[DAGCombiner] Replace masked loads with a zero mask with the passthru value

Similar to what was recently done for gathers in r362015.

llvm-svn: 362337

1 files changed, 7 insertions, 3 deletions

diff --git a/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp b/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
index 949c14f3ce4..a866dbb250a 100644
--- a/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
@@ -8216,13 +8216,17 @@ SDValue DAGCombiner::visitMGATHER(SDNode *N) {
 }
 
 SDValue DAGCombiner::visitMLOAD(SDNode *N) {
-  if (Level >= AfterLegalizeTypes)
-    return SDValue();
-
   MaskedLoadSDNode *MLD = cast<MaskedLoadSDNode>(N);
   SDValue Mask = MLD->getMask();
   SDLoc DL(N);
 
+  // Zap masked loads with a zero mask.
+  if (ISD::isBuildVectorAllZeros(Mask.getNode()))
+    return CombineTo(N, MLD->getPassThru(), MLD->getChain());
+
+  if (Level >= AfterLegalizeTypes)
+    return SDValue();
+
   // If the MLOAD result requires splitting and the mask is provided by a
   // SETCC, then split both nodes and its operands before legalization. This
   // prevents the type legalizer from unrolling SETCC into scalar comparisons