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Fix PR590 and Transforms/Mem2Reg/2005-06-30-ReadBeforeWrite.ll.

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The optimization for locally used allocas was not safe for allocas that
were read before they were written.  This change disables that optimization
in that case.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@22318 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Chris Lattner 2005-06-30 07:29:44 +00:00
parent e04f865da2
commit 6cfd1ebcd3
1 changed files with 65 additions and 19 deletions

84
lib/Transforms/Utils/PromoteMemoryToRegister.cpp

@ -57,6 +57,7 @@ namespace {
/// Allocas - The alloca instructions being promoted.
///
std::vector<AllocaInst*> Allocas;
std::vector<AllocaInst*> &RetryList;
DominatorTree &DT;
DominanceFrontier &DF;
const TargetData &TD;
@ -88,10 +89,11 @@ namespace {
StableBasicBlockNumbering BBNumbers;
public:
PromoteMem2Reg(const std::vector<AllocaInst*> &A, DominatorTree &dt,
PromoteMem2Reg(const std::vector<AllocaInst*> &A,
std::vector<AllocaInst*> &Retry, DominatorTree &dt,
DominanceFrontier &df, const TargetData &td,
AliasSetTracker *ast)
: Allocas(A), DT(dt), DF(df), TD(td), AST(ast) {}
: Allocas(A), RetryList(Retry), DT(dt), DF(df), TD(td), AST(ast) {}
void run();
@ -106,7 +108,7 @@ namespace {
private:
void MarkDominatingPHILive(BasicBlock *BB, unsigned AllocaNum,
std::set<PHINode*> &DeadPHINodes);
void PromoteLocallyUsedAlloca(BasicBlock *BB, AllocaInst *AI);
bool PromoteLocallyUsedAlloca(BasicBlock *BB, AllocaInst *AI);
void PromoteLocallyUsedAllocas(BasicBlock *BB,
const std::vector<AllocaInst*> &AIs);
@ -277,15 +279,21 @@ void PromoteMem2Reg::run() {
// Process all allocas which are only used in a single basic block.
for (std::map<BasicBlock*, std::vector<AllocaInst*> >::iterator I =
LocallyUsedAllocas.begin(), E = LocallyUsedAllocas.end(); I != E; ++I){
const std::vector<AllocaInst*> &Allocas = I->second;
assert(!Allocas.empty() && "empty alloca list??");
const std::vector<AllocaInst*> &LocAllocas = I->second;
assert(!LocAllocas.empty() && "empty alloca list??");
// It's common for there to only be one alloca in the list. Handle it
// efficiently.
if (Allocas.size() == 1)
PromoteLocallyUsedAlloca(I->first, Allocas[0]);
else
PromoteLocallyUsedAllocas(I->first, Allocas);
if (LocAllocas.size() == 1) {
// If we can do the quick promotion pass, do so now.
if (PromoteLocallyUsedAlloca(I->first, LocAllocas[0]))
RetryList.push_back(LocAllocas[0]); // Failed, retry later.
} else {
// Locally promote anything possible. Note that if this is unable to
// promote a particular alloca, it puts the alloca onto the Allocas vector
// for global processing.
PromoteLocallyUsedAllocas(I->first, LocAllocas);
}
}
if (Allocas.empty())
@ -430,7 +438,16 @@ void PromoteMem2Reg::MarkDominatingPHILive(BasicBlock *BB, unsigned AllocaNum,
/// potentially useless PHI nodes by just performing a single linear pass over
/// the basic block using the Alloca.
///
void PromoteMem2Reg::PromoteLocallyUsedAlloca(BasicBlock *BB, AllocaInst *AI) {
/// If we cannot promote this alloca (because it is read before it is written),
/// return true. This is necessary in cases where, due to control flow, the
/// alloca is potentially undefined on some control flow paths. e.g. code like
/// this is potentially correct:
///
/// for (...) { if (c) { A = undef; undef = B; } }
///
/// ... so long as A is not used before undef is set.
///
bool PromoteMem2Reg::PromoteLocallyUsedAlloca(BasicBlock *BB, AllocaInst *AI) {
assert(!AI->use_empty() && "There are no uses of the alloca!");
// Handle degenerate cases quickly.
@ -448,12 +465,14 @@ void PromoteMem2Reg::PromoteLocallyUsedAlloca(BasicBlock *BB, AllocaInst *AI) {
BB->getInstList().erase(U);
} else {
// Uses of the uninitialized memory location shall get undef.
Value *CurVal = UndefValue::get(AI->getAllocatedType());
Value *CurVal = 0;
for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ) {
Instruction *Inst = I++;
if (LoadInst *LI = dyn_cast<LoadInst>(Inst)) {
if (LI->getOperand(0) == AI) {
if (!CurVal) return true; // Could not locally promote!
// Loads just returns the "current value"...
LI->replaceAllUsesWith(CurVal);
if (AST && isa<PointerType>(LI->getType()))
@ -475,6 +494,7 @@ void PromoteMem2Reg::PromoteLocallyUsedAlloca(BasicBlock *BB, AllocaInst *AI) {
assert(AI->use_empty() && "Uses of alloca from more than one BB??");
if (AST) AST->deleteValue(AI);
AI->getParent()->getInstList().erase(AI);
return false;
}
/// PromoteLocallyUsedAllocas - This method is just like
@ -495,13 +515,19 @@ PromoteLocallyUsedAllocas(BasicBlock *BB, const std::vector<AllocaInst*> &AIs) {
if (AllocaInst *AI = dyn_cast<AllocaInst>(LI->getOperand(0))) {
std::map<AllocaInst*, Value*>::iterator AIt = CurValues.find(AI);
if (AIt != CurValues.end()) {
// Loads just returns the "current value"...
if (AIt->second == 0) // Uninitialized value??
AIt->second = UndefValue::get(AIt->first->getAllocatedType());
LI->replaceAllUsesWith(AIt->second);
if (AST && isa<PointerType>(LI->getType()))
AST->deleteValue(LI);
BB->getInstList().erase(LI);
// If loading an uninitialized value, allow the inter-block case to
// handle it. Due to control flow, this might actually be ok.
if (AIt->second == 0) { // Use of locally uninitialized value??
RetryList.push_back(AI); // Retry elsewhere.
CurValues.erase(AIt); // Stop tracking this here.
if (CurValues.empty()) return;
} else {
// Loads just returns the "current value"...
LI->replaceAllUsesWith(AIt->second);
if (AST && isa<PointerType>(LI->getType()))
AST->deleteValue(LI);
BB->getInstList().erase(LI);
}
}
}
} else if (StoreInst *SI = dyn_cast<StoreInst>(Inst)) {
@ -627,5 +653,25 @@ void llvm::PromoteMemToReg(const std::vector<AllocaInst*> &Allocas,
const TargetData &TD, AliasSetTracker *AST) {
// If there is nothing to do, bail out...
if (Allocas.empty()) return;
PromoteMem2Reg(Allocas, DT, DF, TD, AST).run();
std::vector<AllocaInst*> RetryList;
PromoteMem2Reg(Allocas, RetryList, DT, DF, TD, AST).run();
// PromoteMem2Reg may not have been able to promote all of the allocas in one
// pass, run it again if needed.
while (!RetryList.empty()) {
// If we need to retry some allocas, this is due to there being no store
// before a read in a local block. To counteract this, insert a store of
// undef into the alloca right after the alloca itself.
for (unsigned i = 0, e = RetryList.size(); i != e; ++i) {
BasicBlock::iterator BBI = RetryList[i];
new StoreInst(UndefValue::get(RetryList[i]->getAllocatedType()),
RetryList[i], ++BBI);
}
std::vector<AllocaInst*> NewAllocas;
std::swap(NewAllocas, RetryList);
PromoteMem2Reg(NewAllocas, RetryList, DT, DF, TD, AST).run();
}
}