[PATCH] D28448: InstCombine: Canonicalize fast fmuladd to fmul + fadd

[Matt Arsenault via Phabricator via llvm-commits]

arsenm updated this revision to Diff 88659.
arsenm retitled this revision from " InstCombine: Do unsafe math combine of fadd + fmuladd + fmul" to "InstCombine: Canonicalize fast fmuladd to fmul + fadd".
arsenm edited the summary of this revision.

https://reviews.llvm.org/D28448

Files:
  lib/Transforms/InstCombine/InstCombineCalls.cpp
  test/Transforms/InstCombine/fma.ll


Index: test/Transforms/InstCombine/fma.ll
===================================================================
--- test/Transforms/InstCombine/fma.ll
+++ test/Transforms/InstCombine/fma.ll
@@ -78,7 +78,8 @@
 }
 
 ; CHECK-LABEL: @fmuladd_fneg_x_fneg_y_fast(
-; CHECK: %fmuladd = call fast float @llvm.fmuladd.f32(float %x, float %y, float %z)
+; CHECK-NEXT: %1 = fmul fast float %x, %y
+; CHECK-NEXT: %fmuladd = fadd fast float %1, %z
 define float @fmuladd_fneg_x_fneg_y_fast(float %x, float %y, float %z) {
   %x.fneg = fsub float -0.0, %x
   %y.fneg = fsub float -0.0, %y
@@ -122,7 +123,8 @@
 }
 
 ; CHECK-LABEL: @fmuladd_fabs_x_fabs_x_fast(
-; CHECK: %fmuladd = call fast float @llvm.fmuladd.f32(float %x, float %x, float %z)
+; CHECK-NEXT: %1 = fmul fast float %x, %x
+; CHECK-NEXT: %fmuladd = fadd fast float %1, %z
 define float @fmuladd_fabs_x_fabs_x_fast(float %x, float %z) {
   %x.fabs = call float @llvm.fabs.f32(float %x)
   %fmuladd = call fast float @llvm.fmuladd.f32(float %x.fabs, float %x.fabs, float %z)
@@ -144,7 +146,8 @@
 }
 
 ; CHECK-LABEL: @fmuladd_k_y_z_fast(
-; CHECK: %fmuladd = call fast float @llvm.fmuladd.f32(float %y, float 4.000000e+00, float %z)
+; CHECK: %1 = fmul fast float %y, 4.000000e+00
+; CHECK-NEXT: %fmuladd = fadd fast float %1, %z
 define float @fmuladd_k_y_z_fast(float %y, float %z) {
   %fmuladd = call fast float @llvm.fmuladd.f32(float 4.0, float %y, float %z)
   ret float %fmuladd
Index: lib/Transforms/InstCombine/InstCombineCalls.cpp
===================================================================
--- lib/Transforms/InstCombine/InstCombineCalls.cpp
+++ lib/Transforms/InstCombine/InstCombineCalls.cpp
@@ -2044,8 +2044,21 @@
       return replaceInstUsesWith(*II, V);
     break;
   }
-  case Intrinsic::fma:
   case Intrinsic::fmuladd: {
+    // Canonicalize fast fmuladd to the separate fmul + fadd.
+    if (II->hasUnsafeAlgebra()) {
+      BuilderTy::FastMathFlagGuard Guard(*Builder);
+      Builder->setFastMathFlags(II->getFastMathFlags());
+      Value *Mul = Builder->CreateFMul(II->getArgOperand(0),
+                                       II->getArgOperand(1));
+      Value *Add = Builder->CreateFAdd(Mul, II->getArgOperand(2));
+      Add->takeName(II);
+      return replaceInstUsesWith(*II, Add);
+    }
+
+    LLVM_FALLTHROUGH;
+  }
+  case Intrinsic::fma: {
     Value *Src0 = II->getArgOperand(0);
     Value *Src1 = II->getArgOperand(1);
 


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