruction list
+
+
Given a BasicBlock* pb, an Instruction* pi within that + BasicBlock, and a newly-created instruction we wish to insert + before *pi, we do the following:
+ +++ ++BasicBlock *pb = ...; +Instruction *pi = ...; +Instruction *newInst = new Instruction(...); + +pb->getInstList().insert(pi, newInst); // Inserts newInst before pi in pb +
+Appending to the end of a BasicBlock is so common that + the Instruction class and Instruction-derived + classes provide constructors which take a pointer to a + BasicBlock to be appended to. For example code that + looked like:
+ +++ ++BasicBlock *pb = ...; +Instruction *newInst = new Instruction(...); + +pb->getInstList().push_back(newInst); // Appends newInst to pb +
+becomes:
+ +++ ++BasicBlock *pb = ...; +Instruction *newInst = new Instruction(..., pb); +
+which is much cleaner, especially if you are creating + long instruction streams.
+
+ - Insertion into an implicit instruction list
+
+
Instruction instances that are already in BasicBlocks + are implicitly associated with an existing instruction list: the instruction + list of the enclosing basic block. Thus, we could have accomplished the same + thing as the above code without being given a BasicBlock by doing: +
+ +++ ++Instruction *pi = ...; +Instruction *newInst = new Instruction(...); + +pi->getParent()->getInstList().insert(pi, newInst); +
+In fact, this sequence of steps occurs so frequently that the + Instruction class and Instruction-derived classes provide + constructors which take (as a default parameter) a pointer to an + Instruction which the newly-created Instruction should + precede. That is, Instruction constructors are capable of + inserting the newly-created instance into the BasicBlock of a + provided instruction, immediately before that instruction. Using an + Instruction constructor with a insertBefore (default) + parameter, the above code becomes:
+ ++-+Instruction* pi = ...; +Instruction* newInst = new Instruction(..., pi); +
+It is very useful to name the values of instructions when you're able to, as -this facilitates the debugging of your transformations. If you end up looking -at generated LLVM machine code, you definitely want to have logical names -associated with the results of instructions! By supplying a value for the -Name (default) parameter of the Instruction constructor, you -associate a logical name with the result of the instruction's execution at -runtime. For example, say that I'm writing a transformation that dynamically -allocates space for an integer on the stack, and that integer is going to be -used as some kind of index by some other code. To accomplish this, I place an -AllocaInst at the first point in the first BasicBlock of some -Function, and I'm intending to use it within the same -Function. I might do:
+which is much cleaner, especially if you're creating a lot of + instructions and adding them to BasicBlocks.
+
AllocaInst* pa = new AllocaInst(Type::IntTy, 0, "indexLoc");+
where indexLoc is now the logical name of the instruction's -execution value, which is a pointer to an integer on the runtime stack.
+ + -Inserting instructions
+There are essentially two ways to insert an Instruction -into an existing sequence of instructions that form a BasicBlock:
+Deleting an instruction from an existing sequence of instructions that form a +BasicBlock is very straight-forward. First, +you must have a pointer to the instruction that you wish to delete. Second, you +need to obtain the pointer to that instruction's basic block. You use the +pointer to the basic block to get its list of instructions and then use the +erase function to remove your instruction. For example:
+ ++Instruction *I = .. ; +I->eraseFromParent(); ++
Replacing individual instructions
+ +Including "llvm/Transforms/Utils/BasicBlockUtils.h" +permits use of two very useful replace functions: ReplaceInstWithValue +and ReplaceInstWithInst.
+ +Deleting Instructions
-
-
- Insertion into an explicit instruction list +
- ReplaceInstWithValue
-
Given a BasicBlock* pb, an Instruction* pi within that - BasicBlock, and a newly-created instruction we wish to insert - before *pi, we do the following:
+This function replaces all uses of a given instruction with a value, + and then removes the original instruction. The following example + illustrates the replacement of the result of a particular + AllocaInst that allocates memory for a single integer with a null + pointer to an integer.
-BasicBlock *pb = ...;
+
Instruction *pi = ...;
Instruction *newInst = new Instruction(...);
pb->getInstList().insert(pi, newInst); // inserts newInst before pi in pb++AllocaInst* instToReplace = ...; +BasicBlock::iterator ii(instToReplace); -
Appending to the end of a BasicBlock is so common that - the Instruction class and Instruction-derived - classes provide constructors which take a pointer to a - BasicBlock to be appended to. For example code that - looked like:
+ReplaceInstWithValue(instToReplace->getParent()->getInstList(), ii, + Constant::getNullValue(PointerType::getUnqual(Type::Int32Ty))); +
+
+ - ReplaceInstWithInst
+
+
This function replaces a particular instruction with another + instruction, inserting the new instruction into the basic block at the + location where the old instruction was, and replacing any uses of the old + instruction with the new instruction. The following example illustrates + the replacement of one AllocaInst with another.
+ +++AllocaInst* instToReplace = ...; +BasicBlock::iterator ii(instToReplace); + +ReplaceInstWithInst(instToReplace->getParent()->getInstList(), ii, + new AllocaInst(Type::Int32Ty, 0, "ptrToReplacedInt")); +
+
Replacing multiple uses of Users and Values
+ +You can use Value::replaceAllUsesWith and +User::replaceUsesOfWith to change more than one use at a time. See the +doxygen documentation for the Value Class +and User Class, respectively, for more +information.
+ + + +Deleting a global variable from a module is just as easy as deleting an +Instruction. First, you must have a pointer to the global variable that you wish + to delete. You use this pointer to erase it from its parent, the module. + For example:
+ ++GlobalVariable *GV = .. ; + +GV->eraseFromParent(); ++
+This section describes some of the advanced or obscure API's that most clients +do not need to be aware of. These API's tend manage the inner workings of the +LLVM system, and only need to be accessed in unusual circumstances. +
++The LLVM type system has a very simple goal: allow clients to compare types for +structural equality with a simple pointer comparison (aka a shallow compare). +This goal makes clients much simpler and faster, and is used throughout the LLVM +system. +
+ ++Unfortunately achieving this goal is not a simple matter. In particular, +recursive types and late resolution of opaque types makes the situation very +difficult to handle. Fortunately, for the most part, our implementation makes +most clients able to be completely unaware of the nasty internal details. The +primary case where clients are exposed to the inner workings of it are when +building a recursive type. In addition to this case, the LLVM bitcode reader, +assembly parser, and linker also have to be aware of the inner workings of this +system. +
+ ++For our purposes below, we need three concepts. First, an "Opaque Type" is +exactly as defined in the language +reference. Second an "Abstract Type" is any type which includes an +opaque type as part of its type graph (for example "{ opaque, i32 }"). +Third, a concrete type is a type that is not an abstract type (e.g. "{ i32, +float }"). +
+ ++Because the most common question is "how do I build a recursive type with LLVM", +we answer it now and explain it as we go. Here we include enough to cause this +to be emitted to an output .ll file: +
-BasicBlock *pb = ...;+
Instruction *newInst = new Instruction(...);
pb->getInstList().push_back(newInst); // appends newInst to pb
+%mylist = type { %mylist*, i32 }
+
++To build this, use the following LLVM APIs: +
+ ++// Create the initial outer struct +PATypeHolder StructTy = OpaqueType::get(); +std::vector<const Type*> Elts; +Elts.push_back(PointerType::getUnqual(StructTy)); +Elts.push_back(Type::Int32Ty); +StructType *NewSTy = StructType::get(Elts); + +// At this point, NewSTy = "{ opaque*, i32 }". Tell VMCore that +// the struct and the opaque type are actually the same. +cast<OpaqueType>(StructTy.get())->refineAbstractTypeTo(NewSTy); + +// NewSTy is potentially invalidated, but StructTy (a PATypeHolder) is +// kept up-to-date +NewSTy = cast<StructType>(StructTy.get()); + +// Add a name for the type to the module symbol table (optional) +MyModule->addTypeName("mylist", NewSTy); ++
+This code shows the basic approach used to build recursive types: build a +non-recursive type using 'opaque', then use type unification to close the cycle. +The type unification step is performed by the refineAbstractTypeTo method, which is +described next. After that, we describe the PATypeHolder class. +
+ ++The refineAbstractTypeTo method starts the type unification process. +While this method is actually a member of the DerivedType class, it is most +often used on OpaqueType instances. Type unification is actually a recursive +process. After unification, types can become structurally isomorphic to +existing types, and all duplicates are deleted (to preserve pointer equality). +
+ ++In the example above, the OpaqueType object is definitely deleted. +Additionally, if there is an "{ \2*, i32}" type already created in the system, +the pointer and struct type created are also deleted. Obviously whenever +a type is deleted, any "Type*" pointers in the program are invalidated. As +such, it is safest to avoid having any "Type*" pointers to abstract types +live across a call to refineAbstractTypeTo (note that non-abstract +types can never move or be deleted). To deal with this, the PATypeHolder class is used to maintain a stable +reference to a possibly refined type, and the AbstractTypeUser class is used to update more +complex datastructures. +
+ ++PATypeHolder is a form of a "smart pointer" for Type objects. When VMCore +happily goes about nuking types that become isomorphic to existing types, it +automatically updates all PATypeHolder objects to point to the new type. In the +example above, this allows the code to maintain a pointer to the resultant +resolved recursive type, even though the Type*'s are potentially invalidated. +
+ ++PATypeHolder is an extremely light-weight object that uses a lazy union-find +implementation to update pointers. For example the pointer from a Value to its +Type is maintained by PATypeHolder objects. +
+ ++Some data structures need more to perform more complex updates when types get +resolved. To support this, a class can derive from the AbstractTypeUser class. +This class +allows it to get callbacks when certain types are resolved. To register to get +callbacks for a particular type, the DerivedType::{add/remove}AbstractTypeUser +methods can be called on a type. Note that these methods only work for + abstract types. Concrete types (those that do not include any opaque +objects) can never be refined. +
+The +ValueSymbolTable class provides a symbol table that the Function and +Module classes use for naming value definitions. The symbol table +can provide a name for any Value. +The +TypeSymbolTable class is used by the Module class to store +names for types.
+ +Note that the SymbolTable class should not be directly accessed +by most clients. It should only be used when iteration over the symbol table +names themselves are required, which is very special purpose. Note that not +all LLVM +Values have names, and those without names (i.e. they have +an empty name) do not exist in the symbol table. +
+ +These symbol tables support iteration over the values/types in the symbol +table with begin/end/iterator and supports querying to see if a +specific name is in the symbol table (with lookup). The +ValueSymbolTable class exposes no public mutator methods, instead, +simply call setName on a value, which will autoinsert it into the +appropriate symbol table. For types, use the Module::addTypeName method to +insert entries into the symbol table.
+ +The +User class provides a basis for expressing the ownership of User +towards other +Values. The +Use helper class is employed to do the bookkeeping and to facilitate O(1) +addition and removal.
+ + + + ++A subclass of User can choose between incorporating its Use objects +or refer to them out-of-line by means of a pointer. A mixed variant +(some Uses inline others hung off) is impractical and breaks the invariant +that the Use objects belonging to the same User form a contiguous array. +
++We have 2 different layouts in the User (sub)classes: +
-
+
Layout a) +The Use object(s) are inside (resp. at fixed offset) of the User +object and there are a fixed number of them.
+ +Layout b) +The Use object(s) are referenced by a pointer to an +array from the User object and there may be a variable +number of them.
+
+As of v2.4 each layout still possesses a direct pointer to the +start of the array of Uses. Though not mandatory for layout a), +we stick to this redundancy for the sake of simplicity. +The User object also stores the number of Use objects it +has. (Theoretically this information can also be calculated +given the scheme presented below.)
++Special forms of allocation operators (operator new) +enforce the following memory layouts:
+ +-
+
Layout a) is modelled by prepending the User object by the Use[] array.
+ ++...---.---.---.---.-------... + | P | P | P | P | User +'''---'---'---'---'-------''' +
+ +Layout b) is modelled by pointing at the Use[] array.
++.-------... +| User +'-------''' + | + v + .---.---.---.---... + | P | P | P | P | + '---'---'---'---''' +
+
+Since the Use objects are deprived of the direct (back)pointer to +their User objects, there must be a fast and exact method to +recover it. This is accomplished by the following scheme:
+-
+
- 00 —> binary digit 0 +
- 01 —> binary digit 1 +
- 10 —> stop and calculate (s) +
- 11 —> full stop (S) +
+Given a Use*, all we have to do is to walk till we get +a stop and we either have a User immediately behind or +we have to walk to the next stop picking up digits +and calculating the offset:
++.---.---.---.---.---.---.---.---.---.---.---.---.---.---.---.---.---------------- +| 1 | s | 1 | 0 | 1 | 0 | s | 1 | 1 | 0 | s | 1 | 1 | s | 1 | S | User (or User*) +'---'---'---'---'---'---'---'---'---'---'---'---'---'---'---'---'---------------- + |+15 |+10 |+6 |+3 |+1 + | | | | |__> + | | | |__________> + | | |______________________> + | |______________________________________> + |__________________________________________________________> ++
+Only the significant number of bits need to be stored between the +stops, so that the worst case is 20 memory accesses when there are +1000 Use objects associated with a User.
+ + + + ++The following literate Haskell fragment demonstrates the concept:
++> import Test.QuickCheck +> +> digits :: Int -> [Char] -> [Char] +> digits 0 acc = '0' : acc +> digits 1 acc = '1' : acc +> digits n acc = digits (n `div` 2) $ digits (n `mod` 2) acc +> +> dist :: Int -> [Char] -> [Char] +> dist 0 [] = ['S'] +> dist 0 acc = acc +> dist 1 acc = let r = dist 0 acc in 's' : digits (length r) r +> dist n acc = dist (n - 1) $ dist 1 acc +> +> takeLast n ss = reverse $ take n $ reverse ss +> +> test = takeLast 40 $ dist 20 [] +> ++
+Printing <test> gives: "1s100000s11010s10100s1111s1010s110s11s1S"
++The reverse algorithm computes the length of the string just by examining +a certain prefix:
+ +
+> pref :: [Char] -> Int
+> pref "S" = 1
+> pref ('s':'1':rest) = decode 2 1 rest
+> pref (_:rest) = 1 + pref rest
+>
+> decode walk acc ('0':rest) = decode (walk + 1) (acc * 2) rest
+> decode walk acc ('1':rest) = decode (walk + 1) (acc * 2 + 1) rest
+> decode walk acc _ = walk + acc
+>
+
++Now, as expected, printing <pref test> gives 40.
++We can quickCheck this with following property:
+ ++> testcase = dist 2000 [] +> testcaseLength = length testcase +> +> identityProp n = n > 0 && n <= testcaseLength ==> length arr == pref arr +> where arr = takeLast n testcase +> ++
+As expected <quickCheck identityProp> gives:
+ ++*Main> quickCheck identityProp +OK, passed 100 tests. ++
+Let's be a bit more exhaustive:
+ +
+>
+> deepCheck p = check (defaultConfig { configMaxTest = 500 }) p
+>
+
++And here is the result of <deepCheck identityProp>:
+ ++*Main> deepCheck identityProp +OK, passed 500 tests. ++ + + + +
+To maintain the invariant that the 2 LSBits of each Use** in Use +never change after being set up, setters of Use::Prev must re-tag the +new Use** on every modification. Accordingly getters must strip the +tag bits.
++For layout b) instead of the User we find a pointer (User* with LSBit set). +Following this pointer brings us to the User. A portable trick ensures +that the first bytes of User (if interpreted as a pointer) never has +the LSBit set. (Portability is relying on the fact that all known compilers place the +vptr in the first word of the instances.)
+ +#include "llvm/Type.h"
+
doxygen info: Type Class
The Core LLVM classes are the primary means of representing the program +being inspected or transformed. The core LLVM classes are defined in +header files in the include/llvm/ directory, and implemented in +the lib/VMCore directory.
+ +becomes:
+BasicBlock *pb = ...;+
Instruction *newInst = new Instruction(..., pb);
Type is a superclass of all type classes. Every Value has + a Type. Type cannot be instantiated directly but only + through its subclasses. Certain primitive types (VoidType, + LabelType, FloatType and DoubleType) have hidden + subclasses. They are hidden because they offer no useful functionality beyond + what the Type class offers except to distinguish themselves from + other subclasses of Type.
+All other types are subclasses of DerivedType. Types can be + named, but this is not a requirement. There exists exactly + one instance of a given shape at any one time. This allows type equality to + be performed with address equality of the Type Instance. That is, given two + Type* values, the types are identical if the pointers are identical. +
+which is much cleaner, especially if you are creating - long instruction streams.
+ + -Instruction instances that are already in BasicBlocks - are implicitly associated with an existing instruction list: the instruction - list of the enclosing basic block. Thus, we could have accomplished the same - thing as the above code without being given a BasicBlock by doing: -
+-
+
- bool isInteger() const: Returns true for any integer type. -
Instruction *pi = ...;+
Instruction *newInst = new Instruction(...);
pi->getParent()->getInstList().insert(pi, newInst);
In fact, this sequence of steps occurs so frequently that the - Instruction class and Instruction-derived classes provide - constructors which take (as a default parameter) a pointer to an - Instruction which the newly-created Instruction should - precede. That is, Instruction constructors are capable of - inserting the newly-created instance into the BasicBlock of a - provided instruction, immediately before that instruction. Using an - Instruction constructor with a insertBefore (default) - parameter, the above code becomes:
+Instruction* pi = ...;+
Instruction* newInst = new Instruction(..., pi);
which is much cleaner, especially if you're creating a lot of -instructions and adding them to BasicBlocks.
--
+
- IntegerType +
- Subclass of DerivedType that represents integer types of any bit width.
+ Any bit width between IntegerType::MIN_INT_BITS (1) and
+ IntegerType::MAX_INT_BITS (~8 million) can be represented.
+
-
+
- static const IntegerType* get(unsigned NumBits): get an integer + type of a specific bit width. +
- unsigned getBitWidth() const: Get the bit width of an integer + type. +
+ - SequentialType +
- This is subclassed by ArrayType and PointerType
+
-
+
- const Type * getElementType() const: Returns the type of each + of the elements in the sequential type. +
+ - ArrayType +
- This is a subclass of SequentialType and defines the interface for array
+ types.
+
-
+
- unsigned getNumElements() const: Returns the number of + elements in the array. +
+ - PointerType +
- Subclass of SequentialType for pointer types. +
- VectorType +
- Subclass of SequentialType for vector types. A + vector type is similar to an ArrayType but is distinguished because it is + a first class type wherease ArrayType is not. Vector types are used for + vector operations and are usually small vectors of of an integer or floating + point type. +
- StructType +
- Subclass of DerivedTypes for struct types. +
- FunctionType +
- Subclass of DerivedTypes for function types.
+
-
+
- bool isVarArg() const: Returns true if its a vararg + function +
- const Type * getReturnType() const: Returns the + return type of the function. +
- const Type * getParamType (unsigned i): Returns + the type of the ith parameter. +
- const unsigned getNumParams() const: Returns the + number of formal parameters. +
+ - OpaqueType +
- Sublcass of DerivedType for abstract types. This class + defines no content and is used as a placeholder for some other type. Note + that OpaqueType is used (temporarily) during type resolution for forward + references of types. Once the referenced type is resolved, the OpaqueType + is replaced with the actual type. OpaqueType can also be used for data + abstraction. At link time opaque types can be resolved to actual types + of the same name. +
Deleting an instruction from an existing sequence of instructions that form a -BasicBlock is very straight-forward. First, -you must have a pointer to the instruction that you wish to delete. Second, you -need to obtain the pointer to that instruction's basic block. You use the -pointer to the basic block to get its list of instructions and then use the -erase function to remove your instruction. For example:
+#include "llvm/Module.h"
doxygen info:
+Module Class
Instruction *I = .. ;+
BasicBlock *BB = I->getParent();
BB->getInstList().erase(I);
The Module class represents the top level structure present in LLVM +programs. An LLVM module is effectively either a translation unit of the +original program or a combination of several translation units merged by the +linker. The Module class keeps track of a list of Functions, a list of GlobalVariables, and a SymbolTable. Additionally, it contains a few +helpful member functions that try to make common operations easy.
Replacing individual instructions
+-
+
- Module::Module(std::string name = "") +
Including "llvm/Transforms/Utils/BasicBlockUtils.h" -permits use of two very useful replace functions: ReplaceInstWithValue -and ReplaceInstWithInst.
+Constructing a Module is easy. You can optionally +provide a name for it (probably based on the name of the translation unit).
-Deleting Instructions
+-
+
- Module::iterator - Typedef for function list iterator
+ Module::const_iterator - Typedef for const_iterator.
+ + begin(), end() + size(), empty() + +These are forwarding methods that make it easy to access the contents of + a Module object's Function + list.
+
+ - Module::FunctionListType &getFunctionList()
+
+
Returns the list of Functions. This is + necessary to use when you need to update the list or perform a complex + action that doesn't have a forwarding method.
+ +
+
-
-
- ReplaceInstWithValue +
- Module::global_iterator - Typedef for global variable list iterator
-This function replaces all uses (within a basic block) of a given - instruction with a value, and then removes the original instruction. The - following example illustrates the replacement of the result of a particular - AllocaInst that allocates memory for a single integer with an null - pointer to an integer.
+ Module::const_global_iterator - Typedef for const_iterator.
-AllocaInst* instToReplace = ...;
BasicBlock::iterator ii(instToReplace);
ReplaceInstWithValue(instToReplace->getParent()->getInstList(), ii,
Constant::getNullValue(PointerType::get(Type::IntTy)));
+ global_begin(), global_end()
+ global_size(), global_empty()
- - ReplaceInstWithInst
+
These are forwarding methods that make it easy to access the contents of + a Module object's GlobalVariable list.
- - Module::GlobalListType &getGlobalList()
+
+
Returns the list of GlobalVariables. This is necessary to + use when you need to update the list or perform a complex action that + doesn't have a forwarding method.
-AllocaInst* instToReplace = ...;
BasicBlock::iterator ii(instToReplace);
ReplaceInstWithInst(instToReplace->getParent()->getInstList(), ii,
new AllocaInst(Type::IntTy, 0, "ptrToReplacedInt"));
+
This function replaces a particular instruction with another - instruction. The following example illustrates the replacement of one - AllocaInst with another.
+
Replacing multiple uses of Users and Values
+-
You can use Value::replaceAllUsesWith and -User::replaceUsesOfWith to change more than one use at a time. See the -doxygen documentation for the Value Class -and User Class, respectively, for more -information.
+-
+
- SymbolTable *getSymbolTable()
-
+
Return a reference to the SymbolTable + for this Module.
-
-
-
+
- Function *getFunction(const std::string
+ &Name, const FunctionType *Ty)
-
The Core LLVM classes are the primary means of representing the program -being inspected or transformed. The core LLVM classes are defined in -header files in the include/llvm/ directory, and implemented in -the lib/VMCore directory.
+Look up the specified function in the Module SymbolTable. If it does not exist, return + null.
+
+ - Function *getOrInsertFunction(const
+ std::string &Name, const FunctionType *T)
+
+
Look up the specified function in the Module SymbolTable. If it does not exist, add an + external declaration for the function and return it.
+
+ - std::string getTypeName(const Type *Ty)
+
+
If there is at least one entry in the SymbolTable for the specified Type, return it. Otherwise return the empty + string.
+
+ - bool addTypeName(const std::string &Name, const Type *Ty)
+
+
Insert an entry in the SymbolTable + mapping Name to Ty. If there is already an entry for this + name, true is returned and the SymbolTable is not modified.
+
#include "llvm/Value.h"
-doxygen info: Value Class
The Value class is the most important class in the LLVM Source base. It represents a typed value that may be used (among other things) as an @@ -981,9 +2778,13 @@ and this Type is available through the getType() method. In addition, all LLVM values can be named. The "name" of the Value is a symbolic string printed in the LLVM code:
-%foo = add int 1, 2+
+%foo = add i32 1, 2 ++
The name of this instruction is "foo". NOTE +
The name of this instruction is "foo". NOTE that the name of any value may be missing (an empty string), so names should ONLY be used for debugging (making the source code easier to read, debugging printouts), they should not be used to keep track of values or map @@ -1042,7 +2843,12 @@ be aware of the precaution above.
produces a constant value (for example through constant folding), you can replace all uses of the instruction with the constant like this: -Inst->replaceAllUsesWith(ConstVal);+
+Inst->replaceAllUsesWith(ConstVal); ++
- User::op_const_iterator use_iterator op_begin() - -Get an iterator to the start of the operand list.
- use_iterator op_end() - Get an iterator to the end of the + op_iterator op_begin() - Get an iterator to the start of +the operand list.
+ op_iterator op_end() - Get an iterator to the end of the operand list.
Together, these methods make up the iterator based interface to the operands of a User.
-
-
- BasicBlock *getParent()
-
Returns the BasicBlock that -this Instruction is embedded into.
- - bool mayWriteToMemory()
-
Returns true if the instruction writes to memory, i.e. it is a - call,free,invoke, or store.
- - unsigned getOpcode()
-
Returns the opcode for the Instruction.
- - Instruction *clone() const
-
Returns another instance of the specified instruction, identical -in all ways to the original except that the instruction has no parent -(ie it's not embedded into a BasicBlock), -and it has no name
-
#include "llvm/BasicBlock.h"
-doxygen info: BasicBlock
-Class
-Superclass: Value
This class represents a single entry multiple exit section of the code, -commonly known as a basic block by the compiler community. The -BasicBlock class maintains a list of Instructions, which form the body of the block. -Matching the language definition, the last element of this list of instructions -is always a terminator instruction (a subclass of the TerminatorInst class).
- -In addition to tracking the list of instructions that make up the block, the -BasicBlock class also keeps track of the Function that it is embedded into.
- -Note that BasicBlocks themselves are Values, because they are referenced by instructions -like branches and can go in the switch tables. BasicBlocks have type -label.
- --
+
- BinaryOperator
+
This subclasses represents all two operand instructions whose operands + must be the same type, except for the comparison instructions.
+ - CastInst
+
This subclass is the parent of the 12 casting instructions. It provides + common operations on cast instructions.
+ - CmpInst
+
This subclass respresents the two comparison instructions, + ICmpInst (integer opreands), and + FCmpInst (floating point operands).
+ - TerminatorInst
+
This subclass is the parent of all terminator instructions (those which + can terminate a block).
+
-
-
-
- BasicBlock(const std::string &Name = "", Function *Parent = 0)
-
-
The BasicBlock constructor is used to create new basic blocks for -insertion into a function. The constructor optionally takes a name for the new -block, and a Function to insert it into. If -the Parent parameter is specified, the new BasicBlock is -automatically inserted at the end of the specified Function, if not specified, the BasicBlock must be -manually inserted into the Function.
-
- - BasicBlock::iterator - Typedef for instruction list iterator
-BasicBlock::const_iterator - Typedef for const_iterator.
-begin(), end(), front(), back(), -size(), empty(), rbegin(), rend() - -STL-style functions for accessing the instruction list. +
These methods and typedefs are forwarding functions that have the same -semantics as the standard library methods of the same names. These methods -expose the underlying instruction list of a basic block in a way that is easy to -manipulate. To get the full complement of container operations (including -operations to update the list), you must use the getInstList() -method.
+-
+
- BasicBlock *getParent()
+
Returns the BasicBlock that +this Instruction is embedded into.
+ - bool mayWriteToMemory()
+
Returns true if the instruction writes to memory, i.e. it is a + call,free,invoke, or store.
+ - unsigned getOpcode()
+
Returns the opcode for the Instruction.
+ - Instruction *clone() const
+
Returns another instance of the specified instruction, identical +in all ways to the original except that the instruction has no parent +(ie it's not embedded into a BasicBlock), +and it has no name
+
This method is used to get access to the underlying container that actually -holds the Instructions. This method must be used when there isn't a forwarding -function in the BasicBlock class for the operation that you would like -to perform. Because there are no forwarding functions for "updating" -operations, you need to use this if you want to update the contents of a -BasicBlock.
Returns a pointer to Function the block is -embedded into, or a null pointer if it is homeless.
Constant represents a base class for different types of constants. It +is subclassed by ConstantInt, ConstantArray, etc. for representing +the various types of Constants. GlobalValue is also +a subclass, which represents the address of a global variable or function. +
-Returns a pointer to the terminator instruction that appears at the end of -the BasicBlock. If there is no terminator instruction, or if the last -instruction in the block is not a terminator, then a null pointer is -returned.
-
+
- ConstantInt : This subclass of Constant represents an integer constant of
+ any width.
+
-
+
- const APInt& getValue() const: Returns the underlying + value of this constant, an APInt value. +
- int64_t getSExtValue() const: Converts the underlying APInt + value to an int64_t via sign extension. If the value (not the bit width) + of the APInt is too large to fit in an int64_t, an assertion will result. + For this reason, use of this method is discouraged. +
- uint64_t getZExtValue() const: Converts the underlying APInt + value to a uint64_t via zero extension. IF the value (not the bit width) + of the APInt is too large to fit in a uint64_t, an assertion will result. + For this reason, use of this method is discouraged. +
- static ConstantInt* get(const APInt& Val): Returns the + ConstantInt object that represents the value provided by Val. + The type is implied as the IntegerType that corresponds to the bit width + of Val. +
- static ConstantInt* get(const Type *Ty, uint64_t Val): + Returns the ConstantInt object that represents the value provided by + Val for integer type Ty. +
+ - ConstantFP : This class represents a floating point constant.
+
-
+
- double getValue() const: Returns the underlying value of + this constant. +
+ - ConstantArray : This represents a constant array.
+
-
+
- const std::vector<Use> &getValues() const: Returns + a vector of component constants that makeup this array. +
+ - ConstantStruct : This represents a constant struct.
+
-
+
- const std::vector<Use> &getValues() const: Returns + a vector of component constants that makeup this array. +
+ - GlobalValue : This represents either a global variable or a function. In + either case, the value is a constant fixed address (after linking). +
doxygen info: GlobalValue Class
-Superclasses: User, Value +Superclasses: Constant, +User, Value
Global values (GlobalVariables or Functions) are the only LLVM values that are @@ -1292,11 +3096,11 @@ global is always a pointer to its contents. It is important to remember this when using the GetElementPtrInst instruction because this pointer must be dereferenced first. For example, if you have a GlobalVariable (a subclass of GlobalValue) that is an array of 24 ints, type [24 x -int], then the GlobalVariable is a pointer to that array. Although +i32], then the GlobalVariable is a pointer to that array. Although the address of the first element of this array and the value of the GlobalVariable are the same, they have different types. The -GlobalVariable's type is [24 x int]. The first element's type -is int. Because of this, accessing a global value requires you to +GlobalVariable's type is [24 x i32]. The first element's type +is i32. Because of this, accessing a global value requires you to dereference the pointer with GetElementPtrInst first, then its elements can be accessed. This is explained in the LLVM Language Reference Manual.
@@ -1335,15 +3139,17 @@ GlobalValue is currently embedded into.#include "llvm/Function.h"
doxygen
info: Function Class
-Superclasses: GlobalValue, User, Value
The Function class represents a single procedure in LLVM. It is actually one of the more complex classes in the LLVM heirarchy because it must keep track of a large amount of data. The Function class keeps track -of a list of BasicBlocks, a list of formal Arguments, and a SymbolTable.
+of a list of BasicBlocks, a list of formal +Arguments, and a +SymbolTable.The list of BasicBlocks is the most commonly used part of Function objects. The list imposes an implicit @@ -1387,428 +3193,245 @@ is its address (after linking) which is guaranteed to be constant.
- Function(const FunctionType
- *Ty, LinkageTypes Linkage, const std::string &N = "", Module* Parent = 0)
-
-
Constructor used when you need to create new Functions to add - the the program. The constructor must specify the type of the function to - create and what type of linkage the function should have. The FunctionType argument - specifies the formal arguments and return value for the function. The same - FunctionType value can be used to - create multiple functions. The Parent argument specifies the Module - in which the function is defined. If this argument is provided, the function - will automatically be inserted into that module's list of - functions.
-
- - bool isExternal()
-
-
Return whether or not the Function has a body defined. If the - function is "external", it does not have a body, and thus must be resolved - by linking with a function defined in a different translation unit.
-
- - Function::iterator - Typedef for basic block list iterator
- Function::const_iterator - Typedef for const_iterator.
- - begin(), end(), front(), back(), - size(), empty(), rbegin(), rend() - -These are forwarding methods that make it easy to access the contents of - a Function object's BasicBlock - list.
-
- - Function::BasicBlockListType &getBasicBlockList()
-
-
Returns the list of BasicBlocks. This - is necessary to use when you need to update the list or perform a complex - action that doesn't have a forwarding method.
-
- - Function::aiterator - Typedef for the argument list
-iterator
- Function::const_aiterator - Typedef for const_iterator.
- - abegin(), aend(), afront(), aback(), - asize(), aempty(), arbegin(), arend() - -These are forwarding methods that make it easy to access the contents of - a Function object's Argument - list.
-
- - Function::ArgumentListType &getArgumentList()
-
-
Returns the list of Arguments. This is - necessary to use when you need to update the list or perform a complex - action that doesn't have a forwarding method.
-
- - BasicBlock &getEntryBlock()
-
-
Returns the entry BasicBlock for the - function. Because the entry block for the function is always the first - block, this returns the first block of the Function.
-
- - Type *getReturnType()
- FunctionType *getFunctionType() - -This traverses the Type of the - Function and returns the return type of the function, or the FunctionType of the actual - function.
-
- - SymbolTable *getSymbolTable()
-
-
Return a pointer to the SymbolTable - for this Function.
-
#include "llvm/GlobalVariable.h"
-
-doxygen info: GlobalVariable
-Class
Superclasses: GlobalValue, User, Value
Global variables are represented with the (suprise suprise) -GlobalVariable class. Like functions, GlobalVariables are also -subclasses of GlobalValue, and as such are -always referenced by their address (global values must live in memory, so their -"name" refers to their address). See GlobalValue for more on this. Global variables -may have an initial value (which must be a Constant), and if they have an initializer, they -may be marked as "constant" themselves (indicating that their contents never -change at runtime).
- --
-
- GlobalVariable(const Type *Ty, bool
- isConstant, LinkageTypes& Linkage, Constant
- *Initializer = 0, const std::string &Name = "", Module* Parent = 0)
-
-
Create a new global variable of the specified type. If - isConstant is true then the global variable will be marked as - unchanging for the program. The Linkage parameter specifies the type of - linkage (internal, external, weak, linkonce, appending) for the variable. If - the linkage is InternalLinkage, WeakLinkage, or LinkOnceLinkage, then - the resultant global variable will have internal linkage. AppendingLinkage - concatenates together all instances (in different translation units) of the - variable into a single variable but is only applicable to arrays. See - the LLVM Language Reference for - further details on linkage types. Optionally an initializer, a name, and the - module to put the variable into may be specified for the global variable as - well.
-
- - bool isConstant() const
-
-
Returns true if this is a global variable that is known not to - be modified at runtime.
-
- - bool hasInitializer()
-
-
Returns true if this GlobalVariable has an intializer.
-
- - Constant *getInitializer()
-
-
Returns the intial value for a GlobalVariable. It is not legal - to call this method if there is no initializer.
-
#include "llvm/Module.h"
doxygen info:
-Module Class
The Module class represents the top level structure present in LLVM -programs. An LLVM module is effectively either a translation unit of the -original program or a combination of several translation units merged by the -linker. The Module class keeps track of a list of Functions, a list of GlobalVariables, and a SymbolTable. Additionally, it contains a few -helpful member functions that try to make common operations easy.
- --
-
- Module::Module(std::string name = "") -
Constructing a Module is easy. You can optionally -provide a name for it (probably based on the name of the translation unit).
- --
-
- Module::iterator - Typedef for function list iterator
- Module::const_iterator - Typedef for const_iterator.
- - begin(), end(), front(), back(), - size(), empty(), rbegin(), rend() - -These are forwarding methods that make it easy to access the contents of - a Module object's Function - list.
-
- - Module::FunctionListType &getFunctionList()
-
-
Returns the list of Functions. This is - necessary to use when you need to update the list or perform a complex - action that doesn't have a forwarding method.
- -
-
- -
-
-
- Module::giterator - Typedef for global variable list iterator
+ *Ty, LinkageTypes Linkage, const std::string &N = "", Module* Parent = 0) - Module::const_giterator - Typedef for const_iterator.
+Constructor used when you need to create new Functions to add + the the program. The constructor must specify the type of the function to + create and what type of linkage the function should have. The FunctionType argument + specifies the formal arguments and return value for the function. The same + FunctionType value can be used to + create multiple functions. The Parent argument specifies the Module + in which the function is defined. If this argument is provided, the function + will automatically be inserted into that module's list of + functions.
- gbegin(), gend(), gfront(), gback(),
- gsize(), gempty(), grbegin(), grend()
+ - bool isDeclaration()
-
These are forwarding methods that make it easy to access the contents of - a Module object's GlobalVariable list.
+ - Module::GlobalListType &getGlobalList() +
- Function::iterator - Typedef for basic block list iterator
+ Function::const_iterator - Typedef for const_iterator.
-Returns the list of GlobalVariables. This is necessary to - use when you need to update the list or perform a complex action that - doesn't have a forwarding method.
+ begin(), end() + size(), empty() -
-
Return whether or not the Function has a body defined. If the + function is "external", it does not have a body, and thus must be resolved + by linking with a function defined in a different translation unit.
-These are forwarding methods that make it easy to access the contents of + a Function object's BasicBlock + list.
-+
-
-
- SymbolTable *getSymbolTable()
+
Returns the list of BasicBlocks. This + is necessary to use when you need to update the list or perform a complex + action that doesn't have a forwarding method.
- - Function::arg_iterator - Typedef for the argument list
+iterator
+ Function::const_arg_iterator - Typedef for const_iterator.
-
-
Return a reference to the SymbolTable - for this Module.
++
These are forwarding methods that make it easy to access the contents of + a Function object's Argument + list.
-
-
- Function *getFunction(const std::string - &Name, const FunctionType *Ty) +
- Function::ArgumentListType &getArgumentList()
-
Look up the specified function in the Module SymbolTable. If it does not exist, return - null.
+ - Function *getOrInsertFunction(const - std::string &Name, const FunctionType *T) +
- BasicBlock &getEntryBlock()
-
Look up the specified function in the Module SymbolTable. If it does not exist, add an - external declaration for the function and return it.
+ - std::string getTypeName(const Type *Ty) +
- Type *getReturnType()
+ FunctionType *getFunctionType() -If there is at least one entry in the SymbolTable for the specified Type, return it. Otherwise return the empty - string.
+ - bool addTypeName(const std::string &Name, const Type *Ty) +
- SymbolTable *getSymbolTable()
-
Insert an entry in the SymbolTable - mapping Name to Ty. If there is already an entry for this - name, true is returned and the SymbolTable is not modified.
+
Returns the list of Arguments. This is + necessary to use when you need to update the list or perform a complex + action that doesn't have a forwarding method.
-Returns the entry BasicBlock for the + function. Because the entry block for the function is always the first + block, this returns the first block of the Function.
-This traverses the Type of the + Function and returns the return type of the function, or the FunctionType of the actual + function.
-Return a pointer to the SymbolTable + for this Function.
Constant represents a base class for different types of constants. It -is subclassed by ConstantBool, ConstantInt, ConstantSInt, ConstantUInt, -ConstantArray etc for representing the various types of Constants.
+#include "llvm/GlobalVariable.h"
+
+doxygen info: GlobalVariable
+ Class
+Superclasses: GlobalValue,
+Constant,
+User,
+Value
Global variables are represented with the (suprise suprise) +GlobalVariable class. Like functions, GlobalVariables are also +subclasses of GlobalValue, and as such are +always referenced by their address (global values must live in memory, so their +"name" refers to their constant address). See +GlobalValue for more on this. Global +variables may have an initial value (which must be a +Constant), and if they have an initializer, +they may be marked as "constant" themselves (indicating that their contents +never change at runtime).
-
-
- ConstantSInt : This subclass of Constant represents a signed integer
- constant.
-
-
-
- int64_t getValue() const: Returns the underlying value of - this constant. -
- - ConstantUInt : This class represents an unsigned integer.
-
-
-
- uint64_t getValue() const: Returns the underlying value of - this constant. -
- - ConstantFP : This class represents a floating point constant.
-
-
-
- double getValue() const: Returns the underlying value of - this constant. -
- - ConstantBool : This represents a boolean constant.
-
-
-
- bool getValue() const: Returns the underlying value of this - constant. -
- - ConstantArray : This represents a constant array.
-
-
-
- const std::vector<Use> &getValues() const: Returns - a Vecotr of component constants that makeup this array. -
- - ConstantStruct : This represents a constant struct.
-
-
-
- const std::vector<Use> &getValues() const: Returns - a Vector of component constants that makeup this array. -
- - GlobalValue : This represents either a global variable or a function. In - either case, the value is a constant fixed address (after linking). - +
- GlobalVariable(const Type *Ty, bool
+ isConstant, LinkageTypes& Linkage, Constant
+ *Initializer = 0, const std::string &Name = "", Module* Parent = 0)
+
+
Create a new global variable of the specified type. If + isConstant is true then the global variable will be marked as + unchanging for the program. The Linkage parameter specifies the type of + linkage (internal, external, weak, linkonce, appending) for the variable. + If the linkage is InternalLinkage, WeakAnyLinkage, WeakODRLinkage, + LinkOnceAnyLinkage or LinkOnceODRLinkage, then the resultant + global variable will have internal linkage. AppendingLinkage concatenates + together all instances (in different translation units) of the variable + into a single variable but is only applicable to arrays. See + the LLVM Language Reference for + further details on linkage types. Optionally an initializer, a name, and the + module to put the variable into may be specified for the global variable as + well.
+
+ - bool isConstant() const
+
+
Returns true if this is a global variable that is known not to + be modified at runtime.
+
+ - bool hasInitializer()
+
+
Returns true if this GlobalVariable has an intializer.
+
+ - Constant *getInitializer()
+
+
Returns the intial value for a GlobalVariable. It is not legal + to call this method if there is no initializer.
Type as noted earlier is also a subclass of a Value class. Any primitive -type (like int, short etc) in LLVM is an instance of Type Class. All other -types are instances of subclasses of type like FunctionType, ArrayType -etc. DerivedType is the interface for all such dervied types including -FunctionType, ArrayType, PointerType, StructType. Types can have names. They can -be recursive (StructType). There exists exactly one instance of any type -structure at a time. This allows using pointer equality of Type *s for comparing -types.
+#include "llvm/BasicBlock.h"
+doxygen info: BasicBlock
+Class
+Superclass: Value
This class represents a single entry multiple exit section of the code, +commonly known as a basic block by the compiler community. The +BasicBlock class maintains a list of Instructions, which form the body of the block. +Matching the language definition, the last element of this list of instructions +is always a terminator instruction (a subclass of the TerminatorInst class).
+ +In addition to tracking the list of instructions that make up the block, the +BasicBlock class also keeps track of the Function that it is embedded into.
+ +Note that BasicBlocks themselves are Values, because they are referenced by instructions +like branches and can go in the switch tables. BasicBlocks have type +label.
-
-
- bool isSigned() const: Returns whether an integral numeric type - is signed. This is true for SByteTy, ShortTy, IntTy, LongTy. Note that this is - not true for Float and Double. +
- BasicBlock(const std::string &Name = "", Function *Parent = 0)
+
+
The BasicBlock constructor is used to create new basic blocks for +insertion into a function. The constructor optionally takes a name for the new +block, and a Function to insert it into. If +the Parent parameter is specified, the new BasicBlock is +automatically inserted at the end of the specified Function, if not specified, the BasicBlock must be +manually inserted into the Function.
+
+ - BasicBlock::iterator - Typedef for instruction list iterator
+BasicBlock::const_iterator - Typedef for const_iterator.
+begin(), end(), front(), back(), +size(), empty() +STL-style functions for accessing the instruction list. - - bool isUnsigned() const: Returns whether a numeric type is - unsigned. This is not quite the complement of isSigned... nonnumeric types - return false as they do with isSigned. This returns true for UByteTy, - UShortTy, UIntTy, and ULongTy. +
- bool isInteger() const: Equivalent to isSigned() || isUnsigned(). +
- BasicBlock::InstListType &getInstList() -
- bool isIntegral() const: Returns true if this is an integral - type, which is either Bool type or one of the Integer types. +
- bool isFloatingPoint(): Return true if this is one of the two - floating point types. +
- Function *getParent() -
- isLosslesslyConvertableTo (const Type *Ty) const: Return true if - this type can be converted to 'Ty' without any reinterpretation of bits. For - example, uint to int or one pointer type to another. +
- TerminatorInst *getTerminator()
+
+
Returns a pointer to the terminator instruction that appears at the end of +the BasicBlock. If there is no terminator instruction, or if the last +instruction in the block is not a terminator, then a null pointer is +returned.
- - SequentialType : This is subclassed by ArrayType and PointerType
-
-
-
- const Type * getElementType() const: Returns the type of -each of the elements in the sequential type. -
- - ArrayType : This is a subclass of SequentialType and defines
-interface for array types.
-
-
-
- unsigned getNumElements() const: Returns the number of -elements in the array. -
- - PointerType : Subclass of SequentialType for pointer types. -
- StructType : subclass of DerivedTypes for struct types -
- FunctionType : subclass of DerivedTypes for function types.
-
-
-
- bool isVarArg() const: Returns true if its a vararg - function -
- const Type * getReturnType() const: Returns the - return type of the function. -
- const Type * getParamType (unsigned i): Returns - the type of the ith parameter. -
- const unsigned getNumParams() const: Returns the - number of formal parameters. -
-
These methods and typedefs are forwarding functions that have the same +semantics as the standard library methods of the same names. These methods +expose the underlying instruction list of a basic block in a way that is easy to +manipulate. To get the full complement of container operations (including +operations to update the list), you must use the getInstList() +method.
-This method is used to get access to the underlying container that actually +holds the Instructions. This method must be used when there isn't a forwarding +function in the BasicBlock class for the operation that you would like +to perform. Because there are no forwarding functions for "updating" +operations, you need to use this if you want to update the contents of a +BasicBlock.
-Returns a pointer to Function the block is +embedded into, or a null pointer if it is homeless.
--
Derived Types
+-
-
This subclass of Value defines the interface for incoming formal -arguments to a function. A Function maitanis a list of its formal +arguments to a function. A Function maintains a list of its formal arguments. An argument has a pointer to the parent Function.
This class provides a symbol table that the -Function and -Module classes use for naming definitions. The symbol table can -provide a name for any Value or -Type. SymbolTable is an abstract data -type. It hides the data it contains and provides access to it through a -controlled interface.
- -To use the SymbolTable well, you need to understand the -structure of the information it holds. The class contains two -std::map objects. The first, pmap, is a map of -Type* to maps of name (std::string) to Value*. -The second, tmap, is a map of names to Type*. Thus, Values -are stored in two-dimensions and accessed by Type and name. Types, -however, are stored in a single dimension and accessed only by name.
- -The interface of this class provides three basic types of operations: -
-
-
- Accessors. Accessors provide read-only access to information - such as finding a value for a name with the - lookup method. -
- Mutators. Mutators allow the user to add information to the - SymbolTable with methods like - insert. -
- Iterators. Iterators allow the user to traverse the content - of the symbol table in well defined ways, such as the method - type_begin. -
Accessors
--
-
- Value* lookup(const Type* Ty, const std::string& name) const: - -
- The lookup method searches the type plane given by the - Ty parameter for a Value with the provided name. - If a suitable Value is not found, null is returned. - -
- Type* lookupType( const std::string& name) const: -
- The lookupType method searches through the types for a - Type with the provided name. If a suitable Type - is not found, null is returned. - -
- bool hasTypes() const: -
- This function returns true if an entry has been made into the type - map. - -
- bool isEmpty() const: -
- This function returns true if both the value and types maps are - empty - -
- std::string get_name(const Value*) const: -
- This function returns the name of the Value provided or the empty - string if the Value is not in the symbol table. - -
- std::string get_name(const Type*) const: -
- This function returns the name of the Type provided or the empty - string if the Type is not in the symbol table. -
Mutators
--
-
- void insert(Value *Val): -
- This method adds the provided value to the symbol table. The Value must - have both a name and a type which are extracted and used to place the value - in the correct type plane under the value's name. - -
- void insert(const std::string& Name, Value *Val): -
- Inserts a constant or type into the symbol table with the specified - name. There can be a many to one mapping between names and constants - or types. - -
- void insert(const std::string& Name, Type *Typ): -
- Inserts a type into the symbol table with the specified name. There - can be a many-to-one mapping between names and types. This method - allows a type with an existing entry in the symbol table to get - a new name. - -
- void remove(Value* Val): -
- This method removes a named value from the symbol table. The - type and name of the Value are extracted from \p N and used to - lookup the Value in the correct type plane. If the Value is - not in the symbol table, this method silently ignores the - request. - -
- void remove(Type* Typ): -
- This method removes a named type from the symbol table. The - name of the type is extracted from \P T and used to look up - the Type in the type map. If the Type is not in the symbol - table, this method silently ignores the request. - -
- Value* remove(const std::string& Name, Value *Val): -
- Remove a constant or type with the specified name from the - symbol table. - -
- Type* remove(const std::string& Name, Type* T): -
- Remove a type with the specified name from the symbol table. - Returns the removed Type. - -
- Value *value_remove(const value_iterator& It): -
- Removes a specific value from the symbol table. - Returns the removed value. - -
- bool strip(): -
- This method will strip the symbol table of its names leaving - the type and values. - -
- void clear(): -
- Empty the symbol table completely. -
Iteration
-The following functions describe three types of iterators you can obtain -the beginning or end of the sequence for both const and non-const. It is -important to keep track of the different kinds of iterators. There are -three idioms worth pointing out:
-| Units | Iterator | Idiom |
|---|---|---|
| Planes Of name/Value maps | PI | -
-for (SymbolTable::plane_const_iterator PI = ST.plane_begin(),
- PE = ST.plane_end(); PI != PE; ++PI ) {
- PI->first // This is the Type* of the plane
- PI->second // This is the SymbolTable::ValueMap of name/Value pairs
- |
-
| All name/Type Pairs | TI | --for (SymbolTable::type_const_iterator TI = ST.type_begin(), - TE = ST.type_end(); TI != TE; ++TI ) - TI->first // This is the name of the type - TI->second // This is the Type* value associated with the name - |
-
| name/Value pairs in a plane | VI | --for (SymbolTable::value_const_iterator VI = ST.value_begin(SomeType), - VE = ST.value_end(SomeType); VI != VE; ++VI ) - VI->first // This is the name of the Value - VI->second // This is the Value* value associated with the name - |
-
Using the recommended iterator names and idioms will help you avoid -making mistakes. Of particular note, make sure that whenever you use -value_begin(SomeType) that you always compare the resulting iterator -with value_end(SomeType) not value_end(SomeOtherType) or else you -will loop infinitely.
- --
-
-
- plane_iterator plane_begin(): -
- Get an iterator that starts at the beginning of the type planes. - The iterator will iterate over the Type/ValueMap pairs in the - type planes. - -
- plane_const_iterator plane_begin() const: -
- Get a const_iterator that starts at the beginning of the type - planes. The iterator will iterate over the Type/ValueMap pairs - in the type planes. - -
- plane_iterator plane_end(): -
- Get an iterator at the end of the type planes. This serves as - the marker for end of iteration over the type planes. - -
- plane_const_iterator plane_end() const: -
- Get a const_iterator at the end of the type planes. This serves as - the marker for end of iteration over the type planes. - -
- value_iterator value_begin(const Type *Typ): -
- Get an iterator that starts at the beginning of a type plane. - The iterator will iterate over the name/value pairs in the type plane. - Note: The type plane must already exist before using this. - -
- value_const_iterator value_begin(const Type *Typ) const: -
- Get a const_iterator that starts at the beginning of a type plane. - The iterator will iterate over the name/value pairs in the type plane. - Note: The type plane must already exist before using this. - -
- value_iterator value_end(const Type *Typ): -
- Get an iterator to the end of a type plane. This serves as the marker - for end of iteration of the type plane. - Note: The type plane must already exist before using this. - -
- value_const_iterator value_end(const Type *Typ) const: -
- Get a const_iterator to the end of a type plane. This serves as the - marker for end of iteration of the type plane. - Note: the type plane must already exist before using this. - -
- type_iterator type_begin(): -
- Get an iterator to the start of the name/Type map. - -
- type_const_iterator type_begin() cons: -
- Get a const_iterator to the start of the name/Type map. - -
- type_iterator type_end(): -
- Get an iterator to the end of the name/Type map. This serves as the - marker for end of iteration of the types. - -
- type_const_iterator type_end() const: -
- Get a const-iterator to the end of the name/Type map. This serves - as the marker for end of iteration of the types. - -
- plane_const_iterator find(const Type* Typ ) const: -
- This method returns a plane_const_iterator for iteration over - the type planes starting at a specific plane, given by \p Ty. - -
- plane_iterator find( const Type* Typ : -
- This method returns a plane_iterator for iteration over the - type planes starting at a specific plane, given by \p Ty. - -
- const ValueMap* findPlane( const Type* Typ ) cons: -
- This method returns a ValueMap* for a specific type plane. This - interface is deprecated and may go away in the future. -
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