-
@@ -178,7 +179,7 @@ source tree in the lib/Transforms/Hello directory.
- ... not allowed to modify any Functions that are not in the current SCC. -
- ... allowed to inspect any Function's other than those in the +
- ... not allowed to inspect any Function's other than those in the current SCC and the direct callees of the SCC.
- ... required to preserve the current CallGraph object, updating it
@@ -571,7 +602,7 @@ fast).
-The doInitialization method is designed to do simple initialization +
- virtual bool runOnSCC(const std::vector<CallGraphNode *> &SCCM) = 0; + virtual bool runOnSCC(CallGraphSCC &SCC) = 0;
The runOnSCC method performs the interesting work of the pass, and @@ -727,7 +758,7 @@ program, or false if they didn't.
virtual bool doInitialization(Loop *, LPPassManager &LPM);The doInitialization method is designed to do simple initialization type of stuff that does not depend on the functions being processed. The doInitialization method call is not scheduled to overlap with any other pass executions (thus it should be very fast). LPPassManager @@ -873,16 +904,22 @@ finalization.
A MachineFunctionPass is a part of the LLVM code generator that executes on the machine-dependent representation of each LLVM function in the -program. A MachineFunctionPass is also a FunctionPass, so all +program.
+ +Code generator passes are registered and initialized specially by +TargetMachine::addPassesToEmitFile and similar routines, so they +cannot generally be run from the opt or bugpoint +commands.
+ +A MachineFunctionPass is also a FunctionPass, so all the restrictions that apply to a FunctionPass also apply to it. MachineFunctionPasses also have additional restrictions. In particular, MachineFunctionPasses are not allowed to do any of the following:
-
-
- Modify any LLVM Instructions, BasicBlocks or Functions. +
- Modify or create any LLVM IR Instructions, BasicBlocks, Arguments, + Functions, GlobalVariables, GlobalAliases, or Modules.
- Modify a MachineFunction other than the one currently being processed. -
- Add or remove MachineFunctions from the current Module. -
- Add or remove global variables from the current Module.
- Maintain state across invocations of runOnMachineFunction (including global data) @@ -934,7 +971,7 @@ template, which requires you to pass at least two parameters. The first parameter is the name of the pass that is to be used on the command line to specify that the pass should be added to a program (for example, with opt or bugpoint). The second argument is the -name of the pass, which is to be used for the --help output of +name of the pass, which is to be used for the -help output of programs, as well as for debug output generated by the --debug-pass option. @@ -951,7 +988,7 @@ implement the virtual print method:
- virtual void print(llvm::OStream &O, const Module *M) const; + virtual void print(std::ostream &O, const Module *M) const;
The print method must be implemented by "analyses" in order to print @@ -976,7 +1013,7 @@ depended on.
-One of the main responsibilities of the PassManager is the make sure +
One of the main responsibilities of the PassManager is to make sure that passes interact with each other correctly. Because PassManager tries to optimize the execution of passes it must know how the passes interact with each other and what dependencies exist between @@ -1104,7 +1141,8 @@ the fact that it hacks on the CFG.
- The getAnalysis<> and getAnalysisToUpdate<> methods + The getAnalysis<> and +getAnalysisIfAvailable<> methods@@ -1140,18 +1178,18 @@ For example: }-In above example, runOnFunction for DominatorTree is called by pass manager +In above example, runOnFunction for DominatorTree is called by pass manager before returning a reference to the desired pass.
If your pass is capable of updating analyses if they exist (e.g., BreakCriticalEdges, as described above), you can use the -getAnalysisToUpdate method, which returns a pointer to the analysis if -it is active. For example:
+getAnalysisIfAvailable method, which returns a pointer to the analysis +if it is active. For example:... - if (DominatorSet *DS = getAnalysisToUpdate<DominatorSet>()) { + if (DominatorSet *DS = getAnalysisIfAvailable<DominatorSet>()) { // A DominatorSet is active. This code will update it. } ... @@ -1167,7 +1205,7 @@ it is active. For example:-@@ -1355,7 +1394,8 @@ the LLVM program representation for a single function at a time, instead of traversing the entire program. It reduces the memory consumption of compiler, because, for example, only one DominatorSet -needs to be calculated at a time. This also makes it possible some interesting enhancements in the future. @@ -1371,14 +1411,14 @@ allowing any analysis results to live across the execution of your pass. options that is useful for debugging pass execution, seeing how things work, and diagnosing when you should be preserving more analyses than you currently are (To get information about all of the variants of the --debug-pass -option, just type 'opt --help-hidden'). +option, just type 'opt -help-hidden').Now that we understand the basics of how passes are defined, how the are +
Now that we understand the basics of how passes are defined, how they are used, and how they are required from other passes, it's time to get a little bit fancier. All of the pass relationships that we have seen so far are very simple: one pass depends on one other specific pass to be run before it can run. @@ -1289,8 +1327,9 @@ no problem.
Here we show how the default implementation is specified (using the extra argument to the RegisterAnalysisGroup template). There must be exactly one default implementation available at all times for an Analysis Group to be -used. Here we declare that the BasicAliasAnalysis +used. Only default implementation can derive from ImmutablePass. +Here we declare that the + BasicAliasAnalysis pass is the default implementation for the interface.
By using the --debug-pass=Structure option, for example, we can see how our Hello World pass interacts with other passes. Lets try it out with the gcse and licm passes:
-$ opt -load ../../../Debug/lib/Hello.so -gcse -licm --debug-pass=Structure < hello.bc > /dev/null +$ opt -load ../../../Debug+Asserts/lib/Hello.so -gcse -licm --debug-pass=Structure < hello.bc > /dev/null Module Pass Manager Function Pass Manager Dominator Set Construction @@ -1393,8 +1433,8 @@ Module Pass Manager Module Verifier -- Dominator Set Construction -- Module Verifier - Bytecode Writer ---Bytecode Writer + Bitcode Writer +--Bitcode WriterThis output shows us when passes are constructed and when the analysis @@ -1415,7 +1455,7 @@ passes.
World pass in between the two passes:-$ opt -load ../../../Debug/lib/Hello.so -gcse -hello -licm --debug-pass=Structure < hello.bc > /dev/null +$ opt -load ../../../Debug+Asserts/lib/Hello.so -gcse -hello -licm --debug-pass=Structure < hello.bc > /dev/null Module Pass Manager Function Pass Manager Dominator Set Construction @@ -1434,8 +1474,8 @@ Module Pass Manager Module Verifier -- Dominator Set Construction -- Module Verifier - Bytecode Writer ---Bytecode Writer + Bitcode Writer +--Bitcode Writer Hello: __main Hello: puts Hello: main @@ -1456,7 +1496,7 @@ href="#getAnalysisUsage">getAnalysisUsage method to our pass:Now when we run our pass, we get this output:
-$ opt -load ../../../Debug/lib/Hello.so -gcse -hello -licm --debug-pass=Structure < hello.bc > /dev/null +$ opt -load ../../../Debug+Asserts/lib/Hello.so -gcse -hello -licm --debug-pass=Structure < hello.bc > /dev/null Pass Arguments: -gcse -hello -licm Module Pass Manager Function Pass Manager @@ -1474,8 +1514,8 @@ Module Pass Manager Module Verifier -- Dominator Set Construction -- Module Verifier - Bytecode Writer ---Bytecode Writer + Bitcode Writer +--Bitcode Writer Hello: __main Hello: puts Hello: main @@ -1506,7 +1546,7 @@ need some way to free analysis results when they are no longer useful. TheIf you are writing an analysis or any other pass that retains a significant amount of state (for use by another pass which "requires" your pass and uses the getAnalysis method) you should implement -releaseMEmory to, well, release the memory allocated to maintain this +releaseMemory to, well, release the memory allocated to maintain this internal state. This method is called after the run* method for the class, before the next call of run* in your pass.
@@ -1586,12 +1626,12 @@ form;Note the two spaces prior to the help string produces a tidy result on the ---help query.
+-help query.-$ llc --help +$ llc -help ... - -regalloc - Register allocator to use: (default = linearscan) + -regalloc - Register allocator to use (default=linearscan) =linearscan - linear scan register allocator =local - local register allocator =simple - simple register allocator @@ -1634,7 +1674,7 @@ MachinePassRegistry RegisterMyPasses::Registry;cl::opt<RegisterMyPasses::FunctionPassCtor, false, - RegisterPassParser<RegisterMyPasses> > + RegisterPassParser<RegisterMyPasses> > MyPassOpt("mypass", cl::init(&createDefaultMyPass), cl::desc("my pass option help")); @@ -1697,8 +1737,8 @@ want:+(gdb) break llvm::PassManager::run Breakpoint 1 at 0x2413bc: file Pass.cpp, line 70. -(gdb) run test.bc -load $(LLVMTOP)/llvm/Debug/lib/[libname].so -[passoption] -Starting program: opt test.bc -load $(LLVMTOP)/llvm/Debug/lib/[libname].so -[passoption] +(gdb) run test.bc -load $(LLVMTOP)/llvm/Debug+Asserts/lib/[libname].so -[passoption] +Starting program: opt test.bc -load $(LLVMTOP)/llvm/Debug+Asserts/lib/[libname].so -[passoption] Breakpoint 1, PassManager::run (this=0xffbef174, M=@0x70b298) at Pass.cpp:70 70 bool PassManager::run(Module &M) { return PM->run(M); } (gdb) @@ -1778,13 +1818,15 @@ places (for global resources). Although this is a simple extension, we simply haven't had time (or multiprocessor machines, thus a reason) to implement this. Despite that, we have kept the LLVM passes SMP ready, and you should too. +
+ src="http://jigsaw.w3.org/css-validator/images/vcss-blue" alt="Valid CSS">
+ src="http://www.w3.org/Icons/valid-html401-blue" alt="Valid HTML 4.01"> Chris Lattner
The LLVM Compiler Infrastructure
# Makefile for hello pass -# Path to top level of LLVM heirarchy +# Path to top level of LLVM hierarchy LEVEL = ../../.. # Name of the library to build @@ -188,18 +189,13 @@ LIBRARYNAME = Hello # dlopen/dlsym on the resulting library. LOADABLE_MODULE = 1 -# Tell the build system which LLVM libraries your pass needs. You'll probably -# need at least LLVMSystem.a, LLVMSupport.a, LLVMCore.a but possibly several -# others too. -LLVMLIBS = LLVMCore.a LLVMSupport.a LLVMSystem.a - # Include the makefile implementation stuff include $(LEVEL)/Makefile.common
This makefile specifies that all of the .cpp files in the current directory are to be compiled and linked together into a -Debug/lib/Hello.so shared object that can be dynamically loaded by +Debug+Asserts/lib/Hello.so shared object that can be dynamically loaded by the opt or bugpoint tools via their -load options. If your operating system uses a suffix other than .so (such as windows or Mac OS/X), the appropriate extension will be used.
@@ -222,12 +218,14 @@ Start out with:#include "llvm/Pass.h" #include "llvm/Function.h" +#include "llvm/Support/raw_ostream.h"
Which are needed because we are writing a Pass, and +href="http://llvm.org/doxygen/classllvm_1_1Pass.html">Pass, we are operating on Function's.
+href="http://llvm.org/doxygen/classllvm_1_1Function.html">Function's, +and we will be doing some printing.Next we have:
@@ -262,9 +260,17 @@ href="#passtype">later, but for now, know that FunctionPass's operate a function at a time. ++ static char ID; + Hello() : FunctionPass(&ID) {} ++ +
This declares pass identifier used by LLVM to identify pass. This allows LLVM to +avoid using expensive C++ runtime information.
+virtual bool runOnFunction(Function &F) { - llvm::cerr << "Hello: " << F.getName() << "\n"; + errs() << "Hello: " << F.getName() << "\n"; return false; } }; // end of struct Hello @@ -277,37 +283,56 @@ to do our thing, so we just print out our message with the name of each function.+ +- RegisterPass<Hello> X("hello", "Hello World Pass"); + char Hello::ID = 0; +We initialize pass ID here. LLVM uses ID's address to identify pass so +initialization value is not important.
+ ++ RegisterPass<Hello> X("hello", "Hello World Pass", + false /* Only looks at CFG */, + false /* Analysis Pass */); } // end of anonymous namespaceLastly, we register our class Hello, giving it a command line -argument "hello", and a name "Hello World Pass".
+argument "hello", and a name "Hello World Pass". +Last two RegisterPass arguments are optional. Their default value is false. +If a pass walks CFG without modifying it then third argument is set to true. +If a pass is an analysis pass, for example dominator tree pass, then true +is supplied as fourth argument.As a whole, the .cpp file looks like:
#include "llvm/Pass.h" #include "llvm/Function.h" +#include "llvm/Support/raw_ostream.h" using namespace llvm; namespace { struct Hello : public FunctionPass { + + static char ID; + Hello() : FunctionPass(&ID) {} + virtual bool runOnFunction(Function &F) { - llvm::cerr << "Hello: " << F.getName() << "\n"; + errs() << "Hello: " << F.getName() << "\n"; return false; } }; + char Hello::ID = 0; RegisterPass<Hello> X("hello", "Hello World Pass"); }Now that it's all together, compile the file with a simple "gmake" command in the local directory and you should get a new -"Debug/lib/Hello.so file. Note that everything in this file is +"Debug+Asserts/lib/Hello.so file. Note that everything in this file is contained in an anonymous namespace: this reflects the fact that passes are self contained units that do not need external interfaces (although they can have them) to be useful.
@@ -328,12 +353,12 @@ use the opt tool to access it, once loaded.To test it, follow the example at the end of the Getting Started Guide to compile "Hello World" to -LLVM. We can now run the bytecode file (hello.bc) for the program -through our transformation like this (or course, any bytecode file will +LLVM. We can now run the bitcode file (hello.bc) for the program +through our transformation like this (or course, any bitcode file will work):
-$ opt -load ../../../Debug/lib/Hello.so -hello < hello.bc > /dev/null +$ opt -load ../../../Debug+Asserts/lib/Hello.so -hello < hello.bc > /dev/null Hello: __main Hello: puts Hello: main @@ -347,13 +372,13 @@ interesting way, we just throw away the result of opt (sending it to /dev/null).To see what happened to the other string you registered, try running -opt with the --help option:
+opt with the -help option:-$ opt -load ../../../Debug/lib/Hello.so --help +$ opt -load ../../../Debug+Asserts/lib/Hello.so -help OVERVIEW: llvm .bc -> .bc modular optimizer -USAGE: opt [options] <input bytecode> +USAGE: opt [options] <input bitcode> OPTIONS: Optimizations available: @@ -378,7 +403,7 @@ the execution time of your pass along with the other passes you queue up. For example:@@ -462,11 +487,17 @@ invalidated, and are never "run". href="http://llvm.org/doxygen/classllvm_1_1ModulePass.html">ModulePass" class is the most general of all superclasses that you can use. Deriving from ModulePass indicates that your pass uses the entire program as a unit, -refering to function bodies in no predictable order, or adding and removing +referring to function bodies in no predictable order, or adding and removing functions. Because nothing is known about the behavior of ModulePass -subclasses, no optimization can be done for their execution. A module pass -can use function level passes (e.g. dominators) using getAnalysis interface - getAnalysis-$ opt -load ../../../Debug/lib/Hello.so -hello -time-passes < hello.bc > /dev/null +$ opt -load ../../../Debug+Asserts/lib/Hello.so -hello -time-passes < hello.bc > /dev/null Hello: __main Hello: puts Hello: main @@ -388,7 +413,7 @@ Hello: main Total Execution Time: 0.02 seconds (0.0479059 wall clock) ---User Time--- --System Time-- --User+System-- ---Wall Time--- --- Pass Name --- - 0.0100 (100.0%) 0.0000 ( 0.0%) 0.0100 ( 50.0%) 0.0402 ( 84.0%) Bytecode Writer + 0.0100 (100.0%) 0.0000 ( 0.0%) 0.0100 ( 50.0%) 0.0402 ( 84.0%) Bitcode Writer 0.0000 ( 0.0%) 0.0100 (100.0%) 0.0100 ( 50.0%) 0.0031 ( 6.4%) Dominator Set Construction 0.0000 ( 0.0%) 0.0000 ( 0.0%) 0.0000 ( 0.0%) 0.0013 ( 2.7%) Module Verifier 0.0000 ( 0.0%) 0.0000 ( 0.0%) 0.0000 ( 0.0%) 0.0033 ( 6.9%) Hello World Pass @@ -423,7 +448,7 @@ available, from the most general to the most specific.When choosing a superclass for your Pass, you should choose the most specific class possible, while still being able to meet the requirements listed. This gives the LLVM Pass Infrastructure information necessary to -optimize how passes are run, so that the resultant compiler isn't unneccesarily +optimize how passes are run, so that the resultant compiler isn't unnecessarily slow.
(Function) . +subclasses, no optimization can be done for their execution. + +A module pass can use function level passes (e.g. dominators) using +the getAnalysis interface +getAnalysis<DominatorTree>(llvm::Function *) to provide the +function to retrieve analysis result for, if the function pass does not require +any module or immutable passes. Note that this can only be done for functions for which the +analysis ran, e.g. in the case of dominators you should only ask for the +DominatorTree for function definitions, not declarations.
To write a correct ModulePass subclass, derive from ModulePass and overload the runOnModule method with the @@ -518,7 +549,7 @@ href="#BasicBlockPass">BasicBlockPass, you should derive from