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Just as its not safe to blindly transfer the nsw bit from an add 

instruction to an add scev, it's not safe to blindly transfer the
inbounds flag from a gep instruction to an nsw on the scev for the
gep.

llvm-svn: 107117
This commit is contained in:
Dan Gohman 2010-06-29 01:41:41 +00:00
parent de736a6494
commit 90db61d638
1 changed files with 9 additions and 5 deletions
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14
llvm/lib/Analysis/ScalarEvolution.cpp
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@ -2763,7 +2763,11 @@ const SCEV *ScalarEvolution::createNodeForPHI(PHINode *PN) {
///
const SCEV *ScalarEvolution::createNodeForGEP(GEPOperator *GEP) {
bool InBounds = GEP->isInBounds();
// Don't transfer the inbounds flag from the GEP instruction to the
// Add expression, because the Instruction may be guarded by control
// flow and the no-overflow bits may not be valid for the expression in
// any context.
const Type *IntPtrTy = getEffectiveSCEVType(GEP->getType());
Value *Base = GEP->getOperand(0);
// Don't attempt to analyze GEPs over unsized objects.
@ -2781,7 +2785,7 @@ const SCEV *ScalarEvolution::createNodeForGEP(GEPOperator *GEP) {
unsigned FieldNo = cast<ConstantInt>(Index)->getZExtValue();
TotalOffset = getAddExpr(TotalOffset,
getOffsetOfExpr(STy, FieldNo),
/*HasNUW=*/false, /*HasNSW=*/InBounds);
/*HasNUW=*/false, /*HasNSW=*/false);
} else {
// For an array, add the element offset, explicitly scaled.
const SCEV *LocalOffset = getSCEV(Index);
@ -2789,13 +2793,13 @@ const SCEV *ScalarEvolution::createNodeForGEP(GEPOperator *GEP) {
LocalOffset = getTruncateOrSignExtend(LocalOffset, IntPtrTy);
// Lower "inbounds" GEPs to NSW arithmetic.
LocalOffset = getMulExpr(LocalOffset, getSizeOfExpr(*GTI),
/*HasNUW=*/false, /*HasNSW=*/InBounds);
/*HasNUW=*/false, /*HasNSW=*/false);
TotalOffset = getAddExpr(TotalOffset, LocalOffset,
/*HasNUW=*/false, /*HasNSW=*/InBounds);
/*HasNUW=*/false, /*HasNSW=*/false);
}
}
return getAddExpr(getSCEV(Base), TotalOffset,
/*HasNUW=*/false, /*HasNSW=*/InBounds);
/*HasNUW=*/false, /*HasNSW=*/false);
}
/// GetMinTrailingZeros - Determine the minimum number of zero bits that S is