[PATCH] D61028: [DAGCombiner] scale repeated FP divisor by splat factor

[Sanjay Patel via Phabricator via llvm-commits]

spatel updated this revision to Diff 196470.
spatel added a comment.

Patch updated:
Remove reordering of reciprocal estimate and repeated divisor transforms. We still see a diff for the SSE target with an illegal type because we don't try to generate the reciprocal estimate sequence until the types are legal.


CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D61028/new/

https://reviews.llvm.org/D61028

Files:
  llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
  llvm/test/CodeGen/X86/fdiv-combine-vec.ll


Index: llvm/test/CodeGen/X86/fdiv-combine-vec.ll
===================================================================
--- llvm/test/CodeGen/X86/fdiv-combine-vec.ll
+++ llvm/test/CodeGen/X86/fdiv-combine-vec.ll
@@ -5,14 +5,18 @@
 define <2 x double> @splat_fdiv_v2f64(<2 x double> %x, double %y) {
 ; SSE-LABEL: splat_fdiv_v2f64:
 ; SSE:       # %bb.0:
-; SSE-NEXT:    unpcklpd {{.*#+}} xmm1 = xmm1[0,0]
-; SSE-NEXT:    divpd %xmm1, %xmm0
+; SSE-NEXT:    movsd {{.*#+}} xmm2 = mem[0],zero
+; SSE-NEXT:    divsd %xmm1, %xmm2
+; SSE-NEXT:    unpcklpd {{.*#+}} xmm2 = xmm2[0,0]
+; SSE-NEXT:    mulpd %xmm2, %xmm0
 ; SSE-NEXT:    retq
 ;
 ; AVX-LABEL: splat_fdiv_v2f64:
 ; AVX:       # %bb.0:
+; AVX-NEXT:    vmovsd {{.*#+}} xmm2 = mem[0],zero
+; AVX-NEXT:    vdivsd %xmm1, %xmm2, %xmm1
 ; AVX-NEXT:    vmovddup {{.*#+}} xmm1 = xmm1[0,0]
-; AVX-NEXT:    vdivpd %xmm1, %xmm0, %xmm0
+; AVX-NEXT:    vmulpd %xmm1, %xmm0, %xmm0
 ; AVX-NEXT:    retq
   %vy = insertelement <2 x double> undef, double %y, i32 0
   %splaty = shufflevector <2 x double> %vy, <2 x double> undef, <2 x i32> zeroinitializer
@@ -32,9 +36,11 @@
 ;
 ; AVX-LABEL: splat_fdiv_v4f64:
 ; AVX:       # %bb.0:
+; AVX-NEXT:    vmovsd {{.*#+}} xmm2 = mem[0],zero
+; AVX-NEXT:    vdivsd %xmm1, %xmm2, %xmm1
 ; AVX-NEXT:    vmovddup {{.*#+}} xmm1 = xmm1[0,0]
 ; AVX-NEXT:    vinsertf128 $1, %xmm1, %ymm1, %ymm1
-; AVX-NEXT:    vdivpd %ymm1, %ymm0, %ymm0
+; AVX-NEXT:    vmulpd %ymm1, %ymm0, %ymm0
 ; AVX-NEXT:    retq
   %vy = insertelement <4 x double> undef, double %y, i32 0
   %splaty = shufflevector <4 x double> %vy, <4 x double> undef, <4 x i32> zeroinitializer
@@ -75,15 +81,11 @@
 define <8 x float> @splat_fdiv_v8f32(<8 x float> %x, float %y) {
 ; SSE-LABEL: splat_fdiv_v8f32:
 ; SSE:       # %bb.0:
-; SSE-NEXT:    shufps {{.*#+}} xmm2 = xmm2[0,0,0,0]
-; SSE-NEXT:    rcpps %xmm2, %xmm3
-; SSE-NEXT:    mulps %xmm3, %xmm2
-; SSE-NEXT:    movaps {{.*#+}} xmm4 = [1.0E+0,1.0E+0,1.0E+0,1.0E+0]
-; SSE-NEXT:    subps %xmm2, %xmm4
-; SSE-NEXT:    mulps %xmm3, %xmm4
-; SSE-NEXT:    addps %xmm3, %xmm4
-; SSE-NEXT:    mulps %xmm4, %xmm0
-; SSE-NEXT:    mulps %xmm4, %xmm1
+; SSE-NEXT:    movss {{.*#+}} xmm3 = mem[0],zero,zero,zero
+; SSE-NEXT:    divss %xmm2, %xmm3
+; SSE-NEXT:    shufps {{.*#+}} xmm3 = xmm3[0,0,0,0]
+; SSE-NEXT:    mulps %xmm3, %xmm0
+; SSE-NEXT:    mulps %xmm3, %xmm1
 ; SSE-NEXT:    retq
 ;
 ; AVX-LABEL: splat_fdiv_v8f32:
Index: llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
===================================================================
--- llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
+++ llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
@@ -11916,7 +11916,15 @@
   // possibly be enough uses of the divisor to make the transform worthwhile.
   SDValue N1 = N->getOperand(1);
   unsigned MinUses = TLI.combineRepeatedFPDivisors();
-  if (!MinUses || N1->use_size() < MinUses)
+
+  // For splat vectors, scale the number of uses by the splat factor. If we can
+  // convert the division into a scalar op, that will likely be much faster.
+  unsigned NumElts = 1;
+  EVT VT = N->getValueType(0);
+  if (VT.isVector() && DAG.isSplatValue(N1))
+    NumElts = VT.getVectorNumElements();
+
+  if (!MinUses || (N1->use_size() * NumElts) < MinUses)
     return SDValue();
 
   // Find all FDIV users of the same divisor.
@@ -11933,10 +11941,9 @@
 
   // Now that we have the actual number of divisor uses, make sure it meets
   // the minimum threshold specified by the target.
-  if (Users.size() < MinUses)
+  if ((Users.size() * NumElts) < MinUses)
     return SDValue();
 
-  EVT VT = N->getValueType(0);
   SDLoc DL(N);
   SDValue FPOne = DAG.getConstantFP(1.0, DL, VT);
   SDValue Reciprocal = DAG.getNode(ISD::FDIV, DL, VT, FPOne, N1, Flags);


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