X86: Do splat promotion later, so the optimizer can chew on it first.

This catches many cases where we can emit a more efficient shuffle for a
specific mask or when the mask contains undefs. Once the splat is lowered to
unpacks we can't do that anymore.

There is a possibility of moving the promotion after pshufb matching, but I'm
not sure if pshufb with a mask loaded from memory is faster than 3 shuffles, so
I avoided that for now.

llvm-svn: 173569

1 files changed, 10 insertions, 10 deletions

diff --git a/llvm/lib/Target/X86/X86ISelLowering.cpp b/llvm/lib/Target/X86/X86ISelLowering.cpp
index 0c12410361d..6daa9b65e6f 100644
--- a/llvm/lib/Target/X86/X86ISelLowering.cpp
+++ b/llvm/lib/Target/X86/X86ISelLowering.cpp
@@ -5839,6 +5839,11 @@ LowerVECTOR_SHUFFLEv8i16(SDValue Op, const X86Subtarget *Subtarget,
     }
   }
 
+  // Promote splats to a larger type which usually leads to more efficient code.
+  // FIXME: Is this true if pshufb is available?
+  if (SVOp->isSplat())
+    return PromoteSplat(SVOp, DAG);
+
   // If we have SSSE3, and all words of the result are from 1 input vector,
   // case 2 is generated, otherwise case 3 is generated.  If no SSSE3
   // is present, fall back to case 4.
@@ -5972,6 +5977,11 @@ SDValue LowerVECTOR_SHUFFLEv16i8(ShuffleVectorSDNode *SVOp,
   DebugLoc dl = SVOp->getDebugLoc();
   ArrayRef<int> MaskVals = SVOp->getMask();
 
+  // Promote splats to a larger type which usually leads to more efficient code.
+  // FIXME: Is this true if pshufb is available?
+  if (SVOp->isSplat())
+    return PromoteSplat(SVOp, DAG);
+
   // If we have SSSE3, case 1 is generated when all result bytes come from
   // one of  the inputs.  Otherwise, case 2 is generated.  If no SSSE3 is
   // present, fall back to case 3.
@@ -6669,20 +6679,10 @@ X86TargetLowering::NormalizeVectorShuffle(SDValue Op, SelectionDAG &DAG) const {
 
   // Handle splat operations
   if (SVOp->isSplat()) {
-    unsigned NumElem = VT.getVectorNumElements();
-
     // Use vbroadcast whenever the splat comes from a foldable load
     SDValue Broadcast = LowerVectorBroadcast(Op, DAG);
     if (Broadcast.getNode())
       return Broadcast;
-
-    // Handle splats by matching through known shuffle masks
-    if ((VT.is128BitVector() && NumElem <= 4) ||
-        (VT.is256BitVector() && NumElem <= 8))
-      return SDValue();
-
-    // All remaning splats are promoted to target supported vector shuffles.
-    return PromoteSplat(SVOp, DAG);
   }
 
   // Check integer expanding shuffles.