[BUG][INDVAR] Fix for PR21014: wrong SCEV operands commuting for non-commutative...

[oota-llvm.git] / lib / Transforms / Scalar / IndVarSimplify.cpp

diff --git a/lib/Transforms/Scalar/IndVarSimplify.cpp b/lib/Transforms/Scalar/IndVarSimplify.cpp
index 2959c7bd3c7866eaec427667511fad094723a45f..03dffb66f352886e763bf93eba205060f0cb4d89 100644 (file)
--- a/lib/Transforms/Scalar/IndVarSimplify.cpp
+++ b/lib/Transforms/Scalar/IndVarSimplify.cpp
@@ -865,7 +865,8 @@ const SCEVAddRecExpr* WidenIV::GetExtendedOperandRecurrence(NarrowIVDefUse DU) {
 
   // One operand (NarrowDef) has already been extended to WideDef. Now determine
   // if extending the other will lead to a recurrence.
-  unsigned ExtendOperIdx = DU.NarrowUse->getOperand(0) == DU.NarrowDef ? 1 : 0;
+  const unsigned ExtendOperIdx =
+      DU.NarrowUse->getOperand(0) == DU.NarrowDef ? 1 : 0;
   assert(DU.NarrowUse->getOperand(1-ExtendOperIdx) == DU.NarrowDef && "bad DU");
 
   const SCEV *ExtendOperExpr = nullptr;
@@ -885,8 +886,16 @@ const SCEVAddRecExpr* WidenIV::GetExtendedOperandRecurrence(NarrowIVDefUse DU) {
   // 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>(
-      GetSCEVByOpCode(SE->getSCEV(DU.WideDef), ExtendOperExpr, OpCode));
+  const SCEV *lhs = SE->getSCEV(DU.WideDef);
+  const SCEV *rhs = ExtendOperExpr;
+
+  // Let's swap operands to the initial order for the case of non-commutative
+  // operations, like SUB. See PR21014.
+  if (ExtendOperIdx == 0)
+    std::swap(lhs, rhs);
+  const SCEVAddRecExpr *AddRec =
+      dyn_cast<SCEVAddRecExpr>(GetSCEVByOpCode(lhs, rhs, OpCode));
+
   if (!AddRec || AddRec->getLoop() != L)
     return nullptr;
   return AddRec;