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git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@55766 91177308-0d34-0410-b5e6-96231b3b80d8
137 lines
4.8 KiB
C++
137 lines
4.8 KiB
C++
//===-- PartialSpecialization.cpp - Specialize for common constants--------===//
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//
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// The LLVM Compiler Infrastructure
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//
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// This file is distributed under the University of Illinois Open Source
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// License. See LICENSE.TXT for details.
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//
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//===----------------------------------------------------------------------===//
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//
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// This pass finds function arguments that are often a common constant and
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// specializes a version of the called function for that constant.
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//
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// This pass simply does the cloning for functions it specializes. It depends
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// on IPSCCP and DAE to clean up the results.
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//
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// The initial heuristic favors constant arguments that are used in control
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// flow.
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//
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//===----------------------------------------------------------------------===//
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#define DEBUG_TYPE "partialspecialization"
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#include "llvm/Transforms/IPO.h"
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#include "llvm/Constant.h"
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#include "llvm/Instructions.h"
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#include "llvm/Module.h"
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#include "llvm/Pass.h"
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#include "llvm/ADT/Statistic.h"
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#include "llvm/Transforms/Utils/Cloning.h"
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#include "llvm/Support/Compiler.h"
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#include <map>
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using namespace llvm;
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STATISTIC(numSpecialized, "Number of specialized functions created");
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// Call must be used at least occasionally
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static const int CallsMin = 5;
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// Must have 10% of calls having the same constant to specialize on
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static const double ConstValPercent = .1;
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namespace {
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class VISIBILITY_HIDDEN PartSpec : public ModulePass {
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void scanForInterest(Function&, SmallVector<int, 6>&);
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void replaceUsersFor(Function&, int, Constant*, Function*);
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int scanDistribution(Function&, int, std::map<Constant*, int>&);
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public :
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static char ID; // Pass identification, replacement for typeid
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PartSpec() : ModulePass((intptr_t)&ID) {}
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bool runOnModule(Module &M);
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};
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}
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char PartSpec::ID = 0;
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static RegisterPass<PartSpec>
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X("partialspecialization", "Partial Specialization");
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bool PartSpec::runOnModule(Module &M) {
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bool Changed = false;
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for (Module::iterator I = M.begin(); I != M.end(); ++I) {
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Function &F = *I;
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if (F.isDeclaration()) continue;
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SmallVector<int, 6> interestingArgs;
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scanForInterest(F, interestingArgs);
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// Find the first interesting Argument that we can specialize on
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// If there are multiple interesting Arguments, then those will be found
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// when processing the cloned function.
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bool breakOuter = false;
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for (unsigned int x = 0; !breakOuter && x < interestingArgs.size(); ++x) {
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std::map<Constant*, int> distribution;
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int total = scanDistribution(F, interestingArgs[x], distribution);
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if (total > CallsMin)
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for (std::map<Constant*, int>::iterator ii = distribution.begin(),
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ee = distribution.end(); ii != ee; ++ii)
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if (total > ii->second && ii->first &&
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ii->second > total * ConstValPercent) {
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Function* NF = CloneFunction(&F);
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NF->setLinkage(GlobalValue::InternalLinkage);
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M.getFunctionList().push_back(NF);
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replaceUsersFor(F, interestingArgs[x], ii->first, NF);
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breakOuter = true;
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Changed = true;
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}
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}
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}
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return Changed;
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}
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/// scanForInterest - This function decides which arguments would be worth
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/// specializing on.
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void PartSpec::scanForInterest(Function& F, SmallVector<int, 6>& args) {
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for(Function::arg_iterator ii = F.arg_begin(), ee = F.arg_end();
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ii != ee; ++ii) {
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for(Value::use_iterator ui = ii->use_begin(), ue = ii->use_end();
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ui != ue; ++ui) {
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// As an initial proxy for control flow, specialize on arguments
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// that are used in comparisons.
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if (isa<CmpInst>(ui)) {
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args.push_back(std::distance(F.arg_begin(), ii));
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break;
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}
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}
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}
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}
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/// replaceUsersFor - Replace direct calls to F with NF if the arg argnum is
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/// the constant val
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void PartSpec::replaceUsersFor(Function& F , int argnum, Constant* val,
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Function* NF) {
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++numSpecialized;
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for(Value::use_iterator ii = F.use_begin(), ee = F.use_end();
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ii != ee; ++ii)
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if (CallInst* CI = dyn_cast<CallInst>(ii))
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if (CI->getOperand(0) == &F && CI->getOperand(argnum + 1) == val)
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CI->setOperand(0, NF);
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}
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int PartSpec::scanDistribution(Function& F, int arg,
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std::map<Constant*, int>& dist) {
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bool hasIndirect = false;
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int total = 0;
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for(Value::use_iterator ii = F.use_begin(), ee = F.use_end();
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ii != ee; ++ii)
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if (CallInst* CI = dyn_cast<CallInst>(ii)) {
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++dist[dyn_cast<Constant>(CI->getOperand(arg + 1))];
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++total;
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} else
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hasIndirect = true;
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// Preserve the original address taken function even if all other uses
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// will be specialized.
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if (hasIndirect) ++total;
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return total;
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}
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ModulePass* llvm::createPartialSpecializationPass() { return new PartSpec(); }
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