X-Git-Url: http://demsky.eecs.uci.edu/git/?a=blobdiff_plain;f=lib%2FTransforms%2FIPO%2FGlobalDCE.cpp;h=ba04c80508c4fb153dfc4764fb7a3d111e7308af;hb=c226d9f334cd4d552d7fc9ceb4cdaf326dd15352;hp=98202eb0b34583c813d923d51e005f2e072c225c;hpb=844731a7f1909f55935e3514c9e713a62d67662e;p=oota-llvm.git diff --git a/lib/Transforms/IPO/GlobalDCE.cpp b/lib/Transforms/IPO/GlobalDCE.cpp index 98202eb0b34..ba04c80508c 100644 --- a/lib/Transforms/IPO/GlobalDCE.cpp +++ b/lib/Transforms/IPO/GlobalDCE.cpp @@ -15,56 +15,90 @@ // //===----------------------------------------------------------------------===// -#define DEBUG_TYPE "globaldce" #include "llvm/Transforms/IPO.h" -#include "llvm/Constants.h" -#include "llvm/Module.h" -#include "llvm/Pass.h" +#include "llvm/ADT/SmallPtrSet.h" #include "llvm/ADT/Statistic.h" -#include "llvm/Support/Compiler.h" -#include +#include "llvm/IR/Constants.h" +#include "llvm/IR/Instructions.h" +#include "llvm/IR/Module.h" +#include "llvm/Transforms/Utils/CtorUtils.h" +#include "llvm/Transforms/Utils/GlobalStatus.h" +#include "llvm/Pass.h" +#include using namespace llvm; +#define DEBUG_TYPE "globaldce" + +STATISTIC(NumAliases , "Number of global aliases removed"); STATISTIC(NumFunctions, "Number of functions removed"); STATISTIC(NumVariables, "Number of global variables removed"); namespace { - struct VISIBILITY_HIDDEN GlobalDCE : public ModulePass { + struct GlobalDCE : public ModulePass { static char ID; // Pass identification, replacement for typeid - GlobalDCE() : ModulePass((intptr_t)&ID) {} - + GlobalDCE() : ModulePass(ID) { + initializeGlobalDCEPass(*PassRegistry::getPassRegistry()); + } + // run - Do the GlobalDCE pass on the specified module, optionally updating // the specified callgraph to reflect the changes. // - bool runOnModule(Module &M); + bool runOnModule(Module &M) override; private: - std::set AliveGlobals; + SmallPtrSet AliveGlobals; + SmallPtrSet SeenConstants; + std::unordered_multimap ComdatMembers; - /// MarkGlobalIsNeeded - the specific global value as needed, and + /// GlobalIsNeeded - mark the specific global value as needed, and /// recursively mark anything that it uses as also needed. void GlobalIsNeeded(GlobalValue *GV); void MarkUsedGlobalsAsNeeded(Constant *C); - bool SafeToDestroyConstant(Constant* C); bool RemoveUnusedGlobalValue(GlobalValue &GV); }; } +/// Returns true if F contains only a single "ret" instruction. +static bool isEmptyFunction(Function *F) { + BasicBlock &Entry = F->getEntryBlock(); + if (Entry.size() != 1 || !isa(Entry.front())) + return false; + ReturnInst &RI = cast(Entry.front()); + return RI.getReturnValue() == nullptr; +} + char GlobalDCE::ID = 0; -static RegisterPass X("globaldce", "Dead Global Elimination"); +INITIALIZE_PASS(GlobalDCE, "globaldce", + "Dead Global Elimination", false, false) ModulePass *llvm::createGlobalDCEPass() { return new GlobalDCE(); } bool GlobalDCE::runOnModule(Module &M) { bool Changed = false; + + // Remove empty functions from the global ctors list. + Changed |= optimizeGlobalCtorsList(M, isEmptyFunction); + + // Collect the set of members for each comdat. + for (Function &F : M) + if (Comdat *C = F.getComdat()) + ComdatMembers.insert(std::make_pair(C, &F)); + for (GlobalVariable &GV : M.globals()) + if (Comdat *C = GV.getComdat()) + ComdatMembers.insert(std::make_pair(C, &GV)); + for (GlobalAlias &GA : M.aliases()) + if (Comdat *C = GA.getComdat()) + ComdatMembers.insert(std::make_pair(C, &GA)); + // Loop over the module, adding globals which are obviously necessary. for (Module::iterator I = M.begin(), E = M.end(); I != E; ++I) { Changed |= RemoveUnusedGlobalValue(*I); // Functions with external linkage are needed if they have a body - if ((!I->hasInternalLinkage() && !I->hasLinkOnceLinkage()) && - !I->isDeclaration()) - GlobalIsNeeded(I); + if (!I->isDeclaration() && !I->hasAvailableExternallyLinkage()) { + if (!I->isDiscardableIfUnused()) + GlobalIsNeeded(I); + } } for (Module::global_iterator I = M.global_begin(), E = M.global_end(); @@ -72,16 +106,19 @@ bool GlobalDCE::runOnModule(Module &M) { Changed |= RemoveUnusedGlobalValue(*I); // Externally visible & appending globals are needed, if they have an // initializer. - if ((!I->hasInternalLinkage() && !I->hasLinkOnceLinkage()) && - !I->isDeclaration()) - GlobalIsNeeded(I); + if (!I->isDeclaration() && !I->hasAvailableExternallyLinkage()) { + if (!I->isDiscardableIfUnused()) + GlobalIsNeeded(I); + } } - for (Module::alias_iterator I = M.alias_begin(), E = M.alias_end(); I != E; ++I) { - // Aliases are always needed even if they are not used. - MarkUsedGlobalsAsNeeded(I->getAliasee()); + Changed |= RemoveUnusedGlobalValue(*I); + // Externally visible aliases are needed. + if (!I->isDiscardableIfUnused()) { + GlobalIsNeeded(I); + } } // Now that all globals which are needed are in the AliveGlobals set, we loop @@ -90,13 +127,18 @@ bool GlobalDCE::runOnModule(Module &M) { // The first pass is to drop initializers of global variables which are dead. std::vector DeadGlobalVars; // Keep track of dead globals - for (Module::global_iterator I = M.global_begin(), E = M.global_end(); I != E; ++I) + for (Module::global_iterator I = M.global_begin(), E = M.global_end(); + I != E; ++I) if (!AliveGlobals.count(I)) { DeadGlobalVars.push_back(I); // Keep track of dead globals - I->setInitializer(0); + if (I->hasInitializer()) { + Constant *Init = I->getInitializer(); + I->setInitializer(nullptr); + if (isSafeToDestroyConstant(Init)) + Init->destroyConstant(); + } } - // The second pass drops the bodies of functions which are dead... std::vector DeadFunctions; for (Module::iterator I = M.begin(), E = M.end(); I != E; ++I) @@ -106,8 +148,17 @@ bool GlobalDCE::runOnModule(Module &M) { I->deleteBody(); } + // The third pass drops targets of aliases which are dead... + std::vector DeadAliases; + for (Module::alias_iterator I = M.alias_begin(), E = M.alias_end(); I != E; + ++I) + if (!AliveGlobals.count(I)) { + DeadAliases.push_back(I); + I->setAliasee(nullptr); + } + if (!DeadFunctions.empty()) { - // Now that all interreferences have been dropped, delete the actual objects + // Now that all interferences have been dropped, delete the actual objects // themselves. for (unsigned i = 0, e = DeadFunctions.size(); i != e; ++i) { RemoveUnusedGlobalValue(*DeadFunctions[i]); @@ -126,38 +177,59 @@ bool GlobalDCE::runOnModule(Module &M) { Changed = true; } + // Now delete any dead aliases. + if (!DeadAliases.empty()) { + for (unsigned i = 0, e = DeadAliases.size(); i != e; ++i) { + RemoveUnusedGlobalValue(*DeadAliases[i]); + M.getAliasList().erase(DeadAliases[i]); + } + NumAliases += DeadAliases.size(); + Changed = true; + } + // Make sure that all memory is released AliveGlobals.clear(); + SeenConstants.clear(); + ComdatMembers.clear(); + return Changed; } -/// MarkGlobalIsNeeded - the specific global value as needed, and +/// GlobalIsNeeded - the specific global value as needed, and /// recursively mark anything that it uses as also needed. void GlobalDCE::GlobalIsNeeded(GlobalValue *G) { - std::set::iterator I = AliveGlobals.lower_bound(G); - // If the global is already in the set, no need to reprocess it. - if (I != AliveGlobals.end() && *I == G) return; + if (!AliveGlobals.insert(G).second) + return; - // Otherwise insert it now, so we do not infinitely recurse - AliveGlobals.insert(I, G); + if (Comdat *C = G->getComdat()) { + for (auto &&CM : make_range(ComdatMembers.equal_range(C))) + GlobalIsNeeded(CM.second); + } if (GlobalVariable *GV = dyn_cast(G)) { // If this is a global variable, we must make sure to add any global values // referenced by the initializer to the alive set. if (GV->hasInitializer()) MarkUsedGlobalsAsNeeded(GV->getInitializer()); - } else if (!isa(G)) { + } else if (GlobalAlias *GA = dyn_cast(G)) { + // The target of a global alias is needed. + MarkUsedGlobalsAsNeeded(GA->getAliasee()); + } else { // Otherwise this must be a function object. We have to scan the body of // the function looking for constants and global values which are used as // operands. Any operands of these types must be processed to ensure that // any globals used will be marked as needed. Function *F = cast(G); - // For all basic blocks... + + if (F->hasPrefixData()) + MarkUsedGlobalsAsNeeded(F->getPrefixData()); + + if (F->hasPrologueData()) + MarkUsedGlobalsAsNeeded(F->getPrologueData()); + for (Function::iterator BB = F->begin(), E = F->end(); BB != E; ++BB) - // For all instructions... for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ++I) - // For all operands... for (User::op_iterator U = I->op_begin(), E = I->op_end(); U != E; ++U) if (GlobalValue *GV = dyn_cast(*U)) GlobalIsNeeded(GV); @@ -168,12 +240,15 @@ void GlobalDCE::GlobalIsNeeded(GlobalValue *G) { void GlobalDCE::MarkUsedGlobalsAsNeeded(Constant *C) { if (GlobalValue *GV = dyn_cast(C)) - GlobalIsNeeded(GV); - else { - // Loop over all of the operands of the constant, adding any globals they - // use to the list of needed globals. - for (User::op_iterator I = C->op_begin(), E = C->op_end(); I != E; ++I) - MarkUsedGlobalsAsNeeded(cast(*I)); + return GlobalIsNeeded(GV); + + // Loop over all of the operands of the constant, adding any globals they + // use to the list of needed globals. + for (User::op_iterator I = C->op_begin(), E = C->op_end(); I != E; ++I) { + // If we've already processed this constant there's no need to do it again. + Constant *Op = dyn_cast(*I); + if (Op && SeenConstants.insert(Op).second) + MarkUsedGlobalsAsNeeded(Op); } } @@ -188,17 +263,3 @@ bool GlobalDCE::RemoveUnusedGlobalValue(GlobalValue &GV) { GV.removeDeadConstantUsers(); return GV.use_empty(); } - -// SafeToDestroyConstant - It is safe to destroy a constant iff it is only used -// by constants itself. Note that constants cannot be cyclic, so this test is -// pretty easy to implement recursively. -// -bool GlobalDCE::SafeToDestroyConstant(Constant *C) { - for (Value::use_iterator I = C->use_begin(), E = C->use_end(); I != E; ++I) - if (Constant *User = dyn_cast(*I)) { - if (!SafeToDestroyConstant(User)) return false; - } else { - return false; - } - return true; -}