diff options
Diffstat (limited to 'lib/Transforms/Scalar')
| -rw-r--r-- | lib/Transforms/Scalar/GlobalMerge.cpp | 81 | ||||
| -rw-r--r-- | lib/Transforms/Scalar/Scalar.cpp | 1 |
2 files changed, 72 insertions, 10 deletions
diff --git a/lib/Transforms/Scalar/GlobalMerge.cpp b/lib/Transforms/Scalar/GlobalMerge.cpp index 5222712631..ecf9be861e 100644 --- a/lib/Transforms/Scalar/GlobalMerge.cpp +++ b/lib/Transforms/Scalar/GlobalMerge.cpp @@ -81,6 +81,13 @@ EnableGlobalMergeOnConst("global-merge-on-const", cl::Hidden, cl::desc("Enable global merge pass on constants"), cl::init(false)); +// FIXME: this could be a transitional option, and we probably need to remove +// it if only we are sure this optimization could always benefit all targets. +static cl::opt<bool> +EnableGlobalMergeOnExternal("global-merge-on-external", cl::Hidden, + cl::desc("Enable global merge pass on external linkage"), + cl::init(false)); + STATISTIC(NumMerged , "Number of globals merged"); namespace { class GlobalMerge : public FunctionPass { @@ -129,9 +136,19 @@ namespace { } // end anonymous namespace char GlobalMerge::ID = 0; -INITIALIZE_PASS(GlobalMerge, "global-merge", - "Global Merge", false, false) +static void *initializeGlobalMergePassOnce(PassRegistry &Registry) { + PassInfo *PI = new PassInfo( + "Merge global variables", "global-merge", &GlobalMerge::ID, + PassInfo::NormalCtor_t(callDefaultCtor<GlobalMerge>), false, false, + PassInfo::TargetMachineCtor_t(callTargetMachineCtor<GlobalMerge>)); + Registry.registerPass(*PI, true); + return PI; +} + +void llvm::initializeGlobalMergePass(PassRegistry &Registry) { + CALL_ONCE_INITIALIZATION(initializeGlobalMergePassOnce) +} bool GlobalMerge::doMerge(SmallVectorImpl<GlobalVariable*> &Globals, Module &M, bool isConst, unsigned AddrSpace) const { @@ -154,11 +171,23 @@ bool GlobalMerge::doMerge(SmallVectorImpl<GlobalVariable*> &Globals, Type *Int32Ty = Type::getInt32Ty(M.getContext()); + assert(Globals.size() > 1); + + // FIXME: This simple solution merges globals all together as maximum as + // possible. However, with this solution it would be hard to remove dead + // global symbols at link-time. An alternative solution could be checking + // global symbols references function by function, and make the symbols + // being referred in the same function merged and we would probably need + // to introduce heuristic algorithm to solve the merge conflict from + // different functions. for (size_t i = 0, e = Globals.size(); i != e; ) { size_t j = 0; uint64_t MergedSize = 0; std::vector<Type*> Tys; std::vector<Constant*> Inits; + + bool HasExternal = false; + GlobalVariable *TheFirstExternal = 0; for (j = i; j != e; ++j) { Type *Ty = Globals[j]->getType()->getElementType(); MergedSize += DL->getTypeAllocSize(Ty); @@ -167,17 +196,37 @@ bool GlobalMerge::doMerge(SmallVectorImpl<GlobalVariable*> &Globals, } Tys.push_back(Ty); Inits.push_back(Globals[j]->getInitializer()); + + if (Globals[j]->hasExternalLinkage() && !HasExternal) { + HasExternal = true; + TheFirstExternal = Globals[j]; + } } + // If merged variables doesn't have external linkage, we needn't to expose + // the symbol after merging. + GlobalValue::LinkageTypes Linkage = HasExternal + ? GlobalValue::ExternalLinkage + : GlobalValue::InternalLinkage; + + // If merged variables have external linkage, we use symbol name of the + // first variable merged as the suffix of global symbol name. This would + // be able to avoid the link-time naming conflict for globalm symbols. + Twine MergedGVName = HasExternal + ? "_MergedGlobals_" + TheFirstExternal->getName() + : "_MergedGlobals"; + StructType *MergedTy = StructType::get(M.getContext(), Tys); Constant *MergedInit = ConstantStruct::get(MergedTy, Inits); - GlobalVariable *MergedGV = new GlobalVariable(M, MergedTy, isConst, - GlobalValue::InternalLinkage, - MergedInit, "_MergedGlobals", - nullptr, - GlobalVariable::NotThreadLocal, - AddrSpace); + + GlobalVariable *MergedGV = new GlobalVariable( + M, MergedTy, isConst, Linkage, MergedInit, MergedGVName, nullptr, + GlobalVariable::NotThreadLocal, AddrSpace); + for (size_t k = i; k < j; ++k) { + GlobalValue::LinkageTypes Linkage = Globals[k]->getLinkage(); + std::string Name = Globals[k]->getName(); + Constant *Idx[2] = { ConstantInt::get(Int32Ty, 0), ConstantInt::get(Int32Ty, k-i) @@ -185,6 +234,14 @@ bool GlobalMerge::doMerge(SmallVectorImpl<GlobalVariable*> &Globals, Constant *GEP = ConstantExpr::getInBoundsGetElementPtr(MergedGV, Idx); Globals[k]->replaceAllUsesWith(GEP); Globals[k]->eraseFromParent(); + + if (Linkage != GlobalValue::InternalLinkage) { + // Generate a new alias... + auto *PTy = cast<PointerType>(GEP->getType()); + GlobalAlias::create(PTy->getElementType(), PTy->getAddressSpace(), + Linkage, Name, GEP, &M); + } + NumMerged++; } i = j; @@ -245,8 +302,12 @@ bool GlobalMerge::doInitialization(Module &M) { // Grab all non-const globals. for (Module::global_iterator I = M.global_begin(), E = M.global_end(); I != E; ++I) { - // Merge is safe for "normal" internal globals only - if (!I->hasLocalLinkage() || I->isThreadLocal() || I->hasSection()) + // Merge is safe for "normal" internal or external globals only + if (I->isDeclaration() || I->isThreadLocal() || I->hasSection()) + continue; + + if (!(EnableGlobalMergeOnExternal && I->hasExternalLinkage()) && + !I->hasInternalLinkage()) continue; PointerType *PT = dyn_cast<PointerType>(I->getType()); diff --git a/lib/Transforms/Scalar/Scalar.cpp b/lib/Transforms/Scalar/Scalar.cpp index edf012d811..5c7db5b16e 100644 --- a/lib/Transforms/Scalar/Scalar.cpp +++ b/lib/Transforms/Scalar/Scalar.cpp @@ -38,6 +38,7 @@ void llvm::initializeScalarOpts(PassRegistry &Registry) { initializeDSEPass(Registry); initializeGVNPass(Registry); initializeEarlyCSEPass(Registry); + initializeGlobalMergePass(Registry); initializeIndVarSimplifyPass(Registry); initializeJumpThreadingPass(Registry); initializeLICMPass(Registry); |