X-Git-Url: http://plrg.eecs.uci.edu/git/?a=blobdiff_plain;f=lib%2FTransforms%2FIPO%2FConstantMerge.cpp;h=75282fae18bc531bc5a981faccdce66a6ddc311e;hb=90c579de5a383cee278acc3f7e7b9d0a656e6a35;hp=71eadbf9829963bdbc92c973c04f970a7318c617;hpb=af41a12370010325eb163b734d5757a7f0296e67;p=oota-llvm.git diff --git a/lib/Transforms/IPO/ConstantMerge.cpp b/lib/Transforms/IPO/ConstantMerge.cpp index 71eadbf9829..75282fae18b 100644 --- a/lib/Transforms/IPO/ConstantMerge.cpp +++ b/lib/Transforms/IPO/ConstantMerge.cpp @@ -1,74 +1,116 @@ -//===- ConstantMerge.cpp - Merge duplicate global constants -----------------=// +//===- ConstantMerge.cpp - Merge duplicate global constants ---------------===// +// +// The LLVM Compiler Infrastructure +// +// This file is distributed under the University of Illinois Open Source +// License. See LICENSE.TXT for details. +// +//===----------------------------------------------------------------------===// // // This file defines the interface to a pass that merges duplicate global // constants together into a single constant that is shared. This is useful // because some passes (ie TraceValues) insert a lot of string constants into -// the program, regardless of whether or not they duplicate an existing string. +// the program, regardless of whether or not an existing string is available. // // Algorithm: ConstantMerge is designed to build up a map of available constants -// and elminate duplicates when it is initialized. -// -// The DynamicConstantMerge method is a superset of the ConstantMerge algorithm -// that checks for each function to see if constants have been added to the -// constant pool since it was last run... if so, it processes them. +// and eliminate duplicates when it is initialized. // //===----------------------------------------------------------------------===// -#include "llvm/Transforms/ConstantMerge.h" +#define DEBUG_TYPE "constmerge" +#include "llvm/Transforms/IPO.h" +#include "llvm/DerivedTypes.h" #include "llvm/Module.h" #include "llvm/Pass.h" -#include "Support/StatisticReporter.h" +#include "llvm/ADT/DenseMap.h" +#include "llvm/ADT/Statistic.h" +using namespace llvm; -static Statistic<> NumMerged("constmerge\t\t- Number of global constants merged"); +STATISTIC(NumMerged, "Number of global constants merged"); namespace { - struct ConstantMerge : public Pass { + struct ConstantMerge : public ModulePass { + static char ID; // Pass identification, replacement for typeid + ConstantMerge() : ModulePass(ID) {} + // run - For this pass, process all of the globals in the module, // eliminating duplicate constants. // - bool run(Module &M); - - virtual void getAnalysisUsage(AnalysisUsage &AU) const { - AU.preservesCFG(); - } + bool runOnModule(Module &M); }; - -RegisterPass X("constmerge", "Merge Duplicate Global Constants"); } -Pass *createConstantMergePass() { return new ConstantMerge(); } +char ConstantMerge::ID = 0; +INITIALIZE_PASS(ConstantMerge, "constmerge", + "Merge Duplicate Global Constants", false, false); +ModulePass *llvm::createConstantMergePass() { return new ConstantMerge(); } -// ConstantMerge::run - Workhorse for the pass. This eliminates duplicate -// constants, starting at global ConstantNo, and adds vars to the map if they -// are new and unique. -// -bool ConstantMerge::run(Module &M) { - std::map CMap; - bool MadeChanges = false; - - for (Module::giterator GV = M.gbegin(), E = M.gend(); GV != E; ++GV) - if (GV->isConstant()) { // Only process constants - assert(GV->hasInitializer() && "Globals constants must have inits!"); - Constant *Init = GV->getInitializer(); +bool ConstantMerge::runOnModule(Module &M) { + // Map unique constant/section pairs to globals. We don't want to merge + // globals in different sections. + DenseMap CMap; + + // Replacements - This vector contains a list of replacements to perform. + SmallVector, 32> Replacements; - // Check to see if the initializer is already known... - std::map::iterator I = CMap.find(Init); + bool MadeChange = false; - if (I == CMap.end()) { // Nope, add it to the map - CMap.insert(I, std::make_pair(Init, GV)); - } else { // Yup, this is a duplicate! - // Make all uses of the duplicate constant use the cannonical version... - GV->replaceAllUsesWith(I->second); + // Iterate constant merging while we are still making progress. Merging two + // constants together may allow us to merge other constants together if the + // second level constants have initializers which point to the globals that + // were just merged. + while (1) { + // First pass: identify all globals that can be merged together, filling in + // the Replacements vector. We cannot do the replacement in this pass + // because doing so may cause initializers of other globals to be rewritten, + // invalidating the Constant* pointers in CMap. + // + for (Module::global_iterator GVI = M.global_begin(), E = M.global_end(); + GVI != E; ) { + GlobalVariable *GV = GVI++; + + // If this GV is dead, remove it. + GV->removeDeadConstantUsers(); + if (GV->use_empty() && GV->hasLocalLinkage()) { + GV->eraseFromParent(); + continue; + } + + // Only process constants with initializers in the default addres space. + if (!GV->isConstant() ||!GV->hasDefinitiveInitializer() || + GV->getType()->getAddressSpace() != 0 || !GV->getSection().empty()) + continue; + + Constant *Init = GV->getInitializer(); - // Delete the global value from the module... and back up iterator to - // not skip the next global... - GV = --M.getGlobalList().erase(GV); + // Check to see if the initializer is already known. + GlobalVariable *&Slot = CMap[Init]; - ++NumMerged; - MadeChanges = true; + if (Slot == 0) { // Nope, add it to the map. + Slot = GV; + } else if (GV->hasLocalLinkage()) { // Yup, this is a duplicate! + // Make all uses of the duplicate constant use the canonical version. + Replacements.push_back(std::make_pair(GV, Slot)); } } - return MadeChanges; + if (Replacements.empty()) + return MadeChange; + CMap.clear(); + + // Now that we have figured out which replacements must be made, do them all + // now. This avoid invalidating the pointers in CMap, which are unneeded + // now. + for (unsigned i = 0, e = Replacements.size(); i != e; ++i) { + // Eliminate any uses of the dead global. + Replacements[i].first->replaceAllUsesWith(Replacements[i].second); + + // Delete the global value from the module. + Replacements[i].first->eraseFromParent(); + } + + NumMerged += Replacements.size(); + Replacements.clear(); + } }