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7a90b68e5c
* Instead of handling dead functions specially, just nuke them.
* Be more aggressive about cleaning up after constification, in
particular, handle getelementptr instructions and constantexprs.
* Be a little bit more structured about how we process globals.
*** Delete globals that are only stored to, and never read. These are
clearly not useful, so they should go. This implements deadglobal.llx
This last one triggers quite a few times. In particular, 2208 in the
external tests, 1865 of which are in 252.eon. This shrinks eon from
1995094 to 1732341 bytes of bytecode.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@16802 91177308-0d34-0410-b5e6-96231b3b80d8
251 lines
9.4 KiB
C++
251 lines
9.4 KiB
C++
//===- GlobalOpt.cpp - Optimize Global Variables --------------------------===//
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//
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// The LLVM Compiler Infrastructure
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//
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// This file was developed by the LLVM research group and is distributed under
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// the University of Illinois Open Source License. See LICENSE.TXT for details.
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//
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//===----------------------------------------------------------------------===//
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//
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// This pass transforms simple global variables that never have their address
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// taken. If obviously true, it marks read/write globals as constant, deletes
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// variables only stored to, etc.
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//
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//===----------------------------------------------------------------------===//
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#define DEBUG_TYPE "globalopt"
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#include "llvm/Transforms/IPO.h"
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#include "llvm/Constants.h"
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#include "llvm/DerivedTypes.h"
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#include "llvm/Instructions.h"
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#include "llvm/Module.h"
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#include "llvm/Pass.h"
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#include "llvm/Support/Debug.h"
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#include "llvm/ADT/Statistic.h"
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#include <set>
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#include <algorithm>
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using namespace llvm;
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namespace {
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Statistic<> NumMarked ("globalopt", "Number of globals marked constant");
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Statistic<> NumDeleted("globalopt", "Number of globals deleted");
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Statistic<> NumFnDeleted("globalopt", "Number of functions deleted");
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struct GlobalOpt : public ModulePass {
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bool runOnModule(Module &M);
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};
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RegisterOpt<GlobalOpt> X("globalopt", "Global Variable Optimizer");
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}
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ModulePass *llvm::createGlobalOptimizerPass() { return new GlobalOpt(); }
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/// GlobalStatus - As we analyze each global, keep track of some information
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/// about it. If we find out that the address of the global is taken, none of
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/// the other info will be accurate.
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struct GlobalStatus {
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bool isLoaded;
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enum StoredType {
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NotStored, isInitializerStored, isMallocStored, isStored
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} StoredType;
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bool isNotSuitableForSRA;
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GlobalStatus() : isLoaded(false), StoredType(NotStored),
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isNotSuitableForSRA(false) {}
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};
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/// AnalyzeGlobal - Look at all uses of the global and fill in the GlobalStatus
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/// structure. If the global has its address taken, return true to indicate we
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/// can't do anything with it.
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///
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static bool AnalyzeGlobal(Value *V, GlobalStatus &GS,
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std::set<PHINode*> &PHIUsers) {
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for (Value::use_iterator UI = V->use_begin(), E = V->use_end(); UI != E; ++UI)
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if (ConstantExpr *CE = dyn_cast<ConstantExpr>(*UI)) {
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if (AnalyzeGlobal(CE, GS, PHIUsers)) return true;
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if (CE->getOpcode() != Instruction::GetElementPtr)
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GS.isNotSuitableForSRA = true;
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} else if (Instruction *I = dyn_cast<Instruction>(*UI)) {
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if (isa<LoadInst>(I)) {
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GS.isLoaded = true;
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} else if (StoreInst *SI = dyn_cast<StoreInst>(I)) {
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// If this store is just storing the initializer into a global (i.e. not
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// changing the value), ignore it. For now we just handle direct
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// stores, no stores to fields of aggregates.
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if (GlobalVariable *GV = dyn_cast<GlobalVariable>(SI->getOperand(1))) {
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if (SI->getOperand(0) == GV->getInitializer() &&
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GS.StoredType < GlobalStatus::isInitializerStored)
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GS.StoredType = GlobalStatus::isInitializerStored;
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else if (isa<MallocInst>(SI->getOperand(0)) &&
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GS.StoredType < GlobalStatus::isMallocStored)
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GS.StoredType = GlobalStatus::isMallocStored;
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else
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GS.StoredType = GlobalStatus::isStored;
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} else {
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GS.StoredType = GlobalStatus::isStored;
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}
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} else if (I->getOpcode() == Instruction::GetElementPtr) {
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if (AnalyzeGlobal(I, GS, PHIUsers)) return true;
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if (!GS.isNotSuitableForSRA)
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for (unsigned i = 1, e = I->getNumOperands(); i != e; ++i)
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if (!isa<Constant>(I->getOperand(i))) {
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GS.isNotSuitableForSRA = true;
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break;
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}
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} else if (I->getOpcode() == Instruction::Select) {
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if (AnalyzeGlobal(I, GS, PHIUsers)) return true;
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GS.isNotSuitableForSRA = true;
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} else if (PHINode *PN = dyn_cast<PHINode>(I)) {
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// PHI nodes we can check just like select or GEP instructions, but we
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// have to be careful about infinite recursion.
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if (PHIUsers.insert(PN).second) // Not already visited.
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if (AnalyzeGlobal(I, GS, PHIUsers)) return true;
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GS.isNotSuitableForSRA = true;
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} else if (isa<SetCondInst>(I)) {
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GS.isNotSuitableForSRA = true;
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} else {
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return true; // Any other non-load instruction might take address!
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}
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} else {
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// Otherwise must be a global or some other user.
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return true;
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}
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return false;
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}
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static Constant *TraverseGEPInitializer(User *GEP, Constant *Init) {
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if (GEP->getNumOperands() == 1 ||
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!isa<Constant>(GEP->getOperand(1)) ||
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!cast<Constant>(GEP->getOperand(1))->isNullValue())
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return 0;
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for (unsigned i = 2, e = GEP->getNumOperands(); i != e; ++i) {
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ConstantInt *Idx = dyn_cast<ConstantInt>(GEP->getOperand(i));
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if (!Idx) return 0;
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uint64_t IdxV = Idx->getRawValue();
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if (ConstantStruct *CS = dyn_cast<ConstantStruct>(Init)) {
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if (IdxV >= CS->getNumOperands()) return 0;
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Init = CS->getOperand(IdxV);
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} else if (ConstantArray *CA = dyn_cast<ConstantArray>(Init)) {
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if (IdxV >= CA->getNumOperands()) return 0;
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Init = CA->getOperand(IdxV);
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} else if (ConstantPacked *CP = dyn_cast<ConstantPacked>(Init)) {
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if (IdxV >= CP->getNumOperands()) return 0;
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Init = CP->getOperand(IdxV);
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} else if (ConstantAggregateZero *CAZ =
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dyn_cast<ConstantAggregateZero>(Init)) {
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if (const StructType *STy = dyn_cast<StructType>(Init->getType())) {
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if (IdxV >= STy->getNumElements()) return 0;
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Init = Constant::getNullValue(STy->getElementType(IdxV));
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} else if (const SequentialType *STy =
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dyn_cast<SequentialType>(Init->getType())) {
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Init = Constant::getNullValue(STy->getElementType());
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} else {
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return 0;
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}
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} else {
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return 0;
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}
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}
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return Init;
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}
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/// CleanupConstantGlobalUsers - We just marked GV constant. Loop over all
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/// users of the global, cleaning up the obvious ones. This is largely just a
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/// quick scan over the use list to clean up the easy and obvious cruft.
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static void CleanupConstantGlobalUsers(Value *V, Constant *Init) {
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for (Value::use_iterator UI = V->use_begin(), E = V->use_end(); UI != E;) {
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User *U = *UI++;
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if (LoadInst *LI = dyn_cast<LoadInst>(U)) {
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// Replace the load with the initializer.
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LI->replaceAllUsesWith(Init);
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LI->getParent()->getInstList().erase(LI);
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} else if (StoreInst *SI = dyn_cast<StoreInst>(U)) {
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// Store must be unreachable or storing Init into the global.
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SI->getParent()->getInstList().erase(SI);
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} else if (ConstantExpr *CE = dyn_cast<ConstantExpr>(U)) {
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if (CE->getOpcode() == Instruction::GetElementPtr) {
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if (Constant *SubInit = TraverseGEPInitializer(CE, Init))
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CleanupConstantGlobalUsers(CE, SubInit);
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if (CE->use_empty()) CE->destroyConstant();
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}
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} else if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(U)) {
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if (Constant *SubInit = TraverseGEPInitializer(GEP, Init))
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CleanupConstantGlobalUsers(GEP, SubInit);
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if (GEP->use_empty())
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GEP->getParent()->getInstList().erase(GEP);
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}
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}
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}
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bool GlobalOpt::runOnModule(Module &M) {
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bool Changed = false;
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// As a prepass, delete functions that are trivially dead.
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bool LocalChange = true;
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while (LocalChange) {
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LocalChange = false;
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for (Module::iterator FI = M.begin(), E = M.end(); FI != E; ) {
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Function *F = FI++;
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F->removeDeadConstantUsers();
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if (F->use_empty() && (F->hasInternalLinkage() || F->hasWeakLinkage())) {
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M.getFunctionList().erase(F);
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LocalChange = true;
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++NumFnDeleted;
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}
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}
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Changed |= LocalChange;
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}
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std::set<PHINode*> PHIUsers;
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for (Module::giterator GVI = M.gbegin(), E = M.gend(); GVI != E;) {
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GlobalVariable *GV = GVI++;
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if (!GV->isConstant() && GV->hasInternalLinkage() && GV->hasInitializer()) {
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GlobalStatus GS;
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PHIUsers.clear();
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GV->removeDeadConstantUsers();
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if (!AnalyzeGlobal(GV, GS, PHIUsers)) {
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// If the global is never loaded (but may be stored to), it is dead.
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// Delete it now.
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if (!GS.isLoaded) {
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DEBUG(std::cerr << "GLOBAL NEVER LOADED: " << *GV);
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// Delete any stores we can find to the global. We may not be able to
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// make it completely dead though.
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CleanupConstantGlobalUsers(GV, GV->getInitializer());
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// If the global is dead now, delete it.
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if (GV->use_empty()) {
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M.getGlobalList().erase(GV);
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++NumDeleted;
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}
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Changed = true;
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} else if (GS.StoredType <= GlobalStatus::isInitializerStored) {
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DEBUG(std::cerr << "MARKING CONSTANT: " << *GV);
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GV->setConstant(true);
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// Clean up any obviously simplifiable users now.
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CleanupConstantGlobalUsers(GV, GV->getInitializer());
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// If the global is dead now, just nuke it.
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if (GV->use_empty()) {
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M.getGlobalList().erase(GV);
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++NumDeleted;
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}
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++NumMarked;
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Changed = true;
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} else if (!GS.isNotSuitableForSRA &&
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!GV->getInitializer()->getType()->isFirstClassType()) {
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//std::cerr << "COULD SRA: " << *GV;
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}
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}
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}
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}
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return Changed;
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}
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