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c4d81b0388
stored to, but are stored at variable indexes. This occurs at least in 176.gcc, but probably others, and we should handle it for completeness. git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@16876 91177308-0d34-0410-b5e6-96231b3b80d8
576 lines
22 KiB
C++
576 lines
22 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 "llvm/ADT/StringExtras.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<> NumSRA ("globalopt", "Number of aggregate globals broken "
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"into scalars");
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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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/// this info will be accurate.
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struct GlobalStatus {
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/// isLoaded - True if the global is ever loaded. If the global isn't ever
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/// loaded it can be deleted.
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bool isLoaded;
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/// StoredType - Keep track of what stores to the global look like.
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///
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enum StoredType {
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/// NotStored - There is no store to this global. It can thus be marked
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/// constant.
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NotStored,
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/// isInitializerStored - This global is stored to, but the only thing
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/// stored is the constant it was initialized with. This is only tracked
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/// for scalar globals.
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isInitializerStored,
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/// isStoredOnce - This global is stored to, but only its initializer and
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/// one other value is ever stored to it. If this global isStoredOnce, we
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/// track the value stored to it in StoredOnceValue below. This is only
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/// tracked for scalar globals.
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isStoredOnce,
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/// isStored - This global is stored to by multiple values or something else
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/// that we cannot track.
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isStored
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} StoredType;
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/// StoredOnceValue - If only one value (besides the initializer constant) is
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/// ever stored to this global, keep track of what value it is.
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Value *StoredOnceValue;
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/// isNotSuitableForSRA - Keep track of whether any SRA preventing users of
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/// the global exist. Such users include GEP instruction with variable
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/// indexes, and non-gep/load/store users like constant expr casts.
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bool isNotSuitableForSRA;
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GlobalStatus() : isLoaded(false), StoredType(NotStored), StoredOnceValue(0),
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isNotSuitableForSRA(false) {}
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};
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/// ConstantIsDead - Return true if the specified constant is (transitively)
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/// dead. The constant may be used by other constants (e.g. constant arrays and
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/// constant exprs) as long as they are dead, but it cannot be used by anything
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/// else.
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static bool ConstantIsDead(Constant *C) {
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if (isa<GlobalValue>(C)) return false;
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for (Value::use_iterator UI = C->use_begin(), E = C->use_end(); UI != E; ++UI)
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if (Constant *CU = dyn_cast<Constant>(*UI)) {
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if (!ConstantIsDead(CU)) return false;
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} else
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return false;
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return true;
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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 (!GS.isNotSuitableForSRA) {
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// Check to see if this ConstantExpr GEP is SRA'able. In particular, we
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// don't like < 3 operand CE's, and we don't like non-constant integer
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// indices.
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if (CE->getNumOperands() < 3 || !CE->getOperand(1)->isNullValue())
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GS.isNotSuitableForSRA = true;
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else {
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for (unsigned i = 1, e = CE->getNumOperands(); i != e; ++i)
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if (!isa<ConstantInt>(CE->getOperand(i))) {
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GS.isNotSuitableForSRA = true;
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break;
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}
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}
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}
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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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// Don't allow a store OF the address, only stores TO the address.
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if (SI->getOperand(0) == V) return true;
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// If this is a direct store to the global (i.e., the global is a scalar
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// value, not an aggregate), keep more specific information about
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// stores.
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if (GS.StoredType != GlobalStatus::isStored)
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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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if (GS.StoredType < GlobalStatus::isInitializerStored)
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GS.StoredType = GlobalStatus::isInitializerStored;
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} else if (GS.StoredType < GlobalStatus::isStoredOnce) {
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GS.StoredType = GlobalStatus::isStoredOnce;
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GS.StoredOnceValue = SI->getOperand(0);
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} else if (GS.StoredType == GlobalStatus::isStoredOnce &&
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GS.StoredOnceValue == SI->getOperand(0)) {
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// noop.
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} else {
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GS.StoredType = GlobalStatus::isStored;
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}
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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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// Theoretically we could SRA globals with GEP insts if all indexes are
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// constants. In practice, these GEPs would already be constant exprs
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// if that was the case though.
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GS.isNotSuitableForSRA = true;
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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 if (Constant *C = dyn_cast<Constant>(*UI)) {
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// We might have a dead and dangling constant hanging off of here.
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if (!ConstantIsDead(C))
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return true;
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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 *getAggregateConstantElement(Constant *Agg, Constant *Idx) {
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ConstantInt *CI = dyn_cast<ConstantInt>(Idx);
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if (!CI) return 0;
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uint64_t IdxV = CI->getRawValue();
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if (ConstantStruct *CS = dyn_cast<ConstantStruct>(Agg)) {
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if (IdxV < CS->getNumOperands()) return CS->getOperand(IdxV);
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} else if (ConstantArray *CA = dyn_cast<ConstantArray>(Agg)) {
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if (IdxV < CA->getNumOperands()) return CA->getOperand(IdxV);
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} else if (ConstantPacked *CP = dyn_cast<ConstantPacked>(Agg)) {
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if (IdxV < CP->getNumOperands()) return CP->getOperand(IdxV);
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} else if (ConstantAggregateZero *CAZ =
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dyn_cast<ConstantAggregateZero>(Agg)) {
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if (const StructType *STy = dyn_cast<StructType>(Agg->getType())) {
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if (IdxV < STy->getNumElements())
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return Constant::getNullValue(STy->getElementType(IdxV));
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} else if (const SequentialType *STy =
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dyn_cast<SequentialType>(Agg->getType())) {
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return Constant::getNullValue(STy->getElementType());
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}
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}
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return 0;
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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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Init = getAggregateConstantElement(Init, Idx);
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if (Init == 0) return 0;
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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. This
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/// returns true if it made a change.
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static bool CleanupConstantGlobalUsers(Value *V, Constant *Init) {
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bool Changed = false;
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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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Changed = true;
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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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Changed = true;
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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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Changed |= CleanupConstantGlobalUsers(CE, SubInit);
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if (CE->use_empty()) {
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CE->destroyConstant();
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Changed = true;
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}
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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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Changed |= CleanupConstantGlobalUsers(GEP, SubInit);
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else {
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// If this GEP has variable indexes, we should still be able to delete
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// any stores through it.
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for (Value::use_iterator GUI = GEP->use_begin(), E = GEP->use_end();
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GUI != E;)
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if (StoreInst *SI = dyn_cast<StoreInst>(*GUI++)) {
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SI->getParent()->getInstList().erase(SI);
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Changed = true;
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}
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}
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if (GEP->use_empty()) {
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GEP->getParent()->getInstList().erase(GEP);
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Changed = true;
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}
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} else if (Constant *C = dyn_cast<Constant>(U)) {
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// If we have a chain of dead constantexprs or other things dangling from
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// us, and if they are all dead, nuke them without remorse.
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if (ConstantIsDead(C)) {
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C->destroyConstant();
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// This could have incalidated UI, start over from scratch.x
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CleanupConstantGlobalUsers(V, Init);
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return true;
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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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/// SRAGlobal - Perform scalar replacement of aggregates on the specified global
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/// variable. This opens the door for other optimizations by exposing the
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/// behavior of the program in a more fine-grained way. We have determined that
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/// this transformation is safe already. We return the first global variable we
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/// insert so that the caller can reprocess it.
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static GlobalVariable *SRAGlobal(GlobalVariable *GV) {
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assert(GV->hasInternalLinkage() && !GV->isConstant());
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Constant *Init = GV->getInitializer();
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const Type *Ty = Init->getType();
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std::vector<GlobalVariable*> NewGlobals;
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Module::GlobalListType &Globals = GV->getParent()->getGlobalList();
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if (const StructType *STy = dyn_cast<StructType>(Ty)) {
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NewGlobals.reserve(STy->getNumElements());
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for (unsigned i = 0, e = STy->getNumElements(); i != e; ++i) {
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Constant *In = getAggregateConstantElement(Init,
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ConstantUInt::get(Type::UIntTy, i));
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assert(In && "Couldn't get element of initializer?");
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GlobalVariable *NGV = new GlobalVariable(STy->getElementType(i), false,
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GlobalVariable::InternalLinkage,
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In, GV->getName()+"."+utostr(i));
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Globals.insert(GV, NGV);
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NewGlobals.push_back(NGV);
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}
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} else if (const SequentialType *STy = dyn_cast<SequentialType>(Ty)) {
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unsigned NumElements = 0;
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if (const ArrayType *ATy = dyn_cast<ArrayType>(STy))
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NumElements = ATy->getNumElements();
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else if (const PackedType *PTy = dyn_cast<PackedType>(STy))
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NumElements = PTy->getNumElements();
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else
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assert(0 && "Unknown aggregate sequential type!");
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if (NumElements > 16) return 0; // It's not worth it.
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NewGlobals.reserve(NumElements);
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for (unsigned i = 0, e = NumElements; i != e; ++i) {
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Constant *In = getAggregateConstantElement(Init,
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ConstantUInt::get(Type::UIntTy, i));
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assert(In && "Couldn't get element of initializer?");
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GlobalVariable *NGV = new GlobalVariable(STy->getElementType(), false,
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GlobalVariable::InternalLinkage,
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In, GV->getName()+"."+utostr(i));
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Globals.insert(GV, NGV);
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NewGlobals.push_back(NGV);
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}
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}
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if (NewGlobals.empty())
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return 0;
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Constant *NullInt = Constant::getNullValue(Type::IntTy);
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// Loop over all of the uses of the global, replacing the constantexpr geps,
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// with smaller constantexpr geps or direct references.
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while (!GV->use_empty()) {
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ConstantExpr *CE = cast<ConstantExpr>(GV->use_back());
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assert(CE->getOpcode() == Instruction::GetElementPtr &&
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"NonGEP CE's are not SRAable!");
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// Ignore the 1th operand, which has to be zero or else the program is quite
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// broken (undefined). Get the 2nd operand, which is the structure or array
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// index.
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unsigned Val = cast<ConstantInt>(CE->getOperand(2))->getRawValue();
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if (Val >= NewGlobals.size()) Val = 0; // Out of bound array access.
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Constant *NewPtr = NewGlobals[Val];
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// Form a shorter GEP if needed.
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if (CE->getNumOperands() > 3) {
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std::vector<Constant*> Idxs;
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Idxs.push_back(NullInt);
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for (unsigned i = 3, e = CE->getNumOperands(); i != e; ++i)
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Idxs.push_back(CE->getOperand(i));
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NewPtr = ConstantExpr::getGetElementPtr(NewPtr, Idxs);
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}
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CE->replaceAllUsesWith(NewPtr);
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CE->destroyConstant();
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}
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// Delete the old global, now that it is dead.
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Globals.erase(GV);
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++NumSRA;
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return NewGlobals[0];
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}
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/// AllUsesOfValueWillTrapIfNull - Return true if all users of the specified
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/// value will trap if the value is dynamically null.
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static bool AllUsesOfValueWillTrapIfNull(Value *V) {
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for (Value::use_iterator UI = V->use_begin(), E = V->use_end(); UI != E; ++UI)
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if (isa<LoadInst>(*UI)) {
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// Will trap.
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} else if (StoreInst *SI = dyn_cast<StoreInst>(*UI)) {
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if (SI->getOperand(0) == V) {
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//std::cerr << "NONTRAPPING USE: " << **UI;
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return false; // Storing the value.
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}
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} else if (CallInst *CI = dyn_cast<CallInst>(*UI)) {
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if (CI->getOperand(0) != V) {
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//std::cerr << "NONTRAPPING USE: " << **UI;
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return false; // Not calling the ptr
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}
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} else if (InvokeInst *II = dyn_cast<InvokeInst>(*UI)) {
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if (II->getOperand(0) != V) {
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//std::cerr << "NONTRAPPING USE: " << **UI;
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return false; // Not calling the ptr
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}
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} else if (CastInst *CI = dyn_cast<CastInst>(*UI)) {
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if (!AllUsesOfValueWillTrapIfNull(CI)) return false;
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} else if (GetElementPtrInst *GEPI = dyn_cast<GetElementPtrInst>(*UI)) {
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if (!AllUsesOfValueWillTrapIfNull(GEPI)) return false;
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} else {
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//std::cerr << "NONTRAPPING USE: " << **UI;
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return false;
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}
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return true;
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}
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/// AllUsesOfLoadedValueWillTrapIfNull - Return true if all uses of any loads
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/// from GV will trap if the loaded value is null.
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static bool AllUsesOfLoadedValueWillTrapIfNull(GlobalVariable *GV) {
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for (Value::use_iterator UI = GV->use_begin(), E = GV->use_end(); UI!=E; ++UI)
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if (LoadInst *LI = dyn_cast<LoadInst>(*UI)) {
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if (!AllUsesOfValueWillTrapIfNull(LI))
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return false;
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} else if (isa<StoreInst>(*UI)) {
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// Ignore stores to the global.
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} else {
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// We don't know or understand this user, bail out.
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//std::cerr << "UNKNOWN USER OF GLOBAL!: " << **UI;
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return false;
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}
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return true;
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}
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// OptimizeOnceStoredGlobal - Try to optimize globals based on the knowledge
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// that only one value (besides its initializer) is ever stored to the global.
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static bool OptimizeOnceStoredGlobal(GlobalVariable *GV, Value *StoredOnceVal) {
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if (CastInst *CI = dyn_cast<CastInst>(StoredOnceVal))
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StoredOnceVal = CI->getOperand(0);
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else if (GetElementPtrInst *GEPI =dyn_cast<GetElementPtrInst>(StoredOnceVal)){
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bool IsJustACast = true;
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for (unsigned i = 1, e = GEPI->getNumOperands(); i != e; ++i)
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if (!isa<Constant>(GEPI->getOperand(i)) ||
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!cast<Constant>(GEPI->getOperand(i))->isNullValue()) {
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IsJustACast = false;
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break;
|
|
}
|
|
if (IsJustACast)
|
|
StoredOnceVal = GEPI->getOperand(0);
|
|
}
|
|
|
|
// If we are dealing with a pointer global that is initialized to null, only
|
|
// has one (non-null) value stored into, and if we know that all users of the
|
|
// loaded value trap if null, then the load users must never get the
|
|
// initializer. Instead, replace all of the loads with the stored value.
|
|
if (isa<PointerType>(GV->getInitializer()->getType()) &&
|
|
GV->getInitializer()->isNullValue()) {
|
|
if (isa<Constant>(StoredOnceVal) &&
|
|
AllUsesOfLoadedValueWillTrapIfNull(GV)) {
|
|
DEBUG(std::cerr << "REPLACING STORED GLOBAL POINTER: " << *GV);
|
|
|
|
//std::cerr << " Stored Value: " << *StoredOnceVal << "\n";
|
|
|
|
// Replace all uses of loads with uses of uses of the stored value.
|
|
while (!GV->use_empty())
|
|
if (LoadInst *LI = dyn_cast<LoadInst>(GV->use_back())) {
|
|
LI->replaceAllUsesWith(StoredOnceVal);
|
|
LI->getParent()->getInstList().erase(LI); // Nuke the load.
|
|
} else if (StoreInst *SI = dyn_cast<StoreInst>(GV->use_back())) {
|
|
SI->getParent()->getInstList().erase(SI); // Nuke the store
|
|
} else {
|
|
assert(0 && "Unknown user of stored once global!");
|
|
}
|
|
|
|
// Nuke the now-dead global.
|
|
GV->getParent()->getGlobalList().erase(GV);
|
|
return true;
|
|
}
|
|
//if (isa<MallocInst>(StoredOnceValue))
|
|
}
|
|
return false;
|
|
}
|
|
|
|
/// ProcessInternalGlobal - Analyze the specified global variable and optimize
|
|
/// it if possible. If we make a change, return true.
|
|
static bool ProcessInternalGlobal(GlobalVariable *GV, Module::giterator &GVI) {
|
|
std::set<PHINode*> PHIUsers;
|
|
GlobalStatus GS;
|
|
PHIUsers.clear();
|
|
GV->removeDeadConstantUsers();
|
|
|
|
if (GV->use_empty()) {
|
|
DEBUG(std::cerr << "GLOBAL DEAD: " << *GV);
|
|
GV->getParent()->getGlobalList().erase(GV);
|
|
++NumDeleted;
|
|
return true;
|
|
}
|
|
|
|
if (!AnalyzeGlobal(GV, GS, PHIUsers)) {
|
|
// If the global is never loaded (but may be stored to), it is dead.
|
|
// Delete it now.
|
|
if (!GS.isLoaded) {
|
|
DEBUG(std::cerr << "GLOBAL NEVER LOADED: " << *GV);
|
|
|
|
// Delete any stores we can find to the global. We may not be able to
|
|
// make it completely dead though.
|
|
bool Changed = CleanupConstantGlobalUsers(GV, GV->getInitializer());
|
|
|
|
// If the global is dead now, delete it.
|
|
if (GV->use_empty()) {
|
|
GV->getParent()->getGlobalList().erase(GV);
|
|
++NumDeleted;
|
|
Changed = true;
|
|
}
|
|
return Changed;
|
|
|
|
} else if (GS.StoredType <= GlobalStatus::isInitializerStored) {
|
|
DEBUG(std::cerr << "MARKING CONSTANT: " << *GV);
|
|
GV->setConstant(true);
|
|
|
|
// Clean up any obviously simplifiable users now.
|
|
CleanupConstantGlobalUsers(GV, GV->getInitializer());
|
|
|
|
// If the global is dead now, just nuke it.
|
|
if (GV->use_empty()) {
|
|
DEBUG(std::cerr << " *** Marking constant allowed us to simplify "
|
|
"all users and delete global!\n");
|
|
GV->getParent()->getGlobalList().erase(GV);
|
|
++NumDeleted;
|
|
}
|
|
|
|
++NumMarked;
|
|
return true;
|
|
} else if (!GS.isNotSuitableForSRA &&
|
|
!GV->getInitializer()->getType()->isFirstClassType()) {
|
|
DEBUG(std::cerr << "PERFORMING GLOBAL SRA ON: " << *GV);
|
|
if (GlobalVariable *FirstNewGV = SRAGlobal(GV)) {
|
|
GVI = FirstNewGV; // Don't skip the newly produced globals!
|
|
return true;
|
|
}
|
|
} else if (GS.StoredType == GlobalStatus::isStoredOnce) {
|
|
// Try to optimize globals based on the knowledge that only one value
|
|
// (besides its initializer) is ever stored to the global.
|
|
if (OptimizeOnceStoredGlobal(GV, GS.StoredOnceValue))
|
|
return true;
|
|
}
|
|
}
|
|
return false;
|
|
}
|
|
|
|
|
|
bool GlobalOpt::runOnModule(Module &M) {
|
|
bool Changed = false;
|
|
|
|
// As a prepass, delete functions that are trivially dead.
|
|
bool LocalChange = true;
|
|
while (LocalChange) {
|
|
LocalChange = false;
|
|
for (Module::iterator FI = M.begin(), E = M.end(); FI != E; ) {
|
|
Function *F = FI++;
|
|
F->removeDeadConstantUsers();
|
|
if (F->use_empty() && (F->hasInternalLinkage() || F->hasWeakLinkage())) {
|
|
M.getFunctionList().erase(F);
|
|
LocalChange = true;
|
|
++NumFnDeleted;
|
|
}
|
|
}
|
|
Changed |= LocalChange;
|
|
}
|
|
|
|
LocalChange = true;
|
|
while (LocalChange) {
|
|
LocalChange = false;
|
|
for (Module::giterator GVI = M.gbegin(), E = M.gend(); GVI != E;) {
|
|
GlobalVariable *GV = GVI++;
|
|
if (!GV->isConstant() && GV->hasInternalLinkage() &&
|
|
GV->hasInitializer())
|
|
LocalChange |= ProcessInternalGlobal(GV, GVI);
|
|
}
|
|
Changed |= LocalChange;
|
|
}
|
|
return Changed;
|
|
}
|