[LAA] Correctly return a half-open range in expandBounds

This is a latent bug that's been hanging around for a while. For a loop-invariant
pointer, expandBounds would return the range {Ptr, Ptr}, but this was interpreted
as a half-open range, not a closed range. So we ended up planting incorrect
bounds checks. Even worse, they were tautological, so we ended up incorrectly
executing the optimized loop.

llvm-svn: 299526

1 files changed, 4 insertions, 1 deletions

diff --git a/llvm/lib/Analysis/LoopAccessAnalysis.cpp b/llvm/lib/Analysis/LoopAccessAnalysis.cpp
index 72488f1f080..4ba12583ff8 100644
--- a/llvm/lib/Analysis/LoopAccessAnalysis.cpp
+++ b/llvm/lib/Analysis/LoopAccessAnalysis.cpp
@@ -1939,7 +1939,10 @@ expandBounds(const RuntimePointerChecking::CheckingPtrGroup *CG, Loop *TheLoop,
     Value *NewPtr = (Inst && TheLoop->contains(Inst))
                         ? Exp.expandCodeFor(Sc, PtrArithTy, Loc)
                         : Ptr;
-    return {NewPtr, NewPtr};
+    // We must return a half-open range, which means incrementing Sc.
+    const SCEV *ScPlusOne = SE->getAddExpr(Sc, SE->getOne(PtrArithTy));
+    Value *NewPtrPlusOne = Exp.expandCodeFor(ScPlusOne, PtrArithTy, Loc);
+    return {NewPtr, NewPtrPlusOne};
   } else {
     Value *Start = nullptr, *End = nullptr;
     DEBUG(dbgs() << "LAA: Adding RT check for range:\n");