X-Git-Url: http://plrg.eecs.uci.edu/git/?a=blobdiff_plain;f=lib%2FTransforms%2FIPO%2FConstantMerge.cpp;h=0b6ade9eb536b107642292cbffab626069fcf204;hb=9ba744b0890819cb602281779dfacc4efd54db70;hp=e353a455467bc53887f2b653b0c2aaab96ca34eb;hpb=b576c94c15af9a440f69d9d03c2afead7971118c;p=oota-llvm.git diff --git a/lib/Transforms/IPO/ConstantMerge.cpp b/lib/Transforms/IPO/ConstantMerge.cpp index e353a455467..0b6ade9eb53 100644 --- a/lib/Transforms/IPO/ConstantMerge.cpp +++ b/lib/Transforms/IPO/ConstantMerge.cpp @@ -1,10 +1,10 @@ //===- ConstantMerge.cpp - Merge duplicate global constants ---------------===// -// +// // The LLVM Compiler Infrastructure // -// This file was developed by the LLVM research group and is distributed under -// the University of Illinois Open Source License. See LICENSE.TXT for details. -// +// 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 @@ -18,52 +18,218 @@ //===----------------------------------------------------------------------===// #include "llvm/Transforms/IPO.h" -#include "llvm/Module.h" +#include "llvm/ADT/DenseMap.h" +#include "llvm/ADT/PointerIntPair.h" +#include "llvm/ADT/SmallPtrSet.h" +#include "llvm/ADT/Statistic.h" +#include "llvm/IR/Constants.h" +#include "llvm/IR/DataLayout.h" +#include "llvm/IR/DerivedTypes.h" +#include "llvm/IR/Module.h" +#include "llvm/IR/Operator.h" #include "llvm/Pass.h" -#include "Support/Statistic.h" +using namespace llvm; + +#define DEBUG_TYPE "constmerge" + +STATISTIC(NumMerged, "Number of global constants merged"); namespace { - Statistic<> NumMerged("constmerge", "Number of global constants merged"); + struct ConstantMerge : public ModulePass { + static char ID; // Pass identification, replacement for typeid + ConstantMerge() : ModulePass(ID) { + initializeConstantMergePass(*PassRegistry::getPassRegistry()); + } + + // For this pass, process all of the globals in the module, eliminating + // duplicate constants. + bool runOnModule(Module &M) override; - struct ConstantMerge : public Pass { - // run - For this pass, process all of the globals in the module, - // eliminating duplicate constants. - // - bool run(Module &M); + // Return true iff we can determine the alignment of this global variable. + bool hasKnownAlignment(GlobalVariable *GV) const; + + // Return the alignment of the global, including converting the default + // alignment to a concrete value. + unsigned getAlignment(GlobalVariable *GV) const; + + const DataLayout *DL; }; +} + +char ConstantMerge::ID = 0; +INITIALIZE_PASS(ConstantMerge, "constmerge", + "Merge Duplicate Global Constants", false, false) + +ModulePass *llvm::createConstantMergePass() { return new ConstantMerge(); } - RegisterOpt X("constmerge","Merge Duplicate Global Constants"); + + +/// Find values that are marked as llvm.used. +static void FindUsedValues(GlobalVariable *LLVMUsed, + SmallPtrSetImpl &UsedValues) { + if (!LLVMUsed) return; + ConstantArray *Inits = cast(LLVMUsed->getInitializer()); + + for (unsigned i = 0, e = Inits->getNumOperands(); i != e; ++i) { + Value *Operand = Inits->getOperand(i)->stripPointerCastsNoFollowAliases(); + GlobalValue *GV = cast(Operand); + UsedValues.insert(GV); + } } -Pass *createConstantMergePass() { return new ConstantMerge(); } +// True if A is better than B. +static bool IsBetterCanonical(const GlobalVariable &A, + const GlobalVariable &B) { + if (!A.hasLocalLinkage() && B.hasLocalLinkage()) + return true; + if (A.hasLocalLinkage() && !B.hasLocalLinkage()) + return false; -bool ConstantMerge::run(Module &M) { - std::map CMap; - bool MadeChanges = false; + return A.hasUnnamedAddr(); +} + +bool ConstantMerge::hasKnownAlignment(GlobalVariable *GV) const { + return DL || GV->getAlignment() != 0; +} + +unsigned ConstantMerge::getAlignment(GlobalVariable *GV) const { + unsigned Align = GV->getAlignment(); + if (Align) + return Align; + if (DL) + return DL->getPreferredAlignment(GV); + return 0; +} + +bool ConstantMerge::runOnModule(Module &M) { + DataLayoutPass *DLP = getAnalysisIfAvailable(); + DL = DLP ? &DLP->getDataLayout() : nullptr; + + // Find all the globals that are marked "used". These cannot be merged. + SmallPtrSet UsedGlobals; + FindUsedValues(M.getGlobalVariable("llvm.used"), UsedGlobals); + FindUsedValues(M.getGlobalVariable("llvm.compiler.used"), UsedGlobals); - for (Module::giterator GV = M.gbegin(), E = M.gend(); GV != E; ++GV) - // Only process constants with initializers - if (GV->isConstant() && GV->hasInitializer()) { + // Map unique pairs to globals. We don't + // want to merge globals of unknown alignment with those of explicit + // alignment. If we have DataLayout, we always know the alignment. + DenseMap, GlobalVariable*> CMap; + + // Replacements - This vector contains a list of replacements to perform. + SmallVector, 32> Replacements; + + bool MadeChange = false; + + // 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: Find the canonical constants others will be merged with. + 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 address space. + if (!GV->isConstant() || !GV->hasDefinitiveInitializer() || + GV->getType()->getAddressSpace() != 0 || GV->hasSection() || + // Don't touch values marked with attribute(used). + UsedGlobals.count(GV)) + continue; + + // This transformation is legal for weak ODR globals in the sense it + // doesn't change semantics, but we really don't want to perform it + // anyway; it's likely to pessimize code generation, and some tools + // (like the Darwin linker in cases involving CFString) don't expect it. + if (GV->isWeakForLinker()) + continue; + + Constant *Init = GV->getInitializer(); + + // Check to see if the initializer is already known. + PointerIntPair Pair(Init, hasKnownAlignment(GV)); + GlobalVariable *&Slot = CMap[Pair]; + + // If this is the first constant we find or if the old one is local, + // replace with the current one. If the current is externally visible + // it cannot be replace, but can be the canonical constant we merge with. + if (!Slot || IsBetterCanonical(*GV, *Slot)) + Slot = GV; + } + + // Second: 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++; + + // Only process constants with initializers in the default address space. + if (!GV->isConstant() || !GV->hasDefinitiveInitializer() || + GV->getType()->getAddressSpace() != 0 || GV->hasSection() || + // Don't touch values marked with attribute(used). + UsedGlobals.count(GV)) + continue; + + // We can only replace constant with local linkage. + if (!GV->hasLocalLinkage()) + continue; + Constant *Init = GV->getInitializer(); - // Check to see if the initializer is already known... - std::map::iterator I = CMap.find(Init); + // Check to see if the initializer is already known. + PointerIntPair Pair(Init, hasKnownAlignment(GV)); + GlobalVariable *Slot = CMap[Pair]; + + if (!Slot || Slot == GV) + continue; - 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 canonical version... - GV->replaceAllUsesWith(I->second); + if (!Slot->hasUnnamedAddr() && !GV->hasUnnamedAddr()) + continue; - // Delete the global value from the module... and back up iterator to - // not skip the next global... - GV = --M.getGlobalList().erase(GV); + if (!GV->hasUnnamedAddr()) + Slot->setUnnamedAddr(false); - ++NumMerged; - MadeChanges = true; + // Make all uses of the duplicate constant use the canonical version. + Replacements.push_back(std::make_pair(GV, Slot)); + } + + 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) { + // Bump the alignment if necessary. + if (Replacements[i].first->getAlignment() || + Replacements[i].second->getAlignment()) { + Replacements[i].second->setAlignment( + std::max(getAlignment(Replacements[i].first), + getAlignment(Replacements[i].second))); } + + // Eliminate any uses of the dead global. + Replacements[i].first->replaceAllUsesWith(Replacements[i].second); + + // Delete the global value from the module. + assert(Replacements[i].first->hasLocalLinkage() && + "Refusing to delete an externally visible global variable."); + Replacements[i].first->eraseFromParent(); } - return MadeChanges; + NumMerged += Replacements.size(); + Replacements.clear(); + } }