Utilize new SDNode flag functionality to expand current support for fmul

Summary: This patch originated from D46562 and is a proper subset, with some issues addressed for fmul.

Reviewers: spatel, hfinkel, wristow, arsenm

Reviewed By: spatel

Subscribers: nhaehnle, wdng

Differential Revision: https://reviews.llvm.org/D47911

llvm-svn: 334514

llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp

@@ -10542,12 +10542,15 @@ SDValue DAGCombiner::visitFMUL(SDNode *N) {
   if (SDValue NewSel = foldBinOpIntoSelect(N))
     return NewSel;
 
-  if (Options.UnsafeFPMath) {
+  if (Options.UnsafeFPMath || 
+      (Flags.hasNoNaNs() && Flags.hasNoSignedZeros())) {
     // fold (fmul A, 0) -> 0
     if (N1CFP && N1CFP->isZero())
       return N1;
+  } 
 
-    // fmul (fmul X, C1), X2 -> fmul X, C1 * C2
+  if (Options.UnsafeFPMath || Flags.hasAllowReassociation()) {
+    // fmul (fmul X, C1), C2 -> fmul X, C1 * C2
     if (N0.getOpcode() == ISD::FMUL) {
       // Fold scalars or any vector constants (not just splats).
       // This fold is done in general by InstCombine, but extra fmul insts

llvm/test/CodeGen/X86/fmul-combines.ll

@@ -92,7 +92,6 @@ define <4 x float> @fmul_v4f32_two_consts_no_splat_reassoc(<4 x float> %x) {
 ; CHECK-LABEL: fmul_v4f32_two_consts_no_splat_reassoc:
 ; CHECK:       # %bb.0:
 ; CHECK-NEXT:    mulps {{.*}}(%rip), %xmm0
-; CHECK-NEXT:    mulps {{.*}}(%rip), %xmm0
 ; CHECK-NEXT:    retq
   %y = fmul <4 x float> %x, <float 1.0, float 2.0, float 3.0, float 4.0>
   %z = fmul reassoc <4 x float> %y, <float 5.0, float 6.0, float 7.0, float 8.0>
@@ -104,7 +103,6 @@ define <4 x float> @fmul_v4f32_two_consts_no_splat_reassoc(<4 x float> %x) {
 define <4 x float> @fmul_v4f32_two_consts_no_splat_reassoc_2(<4 x float> %x) {
 ; CHECK-LABEL: fmul_v4f32_two_consts_no_splat_reassoc_2:
 ; CHECK:       # %bb.0:
-; CHECK-NEXT:    addps %xmm0, %xmm0
 ; CHECK-NEXT:    mulps {{.*}}(%rip), %xmm0
 ; CHECK-NEXT:    retq
   %y = fadd <4 x float> %x, %x

llvm/test/CodeGen/X86/fp-fold.ll

@@ -101,18 +101,11 @@ define float @fsub_negzero_nsz(float %x) {
   ret float %r
 }
 
-; TODO: handle x*0 for fast flags the same as unsafe
 define float @fmul_zero(float %x) {
-; STRICT-LABEL: fmul_zero:
-; STRICT:       # %bb.0:
-; STRICT-NEXT:    xorps %xmm1, %xmm1
-; STRICT-NEXT:    mulss %xmm1, %xmm0
-; STRICT-NEXT:    retq
-;
-; UNSAFE-LABEL: fmul_zero:
-; UNSAFE:       # %bb.0:
-; UNSAFE-NEXT:    xorps %xmm0, %xmm0
-; UNSAFE-NEXT:    retq
+; ANY-LABEL: fmul_zero:
+; ANY:       # %bb.0:
+; ANY-NEXT:    xorps %xmm0, %xmm0
+; ANY-NEXT:    retq
   %r = fmul nnan nsz float %x, 0.0
   ret float %r
 }
@@ -124,3 +117,13 @@ define float @fmul_one(float %x) {
   %r = fmul float %x, 1.0
   ret float %r
 }
+
+define float @fmul_x_const_const(float %x) {
+; ANY-LABEL: fmul_x_const_const:
+; ANY:       # %bb.0:
+; ANY-NEXT:    mulss {{.*}}(%rip), %xmm0
+; ANY-NEXT:    retq
+  %mul = fmul reassoc float %x, 9.0
+  %r = fmul reassoc float %mul, 4.0
+  ret float %r
+}