[x86] fix predicate for avoiding vblendv

It only makes sense to produce the logic ops when 1 of the
constants is +0.0. Otherwise, go with vblendv to reduce code.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@347403 91177308-0d34-0410-b5e6-96231b3b80d8

Author: rotateright

lib/Target/X86/X86ISelLowering.cpp

@@ -19632,21 +19632,18 @@ SDValue X86TargetLowering::LowerSELECT(SDValue Op, SelectionDAG &DAG) const {
       // of 3 logic instructions for size savings and potentially speed.
       // Unfortunately, there is no scalar form of VBLENDV.
 
-      // If either operand is a constant, don't try this. We can expect to
+      // If either operand is a +0.0 constant, don't try this. We can expect to
       // optimize away at least one of the logic instructions later in that
       // case, so that sequence would be faster than a variable blend.
 
       // BLENDV was introduced with SSE 4.1, but the 2 register form implicitly
       // uses XMM0 as the selection register. That may need just as many
       // instructions as the AND/ANDN/OR sequence due to register moves, so
       // don't bother.
-
-      if (Subtarget.hasAVX() &&
-          !isa<ConstantFPSDNode>(Op1) && !isa<ConstantFPSDNode>(Op2)) {
-
+      if (Subtarget.hasAVX() && !isNullFPConstant(Op1) &&
+          !isNullFPConstant(Op2)) {
         // Convert to vectors, do a VSELECT, and convert back to scalar.
         // All of the conversions should be optimized away.
-
         MVT VecVT = VT == MVT::f32 ? MVT::v4f32 : MVT::v2f64;
         SDValue VOp1 = DAG.getNode(ISD::SCALAR_TO_VECTOR, DL, VecVT, Op1);
         SDValue VOp2 = DAG.getNode(ISD::SCALAR_TO_VECTOR, DL, VecVT, Op2);

test/CodeGen/X86/vselect-zero.ll

@@ -88,10 +88,8 @@ define double @fsel_nonzero_false_val(double %x, double %y, double %z) {
 ; AVX-LABEL: fsel_nonzero_false_val:
 ; AVX:       # %bb.0:
 ; AVX-NEXT:    vcmpeqsd %xmm1, %xmm0, %xmm0
-; AVX-NEXT:    vandpd %xmm2, %xmm0, %xmm1
-; AVX-NEXT:    vmovsd {{.*#+}} xmm2 = mem[0],zero
-; AVX-NEXT:    vandnpd %xmm2, %xmm0, %xmm0
-; AVX-NEXT:    vorpd %xmm1, %xmm0, %xmm0
+; AVX-NEXT:    vmovsd {{.*#+}} xmm1 = mem[0],zero
+; AVX-NEXT:    vblendvpd %xmm0, %xmm2, %xmm1, %xmm0
 ; AVX-NEXT:    retq
   %cond = fcmp oeq double %x, %y
   %r = select i1 %cond, double %z, double 42.0
@@ -112,9 +110,7 @@ define double @fsel_nonzero_true_val(double %x, double %y, double %z) {
 ; AVX:       # %bb.0:
 ; AVX-NEXT:    vcmpeqsd %xmm1, %xmm0, %xmm0
 ; AVX-NEXT:    vmovsd {{.*#+}} xmm1 = mem[0],zero
-; AVX-NEXT:    vandpd %xmm1, %xmm0, %xmm1
-; AVX-NEXT:    vandnpd %xmm2, %xmm0, %xmm0
-; AVX-NEXT:    vorpd %xmm1, %xmm0, %xmm0
+; AVX-NEXT:    vblendvpd %xmm0, %xmm1, %xmm2, %xmm0
 ; AVX-NEXT:    retq
   %cond = fcmp oeq double %x, %y
   %r = select i1 %cond, double 42.0, double %z