[X86][SSE] Use raw shuffle mask decode in SimplifyDemandedVectorEltsForTargetNode (PR39549)

We were using the 'normalized' shuffle mask from resolveTargetShuffleInputs, which replaces zero/undef inputs with sentinel values. For SimplifyDemandedVectorElts we need the raw mask so we can correctly demand those 'zero' inputs that got normalized away, this requires an extra bit of logic to locally normalize undef inputs.

llvm-svn: 347158

1 files changed, 10 insertions, 4 deletions

diff --git a/llvm/lib/Target/X86/X86ISelLowering.cpp b/llvm/lib/Target/X86/X86ISelLowering.cpp
index 7eae08e54c2..d2a5f396d64 100644
--- a/llvm/lib/Target/X86/X86ISelLowering.cpp
+++ b/llvm/lib/Target/X86/X86ISelLowering.cpp
@@ -32085,13 +32085,15 @@ bool X86TargetLowering::SimplifyDemandedVectorEltsForTargetNode(
   }
 
   // Simplify target shuffles.
-  if (!isTargetShuffle(Opc))
+  if (!isTargetShuffle(Opc) || !VT.isSimple())
     return false;
 
   // Get target shuffle mask.
+  bool IsUnary;
   SmallVector<int, 64> OpMask;
   SmallVector<SDValue, 2> OpInputs;
-  if (!resolveTargetShuffleInputs(Op, OpInputs, OpMask, TLO.DAG))
+  if (!getTargetShuffleMask(Op.getNode(), VT.getSimpleVT(), true, OpInputs,
+                            OpMask, IsUnary))
     return false;
 
   // Shuffle inputs must be the same type as the result.
@@ -32101,9 +32103,13 @@ bool X86TargetLowering::SimplifyDemandedVectorEltsForTargetNode(
 
   // Check if shuffle mask can be simplified to undef/zero/identity.
   int NumSrcs = OpInputs.size();
-  for (int i = 0; i != NumElts; ++i)
+  for (int i = 0; i != NumElts; ++i) {
+    int &M = OpMask[i];
     if (!DemandedElts[i])
-      OpMask[i] = SM_SentinelUndef;
+      M = SM_SentinelUndef;
+    else if (0 <= M && OpInputs[M / NumElts].isUndef())
+      M = SM_SentinelUndef;
+  }
 
   if (isUndefInRange(OpMask, 0, NumElts)) {
     KnownUndef.setAllBits();