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Diffstat (limited to 'llvm/lib/CodeGen/GlobalMerge.cpp')
| -rw-r--r-- | llvm/lib/CodeGen/GlobalMerge.cpp | 681 |
1 files changed, 681 insertions, 0 deletions
diff --git a/llvm/lib/CodeGen/GlobalMerge.cpp b/llvm/lib/CodeGen/GlobalMerge.cpp new file mode 100644 index 000000000000..d4fa45fcb405 --- /dev/null +++ b/llvm/lib/CodeGen/GlobalMerge.cpp @@ -0,0 +1,681 @@ +//===- GlobalMerge.cpp - Internal globals merging -------------------------===// +// +// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions. +// See https://llvm.org/LICENSE.txt for license information. +// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception +// +//===----------------------------------------------------------------------===// +// +// This pass merges globals with internal linkage into one. This way all the +// globals which were merged into a biggest one can be addressed using offsets +// from the same base pointer (no need for separate base pointer for each of the +// global). Such a transformation can significantly reduce the register pressure +// when many globals are involved. +// +// For example, consider the code which touches several global variables at +// once: +// +// static int foo[N], bar[N], baz[N]; +// +// for (i = 0; i < N; ++i) { +// foo[i] = bar[i] * baz[i]; +// } +// +// On ARM the addresses of 3 arrays should be kept in the registers, thus +// this code has quite large register pressure (loop body): +// +// ldr r1, [r5], #4 +// ldr r2, [r6], #4 +// mul r1, r2, r1 +// str r1, [r0], #4 +// +// Pass converts the code to something like: +// +// static struct { +// int foo[N]; +// int bar[N]; +// int baz[N]; +// } merged; +// +// for (i = 0; i < N; ++i) { +// merged.foo[i] = merged.bar[i] * merged.baz[i]; +// } +// +// and in ARM code this becomes: +// +// ldr r0, [r5, #40] +// ldr r1, [r5, #80] +// mul r0, r1, r0 +// str r0, [r5], #4 +// +// note that we saved 2 registers here almostly "for free". +// +// However, merging globals can have tradeoffs: +// - it confuses debuggers, tools, and users +// - it makes linker optimizations less useful (order files, LOHs, ...) +// - it forces usage of indexed addressing (which isn't necessarily "free") +// - it can increase register pressure when the uses are disparate enough. +// +// We use heuristics to discover the best global grouping we can (cf cl::opts). +// +// ===---------------------------------------------------------------------===// + +#include "llvm/ADT/BitVector.h" +#include "llvm/ADT/DenseMap.h" +#include "llvm/ADT/SmallPtrSet.h" +#include "llvm/ADT/SmallVector.h" +#include "llvm/ADT/Statistic.h" +#include "llvm/ADT/StringRef.h" +#include "llvm/ADT/Triple.h" +#include "llvm/ADT/Twine.h" +#include "llvm/CodeGen/Passes.h" +#include "llvm/IR/BasicBlock.h" +#include "llvm/IR/Constants.h" +#include "llvm/IR/DataLayout.h" +#include "llvm/IR/DerivedTypes.h" +#include "llvm/IR/Function.h" +#include "llvm/IR/GlobalAlias.h" +#include "llvm/IR/GlobalValue.h" +#include "llvm/IR/GlobalVariable.h" +#include "llvm/IR/Instruction.h" +#include "llvm/IR/Module.h" +#include "llvm/IR/Type.h" +#include "llvm/IR/Use.h" +#include "llvm/IR/User.h" +#include "llvm/Pass.h" +#include "llvm/Support/Casting.h" +#include "llvm/Support/CommandLine.h" +#include "llvm/Support/Debug.h" +#include "llvm/Support/raw_ostream.h" +#include "llvm/Target/TargetLoweringObjectFile.h" +#include "llvm/Target/TargetMachine.h" +#include <algorithm> +#include <cassert> +#include <cstddef> +#include <cstdint> +#include <string> +#include <vector> + +using namespace llvm; + +#define DEBUG_TYPE "global-merge" + +// FIXME: This is only useful as a last-resort way to disable the pass. +static cl::opt<bool> +EnableGlobalMerge("enable-global-merge", cl::Hidden, + cl::desc("Enable the global merge pass"), + cl::init(true)); + +static cl::opt<unsigned> +GlobalMergeMaxOffset("global-merge-max-offset", cl::Hidden, + cl::desc("Set maximum offset for global merge pass"), + cl::init(0)); + +static cl::opt<bool> GlobalMergeGroupByUse( + "global-merge-group-by-use", cl::Hidden, + cl::desc("Improve global merge pass to look at uses"), cl::init(true)); + +static cl::opt<bool> GlobalMergeIgnoreSingleUse( + "global-merge-ignore-single-use", cl::Hidden, + cl::desc("Improve global merge pass to ignore globals only used alone"), + cl::init(true)); + +static cl::opt<bool> +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<cl::boolOrDefault> +EnableGlobalMergeOnExternal("global-merge-on-external", cl::Hidden, + cl::desc("Enable global merge pass on external linkage")); + +STATISTIC(NumMerged, "Number of globals merged"); + +namespace { + + class GlobalMerge : public FunctionPass { + const TargetMachine *TM = nullptr; + + // FIXME: Infer the maximum possible offset depending on the actual users + // (these max offsets are different for the users inside Thumb or ARM + // functions), see the code that passes in the offset in the ARM backend + // for more information. + unsigned MaxOffset; + + /// Whether we should try to optimize for size only. + /// Currently, this applies a dead simple heuristic: only consider globals + /// used in minsize functions for merging. + /// FIXME: This could learn about optsize, and be used in the cost model. + bool OnlyOptimizeForSize = false; + + /// Whether we should merge global variables that have external linkage. + bool MergeExternalGlobals = false; + + bool IsMachO; + + bool doMerge(SmallVectorImpl<GlobalVariable*> &Globals, + Module &M, bool isConst, unsigned AddrSpace) const; + + /// Merge everything in \p Globals for which the corresponding bit + /// in \p GlobalSet is set. + bool doMerge(const SmallVectorImpl<GlobalVariable *> &Globals, + const BitVector &GlobalSet, Module &M, bool isConst, + unsigned AddrSpace) const; + + /// Check if the given variable has been identified as must keep + /// \pre setMustKeepGlobalVariables must have been called on the Module that + /// contains GV + bool isMustKeepGlobalVariable(const GlobalVariable *GV) const { + return MustKeepGlobalVariables.count(GV); + } + + /// Collect every variables marked as "used" or used in a landing pad + /// instruction for this Module. + void setMustKeepGlobalVariables(Module &M); + + /// Collect every variables marked as "used" + void collectUsedGlobalVariables(Module &M, StringRef Name); + + /// Keep track of the GlobalVariable that must not be merged away + SmallPtrSet<const GlobalVariable *, 16> MustKeepGlobalVariables; + + public: + static char ID; // Pass identification, replacement for typeid. + + explicit GlobalMerge() + : FunctionPass(ID), MaxOffset(GlobalMergeMaxOffset) { + initializeGlobalMergePass(*PassRegistry::getPassRegistry()); + } + + explicit GlobalMerge(const TargetMachine *TM, unsigned MaximalOffset, + bool OnlyOptimizeForSize, bool MergeExternalGlobals) + : FunctionPass(ID), TM(TM), MaxOffset(MaximalOffset), + OnlyOptimizeForSize(OnlyOptimizeForSize), + MergeExternalGlobals(MergeExternalGlobals) { + initializeGlobalMergePass(*PassRegistry::getPassRegistry()); + } + + bool doInitialization(Module &M) override; + bool runOnFunction(Function &F) override; + bool doFinalization(Module &M) override; + + StringRef getPassName() const override { return "Merge internal globals"; } + + void getAnalysisUsage(AnalysisUsage &AU) const override { + AU.setPreservesCFG(); + FunctionPass::getAnalysisUsage(AU); + } + }; + +} // end anonymous namespace + +char GlobalMerge::ID = 0; + +INITIALIZE_PASS(GlobalMerge, DEBUG_TYPE, "Merge global variables", false, false) + +bool GlobalMerge::doMerge(SmallVectorImpl<GlobalVariable*> &Globals, + Module &M, bool isConst, unsigned AddrSpace) const { + auto &DL = M.getDataLayout(); + // FIXME: Find better heuristics + llvm::stable_sort( + Globals, [&DL](const GlobalVariable *GV1, const GlobalVariable *GV2) { + return DL.getTypeAllocSize(GV1->getValueType()) < + DL.getTypeAllocSize(GV2->getValueType()); + }); + + // If we want to just blindly group all globals together, do so. + if (!GlobalMergeGroupByUse) { + BitVector AllGlobals(Globals.size()); + AllGlobals.set(); + return doMerge(Globals, AllGlobals, M, isConst, AddrSpace); + } + + // If we want to be smarter, look at all uses of each global, to try to + // discover all sets of globals used together, and how many times each of + // these sets occurred. + // + // Keep this reasonably efficient, by having an append-only list of all sets + // discovered so far (UsedGlobalSet), and mapping each "together-ness" unit of + // code (currently, a Function) to the set of globals seen so far that are + // used together in that unit (GlobalUsesByFunction). + // + // When we look at the Nth global, we know that any new set is either: + // - the singleton set {N}, containing this global only, or + // - the union of {N} and a previously-discovered set, containing some + // combination of the previous N-1 globals. + // Using that knowledge, when looking at the Nth global, we can keep: + // - a reference to the singleton set {N} (CurGVOnlySetIdx) + // - a list mapping each previous set to its union with {N} (EncounteredUGS), + // if it actually occurs. + + // We keep track of the sets of globals used together "close enough". + struct UsedGlobalSet { + BitVector Globals; + unsigned UsageCount = 1; + + UsedGlobalSet(size_t Size) : Globals(Size) {} + }; + + // Each set is unique in UsedGlobalSets. + std::vector<UsedGlobalSet> UsedGlobalSets; + + // Avoid repeating the create-global-set pattern. + auto CreateGlobalSet = [&]() -> UsedGlobalSet & { + UsedGlobalSets.emplace_back(Globals.size()); + return UsedGlobalSets.back(); + }; + + // The first set is the empty set. + CreateGlobalSet().UsageCount = 0; + + // We define "close enough" to be "in the same function". + // FIXME: Grouping uses by function is way too aggressive, so we should have + // a better metric for distance between uses. + // The obvious alternative would be to group by BasicBlock, but that's in + // turn too conservative.. + // Anything in between wouldn't be trivial to compute, so just stick with + // per-function grouping. + + // The value type is an index into UsedGlobalSets. + // The default (0) conveniently points to the empty set. + DenseMap<Function *, size_t /*UsedGlobalSetIdx*/> GlobalUsesByFunction; + + // Now, look at each merge-eligible global in turn. + + // Keep track of the sets we already encountered to which we added the + // current global. + // Each element matches the same-index element in UsedGlobalSets. + // This lets us efficiently tell whether a set has already been expanded to + // include the current global. + std::vector<size_t> EncounteredUGS; + + for (size_t GI = 0, GE = Globals.size(); GI != GE; ++GI) { + GlobalVariable *GV = Globals[GI]; + + // Reset the encountered sets for this global... + std::fill(EncounteredUGS.begin(), EncounteredUGS.end(), 0); + // ...and grow it in case we created new sets for the previous global. + EncounteredUGS.resize(UsedGlobalSets.size()); + + // We might need to create a set that only consists of the current global. + // Keep track of its index into UsedGlobalSets. + size_t CurGVOnlySetIdx = 0; + + // For each global, look at all its Uses. + for (auto &U : GV->uses()) { + // This Use might be a ConstantExpr. We're interested in Instruction + // users, so look through ConstantExpr... + Use *UI, *UE; + if (ConstantExpr *CE = dyn_cast<ConstantExpr>(U.getUser())) { + if (CE->use_empty()) + continue; + UI = &*CE->use_begin(); + UE = nullptr; + } else if (isa<Instruction>(U.getUser())) { + UI = &U; + UE = UI->getNext(); + } else { + continue; + } + + // ...to iterate on all the instruction users of the global. + // Note that we iterate on Uses and not on Users to be able to getNext(). + for (; UI != UE; UI = UI->getNext()) { + Instruction *I = dyn_cast<Instruction>(UI->getUser()); + if (!I) + continue; + + Function *ParentFn = I->getParent()->getParent(); + + // If we're only optimizing for size, ignore non-minsize functions. + if (OnlyOptimizeForSize && !ParentFn->hasMinSize()) + continue; + + size_t UGSIdx = GlobalUsesByFunction[ParentFn]; + + // If this is the first global the basic block uses, map it to the set + // consisting of this global only. + if (!UGSIdx) { + // If that set doesn't exist yet, create it. + if (!CurGVOnlySetIdx) { + CurGVOnlySetIdx = UsedGlobalSets.size(); + CreateGlobalSet().Globals.set(GI); + } else { + ++UsedGlobalSets[CurGVOnlySetIdx].UsageCount; + } + + GlobalUsesByFunction[ParentFn] = CurGVOnlySetIdx; + continue; + } + + // If we already encountered this BB, just increment the counter. + if (UsedGlobalSets[UGSIdx].Globals.test(GI)) { + ++UsedGlobalSets[UGSIdx].UsageCount; + continue; + } + + // If not, the previous set wasn't actually used in this function. + --UsedGlobalSets[UGSIdx].UsageCount; + + // If we already expanded the previous set to include this global, just + // reuse that expanded set. + if (size_t ExpandedIdx = EncounteredUGS[UGSIdx]) { + ++UsedGlobalSets[ExpandedIdx].UsageCount; + GlobalUsesByFunction[ParentFn] = ExpandedIdx; + continue; + } + + // If not, create a new set consisting of the union of the previous set + // and this global. Mark it as encountered, so we can reuse it later. + GlobalUsesByFunction[ParentFn] = EncounteredUGS[UGSIdx] = + UsedGlobalSets.size(); + + UsedGlobalSet &NewUGS = CreateGlobalSet(); + NewUGS.Globals.set(GI); + NewUGS.Globals |= UsedGlobalSets[UGSIdx].Globals; + } + } + } + + // Now we found a bunch of sets of globals used together. We accumulated + // the number of times we encountered the sets (i.e., the number of blocks + // that use that exact set of globals). + // + // Multiply that by the size of the set to give us a crude profitability + // metric. + llvm::stable_sort(UsedGlobalSets, + [](const UsedGlobalSet &UGS1, const UsedGlobalSet &UGS2) { + return UGS1.Globals.count() * UGS1.UsageCount < + UGS2.Globals.count() * UGS2.UsageCount; + }); + + // We can choose to merge all globals together, but ignore globals never used + // with another global. This catches the obviously non-profitable cases of + // having a single global, but is aggressive enough for any other case. + if (GlobalMergeIgnoreSingleUse) { + BitVector AllGlobals(Globals.size()); + for (size_t i = 0, e = UsedGlobalSets.size(); i != e; ++i) { + const UsedGlobalSet &UGS = UsedGlobalSets[e - i - 1]; + if (UGS.UsageCount == 0) + continue; + if (UGS.Globals.count() > 1) + AllGlobals |= UGS.Globals; + } + return doMerge(Globals, AllGlobals, M, isConst, AddrSpace); + } + + // Starting from the sets with the best (=biggest) profitability, find a + // good combination. + // The ideal (and expensive) solution can only be found by trying all + // combinations, looking for the one with the best profitability. + // Don't be smart about it, and just pick the first compatible combination, + // starting with the sets with the best profitability. + BitVector PickedGlobals(Globals.size()); + bool Changed = false; + + for (size_t i = 0, e = UsedGlobalSets.size(); i != e; ++i) { + const UsedGlobalSet &UGS = UsedGlobalSets[e - i - 1]; + if (UGS.UsageCount == 0) + continue; + if (PickedGlobals.anyCommon(UGS.Globals)) + continue; + PickedGlobals |= UGS.Globals; + // If the set only contains one global, there's no point in merging. + // Ignore the global for inclusion in other sets though, so keep it in + // PickedGlobals. + if (UGS.Globals.count() < 2) + continue; + Changed |= doMerge(Globals, UGS.Globals, M, isConst, AddrSpace); + } + + return Changed; +} + +bool GlobalMerge::doMerge(const SmallVectorImpl<GlobalVariable *> &Globals, + const BitVector &GlobalSet, Module &M, bool isConst, + unsigned AddrSpace) const { + assert(Globals.size() > 1); + + Type *Int32Ty = Type::getInt32Ty(M.getContext()); + Type *Int8Ty = Type::getInt8Ty(M.getContext()); + auto &DL = M.getDataLayout(); + + LLVM_DEBUG(dbgs() << " Trying to merge set, starts with #" + << GlobalSet.find_first() << "\n"); + + bool Changed = false; + ssize_t i = GlobalSet.find_first(); + while (i != -1) { + ssize_t j = 0; + uint64_t MergedSize = 0; + std::vector<Type*> Tys; + std::vector<Constant*> Inits; + std::vector<unsigned> StructIdxs; + + bool HasExternal = false; + StringRef FirstExternalName; + Align MaxAlign; + unsigned CurIdx = 0; + for (j = i; j != -1; j = GlobalSet.find_next(j)) { + Type *Ty = Globals[j]->getValueType(); + + // Make sure we use the same alignment AsmPrinter would use. + Align Alignment(DL.getPreferredAlignment(Globals[j])); + unsigned Padding = alignTo(MergedSize, Alignment) - MergedSize; + MergedSize += Padding; + MergedSize += DL.getTypeAllocSize(Ty); + if (MergedSize > MaxOffset) { + break; + } + if (Padding) { + Tys.push_back(ArrayType::get(Int8Ty, Padding)); + Inits.push_back(ConstantAggregateZero::get(Tys.back())); + ++CurIdx; + } + Tys.push_back(Ty); + Inits.push_back(Globals[j]->getInitializer()); + StructIdxs.push_back(CurIdx++); + + MaxAlign = std::max(MaxAlign, Alignment); + + if (Globals[j]->hasExternalLinkage() && !HasExternal) { + HasExternal = true; + FirstExternalName = Globals[j]->getName(); + } + } + + // Exit early if there is only one global to merge. + if (Tys.size() < 2) { + i = j; + continue; + } + + // 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; + // Use a packed struct so we can control alignment. + StructType *MergedTy = StructType::get(M.getContext(), Tys, true); + Constant *MergedInit = ConstantStruct::get(MergedTy, Inits); + + // On Darwin external linkage needs to be preserved, otherwise + // dsymutil cannot preserve the debug info for the merged + // variables. If they have external linkage, use the symbol name + // of the first variable merged as the suffix of global symbol + // name. This avoids a link-time naming conflict for the + // _MergedGlobals symbols. + Twine MergedName = + (IsMachO && HasExternal) + ? "_MergedGlobals_" + FirstExternalName + : "_MergedGlobals"; + auto MergedLinkage = IsMachO ? Linkage : GlobalValue::PrivateLinkage; + auto *MergedGV = new GlobalVariable( + M, MergedTy, isConst, MergedLinkage, MergedInit, MergedName, nullptr, + GlobalVariable::NotThreadLocal, AddrSpace); + + MergedGV->setAlignment(MaxAlign); + MergedGV->setSection(Globals[i]->getSection()); + + const StructLayout *MergedLayout = DL.getStructLayout(MergedTy); + for (ssize_t k = i, idx = 0; k != j; k = GlobalSet.find_next(k), ++idx) { + GlobalValue::LinkageTypes Linkage = Globals[k]->getLinkage(); + std::string Name = Globals[k]->getName(); + GlobalValue::DLLStorageClassTypes DLLStorage = + Globals[k]->getDLLStorageClass(); + + // Copy metadata while adjusting any debug info metadata by the original + // global's offset within the merged global. + MergedGV->copyMetadata(Globals[k], + MergedLayout->getElementOffset(StructIdxs[idx])); + + Constant *Idx[2] = { + ConstantInt::get(Int32Ty, 0), + ConstantInt::get(Int32Ty, StructIdxs[idx]), + }; + Constant *GEP = + ConstantExpr::getInBoundsGetElementPtr(MergedTy, MergedGV, Idx); + Globals[k]->replaceAllUsesWith(GEP); + Globals[k]->eraseFromParent(); + + // When the linkage is not internal we must emit an alias for the original + // variable name as it may be accessed from another object. On non-Mach-O + // we can also emit an alias for internal linkage as it's safe to do so. + // It's not safe on Mach-O as the alias (and thus the portion of the + // MergedGlobals variable) may be dead stripped at link time. + if (Linkage != GlobalValue::InternalLinkage || !IsMachO) { + GlobalAlias *GA = GlobalAlias::create(Tys[StructIdxs[idx]], AddrSpace, + Linkage, Name, GEP, &M); + GA->setDLLStorageClass(DLLStorage); + } + + NumMerged++; + } + Changed = true; + i = j; + } + + return Changed; +} + +void GlobalMerge::collectUsedGlobalVariables(Module &M, StringRef Name) { + // Extract global variables from llvm.used array + const GlobalVariable *GV = M.getGlobalVariable(Name); + if (!GV || !GV->hasInitializer()) return; + + // Should be an array of 'i8*'. + const ConstantArray *InitList = cast<ConstantArray>(GV->getInitializer()); + + for (unsigned i = 0, e = InitList->getNumOperands(); i != e; ++i) + if (const GlobalVariable *G = + dyn_cast<GlobalVariable>(InitList->getOperand(i)->stripPointerCasts())) + MustKeepGlobalVariables.insert(G); +} + +void GlobalMerge::setMustKeepGlobalVariables(Module &M) { + collectUsedGlobalVariables(M, "llvm.used"); + collectUsedGlobalVariables(M, "llvm.compiler.used"); + + for (Function &F : M) { + for (BasicBlock &BB : F) { + Instruction *Pad = BB.getFirstNonPHI(); + if (!Pad->isEHPad()) + continue; + + // Keep globals used by landingpads and catchpads. + for (const Use &U : Pad->operands()) { + if (const GlobalVariable *GV = + dyn_cast<GlobalVariable>(U->stripPointerCasts())) + MustKeepGlobalVariables.insert(GV); + } + } + } +} + +bool GlobalMerge::doInitialization(Module &M) { + if (!EnableGlobalMerge) + return false; + + IsMachO = Triple(M.getTargetTriple()).isOSBinFormatMachO(); + + auto &DL = M.getDataLayout(); + DenseMap<std::pair<unsigned, StringRef>, SmallVector<GlobalVariable *, 16>> + Globals, ConstGlobals, BSSGlobals; + bool Changed = false; + setMustKeepGlobalVariables(M); + + // Grab all non-const globals. + for (auto &GV : M.globals()) { + // Merge is safe for "normal" internal or external globals only + if (GV.isDeclaration() || GV.isThreadLocal() || GV.hasImplicitSection()) + continue; + + // It's not safe to merge globals that may be preempted + if (TM && !TM->shouldAssumeDSOLocal(M, &GV)) + continue; + + if (!(MergeExternalGlobals && GV.hasExternalLinkage()) && + !GV.hasInternalLinkage()) + continue; + + PointerType *PT = dyn_cast<PointerType>(GV.getType()); + assert(PT && "Global variable is not a pointer!"); + + unsigned AddressSpace = PT->getAddressSpace(); + StringRef Section = GV.getSection(); + + // Ignore all 'special' globals. + if (GV.getName().startswith("llvm.") || + GV.getName().startswith(".llvm.")) + continue; + + // Ignore all "required" globals: + if (isMustKeepGlobalVariable(&GV)) + continue; + + Type *Ty = GV.getValueType(); + if (DL.getTypeAllocSize(Ty) < MaxOffset) { + if (TM && + TargetLoweringObjectFile::getKindForGlobal(&GV, *TM).isBSS()) + BSSGlobals[{AddressSpace, Section}].push_back(&GV); + else if (GV.isConstant()) + ConstGlobals[{AddressSpace, Section}].push_back(&GV); + else + Globals[{AddressSpace, Section}].push_back(&GV); + } + } + + for (auto &P : Globals) + if (P.second.size() > 1) + Changed |= doMerge(P.second, M, false, P.first.first); + + for (auto &P : BSSGlobals) + if (P.second.size() > 1) + Changed |= doMerge(P.second, M, false, P.first.first); + + if (EnableGlobalMergeOnConst) + for (auto &P : ConstGlobals) + if (P.second.size() > 1) + Changed |= doMerge(P.second, M, true, P.first.first); + + return Changed; +} + +bool GlobalMerge::runOnFunction(Function &F) { + return false; +} + +bool GlobalMerge::doFinalization(Module &M) { + MustKeepGlobalVariables.clear(); + return false; +} + +Pass *llvm::createGlobalMergePass(const TargetMachine *TM, unsigned Offset, + bool OnlyOptimizeForSize, + bool MergeExternalByDefault) { + bool MergeExternal = (EnableGlobalMergeOnExternal == cl::BOU_UNSET) ? + MergeExternalByDefault : (EnableGlobalMergeOnExternal == cl::BOU_TRUE); + return new GlobalMerge(TM, Offset, OnlyOptimizeForSize, MergeExternal); +} |