SCEV fix. In general, Add/Mul expressions should not inherit NSW/NUW.

This reverts r139450, fixes r139453, and adds much needed comments and a
unit test.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@145367 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 6 insertions, 2 deletions

diff --git a/lib/Transforms/Scalar/IndVarSimplify.cpp b/lib/Transforms/Scalar/IndVarSimplify.cpp
index 1f5ba51824..ea083e36ca 100644
--- a/lib/Transforms/Scalar/IndVarSimplify.cpp
+++ b/lib/Transforms/Scalar/IndVarSimplify.cpp
@@ -944,9 +944,13 @@ const SCEVAddRecExpr* WidenIV::GetExtendedOperandRecurrence(NarrowIVDefUse DU) {
   else
     return 0;
 
+  // When creating this AddExpr, don't apply the current operations NSW or NUW
+  // flags. This instruction may be guarded by control flow that the no-wrap
+  // behavior depends on. Non-control-equivalent instructions can be mapped to
+  // the same SCEV expression, and it would be incorrect to transfer NSW/NUW
+  // semantics to those operations.
   const SCEVAddRecExpr *AddRec = dyn_cast<SCEVAddRecExpr>(
-    SE->getAddExpr(SE->getSCEV(DU.WideDef), ExtendOperExpr,
-                   IsSigned ? SCEV::FlagNSW : SCEV::FlagNUW));
+    SE->getAddExpr(SE->getSCEV(DU.WideDef), ExtendOperExpr));
 
   if (!AddRec || AddRec->getLoop() != L)
     return 0;