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Watch out for a constant offset cancelling out a base register, forming

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a zero. This situation arrises in Fortran code with induction variables
that start at 1 instead of 0. This fixes PR7651.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@108424 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Dan Gohman
2010-07-15 15:14:45 +00:00
parent 96fe621e07
commit c88c1a4581
2 changed files with 53 additions and 2 deletions
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lib/Transforms/Scalar/LoopStrengthReduce.cpp
+9 -2
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@@ -2362,7 +2362,7 @@ void LSRInstance::GenerateConstantOffsets(LSRUse &LU, unsigned LUIdx,
Formula Base) {
// TODO: For now, just add the min and max offset, because it usually isn't
// worthwhile looking at everything inbetween.
SmallVector<int64_t, 4> Worklist;
SmallVector<int64_t, 2> Worklist;
Worklist.push_back(LU.MinOffset);
if (LU.MaxOffset != LU.MinOffset)
Worklist.push_back(LU.MaxOffset);
@@ -2376,7 +2376,14 @@ void LSRInstance::GenerateConstantOffsets(LSRUse &LU, unsigned LUIdx,
F.AM.BaseOffs = (uint64_t)Base.AM.BaseOffs - *I;
if (isLegalUse(F.AM, LU.MinOffset - *I, LU.MaxOffset - *I,
LU.Kind, LU.AccessTy, TLI)) {
F.BaseRegs[i] = SE.getAddExpr(G, SE.getConstant(G->getType(), *I));
// Add the offset to the base register.
const SCEV *NewG = SE.getAddExpr(G, SE.getConstant(G->getType(), *I));
// If it cancelled out, drop the base register, otherwise update it.
if (NewG->isZero()) {
std::swap(F.BaseRegs[i], F.BaseRegs.back());
F.BaseRegs.pop_back();
} else
F.BaseRegs[i] = NewG;
(void)InsertFormula(LU, LUIdx, F);
}