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LSR: handle the expansion of phi operands that use postinc forms of the IV.

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Fixes PR11431: SCEVExpander::expandAddRecExprLiterally(const llvm::SCEVAddRecExpr*): Assertion `(!isa<Instruction>(Result) || SE.DT->dominates(cast<Instruction>(Result), Builder.GetInsertPoint())) && "postinc expansion does not dominate use"' failed.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@145482 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Andrew Trick
2011-11-30 06:07:54 +00:00
parent caebb1e00b
commit 553fe05f23
3 changed files with 126 additions and 36 deletions
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104
lib/Analysis/ScalarEvolutionExpander.cpp
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@ -929,6 +929,36 @@ bool SCEVExpander::isExpandedAddRecExprPHI(PHINode *PN, Instruction *IncV,
}
}
/// expandIVInc - Expand an IV increment at Builder's current InsertPos.
/// Typically this is the LatchBlock terminator or IVIncInsertPos, but we may
/// need to materialize IV increments elsewhere to handle difficult situations.
Value *SCEVExpander::expandIVInc(PHINode *PN, Value *StepV, const Loop *L,
Type *ExpandTy, Type *IntTy,
bool useSubtract) {
Value *IncV;
// If the PHI is a pointer, use a GEP, otherwise use an add or sub.
if (ExpandTy->isPointerTy()) {
PointerType *GEPPtrTy = cast<PointerType>(ExpandTy);
// If the step isn't constant, don't use an implicitly scaled GEP, because
// that would require a multiply inside the loop.
if (!isa<ConstantInt>(StepV))
GEPPtrTy = PointerType::get(Type::getInt1Ty(SE.getContext()),
GEPPtrTy->getAddressSpace());
const SCEV *const StepArray[1] = { SE.getSCEV(StepV) };
IncV = expandAddToGEP(StepArray, StepArray+1, GEPPtrTy, IntTy, PN);
if (IncV->getType() != PN->getType()) {
IncV = Builder.CreateBitCast(IncV, PN->getType());
rememberInstruction(IncV);
}
} else {
IncV = useSubtract ?
Builder.CreateSub(PN, StepV, Twine(IVName) + ".iv.next") :
Builder.CreateAdd(PN, StepV, Twine(IVName) + ".iv.next");
rememberInstruction(IncV);
}
return IncV;
}
/// getAddRecExprPHILiterally - Helper for expandAddRecExprLiterally. Expand
/// the base addrec, which is the addrec without any non-loop-dominating
/// values, and return the PHI.
@ -993,16 +1023,16 @@ SCEVExpander::getAddRecExprPHILiterally(const SCEVAddRecExpr *Normalized,
SE.DT->properlyDominates(cast<Instruction>(StartV)->getParent(),
L->getHeader()));
// Expand code for the step value. Insert instructions right before the
// terminator corresponding to the back-edge. Do this before creating the PHI
// so that PHI reuse code doesn't see an incomplete PHI. If the stride is
// negative, insert a sub instead of an add for the increment (unless it's a
// constant, because subtracts of constants are canonicalized to adds).
// Expand code for the step value. Do this before creating the PHI so that PHI
// reuse code doesn't see an incomplete PHI.
const SCEV *Step = Normalized->getStepRecurrence(SE);
bool isPointer = ExpandTy->isPointerTy();
bool isNegative = !isPointer && isNonConstantNegative(Step);
if (isNegative)
// If the stride is negative, insert a sub instead of an add for the increment
// (unless it's a constant, because subtracts of constants are canonicalized
// to adds).
bool useSubtract = !ExpandTy->isPointerTy() && isNonConstantNegative(Step);
if (useSubtract)
Step = SE.getNegativeSCEV(Step);
// Expand the step somewhere that dominates the loop header.
Value *StepV = expandCodeFor(Step, IntTy, L->getHeader()->begin());
// Create the PHI.
@ -1023,33 +1053,14 @@ SCEVExpander::getAddRecExprPHILiterally(const SCEVAddRecExpr *Normalized,
continue;
}
// Create a step value and add it to the PHI. If IVIncInsertLoop is
// non-null and equal to the addrec's loop, insert the instructions
// at IVIncInsertPos.
// Create a step value and add it to the PHI.
// If IVIncInsertLoop is non-null and equal to the addrec's loop, insert the
// instructions at IVIncInsertPos.
Instruction *InsertPos = L == IVIncInsertLoop ?
IVIncInsertPos : Pred->getTerminator();
Builder.SetInsertPoint(InsertPos);
Value *IncV;
// If the PHI is a pointer, use a GEP, otherwise use an add or sub.
if (isPointer) {
PointerType *GEPPtrTy = cast<PointerType>(ExpandTy);
// If the step isn't constant, don't use an implicitly scaled GEP, because
// that would require a multiply inside the loop.
if (!isa<ConstantInt>(StepV))
GEPPtrTy = PointerType::get(Type::getInt1Ty(SE.getContext()),
GEPPtrTy->getAddressSpace());
const SCEV *const StepArray[1] = { SE.getSCEV(StepV) };
IncV = expandAddToGEP(StepArray, StepArray+1, GEPPtrTy, IntTy, PN);
if (IncV->getType() != PN->getType()) {
IncV = Builder.CreateBitCast(IncV, PN->getType());
rememberInstruction(IncV);
}
} else {
IncV = isNegative ?
Builder.CreateSub(PN, StepV, Twine(IVName) + ".iv.next") :
Builder.CreateAdd(PN, StepV, Twine(IVName) + ".iv.next");
rememberInstruction(IncV);
}
Value *IncV = expandIVInc(PN, StepV, L, ExpandTy, IntTy, useSubtract);
PN->addIncoming(IncV, Pred);
}
@ -1124,10 +1135,31 @@ Value *SCEVExpander::expandAddRecExprLiterally(const SCEVAddRecExpr *S) {
// For an expansion to use the postinc form, the client must call
// expandCodeFor with an InsertPoint that is either outside the PostIncLoop
// or dominated by IVIncInsertPos.
assert((!isa<Instruction>(Result) ||
SE.DT->dominates(cast<Instruction>(Result),
Builder.GetInsertPoint())) &&
"postinc expansion does not dominate use");
if (isa<Instruction>(Result)
&& !SE.DT->dominates(cast<Instruction>(Result),
Builder.GetInsertPoint())) {
// The induction variable's postinc expansion does not dominate this use.
// IVUsers tries to prevent this case, so it is rare. However, it can
// happen when an IVUser outside the loop is not dominated by the latch
// block. Adjusting IVIncInsertPos before expansion begins cannot handle
// all cases. Consider a phi outide whose operand is replaced during
// expansion with the value of the postinc user. Without fundamentally
// changing the way postinc users are tracked, the only remedy is
// inserting an extra IV increment. StepV might fold into PostLoopOffset,
// but hopefully expandCodeFor handles that.
bool useSubtract =
!ExpandTy->isPointerTy() && isNonConstantNegative(Step);
if (useSubtract)
Step = SE.getNegativeSCEV(Step);
// Expand the step somewhere that dominates the loop header.
BasicBlock *SaveInsertBB = Builder.GetInsertBlock();
BasicBlock::iterator SaveInsertPt = Builder.GetInsertPoint();
Value *StepV = expandCodeFor(Step, IntTy, L->getHeader()->begin());
// Restore the insertion point to the place where the caller has
// determined dominates all uses.
restoreInsertPoint(SaveInsertBB, SaveInsertPt);
Result = expandIVInc(PN, StepV, L, ExpandTy, IntTy, useSubtract);
}
}
// Re-apply any non-loop-dominating scale.