[TargetLowering] SimplifyDemandedVectorElts - don't alter DemandedElts mask

Fix potential issue with the ISD::INSERT_VECTOR_ELT case tweaking the DemandedElts mask instead of using a local copy - so later uses of the mask use the tweaked version.....

Noticed while investigating adding zero/undef folding to SimplifyDemandedVectorElts and the altered DemandedElts mask was causing mismatches.

llvm-svn: 348348

1 files changed, 3 insertions, 2 deletions

diff --git a/llvm/lib/CodeGen/SelectionDAG/TargetLowering.cpp b/llvm/lib/CodeGen/SelectionDAG/TargetLowering.cpp
index 33dad187d4a..04303d682d3 100644
--- a/llvm/lib/CodeGen/SelectionDAG/TargetLowering.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/TargetLowering.cpp
@@ -1614,9 +1614,10 @@ bool TargetLowering::SimplifyDemandedVectorElts(
       unsigned Idx = CIdx->getZExtValue();
       if (!DemandedElts[Idx])
         return TLO.CombineTo(Op, Vec);
-      DemandedElts.clearBit(Idx);
 
-      if (SimplifyDemandedVectorElts(Vec, DemandedElts, KnownUndef,
+      APInt DemandedVecElts(DemandedElts);
+      DemandedVecElts.clearBit(Idx);
+      if (SimplifyDemandedVectorElts(Vec, DemandedVecElts, KnownUndef,
                                      KnownZero, TLO, Depth + 1))
         return true;