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e572809aa1
Also add some checks to not merge globals used within landing pad instructions or marked as "used". git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@177331 91177308-0d34-0410-b5e6-96231b3b80d8
313 lines
11 KiB
C++
313 lines
11 KiB
C++
//===-- GlobalMerge.cpp - Internal globals merging -----------------------===//
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//
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// The LLVM Compiler Infrastructure
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//
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// This file is distributed under the University of Illinois Open Source
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// License. See LICENSE.TXT for details.
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//
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//===----------------------------------------------------------------------===//
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// This pass merges globals with internal linkage into one. This way all the
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// globals which were merged into a biggest one can be addressed using offsets
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// from the same base pointer (no need for separate base pointer for each of the
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// global). Such a transformation can significantly reduce the register pressure
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// when many globals are involved.
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//
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// For example, consider the code which touches several global variables at
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// once:
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//
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// static int foo[N], bar[N], baz[N];
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//
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// for (i = 0; i < N; ++i) {
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// foo[i] = bar[i] * baz[i];
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// }
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//
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// On ARM the addresses of 3 arrays should be kept in the registers, thus
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// this code has quite large register pressure (loop body):
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//
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// ldr r1, [r5], #4
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// ldr r2, [r6], #4
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// mul r1, r2, r1
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// str r1, [r0], #4
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//
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// Pass converts the code to something like:
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//
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// static struct {
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// int foo[N];
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// int bar[N];
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// int baz[N];
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// } merged;
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//
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// for (i = 0; i < N; ++i) {
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// merged.foo[i] = merged.bar[i] * merged.baz[i];
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// }
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//
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// and in ARM code this becomes:
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//
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// ldr r0, [r5, #40]
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// ldr r1, [r5, #80]
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// mul r0, r1, r0
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// str r0, [r5], #4
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//
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// note that we saved 2 registers here almostly "for free".
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// ===---------------------------------------------------------------------===//
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#define DEBUG_TYPE "global-merge"
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#include "llvm/Transforms/Scalar.h"
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#include "llvm/ADT/SmallPtrSet.h"
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#include "llvm/ADT/Statistic.h"
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#include "llvm/IR/Attributes.h"
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#include "llvm/IR/Constants.h"
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#include "llvm/IR/DataLayout.h"
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#include "llvm/IR/DerivedTypes.h"
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#include "llvm/IR/Function.h"
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#include "llvm/IR/GlobalVariable.h"
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#include "llvm/IR/InlineAsm.h"
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#include "llvm/IR/Instructions.h"
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#include "llvm/IR/Intrinsics.h"
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#include "llvm/IR/IntrinsicInst.h"
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#include "llvm/IR/Module.h"
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#include "llvm/Pass.h"
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#include "llvm/Support/CommandLine.h"
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#include "llvm/Target/TargetLowering.h"
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#include "llvm/Target/TargetLoweringObjectFile.h"
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using namespace llvm;
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static cl::opt<bool>
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EnableGlobalMergeOnConst("global-merge-on-const", cl::Hidden,
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cl::desc("Enable global merge pass on constants"),
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cl::init(false));
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STATISTIC(NumMerged , "Number of globals merged");
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namespace {
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class GlobalMerge : public FunctionPass {
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/// TLI - Keep a pointer of a TargetLowering to consult for determining
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/// target type sizes.
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const TargetLowering *TLI;
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bool doMerge(SmallVectorImpl<GlobalVariable*> &Globals,
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Module &M, bool isConst, unsigned AddrSpace) const;
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/// \brief Check if the given variable has been identified as must keep
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/// \pre setMustKeepGlobalVariables must have been called on the Module that
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/// contains GV
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bool isMustKeepGlobalVariable(const GlobalVariable *GV) const {
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return MustKeepGlobalVariables.count(GV);
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}
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/// Collect every variables marked as "used" or used in a landing pad
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/// instruction for this Module.
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void setMustKeepGlobalVariables(Module &M);
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/// Collect every variables marked as "used"
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void collectUsedGlobalVariables(Module &M);
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/// Keep track of the GlobalVariable that are marked as "used"
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SmallPtrSet<const GlobalVariable *, 16> MustKeepGlobalVariables;
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public:
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static char ID; // Pass identification, replacement for typeid.
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explicit GlobalMerge(const TargetLowering *tli = 0)
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: FunctionPass(ID), TLI(tli) {
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initializeGlobalMergePass(*PassRegistry::getPassRegistry());
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}
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virtual bool doInitialization(Module &M);
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virtual bool runOnFunction(Function &F);
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const char *getPassName() const {
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return "Merge internal globals";
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}
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virtual void getAnalysisUsage(AnalysisUsage &AU) const {
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AU.setPreservesCFG();
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FunctionPass::getAnalysisUsage(AU);
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}
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struct GlobalCmp {
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const DataLayout *TD;
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GlobalCmp(const DataLayout *td) : TD(td) { }
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bool operator()(const GlobalVariable *GV1, const GlobalVariable *GV2) {
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Type *Ty1 = cast<PointerType>(GV1->getType())->getElementType();
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Type *Ty2 = cast<PointerType>(GV2->getType())->getElementType();
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return (TD->getTypeAllocSize(Ty1) < TD->getTypeAllocSize(Ty2));
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}
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};
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};
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} // end anonymous namespace
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char GlobalMerge::ID = 0;
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INITIALIZE_PASS(GlobalMerge, "global-merge",
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"Global Merge", false, false)
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bool GlobalMerge::doMerge(SmallVectorImpl<GlobalVariable*> &Globals,
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Module &M, bool isConst, unsigned AddrSpace) const {
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const DataLayout *TD = TLI->getDataLayout();
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// FIXME: Infer the maximum possible offset depending on the actual users
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// (these max offsets are different for the users inside Thumb or ARM
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// functions)
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unsigned MaxOffset = TLI->getMaximalGlobalOffset();
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// FIXME: Find better heuristics
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std::stable_sort(Globals.begin(), Globals.end(), GlobalCmp(TD));
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Type *Int32Ty = Type::getInt32Ty(M.getContext());
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for (size_t i = 0, e = Globals.size(); i != e; ) {
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size_t j = 0;
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uint64_t MergedSize = 0;
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std::vector<Type*> Tys;
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std::vector<Constant*> Inits;
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for (j = i; j != e; ++j) {
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Type *Ty = Globals[j]->getType()->getElementType();
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MergedSize += TD->getTypeAllocSize(Ty);
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if (MergedSize > MaxOffset) {
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break;
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}
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Tys.push_back(Ty);
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Inits.push_back(Globals[j]->getInitializer());
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}
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StructType *MergedTy = StructType::get(M.getContext(), Tys);
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Constant *MergedInit = ConstantStruct::get(MergedTy, Inits);
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GlobalVariable *MergedGV = new GlobalVariable(M, MergedTy, isConst,
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GlobalValue::InternalLinkage,
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MergedInit, "_MergedGlobals",
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0, GlobalVariable::NotThreadLocal,
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AddrSpace);
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for (size_t k = i; k < j; ++k) {
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Constant *Idx[2] = {
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ConstantInt::get(Int32Ty, 0),
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ConstantInt::get(Int32Ty, k-i)
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};
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Constant *GEP = ConstantExpr::getInBoundsGetElementPtr(MergedGV, Idx);
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Globals[k]->replaceAllUsesWith(GEP);
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Globals[k]->eraseFromParent();
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NumMerged++;
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}
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i = j;
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}
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return true;
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}
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void GlobalMerge::collectUsedGlobalVariables(Module &M) {
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// Extract global variables from llvm.used array
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const GlobalVariable *GV = M.getGlobalVariable("llvm.used");
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if (!GV || !GV->hasInitializer()) return;
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// Should be an array of 'i8*'.
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const ConstantArray *InitList = dyn_cast<ConstantArray>(GV->getInitializer());
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if (InitList == 0) return;
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for (unsigned i = 0, e = InitList->getNumOperands(); i != e; ++i)
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if (const GlobalVariable *G =
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dyn_cast<GlobalVariable>(InitList->getOperand(i)->stripPointerCasts()))
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MustKeepGlobalVariables.insert(G);
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}
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void GlobalMerge::setMustKeepGlobalVariables(Module &M) {
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// If we already processed a Module, UsedGlobalVariables may have been
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// populated. Reset the information for this module.
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MustKeepGlobalVariables.clear();
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collectUsedGlobalVariables(M);
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for (Module::iterator IFn = M.begin(), IEndFn = M.end(); IFn != IEndFn;
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++IFn) {
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for (Function::iterator IBB = IFn->begin(), IEndBB = IFn->end();
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IBB != IEndBB; ++IBB) {
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// Follow the inwoke link to find the landing pad instruction
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const InvokeInst *II = dyn_cast<InvokeInst>(IBB->getTerminator());
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if (!II) continue;
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const LandingPadInst *LPInst = II->getUnwindDest()->getLandingPadInst();
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// Look for globals in the clauses of the landing pad instruction
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for (unsigned Idx = 0, NumClauses = LPInst->getNumClauses();
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Idx != NumClauses; ++Idx)
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if (const GlobalVariable *GV =
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dyn_cast<GlobalVariable>(LPInst->getClause(Idx)
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->stripPointerCasts()))
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MustKeepGlobalVariables.insert(GV);
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}
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}
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}
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bool GlobalMerge::doInitialization(Module &M) {
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DenseMap<unsigned, SmallVector<GlobalVariable*, 16> > Globals, ConstGlobals,
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BSSGlobals;
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const DataLayout *TD = TLI->getDataLayout();
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unsigned MaxOffset = TLI->getMaximalGlobalOffset();
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bool Changed = false;
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setMustKeepGlobalVariables(M);
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// Grab all non-const globals.
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for (Module::global_iterator I = M.global_begin(),
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E = M.global_end(); I != E; ++I) {
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// Merge is safe for "normal" internal globals only
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if (!I->hasLocalLinkage() || I->isThreadLocal() || I->hasSection())
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continue;
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PointerType *PT = dyn_cast<PointerType>(I->getType());
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assert(PT && "Global variable is not a pointer!");
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unsigned AddressSpace = PT->getAddressSpace();
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// Ignore fancy-aligned globals for now.
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unsigned Alignment = TD->getPreferredAlignment(I);
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Type *Ty = I->getType()->getElementType();
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if (Alignment > TD->getABITypeAlignment(Ty))
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continue;
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// Ignore all 'special' globals.
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if (I->getName().startswith("llvm.") ||
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I->getName().startswith(".llvm."))
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continue;
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// Ignore all "required" globals:
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// - the ones used for EH
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// - the ones marked with "used" attribute
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if (isMustKeepGlobalVariable(I))
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continue;
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if (TD->getTypeAllocSize(Ty) < MaxOffset) {
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if (TargetLoweringObjectFile::getKindForGlobal(I, TLI->getTargetMachine())
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.isBSSLocal())
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BSSGlobals[AddressSpace].push_back(I);
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else if (I->isConstant())
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ConstGlobals[AddressSpace].push_back(I);
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else
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Globals[AddressSpace].push_back(I);
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}
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}
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for (DenseMap<unsigned, SmallVector<GlobalVariable*, 16> >::iterator
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I = Globals.begin(), E = Globals.end(); I != E; ++I)
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if (I->second.size() > 1)
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Changed |= doMerge(I->second, M, false, I->first);
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for (DenseMap<unsigned, SmallVector<GlobalVariable*, 16> >::iterator
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I = BSSGlobals.begin(), E = BSSGlobals.end(); I != E; ++I)
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if (I->second.size() > 1)
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Changed |= doMerge(I->second, M, false, I->first);
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if (EnableGlobalMergeOnConst)
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for (DenseMap<unsigned, SmallVector<GlobalVariable*, 16> >::iterator
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I = ConstGlobals.begin(), E = ConstGlobals.end(); I != E; ++I)
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if (I->second.size() > 1)
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Changed |= doMerge(I->second, M, true, I->first);
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return Changed;
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}
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bool GlobalMerge::runOnFunction(Function &F) {
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return false;
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}
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Pass *llvm::createGlobalMergePass(const TargetLowering *tli) {
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return new GlobalMerge(tli);
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}
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