X-Git-Url: http://demsky.eecs.uci.edu/git/?a=blobdiff_plain;f=lib%2FTransforms%2FIPO%2FConstantMerge.cpp;h=8ce7646621ff74c92a121397f45b51161dc5e506;hb=4556b1fe22ace7ced5cd37f171ca4418826d46c4;hp=3c05f88027a623d9804d0bd65233b5c560840477;hpb=c3b6ffc431bbf01f615c6695a0dc1b9368102cad;p=oota-llvm.git diff --git a/lib/Transforms/IPO/ConstantMerge.cpp b/lib/Transforms/IPO/ConstantMerge.cpp index 3c05f88027a..8ce7646621f 100644 --- a/lib/Transforms/IPO/ConstantMerge.cpp +++ b/lib/Transforms/IPO/ConstantMerge.cpp @@ -17,39 +17,93 @@ // //===----------------------------------------------------------------------===// -#define DEBUG_TYPE "constmerge" #include "llvm/Transforms/IPO.h" -#include "llvm/DerivedTypes.h" -#include "llvm/Module.h" -#include "llvm/Pass.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" using namespace llvm; +#define DEBUG_TYPE "constmerge" + STATISTIC(NumMerged, "Number of global constants merged"); namespace { struct ConstantMerge : public ModulePass { static char ID; // Pass identification, replacement for typeid - ConstantMerge() : ModulePass(&ID) {} + 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; + + // 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; - // run - For this pass, process all of the globals in the module, - // eliminating duplicate constants. - // - bool runOnModule(Module &M); }; } char ConstantMerge::ID = 0; -static RegisterPass -X("constmerge", "Merge Duplicate Global Constants"); +INITIALIZE_PASS(ConstantMerge, "constmerge", + "Merge Duplicate Global Constants", false, false) ModulePass *llvm::createConstantMergePass() { return new ConstantMerge(); } + + +/// 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); + } +} + +// 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; + + return A.hasUnnamedAddr(); +} + +unsigned ConstantMerge::getAlignment(GlobalVariable *GV) const { + unsigned Align = GV->getAlignment(); + if (Align) + return Align; + return GV->getParent()->getDataLayout().getPreferredAlignment(GV); +} + bool ConstantMerge::runOnModule(Module &M) { - // Map unique constant/section pairs to globals. We don't want to merge - // globals in different sections. - DenseMap CMap; + + // 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); + + // Map unique constants to globals. + DenseMap CMap; // Replacements - This vector contains a list of replacements to perform. SmallVector, 32> Replacements; @@ -61,38 +115,80 @@ bool ConstantMerge::runOnModule(Module &M) { // 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. - // + + // 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 addres space. - if (!GV->isConstant() ||!GV->hasDefinitiveInitializer() || - GV->getType()->getAddressSpace() != 0 || !GV->getSection().empty()) + + // 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. GlobalVariable *&Slot = CMap[Init]; - if (Slot == 0) { // Nope, add it to the map. + // 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; - } 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)); - } + } + + // 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. + GlobalVariable *Slot = CMap[Init]; + + if (!Slot || Slot == GV) + continue; + + if (!Slot->hasUnnamedAddr() && !GV->hasUnnamedAddr()) + continue; + + if (!GV->hasUnnamedAddr()) + Slot->setUnnamedAddr(false); + + // Make all uses of the duplicate constant use the canonical version. + Replacements.push_back(std::make_pair(GV, Slot)); } if (Replacements.empty()) @@ -103,10 +199,20 @@ bool ConstantMerge::runOnModule(Module &M) { // 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(); }