1 files changed, 20 insertions, 2 deletions
diff --git a/llvm/lib/Analysis/DependenceAnalysis.cpp b/llvm/lib/Analysis/DependenceAnalysis.cpp
index 3374b48c141..808a38b6346 100644
--- a/llvm/lib/Analysis/DependenceAnalysis.cpp
+++ b/llvm/lib/Analysis/DependenceAnalysis.cpp
@@ -830,6 +830,14 @@ bool DependenceAnalysis::checkSrcSubscript(const SCEV *Src,
     return isLoopInvariant(Src, LoopNest);
   const SCEV *Start = AddRec->getStart();
   const SCEV *Step = AddRec->getStepRecurrence(*SE);
+  const SCEV *UB = SE->getBackedgeTakenCount(AddRec->getLoop());
+  if (!isa<SCEVCouldNotCompute>(UB)) {
+    if (SE->getTypeSizeInBits(Start->getType()) <
+        SE->getTypeSizeInBits(UB->getType())) {
+      if (!AddRec->getNoWrapFlags())
+        return false;
+    }
+  }
   if (!isLoopInvariant(Step, LoopNest))
     return false;
   Loops.set(mapSrcLoop(AddRec->getLoop()));
@@ -848,6 +856,14 @@ bool DependenceAnalysis::checkDstSubscript(const SCEV *Dst,
     return isLoopInvariant(Dst, LoopNest);
   const SCEV *Start = AddRec->getStart();
   const SCEV *Step = AddRec->getStepRecurrence(*SE);
+  const SCEV *UB = SE->getBackedgeTakenCount(AddRec->getLoop());
+  if (!isa<SCEVCouldNotCompute>(UB)) {
+    if (SE->getTypeSizeInBits(Start->getType()) <
+        SE->getTypeSizeInBits(UB->getType())) {
+      if (!AddRec->getNoWrapFlags())
+        return false;
+    }
+  }
   if (!isLoopInvariant(Step, LoopNest))
     return false;
   Loops.set(mapDstLoop(AddRec->getLoop()));
@@ -942,13 +958,15 @@ bool DependenceAnalysis::isKnownPredicate(ICmpInst::Predicate Pred,
 // All subscripts are all the same type.
 // Loop bound may be smaller (e.g., a char).
 // Should zero extend loop bound, since it's always >= 0.
-// This routine collects upper bound and extends if needed.
+// This routine collects upper bound and extends or truncates if needed.
+// Truncating is safe when subscripts are known not to wrap. Cases without
+// nowrap flags should have been rejected earlier.
 // Return null if no bound available.
 const SCEV *DependenceAnalysis::collectUpperBound(const Loop *L,
                                                   Type *T) const {
   if (SE->hasLoopInvariantBackedgeTakenCount(L)) {
     const SCEV *UB = SE->getBackedgeTakenCount(L);
-    return SE->getNoopOrZeroExtend(UB, T);
+    return SE->getTruncateOrZeroExtend(UB, T);
   }
   return nullptr;
 }