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git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@128183 91177308-0d34-0410-b5e6-96231b3b80d8
218 lines
6.7 KiB
C++
218 lines
6.7 KiB
C++
//===-- ARMGlobalMerge.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 "arm-global-merge"
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#include "ARM.h"
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#include "llvm/CodeGen/Passes.h"
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#include "llvm/Attributes.h"
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#include "llvm/Constants.h"
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#include "llvm/DerivedTypes.h"
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#include "llvm/Function.h"
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#include "llvm/GlobalVariable.h"
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#include "llvm/Instructions.h"
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#include "llvm/Intrinsics.h"
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#include "llvm/Module.h"
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#include "llvm/Pass.h"
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#include "llvm/Target/TargetData.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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namespace {
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class ARMGlobalMerge : 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) const;
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public:
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static char ID; // Pass identification, replacement for typeid.
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explicit ARMGlobalMerge(const TargetLowering *tli)
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: FunctionPass(ID), TLI(tli) {}
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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 TargetData *TD;
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GlobalCmp(const TargetData *td) : TD(td) { }
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bool operator()(const GlobalVariable *GV1, const GlobalVariable *GV2) {
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const Type *Ty1 = cast<PointerType>(GV1->getType())->getElementType();
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const 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 ARMGlobalMerge::ID = 0;
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bool ARMGlobalMerge::doMerge(SmallVectorImpl<GlobalVariable*> &Globals,
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Module &M, bool isConst) const {
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const TargetData *TD = TLI->getTargetData();
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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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const 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<const Type*> Tys;
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std::vector<Constant*> Inits;
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for (j = i; j != e; ++j) {
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const 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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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, 2);
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Globals[k]->replaceAllUsesWith(GEP);
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Globals[k]->eraseFromParent();
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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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bool ARMGlobalMerge::doInitialization(Module &M) {
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SmallVector<GlobalVariable*, 16> Globals, ConstGlobals, BSSGlobals;
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const TargetData *TD = TLI->getTargetData();
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unsigned MaxOffset = TLI->getMaximalGlobalOffset();
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bool Changed = false;
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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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// Ignore fancy-aligned globals for now.
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if (I->getAlignment() != 0)
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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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if (TD->getTypeAllocSize(I->getType()->getElementType()) < MaxOffset) {
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const TargetLoweringObjectFile &TLOF = TLI->getObjFileLowering();
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if (TLOF.getKindForGlobal(I, TLI->getTargetMachine()).isBSSLocal())
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BSSGlobals.push_back(I);
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else if (I->isConstant())
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ConstGlobals.push_back(I);
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else
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Globals.push_back(I);
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}
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}
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if (Globals.size() > 1)
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Changed |= doMerge(Globals, M, false);
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if (BSSGlobals.size() > 1)
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Changed |= doMerge(BSSGlobals, M, false);
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// FIXME: This currently breaks the EH processing due to way how the
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// typeinfo detection works. We might want to detect the TIs and ignore
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// them in the future.
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// if (ConstGlobals.size() > 1)
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// Changed |= doMerge(ConstGlobals, M, true);
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return Changed;
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}
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bool ARMGlobalMerge::runOnFunction(Function &F) {
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return false;
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}
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FunctionPass *llvm::createARMGlobalMergePass(const TargetLowering *tli) {
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return new ARMGlobalMerge(tli);
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}
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