[DAGCombiner][x86] scalarize splatted vector FP ops

There are a variety of vector patterns that may be profitably reduced to a
scalar op when scalar ops are performed using a subset (typically, the
first lane) of the vector register file.

For x86, this is true for float/double ops and element 0 because
insert/extract is just a sub-register rename.

Other targets should likely enable the hook in a similar way.

Differential Revision: https://reviews.llvm.org/D60150

llvm-svn: 357760

1 files changed, 19 insertions, 2 deletions

diff --git a/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp b/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
index 6306ad52db5..5d7890ee08f 100644
--- a/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
@@ -18078,11 +18078,28 @@ SDValue DAGCombiner::visitVECTOR_SHUFFLE(SDNode *N) {
   // If it is a splat, check if the argument vector is another splat or a
   // build_vector.
   if (SVN->isSplat() && SVN->getSplatIndex() < (int)NumElts) {
-    SDNode *V = N0.getNode();
+    int SplatIndex = SVN->getSplatIndex();
+    if (TLI.isExtractVecEltCheap(VT, SplatIndex) &&
+        ISD::isBinaryOp(N0.getNode())) {
+      // splat (vector_bo L, R), Index -->
+      // splat (scalar_bo (extelt L, Index), (extelt R, Index))
+      SDValue L = N0.getOperand(0), R = N0.getOperand(1);
+      SDLoc DL(N);
+      EVT EltVT = VT.getScalarType();
+      SDValue Index = DAG.getIntPtrConstant(SplatIndex, DL);
+      SDValue ExtL = DAG.getNode(ISD::EXTRACT_VECTOR_ELT, DL, EltVT, L, Index);
+      SDValue ExtR = DAG.getNode(ISD::EXTRACT_VECTOR_ELT, DL, EltVT, R, Index);
+      SDValue NewBO = DAG.getNode(N0.getOpcode(), DL, EltVT, ExtL, ExtR,
+                                  N0.getNode()->getFlags());
+      SDValue Insert = DAG.getNode(ISD::SCALAR_TO_VECTOR, DL, VT, NewBO);
+      SmallVector<int, 16> ZeroMask(VT.getVectorNumElements(), 0);
+      return DAG.getVectorShuffle(VT, DL, Insert, DAG.getUNDEF(VT), ZeroMask);
+    }
 
     // If this is a bit convert that changes the element type of the vector but
     // not the number of vector elements, look through it.  Be careful not to
     // look though conversions that change things like v4f32 to v2f64.
+    SDNode *V = N0.getNode();
     if (V->getOpcode() == ISD::BITCAST) {
       SDValue ConvInput = V->getOperand(0);
       if (ConvInput.getValueType().isVector() &&
@@ -18115,7 +18132,7 @@ SDValue DAGCombiner::visitVECTOR_SHUFFLE(SDNode *N) {
         return N0;
 
       // Canonicalize any other splat as a build_vector.
-      const SDValue &Splatted = V->getOperand(SVN->getSplatIndex());
+      SDValue Splatted = V->getOperand(SplatIndex);
       SmallVector<SDValue, 8> Ops(NumElts, Splatted);
       SDValue NewBV = DAG.getBuildVector(V->getValueType(0), SDLoc(N), Ops);