[DAGCombiner] Masked merge: don't touch "not" xor's.

Summary:
Split off form D46031.

It seems we don't want to transform the pattern if the `xor`'s are actually `not`'s.
In vector case, this breaks `andnpd` / `vandnps` patterns.

That being said, we may want to re-visit this `not` handling, maybe in D46073.

Reviewers: spatel, craig.topper, javed.absar

Reviewed By: spatel

Subscribers: llvm-commits

Differential Revision: https://reviews.llvm.org/D46492

llvm-svn: 331595

1 files changed, 10 insertions, 0 deletions

diff --git a/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp b/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
index e5ef26f52d3..9bcdcdc1578 100644
--- a/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
@@ -5372,9 +5372,16 @@ SDValue DAGCombiner::MatchLoadCombine(SDNode *N) {
 //    |  D  |
 // Into:
 //   (x & m) | (y & ~m)
+// NOTE: we don't unfold the pattern if 'xor' is actually a 'not', because at
+//       the very least that breaks andnpd / andnps patterns, and because those
+//       patterns are simplified in IR and shouldn't be created in the DAG
 SDValue DAGCombiner::unfoldMaskedMerge(SDNode *N) {
   assert(N->getOpcode() == ISD::XOR);
 
+  // Don't touch 'not' (i.e. where y = -1).
+  if (isAllOnesConstantOrAllOnesSplatConstant(N->getOperand(1)))
+    return SDValue();
+
   EVT VT = N->getValueType(0);
 
   // FIXME
@@ -5392,6 +5399,9 @@ SDValue DAGCombiner::unfoldMaskedMerge(SDNode *N) {
       return false;
     SDValue Xor0 = Xor.getOperand(0);
     SDValue Xor1 = Xor.getOperand(1);
+    // Don't touch 'not' (i.e. where y = -1).
+    if (isAllOnesConstantOrAllOnesSplatConstant(Xor1))
+      return false;
     if (Other == Xor0)
       std::swap(Xor0, Xor1);
     if (Other != Xor1)