Fix PR15155: lost vadd/vsplat optimization.

During lowering of a BUILD_VECTOR, we look for opportunities to use a
vector splat.  When the splatted value fits in 5 signed bits, a single
splat does the job.  When it doesn't fit in 5 bits but does fit in 6,
and is an even value, we can splat on half the value and add the result
to itself.

This last optimization hasn't been working recently because of improved
constant folding.  To circumvent this, create a pseudo VADD_SPLAT that
can be expanded during instruction selection.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@175632 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 8 insertions, 8 deletions

diff --git a/lib/Target/PowerPC/PPCISelLowering.cpp b/lib/Target/PowerPC/PPCISelLowering.cpp
index e789112de2..f3ef38a3dc 100644
--- a/lib/Target/PowerPC/PPCISelLowering.cpp
+++ b/lib/Target/PowerPC/PPCISelLowering.cpp
@@ -594,6 +594,7 @@ const char *PPCTargetLowering::getTargetNodeName(unsigned Opcode) const {
   case PPCISD::GET_TLSLD_ADDR:  return "PPCISD::GET_TLSLD_ADDR";
   case PPCISD::ADDIS_DTPREL_HA: return "PPCISD::ADDIS_DTPREL_HA";
   case PPCISD::ADDI_DTPREL_L:   return "PPCISD::ADDI_DTPREL_L";
+  case PPCISD::VADD_SPLAT:      return "PPCISD::VADD_SPLAT";
   }
 }
 
@@ -5020,14 +5021,13 @@ SDValue PPCTargetLowering::LowerBUILD_VECTOR(SDValue Op,
   // If this value is in the range [-32,30] and is even, use:
   //    tmp = VSPLTI[bhw], result = add tmp, tmp
   if (SextVal >= -32 && SextVal <= 30 && (SextVal & 1) == 0) {
-    // FIXME: This is currently disabled because the ADD will be folded back
-    // into an invalid BUILD_VECTOR immediately.
-    return SDValue();
-#if 0
-    SDValue Res = BuildSplatI(SextVal >> 1, SplatSize, MVT::Other, DAG, dl);
-    Res = DAG.getNode(ISD::ADD, dl, Res.getValueType(), Res, Res);
-    return DAG.getNode(ISD::BITCAST, dl, Op.getValueType(), Res);
-#endif
+    // To avoid having the optimization undone by constant folding, we
+    // convert to a pseudo that will be expanded later.
+    SDValue Elt = DAG.getConstant(SextVal >> 1, MVT::i32);
+    EVT VT = Op.getValueType();
+    int Size = VT == MVT::v16i8 ? 1 : (VT == MVT::v8i16 ? 2 : 4);
+    SDValue EltSize = DAG.getConstant(Size, MVT::i32);
+    return DAG.getNode(PPCISD::VADD_SPLAT, dl, VT, Elt, EltSize);
   }
 
   // If this is 0x8000_0000 x 4, turn into vspltisw + vslw.  If it is