The cast<> operator is a "checked cast" operation. It - converts a pointer or reference from a base class to a derived cast, causing + 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<> @@ -385,6 +437,106 @@ are lots of examples in the LLVM source base.
Although LLVM generally does not do much string manipulation, we do have +several important APIs which take strings. Two important examples are the +Value class -- which has names for instructions, functions, etc. -- and the +StringMap class which is used extensively in LLVM and Clang.
+ +These are generic classes, and they need to be able to accept strings which +may have embedded null characters. Therefore, they cannot simply take +a const char *, and taking a const std::string& requires +clients to perform a heap allocation which is usually unnecessary. Instead, +many LLVM APIs use a StringRef or a const Twine& for +passing strings efficiently.
+ +The StringRef data type represents a reference to a constant string +(a character array and a length) and supports the common operations available +on std:string, but does not require heap allocation.
+ +It can be implicitly constructed using a C style null-terminated string, +an std::string, or explicitly with a character pointer and length. +For example, the StringRef find function is declared as:
+ ++ iterator find(StringRef Key); ++ +
and clients can call it using any one of:
+ +
+ Map.find("foo"); // Lookup "foo"
+ Map.find(std::string("bar")); // Lookup "bar"
+ Map.find(StringRef("\0baz", 4)); // Lookup "\0baz"
+
+
+Similarly, APIs which need to return a string may return a StringRef +instance, which can be used directly or converted to an std::string +using the str member function. See +"llvm/ADT/StringRef.h" +for more information.
+ +You should rarely use the StringRef class directly, because it contains +pointers to external memory it is not generally safe to store an instance of the +class (unless you know that the external storage will not be freed). StringRef is +small and pervasive enough in LLVM that it should always be passed by value.
+ +The Twine class is an efficient way for APIs to accept concatenated +strings. For example, a common LLVM paradigm is to name one instruction based on +the name of another instruction with a suffix, for example:
+ ++ New = CmpInst::Create(..., SO->getName() + ".cmp"); ++
The Twine class is effectively a +lightweight rope +which points to temporary (stack allocated) objects. Twines can be implicitly +constructed as the result of the plus operator applied to strings (i.e., a C +strings, an std::string, or a StringRef). The twine delays the +actual concatenation of strings until it is actually required, at which point +it can be efficiently rendered directly into a character array. This avoids +unnecessary heap allocation involved in constructing the temporary results of +string concatenation. See +"llvm/ADT/Twine.h" +for more information.
+ +As with a StringRef, Twine objects point to external memory +and should almost never be stored or mentioned directly. They are intended +solely for use when defining a function which should be able to efficiently +accept concatenated strings.
+ +-DOUT << "I am here!\n"; +DEBUG(errs() << "I am here!\n");
-DOUT << "No debug type\n"; #undef DEBUG_TYPE +DEBUG(errs() << "No debug type\n"); #define DEBUG_TYPE "foo" -DOUT << "'foo' debug type\n"; +DEBUG(errs() << "'foo' debug type\n"); #undef DEBUG_TYPE #define DEBUG_TYPE "bar" -DOUT << "'bar' debug type\n"; +DEBUG(errs() << "'bar' debug type\n")); #undef DEBUG_TYPE #define DEBUG_TYPE "" -DOUT << "No debug type (2)\n"; +DEBUG(errs() << "No debug type (2)\n");
The DEBUG_WITH_TYPE macro is also available for situations where you +would like to set DEBUG_TYPE, but only for one specific DEBUG +statement. It takes an additional first parameter, which is the type to use. For +example, the preceding example could be written as:
+ + +
+DEBUG_WITH_TYPE("", errs() << "No debug type\n");
+DEBUG_WITH_TYPE("foo", errs() << "'foo' debug type\n");
+DEBUG_WITH_TYPE("bar", errs() << "'bar' debug type\n"));
+DEBUG_WITH_TYPE("", errs() << "No debug type (2)\n");
+
+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
+ 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
@@ -628,14 +795,14 @@ 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 whereever you install
+/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 hilight the node in 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
@@ -654,8 +821,8 @@ attributes, then you can call DAG.clearGraphAttrs().
-LLVM has a plethora of datastructures in the llvm/ADT/ directory,
- and we commonly use STL datastructures. This section describes the tradeoffs
+
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.
@@ -665,7 +832,7 @@ 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 lookup
+
- 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
@@ -684,15 +851,24 @@ access the container. Based on that, you should use:
- 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 lookup based on a key.
+ iteration, but do not support efficient look-up based on a key.
+- a string container is a specialized sequential
+ container or reference structure that is used for character or byte
+ arrays.
+
+- 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 catagory of container is determined, you can fine tune the
+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 catagory. Note that constant factors and cache behavior
+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
@@ -734,7 +910,7 @@ 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 (resizable vectors only
+destructors will be run for every element in the array (re-sizable vectors only
construct those elements actually used).
@@ -780,6 +956,49 @@ 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 :).
+
+One worthwhile note about std::vector: avoid code like this:
+
+
+
+for ( ... ) {
+ std::vector<foo> V;
+ use V;
+}
+
+
+
+Instead, write this as:
+
+
+
+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.
+ +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.
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. -
+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.
-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 +
- Sentinels +
Other STL containers are available, such as std::deque (which has similar -characteristics to std::vector, but has higher constant factors and provides -efficient push_front/pop_front methods) and std::string.
- -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.
+ilist_traits<T> is ilist<T>'s customization +mechanism. iplist<T> (and consequently ilist<T>) +publicly derive from this traits class.
+iplist<T> is ilist<T>'s base and as such +supports a slightly narrower interface. Notably, inserters from +T& are absent.
- -ilist_traits<T> is a public base of this class and can be +used for a wide variety of customizations.
-SmallPtrSet -SmallSet -sorted vector -FoldingSet -hash_set -UniqueVector -SetVector -
+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>.
ilists have another specialty that must be considered. To be a good +citizen in the C++ ecosystem, it needs to support the standard container +operations, such as begin and end iterators, etc. Also, the +operator-- must work correctly on the end iterator in the +case of non-empty ilists.
+The only sensible solution to this problem is to allocate a so-called +sentinel along with the intrusive list, which serves as the end +iterator, providing the back-link to the last element. However conforming to the +C++ convention it is illegal to operator++ beyond the sentinel and it +also must not be dereferenced.
- -These constraints allow for some implementation freedom to the ilist +how to allocate and store the sentinel. The corresponding policy is dictated +by ilist_traits<T>. By default a T gets heap-allocated +whenever the need for a sentinel arises.
+ +While the default policy is sufficient in most cases, it may break down when +T does not provide a default constructor. Also, in the case of many +instances of ilists, the memory overhead of the associated sentinels +is wasted. To alleviate the situation with numerous and voluminous +T-sentinels, sometimes a trick is employed, leading to ghostly +sentinels.
+ +Ghostly sentinels are obtained by specially-crafted ilist_traits<T> +which superpose the sentinel with the ilist instance in memory. Pointer +arithmetic is used to obtain the sentinel, which is relative to the +ilist's this pointer. The ilist is augmented by an +extra pointer, which serves as the back-link of the sentinel. This is the only +field in the ghostly sentinel which can be legally accessed.
+Other STL containers are available, such as std::string.
-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.
+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.
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.
+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.
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"; --
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. +
-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.
++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.
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:
+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).
+ +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.
--// 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";.
+ + + +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.
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:
+
+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. +
--#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:
+-std::set<Instruction*> worklist; -worklist.insert(inst_begin(F), inst_end(F)); --
+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. +
-The STL set worklist would now contain all instructions in the -Function pointed to by F.
+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. +
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:
+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.
--Instruction& inst = *i; // Grab reference to instruction reference -Instruction* pinst = &*i; // Grab pointer to instruction reference -const Instruction& inst = *j; -+
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 looking 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.
+ +
+ValueMap is a wrapper around a DenseMap mapping
+Value*s (or subclasses) to another type. When a Value is deleted or RAUW'ed,
+ValueMap will update itself so the new version of the key is mapped to the same
+value, just as if the key were a WeakVH. You can configure exactly how this
+happens, and what else happens on these two events, by passing
+a Config parameter to the ValueMap template.
+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.
+ ++TODO: const char* vs stringref vs smallstring vs std::string. Describe twine, +xref to #string_apis. +
+ +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 dynamic 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 SmallBitVector container provides the same interface as BitVector, but +it is optimized for the case where only a small number of bits, less than +25 or so, are needed. It also transparently supports larger bit counts, but +slightly less efficiently than a plain BitVector, so SmallBitVector should +only be used when larger counts are rare. +
+ ++At this time, SmallBitVector does not support set operations (and, or, xor), +and its operator[] does not provide an assignable lvalue. +
+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 + errs() << "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& + errs() << *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: errs() << *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) + errs() << *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 @@ -1055,7 +1812,7 @@ the last line of the last example,
-Instruction* pinst = &*i; +Instruction *pinst = &*i;
-Instruction* pinst = i; +Instruction *pinst = i;
Unfortunately, these implicit conversions come at a cost; they prevent +these iterators from conforming to standard iterator conventions, and thus +from being usable with standard algorithms and containers. For example, they +prevent the following code, where B is a BasicBlock, +from compiling:
+ ++ llvm::SmallVector<llvm::Instruction *, 16>(B->begin(), B->end()); ++
Because of this, these implicit conversions may be removed some day, +and operator* changed to return a pointer instead of a reference.
+
-Function* 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";
+ errs() << "F is used in instruction:\n";
+ errs() << *Inst << "\n";
}
Alternately, it's common to have an instance of the Note that dereferencing a Value::use_iterator is not a very cheap +operation. Instead of performing *i above several times, consider +doing it only once in the loop body and reusing its result.
+ +Alternatively, 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 @@ -1213,22 +1988,55 @@ the particular Instruction):
-Instruction* pi = ...;
+Instruction *pi = ...;
for (User::op_iterator i = pi->op_begin(), e = pi->op_end(); i != e; ++i) {
- Value* v = *i;
+ Value *v = *i;
// ...
}
Declaring objects as const is an important tool of enforcing +mutation free algorithms (such as analyses, etc.). For this purpose above +iterators come in constant flavors as Value::const_use_iterator +and Value::const_op_iterator. They automatically arise when +calling use/op_begin() on const Value*s or +const User*s respectively. Upon dereferencing, they return +const Use*s. Otherwise the above patterns remain unchanged.
+ +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.
-AllocaInst* ai = new AllocaInst(Type::IntTy); +AllocaInst* ai = new AllocaInst(Type::Int32Ty);
will create an AllocaInst instance that represents the allocation of
-one integer in the current stack frame, at runtime. Each Instruction
+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
@@ -1280,7 +2088,7 @@ 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
+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
@@ -1289,12 +2097,12 @@ used as some kind of index by some other code. To accomplish this, I place an
where indexLoc is now the logical name of the instruction's
-execution value, which is a pointer to an integer on the runtime stack.
-AllocaInst* pa = new AllocaInst(Type::IntTy, 0, "indexLoc");
+AllocaInst* pa = new AllocaInst(Type::Int32Ty, 0, "indexLoc");
Inserting instructions
@@ -1402,9 +2210,7 @@ erase function to remove your instruction. For example:Instruction *I = .. ; -BasicBlock *BB = I->getParent(); - -BB->getInstList().erase(I); +I->eraseFromParent();
- ReplaceInstWithValue
-
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 +
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.
@@ -1441,14 +2247,16 @@ AllocaInst* instToReplace = ...; BasicBlock::iterator ii(instToReplace); ReplaceInstWithValue(instToReplace->getParent()->getInstList(), ii, - Constant::getNullValue(PointerType::get(Type::IntTy))); + Constant::getNullValue(PointerType::getUnqual(Type::Int32Ty)));
This function replaces a particular instruction with another - instruction. The following example illustrates the replacement of one - AllocaInst 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.@@ -1456,7 +2264,7 @@ AllocaInst* instToReplace = ...; BasicBlock::iterator ii(instToReplace); ReplaceInstWithInst(instToReplace->getParent()->getInstList(), ii, - new AllocaInst(Type::IntTy, 0, "ptrToReplacedInt")); + new AllocaInst(Type::Int32Ty, 0, "ptrToReplacedInt"));
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(); ++
In generating IR, you may need some complex types. If you know these types +statically, you can use TypeBuilder<...>::get(), defined +in llvm/Support/TypeBuilder.h, to retrieve them. TypeBuilder +has two forms depending on whether you're building types for cross-compilation +or native library use. TypeBuilder<T, true> requires +that T be independent of the host environment, meaning that it's built +out of types from +the llvm::types +namespace and pointers, functions, arrays, etc. built of +those. TypeBuilder<T, false> additionally allows native C types +whose size may depend on the host compiler. For example,
+ ++FunctionType *ft = TypeBuilder<types::i<8>(types::i<32>*), true>::get(); ++
is easier to read and write than the equivalent
+ ++std::vector<const Type*> params; +params.push_back(PointerType::getUnqual(Type::Int32Ty)); +FunctionType *ft = FunctionType::get(Type::Int8Ty, params, false); ++
See the class +comment for more details.
+ ++This section describes the interaction of the LLVM APIs with multithreading, +both on the part of client applications, and in the JIT, in the hosted +application. +
+ ++Note that LLVM's support for multithreading is still relatively young. Up +through version 2.5, the execution of threaded hosted applications was +supported, but not threaded client access to the APIs. While this use case is +now supported, clients must adhere to the guidelines specified below to +ensure proper operation in multithreaded mode. +
+ ++Note that, on Unix-like platforms, LLVM requires the presence of GCC's atomic +intrinsics in order to support threaded operation. If you need a +multhreading-capable LLVM on a platform without a suitably modern system +compiler, consider compiling LLVM and LLVM-GCC in single-threaded mode, and +using the resultant compiler to build a copy of LLVM with multithreading +support. +
++In order to properly protect its internal data structures while avoiding +excessive locking overhead in the single-threaded case, the LLVM must intialize +certain data structures necessary to provide guards around its internals. To do +so, the client program must invoke llvm_start_multithreaded() before +making any concurrent LLVM API calls. To subsequently tear down these +structures, use the llvm_stop_multithreaded() call. You can also use +the llvm_is_multithreaded() call to check the status of multithreaded +mode. +
+ ++Note that both of these calls must be made in isolation. That is to +say that no other LLVM API calls may be executing at any time during the +execution of llvm_start_multithreaded() or llvm_stop_multithreaded +. It's is the client's responsibility to enforce this isolation. +
+ ++The return value of llvm_start_multithreaded() indicates the success or +failure of the initialization. Failure typically indicates that your copy of +LLVM was built without multithreading support, typically because GCC atomic +intrinsics were not found in your system compiler. In this case, the LLVM API +will not be safe for concurrent calls. However, it will be safe for +hosting threaded applications in the JIT, though care +must be taken to ensure that side exits and the like do not accidentally +result in concurrent LLVM API calls. +
++When you are done using the LLVM APIs, you should call llvm_shutdown() +to deallocate memory used for internal structures. This will also invoke +llvm_stop_multithreaded() if LLVM is operating in multithreaded mode. +As such, llvm_shutdown() requires the same isolation guarantees as +llvm_stop_multithreaded(). +
+ ++Note that, if you use scope-based shutdown, you can use the +llvm_shutdown_obj class, which calls llvm_shutdown() in its +destructor. +
+ManagedStatic is a utility class in LLVM used to implement static +initialization of static resources, such as the global type tables. Before the +invocation of llvm_shutdown(), it implements a simple lazy +initialization scheme. Once llvm_start_multithreaded() returns, +however, it uses double-checked locking to implement thread-safe lazy +initialization. +
+ ++Note that, because no other threads are allowed to issue LLVM API calls before +llvm_start_multithreaded() returns, it is possible to have +ManagedStatics of llvm::sys::Mutexs. +
+ ++The llvm_acquire_global_lock() and llvm_release_global_lock +APIs provide access to the global lock used to implement the double-checked +locking for lazy initialization. These should only be used internally to LLVM, +and only if you know what you're doing! +
++LLVMContext is an opaque class in the LLVM API which clients can use +to operate multiple, isolated instances of LLVM concurrently within the same +address space. For instance, in a hypothetical compile-server, the compilation +of an individual translation unit is conceptually independent from all the +others, and it would be desirable to be able to compile incoming translation +units concurrently on independent server threads. Fortunately, +LLVMContext exists to enable just this kind of scenario! +
+ ++Conceptually, LLVMContext provides isolation. Every LLVM entity +(Modules, Values, Types, Constants, etc.) +in LLVM's in-memory IR belongs to an LLVMContext. Entities in +different contexts cannot interact with each other: Modules in +different contexts cannot be linked together, Functions cannot be added +to Modules in different contexts, etc. What this means is that is is +safe to compile on multiple threads simultaneously, as long as no two threads +operate on entities within the same context. +
+ ++In practice, very few places in the API require the explicit specification of a +LLVMContext, other than the Type creation/lookup APIs. +Because every Type carries a reference to its owning context, most +other entities can determine what context they belong to by looking at their +own Type. If you are adding new entities to LLVM IR, please try to +maintain this interface design. +
+ ++For clients that do not require the benefits of isolation, LLVM +provides a convenience API getGlobalContext(). This returns a global, +lazily initialized LLVMContext that may be used in situations where +isolation is not a concern. +
++LLVM's "eager" JIT compiler is safe to use in threaded programs. Multiple +threads can call ExecutionEngine::getPointerToFunction() or +ExecutionEngine::runFunction() concurrently, and multiple threads can +run code output by the JIT concurrently. The user must still ensure that only +one thread accesses IR in a given LLVMContext while another thread +might be modifying it. One way to do that is to always hold the JIT lock while +accessing IR outside the JIT (the JIT modifies the IR by adding +CallbackVHs). Another way is to only +call getPointerToFunction() from the LLVMContext's thread. +
+ +When the JIT is configured to compile lazily (using +ExecutionEngine::DisableLazyCompilation(false)), there is currently a +race condition in +updating call sites after a function is lazily-jitted. It's still possible to +use the lazy JIT in a threaded program if you ensure that only one thread at a +time can call any particular lazy stub and that the JIT lock guards any IR +access, but we suggest using only the eager JIT in threaded programs. +
+Some data structures need more to perform more complex updates when types get -resolved. The SymbolTable class, for example, needs -move and potentially merge type planes in its representation when a pointer -changes.
- -
-To support this, a class can derive from the AbstractTypeUser class. This class
+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
@@ -1658,183 +2713,265 @@ objects) can never be refined.
This class provides a symbol table that the The
+ValueSymbolTable 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.
-SymbolTable is an abstract data type. It hides the data it contains
-and provides access to it through a controlled interface. 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
+Values have names, and those without names (i.e. they have
an empty name) do not exist in the symbol table.
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*.
-Thus, Values are stored in two-dimensions and accessed by Type and
-name. 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 interface of this class provides three basic types of operations:
-
-
+Accessors
-
-
-Mutators
-
-
-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
-}
- |
-
| 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.
+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.
--
+
+
+
+
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.
+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 | + '---'---'---'---''' +
+- 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. +A bit-encoding in the 2 LSBits (least significant bits) of the Use::Prev allows to find the +start of the User object: +
- 00 —> binary digit 0 +
- 01 —> binary digit 1 +
- 10 —> stop and calculate (s) +
- 11 —> full stop (S) +
- 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. +
- 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. +
+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: +
-
+
+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:
+ +-
+
+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:
+-
+
+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.)
+-
-
- bool isInteger() const: Returns true for any integer type. +
- bool isIntegerTy() const: Returns true for any integer type. -
- bool isFloatingPoint(): Return true if this is one of the two +
- bool isFloatingPointTy(): Return true if this is one of the five floating point types.
- bool isAbstract(): Return true if the type is abstract (contains
@@ -1897,7 +3034,7 @@ the lib/VMCore directory.
+ + + +
-
@@ -1929,18 +3066,18 @@ the lib/VMCore directory.
- PointerType
- Subclass of SequentialType for pointer types. -
- PackedType -
- Subclass of SequentialType for packed (vector) types. A - packed type is similar to an ArrayType but is distinguished because it is - a first class type wherease ArrayType is not. Packed types are used for +
- 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 whereas 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 +
- FunctionType
- Subclass of DerivedTypes for function types.
-
-
- bool isVarArg() const: Returns true if its a vararg +
- bool isVarArg() const: Returns true if it's a vararg function
- const Type * getReturnType() const: Returns the return type of the function. @@ -1961,12 +3098,141 @@ the lib/VMCore directory.
+ The Module class ++ ++ ++ + + + +#include "llvm/Module.h"
+ +
doxygen info: +Module ClassThe 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() + 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.
+ +
+
+ +-
+
- Module::global_iterator - Typedef for global variable list iterator
+ + Module::const_global_iterator - Typedef for const_iterator.
+ + global_begin(), global_end() + global_size(), global_empty() + +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.
+ +
+
+ +-
+
- SymbolTable *getSymbolTable()
+
+
Return a reference to the SymbolTable + for this Module.
+ +
+
+ +-
+
- Function *getFunction(const std::string
+ &Name, const FunctionType *Ty)
+
+
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"
@@ -2002,7 +3268,7 @@ method. In addition, all LLVM values can be named. The "name" of theThe 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 @@ -2029,7 +3295,7 @@ simplifies the representation and makes it easier to manipulate.
- Value::use_iterator - Typedef for iterator over the
use-list
- Value::use_const_iterator - Typedef for const_iterator over + Value::const_use_iterator - Typedef for const_iterator over the use-list
unsigned use_size() - Returns the number of users of the value.
@@ -2210,99 +3476,74 @@ in all ways to the original except that the instruction has no parent and it has no name
- -- - - - -#include "llvm/BasicBlock.h"
- -
-doxygen info: BasicBlock -Class
-Superclass: ValueThis 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.
- -- ---
-
-
- 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. - -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::InstListType &getInstList()
-
-
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.
+
- Function *getParent()
+
+
-
Returns a pointer to Function the block is -embedded into, or a null pointer if it is homeless.
+ - TerminatorInst *getTerminator()
+
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). +
- bool isExternal() +
- bool isDeclaration()
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 @@ -2527,7 +3768,7 @@ Superclasses: GlobalValue, User, Value
-Global variables are represented with the (suprise suprise) +
Global variables are represented with the (surprise surprise) 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 @@ -2555,11 +3796,12 @@ never change at runtime).
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 + 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 @@ -2576,202 +3818,104 @@ never change at runtime).
- Constant *getInitializer()
-
Returns the intial value for a GlobalVariable. It is not legal +
Returns the initial value for a GlobalVariable. It is not legal to call this method if there is no initializer.
- Module::Module(std::string name = "") -
- 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.
- -
- - Module::global_iterator - Typedef for global variable list iterator
- - Module::const_global_iterator - Typedef for const_iterator.
- - global_begin(), global_end() - global_size(), global_empty() - -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.
- -
- - SymbolTable *getSymbolTable()
-
Return a reference to the SymbolTable - for this Module.
+ - BasicBlock(const std::string &Name = "", Function *Parent = 0) - -
- 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. --
-
- Function *getFunction(const std::string
- &Name, const FunctionType *Ty)
+
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.
-
Look up the specified function in the Module SymbolTable. If it does not exist, return - null.
+ - Function *getFunction(const std::string
- &Name, const FunctionType *Ty)
+
- BasicBlock::InstListType &getInstList() -
- Function *getOrInsertFunction(const
- std::string &Name, const FunctionType *T)
+
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.
- - Function *getParent() -
- std::string getTypeName(const Type *Ty)
+
Returns a pointer to Function the block is +embedded into, or a null pointer if it is homeless.
- - TerminatorInst *getTerminator() -
- bool addTypeName(const std::string &Name, const Type *Ty)
+
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, including boolean (1 bit integer).
-
-
-
- int64_t getSExtValue() const: Returns the underlying value of - this constant as a sign extended signed integer value. -
- uint64_t getZExtValue() const: Returns the underlying value - of this constant as a zero extended unsigned integer value. -
- 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. -
- - bool 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). - -
-
+
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 +actually one of the more complex classes in the LLVM hierarchy 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 @@ -2397,7 +3638,7 @@ of a list of BasicBlocks, a list of formal
The list of BasicBlocks is the most commonly used part of Function objects. The list imposes an implicit ordering of the blocks in the function, which indicate how the code will be -layed out by the backend. Additionally, the first BasicBlock is the implicit entry node for the Function. It is not legal in LLVM to explicitly branch to this initial block. There are no implicit exit nodes, and in fact there may be multiple exit @@ -2443,13 +3684,13 @@ is its address (after linking) which is guaranteed to be constant.
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 + 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. -#include "llvm/Module.h"
doxygen info:
-Module Class
+doxygen info: BasicBlock +Class
+Superclass: Value -
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.
+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.
-
-
Constructing a Module is easy. You can optionally -provide a name for it (probably based on the name of the translation unit).
- --
-
- -
-
-
-
-
-
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.
-+
Look up the specified function in the Module SymbolTable. If it does not exist, add an - external declaration for the function and return it.
+If there is at least one entry in the SymbolTable for the specified Type, return it. Otherwise return the empty - string.
+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.
Constant represents a base class for different types of constants. It -is subclassed by ConstantInt, ConstantArray, etc. for representing -the various types of Constants.
- --
-
-
-
+ src="http://jigsaw.w3.org/css-validator/images/vcss-blue" alt="Valid CSS">