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-rw-r--r--lib/Transforms/Scalar/GlobalMerge.cpp313
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diff --git a/lib/Transforms/Scalar/GlobalMerge.cpp b/lib/Transforms/Scalar/GlobalMerge.cpp
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-//===-- GlobalMerge.cpp - Internal globals merging -----------------------===//
-//
-// The LLVM Compiler Infrastructure
-//
-// This file is distributed under the University of Illinois Open Source
-// License. See LICENSE.TXT for details.
-//
-//===----------------------------------------------------------------------===//
-// 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".
-// ===---------------------------------------------------------------------===//
-
-#include "llvm/Transforms/Scalar.h"
-#include "llvm/ADT/SmallPtrSet.h"
-#include "llvm/ADT/Statistic.h"
-#include "llvm/IR/Attributes.h"
-#include "llvm/IR/Constants.h"
-#include "llvm/IR/DataLayout.h"
-#include "llvm/IR/DerivedTypes.h"
-#include "llvm/IR/Function.h"
-#include "llvm/IR/GlobalVariable.h"
-#include "llvm/IR/Instructions.h"
-#include "llvm/IR/Intrinsics.h"
-#include "llvm/IR/Module.h"
-#include "llvm/Pass.h"
-#include "llvm/Support/CommandLine.h"
-#include "llvm/Target/TargetLowering.h"
-#include "llvm/Target/TargetLoweringObjectFile.h"
-using namespace llvm;
-
-#define DEBUG_TYPE "global-merge"
-
-cl::opt<bool>
-EnableGlobalMerge("global-merge", cl::Hidden,
- cl::desc("Enable global merge pass"),
- 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));
-
-STATISTIC(NumMerged , "Number of globals merged");
-namespace {
- class GlobalMerge : public FunctionPass {
- const TargetMachine *TM;
-
- bool doMerge(SmallVectorImpl<GlobalVariable*> &Globals,
- Module &M, bool isConst, unsigned AddrSpace) const;
-
- /// \brief 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);
-
- /// 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(const TargetMachine *TM = nullptr)
- : FunctionPass(ID), TM(TM) {
- initializeGlobalMergePass(*PassRegistry::getPassRegistry());
- }
-
- bool doInitialization(Module &M) override;
- bool runOnFunction(Function &F) override;
- bool doFinalization(Module &M) override;
-
- const char *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, "global-merge",
- "Global Merge", false, false)
-
-
-bool GlobalMerge::doMerge(SmallVectorImpl<GlobalVariable*> &Globals,
- Module &M, bool isConst, unsigned AddrSpace) const {
- const TargetLowering *TLI = TM->getTargetLowering();
- const DataLayout *DL = TLI->getDataLayout();
-
- // FIXME: Infer the maximum possible offset depending on the actual users
- // (these max offsets are different for the users inside Thumb or ARM
- // functions)
- unsigned MaxOffset = TLI->getMaximalGlobalOffset();
-
- // FIXME: Find better heuristics
- std::stable_sort(Globals.begin(), Globals.end(),
- [DL](const GlobalVariable *GV1, const GlobalVariable *GV2) {
- Type *Ty1 = cast<PointerType>(GV1->getType())->getElementType();
- Type *Ty2 = cast<PointerType>(GV2->getType())->getElementType();
-
- return (DL->getTypeAllocSize(Ty1) < DL->getTypeAllocSize(Ty2));
- });
-
- Type *Int32Ty = Type::getInt32Ty(M.getContext());
-
- 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;
- for (j = i; j != e; ++j) {
- Type *Ty = Globals[j]->getType()->getElementType();
- MergedSize += DL->getTypeAllocSize(Ty);
- if (MergedSize > MaxOffset) {
- break;
- }
- Tys.push_back(Ty);
- Inits.push_back(Globals[j]->getInitializer());
- }
-
- 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);
- for (size_t k = i; k < j; ++k) {
- Constant *Idx[2] = {
- ConstantInt::get(Int32Ty, 0),
- ConstantInt::get(Int32Ty, k-i)
- };
- Constant *GEP = ConstantExpr::getInBoundsGetElementPtr(MergedGV, Idx);
- Globals[k]->replaceAllUsesWith(GEP);
- Globals[k]->eraseFromParent();
- NumMerged++;
- }
- i = j;
- }
-
- return true;
-}
-
-void GlobalMerge::collectUsedGlobalVariables(Module &M) {
- // Extract global variables from llvm.used array
- const GlobalVariable *GV = M.getGlobalVariable("llvm.used");
- 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);
-
- for (Module::iterator IFn = M.begin(), IEndFn = M.end(); IFn != IEndFn;
- ++IFn) {
- for (Function::iterator IBB = IFn->begin(), IEndBB = IFn->end();
- IBB != IEndBB; ++IBB) {
- // Follow the invoke link to find the landing pad instruction
- const InvokeInst *II = dyn_cast<InvokeInst>(IBB->getTerminator());
- if (!II) continue;
-
- const LandingPadInst *LPInst = II->getUnwindDest()->getLandingPadInst();
- // Look for globals in the clauses of the landing pad instruction
- for (unsigned Idx = 0, NumClauses = LPInst->getNumClauses();
- Idx != NumClauses; ++Idx)
- if (const GlobalVariable *GV =
- dyn_cast<GlobalVariable>(LPInst->getClause(Idx)
- ->stripPointerCasts()))
- MustKeepGlobalVariables.insert(GV);
- }
- }
-}
-
-bool GlobalMerge::doInitialization(Module &M) {
- if (!EnableGlobalMerge)
- return false;
-
- DenseMap<unsigned, SmallVector<GlobalVariable*, 16> > Globals, ConstGlobals,
- BSSGlobals;
- const TargetLowering *TLI = TM->getTargetLowering();
- const DataLayout *DL = TLI->getDataLayout();
- unsigned MaxOffset = TLI->getMaximalGlobalOffset();
- bool Changed = false;
- setMustKeepGlobalVariables(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())
- continue;
-
- PointerType *PT = dyn_cast<PointerType>(I->getType());
- assert(PT && "Global variable is not a pointer!");
-
- unsigned AddressSpace = PT->getAddressSpace();
-
- // Ignore fancy-aligned globals for now.
- unsigned Alignment = DL->getPreferredAlignment(I);
- Type *Ty = I->getType()->getElementType();
- if (Alignment > DL->getABITypeAlignment(Ty))
- continue;
-
- // Ignore all 'special' globals.
- if (I->getName().startswith("llvm.") ||
- I->getName().startswith(".llvm."))
- continue;
-
- // Ignore all "required" globals:
- if (isMustKeepGlobalVariable(I))
- continue;
-
- if (DL->getTypeAllocSize(Ty) < MaxOffset) {
- if (TargetLoweringObjectFile::getKindForGlobal(I, TLI->getTargetMachine())
- .isBSSLocal())
- BSSGlobals[AddressSpace].push_back(I);
- else if (I->isConstant())
- ConstGlobals[AddressSpace].push_back(I);
- else
- Globals[AddressSpace].push_back(I);
- }
- }
-
- for (DenseMap<unsigned, SmallVector<GlobalVariable*, 16> >::iterator
- I = Globals.begin(), E = Globals.end(); I != E; ++I)
- if (I->second.size() > 1)
- Changed |= doMerge(I->second, M, false, I->first);
-
- for (DenseMap<unsigned, SmallVector<GlobalVariable*, 16> >::iterator
- I = BSSGlobals.begin(), E = BSSGlobals.end(); I != E; ++I)
- if (I->second.size() > 1)
- Changed |= doMerge(I->second, M, false, I->first);
-
- if (EnableGlobalMergeOnConst)
- for (DenseMap<unsigned, SmallVector<GlobalVariable*, 16> >::iterator
- I = ConstGlobals.begin(), E = ConstGlobals.end(); I != E; ++I)
- if (I->second.size() > 1)
- Changed |= doMerge(I->second, M, true, I->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) {
- return new GlobalMerge(TM);
-}