Note that you should not use an isa<> test followed @@ -312,21 +330,12 @@ file (note that you very rarely have to include this file directly).
call to isa<> and a call to cast<> into one statement, which is very convenient. -Another common example is:
- -- // 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.
+ InstVisitor class to dispatch over the instruction type directly. @@ -370,7 +379,7 @@ across). 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 @@ -398,7 +407,7 @@ program hasn't been started yet, you can always just run it with
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 @@ -437,7 +446,7 @@ even if the source lives in multiple files.
The "Support/Statistic.h" file +href="/doxygen/Statistic_8h-source.html">llvm/ADT/Statistic.h" file provides a template 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 @@ -564,18 +573,18 @@ 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&
cerr << *i << "\n";
+ // 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& + std::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: cerr << *blk << "\n";.
- -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*.
+basic block itself: std::cerr << *blk << "\n";.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 + AllocaInst that allocates memory for a single integer with a null pointer to an integer.
AllocaInst* instToReplace = ...;
BasicBlock::iterator ii(instToReplace);
ReplaceInstWithValue(instToReplace->getParent()->getInstList(), ii,
Constant::getNullValue(PointerType::get(Type::IntTy)));
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.
- ++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. +
#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 -operand to an instruction. There are many different types of Values, -such as Constants,Arguments. Even Instructions and Functions are Values.
- -A particular Value may be used many times in the LLVM representation -for a program. For example, an incoming argument to a function (represented -with an instance of the Argument class) is "used" by -every instruction in the function that references the argument. To keep track -of this relationship, the Value class keeps a list of all of the Users that is using it (the User class is a base class for all nodes in the LLVM -graph that can refer to Values). This use list is how LLVM represents -def-use information in the program, and is accessible through the use_* -methods, shown below.
- -Because LLVM is a typed representation, every LLVM Value is typed, -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+
+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. +
-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 -between them. For this purpose, use a std::map of pointers to the -Value itself instead.
++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 bytecode reader, +assembly parser, and linker also have to be aware of the inner workings of this +system. +
-One important aspect of LLVM is that there is no distinction between an SSA -variable and the operation that produces it. Because of this, any reference to -the value produced by an instruction (or the value available as an incoming -argument, for example) is represented as a direct pointer to the instance of -the class that -represents this value. Although this may take some getting used to, it -simplifies the representation and makes it easier to manipulate.
++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, int }"). +Third, a concrete type is a type that is not an abstract type (e.g. "[ int, +float }"). +
These methods are the interface to access the def-use -information in LLVM. As with all other iterators in LLVM, the naming -conventions follow the conventions defined by the STL.
-This method returns the Type of the Value.
-This family of methods is used to access and assign a name to a Value, -be aware of the precaution above.
-+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: +
-This method traverses the use list of a Value changing all Users of the current value to refer to - "V" instead. For example, if you detect that an instruction always - produces a constant value (for example through constant folding), you can - replace all uses of the instruction with the constant like this:
+
+ %mylist = type { %mylist*, int }
+
- Inst->replaceAllUsesWith(ConstVal);-
+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::get(StructTy)); + Elts.push_back(Type::IntTy); + StructType *NewSTy = StructType::get(Elts); - -- The User class -+ // At this point, NewSTy = "{ opaque*, int }". Tell VMCore that + // the struct and the opaque type are actually the same. + cast<OpaqueType>(StructTy.get())->refineAbstractTypeTo(NewSTy); -- -- +-#include "llvm/User.h"
+ // NewSTy is potentially invalidated, but StructTy (a PATypeHolder) is + // kept up-to-date. + NewSTy = cast<StructType>(StructTy.get()); -
-doxygen info: User Class
-Superclass: ValueThe User class is the common base class of all LLVM nodes that may -refer to Values. It exposes a list of "Operands" -that are all of the Values that the User is -referring to. The User class itself is a subclass of -Value.
+ // Add a name for the type to the module symbol table (optional). + MyModule->addTypeName("mylist", NewSTy); + -The operands of a User point directly to the LLVM Value that it refers to. Because LLVM uses Static -Single Assignment (SSA) form, there can only be one definition referred to, -allowing this direct connection. This connection provides the use-def -information in LLVM.
++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). +
-The User class exposes the operand list in two ways: through -an index access interface and through an iterator based interface.
- --
- -- Value *getOperand(unsigned i)
- -
- unsigned getNumOperands() -These two methods expose the operands of the User in a -convenient form for direct access.
- User::op_iterator - Typedef for iterator over the operand -list
-
- 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 -operand list. -Together, these methods make up the iterator based interface to -the operands of a User.
- The Instruction class ++ + ++In the example above, the OpaqueType object is definitely deleted. +Additionally, if there is an "{ \2*, int}" 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. +
-#include "llvm/Instruction.h"
- -
-doxygen info: Instruction Class
-Superclasses: User, ValueThe Instruction class is the common base class for all LLVM -instructions. It provides only a few methods, but is a very commonly used -class. The primary data tracked by the Instruction class itself is the -opcode (instruction type) and the parent BasicBlock the Instruction is embedded -into. To represent a specific type of instruction, one of many subclasses of -Instruction are used.
- -Because the Instruction class subclasses the User class, its operands can be accessed in the same -way as for other Users (with the -getOperand()/getNumOperands() and -op_begin()/op_end() methods).
An important file for -the Instruction class is the llvm/Instruction.def file. This -file contains some meta-data about the various different types of instructions -in LLVM. It describes the enum values that are used as opcodes (for example -Instruction::Add and Instruction::SetLE), as well as the -concrete sub-classes of Instruction that implement the instruction (for -example BinaryOperator and SetCondInst). Unfortunately, the use of macros in -this file confuses doxygen, so these enum values don't show up correctly in the -doxygen output.
++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. +
-+-
+- 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
+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 +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 an opaque objects +somewhere) can never be refined. +
++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.
-#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 the symbol table class is 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. +
-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.
+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
+
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.
+ +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.
+ +#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 +operand to an instruction. There are many different types of Values, +such as Constants,Arguments. Even Instructions and Functions are Values.
+ +A particular Value may be used many times in the LLVM representation +for a program. For example, an incoming argument to a function (represented +with an instance of the Argument class) is "used" by +every instruction in the function that references the argument. To keep track +of this relationship, the Value class keeps a list of all of the Users that is using it (the User class is a base class for all nodes in the LLVM +graph that can refer to Values). This use list is how LLVM represents +def-use information in the program, and is accessible through the use_* +methods, shown below.
+ +Because LLVM is a typed representation, every LLVM Value is typed, +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+ +
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 +between them. For this purpose, use a std::map of pointers to the +Value itself instead.
+ +One important aspect of LLVM is that there is no distinction between an SSA +variable and the operation that produces it. Because of this, any reference to +the value produced by an instruction (or the value available as an incoming +argument, for example) is represented as a direct pointer to the instance of +the class that +represents this value. Although this may take some getting used to, it +simplifies the representation and makes it easier to manipulate.
+ +These methods are the interface to access the def-use +information in LLVM. As with all other iterators in LLVM, the naming +conventions follow the conventions defined by the STL.
+This method returns the Type of the Value.
+This family of methods is used to access and assign a name to a Value, +be aware of the precaution above.
+This method traverses the use list of a Value changing all Users of the current value to refer to + "V" instead. For example, if you detect that an instruction always + 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);+
+#include "llvm/User.h"
+doxygen info: User Class
+Superclass: Value
The User class is the common base class of all LLVM nodes that may +refer to Values. It exposes a list of "Operands" +that are all of the Values that the User is +referring to. The User class itself is a subclass of +Value.
+ +The operands of a User point directly to the LLVM Value that it refers to. Because LLVM uses Static +Single Assignment (SSA) form, there can only be one definition referred to, +allowing this direct connection. This connection provides the use-def +information in LLVM.
+ +The User class exposes the operand list in two ways: through +an index access interface and through an iterator based interface.
+ +These two methods expose the operands of the User in a +convenient form for direct access.
Together, these methods make up the iterator based interface to +the operands of a User.
#include "llvm/Instruction.h"
+doxygen info: Instruction Class
+Superclasses: User, Value
The Instruction class is the common base class for all LLVM +instructions. It provides only a few methods, but is a very commonly used +class. The primary data tracked by the Instruction class itself is the +opcode (instruction type) and the parent BasicBlock the Instruction is embedded +into. To represent a specific type of instruction, one of many subclasses of +Instruction are used.
+ +Because the Instruction class subclasses the User class, its operands can be accessed in the same +way as for other Users (with the +getOperand()/getNumOperands() and +op_begin()/op_end() methods).
An important file for +the Instruction class is the llvm/Instruction.def file. This +file contains some meta-data about the various different types of instructions +in LLVM. It describes the enum values that are used as opcodes (for example +Instruction::Add and Instruction::SetLE), as well as the +concrete sub-classes of Instruction that implement the instruction (for +example BinaryOperator and SetCondInst). Unfortunately, the use of macros in +this file confuses doxygen, so these enum values don't show up correctly in the +doxygen output.
+ +Returns the BasicBlock that +this Instruction is embedded into.
Returns true if the instruction writes to memory, i.e. it is a + call,free,invoke, or store.
Returns the opcode for the Instruction.
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.
+ +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.
-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.
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.
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.
+ +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.
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.
If a GlobalValue has internal linkage (equivalent to being static in C), it is not visible to code outside the current translation @@ -1353,6 +1774,9 @@ href="#Instruction">Instructions, BasicBlocks, or Arguments in the function body.
+Note that Function is a GlobalValue +and therefore also a Constant. The value of the function +is its address (after linking) which is guaranteed to be constant.
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 whether or not it should start out with internal or external - linkage. The FunctionType argument + 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 @@ -1387,8 +1811,8 @@ href="#Argument">Arguments in the function body.
These are forwarding methods that make it easy to access the contents of a Function object's BasicBlock @@ -1400,12 +1824,12 @@ href="#Argument">Arguments in the function body.
is necessary to use when you need to update the list or perform a complex action that doesn't have a forwarding method.These are forwarding methods that make it easy to access the contents of
a Function object's Argument
@@ -1449,7 +1873,7 @@ iterator
#include "llvm/GlobalVariable.h"
-doxygen info: GlobalVariable
+doxygen info: GlobalVariable
Class
Superclasses: GlobalValue, User, Value
#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 @@ -1549,8 +1973,8 @@ provide a name for it (probably based on the name of the translation unit).
These are forwarding methods that make it easy to access the contents of a Module object's Function @@ -1568,12 +1992,12 @@ provide a name for it (probably based on the name of the translation unit).
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: -
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.
- -