Watch out for a constant offset cancelling out a base register, forming
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
diff --git a/lib/Transforms/Scalar/LoopStrengthReduce.cpp b/lib/Transforms/Scalar/LoopStrengthReduce.cpp
index a250a88..1f9b415 100644
--- a/lib/Transforms/Scalar/LoopStrengthReduce.cpp
+++ b/lib/Transforms/Scalar/LoopStrengthReduce.cpp
@@ -2362,7 +2362,7 @@
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 @@
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);
}