teach SCEV that the scale and addition of an inbounds gep don't NSW.

This fixes a FIXME in scev-aa.ll (allowing a new no-alias result) and
generally makes things more precise.

llvm-svn: 125449

1 files changed, 5 insertions, 2 deletions

diff --git a/llvm/lib/Analysis/ScalarEvolution.cpp b/llvm/lib/Analysis/ScalarEvolution.cpp
index aab95ae..62244cc 100644
--- a/llvm/lib/Analysis/ScalarEvolution.cpp
+++ b/llvm/lib/Analysis/ScalarEvolution.cpp
@@ -2870,6 +2870,7 @@ const SCEV *ScalarEvolution::createNodeForGEP(GEPOperator *GEP) {
   // 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.
+  bool isInBounds = GEP->isInBounds();
 
   const Type *IntPtrTy = getEffectiveSCEVType(GEP->getType());
   Value *Base = GEP->getOperand(0);
@@ -2898,7 +2899,8 @@ const SCEV *ScalarEvolution::createNodeForGEP(GEPOperator *GEP) {
       IndexS = getTruncateOrSignExtend(IndexS, IntPtrTy);
 
       // Multiply the index by the element size to compute the element offset.
-      const SCEV *LocalOffset = getMulExpr(IndexS, ElementSize);
+      const SCEV *LocalOffset = getMulExpr(IndexS, ElementSize, /*NUW*/ false,
+                                           /*NSW*/ isInBounds);
 
       // Add the element offset to the running total offset.
       TotalOffset = getAddExpr(TotalOffset, LocalOffset);
@@ -2909,7 +2911,8 @@ const SCEV *ScalarEvolution::createNodeForGEP(GEPOperator *GEP) {
   const SCEV *BaseS = getSCEV(Base);
 
   // Add the total offset from all the GEP indices to the base.
-  return getAddExpr(BaseS, TotalOffset);
+  return getAddExpr(BaseS, TotalOffset, /*NUW*/ false,
+                    /*NSW*/ isInBounds);
 }
 
 /// GetMinTrailingZeros - Determine the minimum number of zero bits that S is