| //===-- PartialSpecialization.cpp - Specialize for common constants--------===// |
| // |
| // The LLVM Compiler Infrastructure |
| // |
| // This file is distributed under the University of Illinois Open Source |
| // License. See LICENSE.TXT for details. |
| // |
| //===----------------------------------------------------------------------===// |
| // |
| // This pass finds function arguments that are often a common constant and |
| // specializes a version of the called function for that constant. |
| // |
| // This pass simply does the cloning for functions it specializes. It depends |
| // on IPSCCP and DAE to clean up the results. |
| // |
| // The initial heuristic favors constant arguments that are used in control |
| // flow. |
| // |
| //===----------------------------------------------------------------------===// |
| |
| #define DEBUG_TYPE "partialspecialization" |
| #include "llvm/Transforms/IPO.h" |
| #include "llvm/Constant.h" |
| #include "llvm/Instructions.h" |
| #include "llvm/Module.h" |
| #include "llvm/Pass.h" |
| #include "llvm/ADT/Statistic.h" |
| #include "llvm/Transforms/Utils/Cloning.h" |
| #include "llvm/Support/Compiler.h" |
| #include <map> |
| using namespace llvm; |
| |
| STATISTIC(numSpecialized, "Number of specialized functions created"); |
| |
| // Call must be used at least occasionally |
| static const int CallsMin = 5; |
| |
| // Must have 10% of calls having the same constant to specialize on |
| static const double ConstValPercent = .1; |
| |
| namespace { |
| class VISIBILITY_HIDDEN PartSpec : public ModulePass { |
| void scanForInterest(Function&, SmallVector<int, 6>&); |
| void replaceUsersFor(Function&, int, Constant*, Function*); |
| int scanDistribution(Function&, int, std::map<Constant*, int>&); |
| public : |
| static char ID; // Pass identification, replacement for typeid |
| PartSpec() : ModulePass(&ID) {} |
| bool runOnModule(Module &M); |
| }; |
| } |
| |
| char PartSpec::ID = 0; |
| static RegisterPass<PartSpec> |
| X("partialspecialization", "Partial Specialization"); |
| |
| bool PartSpec::runOnModule(Module &M) { |
| bool Changed = false; |
| for (Module::iterator I = M.begin(); I != M.end(); ++I) { |
| Function &F = *I; |
| if (F.isDeclaration()) continue; |
| SmallVector<int, 6> interestingArgs; |
| scanForInterest(F, interestingArgs); |
| |
| // Find the first interesting Argument that we can specialize on |
| // If there are multiple interesting Arguments, then those will be found |
| // when processing the cloned function. |
| bool breakOuter = false; |
| for (unsigned int x = 0; !breakOuter && x < interestingArgs.size(); ++x) { |
| std::map<Constant*, int> distribution; |
| int total = scanDistribution(F, interestingArgs[x], distribution); |
| if (total > CallsMin) |
| for (std::map<Constant*, int>::iterator ii = distribution.begin(), |
| ee = distribution.end(); ii != ee; ++ii) |
| if (total > ii->second && ii->first && |
| ii->second > total * ConstValPercent) { |
| Function* NF = CloneFunction(&F); |
| NF->setLinkage(GlobalValue::InternalLinkage); |
| M.getFunctionList().push_back(NF); |
| replaceUsersFor(F, interestingArgs[x], ii->first, NF); |
| breakOuter = true; |
| Changed = true; |
| } |
| } |
| } |
| return Changed; |
| } |
| |
| /// scanForInterest - This function decides which arguments would be worth |
| /// specializing on. |
| void PartSpec::scanForInterest(Function& F, SmallVector<int, 6>& args) { |
| for(Function::arg_iterator ii = F.arg_begin(), ee = F.arg_end(); |
| ii != ee; ++ii) { |
| for(Value::use_iterator ui = ii->use_begin(), ue = ii->use_end(); |
| ui != ue; ++ui) { |
| // As an initial proxy for control flow, specialize on arguments |
| // that are used in comparisons. |
| if (isa<CmpInst>(ui)) { |
| args.push_back(std::distance(F.arg_begin(), ii)); |
| break; |
| } |
| } |
| } |
| } |
| |
| /// replaceUsersFor - Replace direct calls to F with NF if the arg argnum is |
| /// the constant val |
| void PartSpec::replaceUsersFor(Function& F , int argnum, Constant* val, |
| Function* NF) { |
| ++numSpecialized; |
| for(Value::use_iterator ii = F.use_begin(), ee = F.use_end(); |
| ii != ee; ++ii) |
| if (CallInst* CI = dyn_cast<CallInst>(ii)) |
| if (CI->getOperand(0) == &F && CI->getOperand(argnum + 1) == val) |
| CI->setOperand(0, NF); |
| } |
| |
| int PartSpec::scanDistribution(Function& F, int arg, |
| std::map<Constant*, int>& dist) { |
| bool hasIndirect = false; |
| int total = 0; |
| for(Value::use_iterator ii = F.use_begin(), ee = F.use_end(); |
| ii != ee; ++ii) |
| if (CallInst* CI = dyn_cast<CallInst>(ii)) { |
| ++dist[dyn_cast<Constant>(CI->getOperand(arg + 1))]; |
| ++total; |
| } else |
| hasIndirect = true; |
| |
| // Preserve the original address taken function even if all other uses |
| // will be specialized. |
| if (hasIndirect) ++total; |
| return total; |
| } |
| |
| ModulePass* llvm::createPartialSpecializationPass() { return new PartSpec(); } |