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Avoid unsafe promotion.

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git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@42149 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Devang Patel 2007-09-19 20:18:51 +00:00
parent fab7eff0fa
commit f2038b1d93
2 changed files with 76 additions and 9 deletions
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50
lib/Transforms/Scalar/LICM.cpp
View File

@ -759,15 +759,24 @@ void LICM::PromoteValuesInLoop() {
}
/// FindPromotableValuesInLoop - Check the current loop for stores to definite
/// pointers, which are not loaded and stored through may aliases. If these are
/// found, create an alloca for the value, add it to the PromotedValues list,
/// and keep track of the mapping from value to alloca.
///
/// pointers, which are not loaded and stored through may aliases and are safe
/// for promotion. If these are found, create an alloca for the value, add it
/// to the PromotedValues list, and keep track of the mapping from value to
/// alloca.
void LICM::FindPromotableValuesInLoop(
std::vector<std::pair<AllocaInst*, Value*> > &PromotedValues,
std::map<Value*, AllocaInst*> &ValueToAllocaMap) {
Instruction *FnStart = CurLoop->getHeader()->getParent()->begin()->begin();
SmallVector<Instruction *, 4> LoopExits;
SmallVector<BasicBlock *, 4> Blocks;
CurLoop->getExitingBlocks(Blocks);
for (SmallVector<BasicBlock *, 4>::iterator BI = Blocks.begin(),
BE = Blocks.end(); BI != BE; ++BI) {
BasicBlock *BB = *BI;
LoopExits.push_back(BB->getTerminator());
}
// Loop over all of the alias sets in the tracker object.
for (AliasSetTracker::iterator I = CurAST->begin(), E = CurAST->end();
I != E; ++I) {
@ -791,14 +800,37 @@ void LICM::FindPromotableValuesInLoop(
break;
}
// If GEP base is NULL then the calculated address used by Store or
// Load instruction is invalid. Do not promote this value because
// it may expose load and store instruction that are covered by
// condition which may not yet folded.
if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(V))
if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(V)) {
// If GEP base is NULL then the calculated address used by Store or
// Load instruction is invalid. Do not promote this value because
// it may expose load and store instruction that are covered by
// condition which may not yet folded.
if (isa<ConstantPointerNull>(GEP->getOperand(0)))
PointerOk = false;
// If GEP is use is not dominating loop exit then promoting
// GEP may expose unsafe load and store instructions unconditinally.
if (PointerOk)
for(Value::use_iterator UI = V->use_begin(), UE = V->use_end();
UI != UE && PointerOk; ++UI) {
Instruction *Use = dyn_cast<Instruction>(*UI);
if (!Use)
continue;
for (SmallVector<Instruction *, 4>::iterator
ExitI = LoopExits.begin(), ExitE = LoopExits.end();
ExitI != ExitE; ++ExitI) {
Instruction *Ex = *ExitI;
if (!DT->dominates(Use, Ex)){
PointerOk = false;
break;
}
}
if (!PointerOk)
break;
}
}
if (PointerOk) {
const Type *Ty = cast<PointerType>(V->getType())->getElementType();
AllocaInst *AI = new AllocaInst(Ty, 0, V->getName()+".tmp", FnStart);

35
test/Transforms/LICM/2007-09-17-PromoteValue.ll
View File

@ -23,4 +23,39 @@ clear_modes.exit: ; preds = %blah.i
unreachable
}
define i32 @f(i8* %ptr) {
entry:
br label %loop.head
loop.head: ; preds = %cond.true, %entry
%x = phi i8* [ %ptr, %entry ], [ %ptr.i, %cond.true ] ; <i8*> [#uses=1]
%tmp3.i = icmp ne i8* %ptr, %x ; <i1> [#uses=1]
br i1 %tmp3.i, label %cond.true, label %exit
cond.true: ; preds = %loop.head
%ptr.i = getelementptr i8* %ptr, i32 0 ; <i8*> [#uses=2]
store i8 0, i8* %ptr.i
br label %loop.head
exit: ; preds = %loop.head
ret i32 0
}
define i32 @f2(i8* %p, i8* %q) {
entry:
br label %loop.head
loop.head: ; preds = %cond.true, %entry
%tmp3.i = icmp eq i8* null, %q ; <i1> [#uses=1]
br i1 %tmp3.i, label %exit, label %cond.true
cond.true: ; preds = %loop.head
%ptr.i = getelementptr i8* %p, i32 0 ; <i8*> [#uses=2]
store i8 0, i8* %ptr.i
br label %loop.head
exit: ; preds = %loop.head
ret i32 0
}
declare void @exit(i32)