[InstCombine] Removing the combine of fmuladd with fast flag

We should treat fmuladd like an fma intrinsic, and any regressions need to be
addressed by dealing with fma/fmuladd in other contexts.

Author: vfdff

llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp

@@ -2424,17 +2424,6 @@ Instruction *InstCombinerImpl::visitCallInst(CallInst &CI) {
     break;
   }
   case Intrinsic::fmuladd: {
-    // Canonicalize fast fmuladd to the separate fmul + fadd.
-    if (II->isFast()) {
-      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);
-    }
-
     // Try to simplify the underlying FMul.
     if (Value *V = simplifyFMulInst(II->getArgOperand(0), II->getArgOperand(1),
                                     II->getFastMathFlags(),

llvm/test/Transforms/InstCombine/fma.ll

@@ -194,8 +194,7 @@ define float @fmuladd_unary_fneg_x_unary_fneg_y(float %x, float %y, float %z) {
 
 define float @fmuladd_fneg_x_fneg_y_fast(float %x, float %y, float %z) {
 ; CHECK-LABEL: @fmuladd_fneg_x_fneg_y_fast(
-; CHECK-NEXT:    [[TMP1:%.*]] = fmul fast float [[X:%.*]], [[Y:%.*]]
-; CHECK-NEXT:    [[FMULADD:%.*]] = fadd fast float [[TMP1]], [[Z:%.*]]
+; CHECK-NEXT:    [[FMULADD:%.*]] = call fast float @llvm.fmuladd.f32(float [[X:%.*]], float [[Y:%.*]], float [[Z:%.*]])
 ; CHECK-NEXT:    ret float [[FMULADD]]
 ;
   %x.fneg = fsub float -0.0, %x
@@ -206,8 +205,7 @@ define float @fmuladd_fneg_x_fneg_y_fast(float %x, float %y, float %z) {
 
 define float @fmuladd_unary_fneg_x_unary_fneg_y_fast(float %x, float %y, float %z) {
 ; CHECK-LABEL: @fmuladd_unary_fneg_x_unary_fneg_y_fast(
-; CHECK-NEXT:    [[TMP1:%.*]] = fmul fast float [[X:%.*]], [[Y:%.*]]
-; CHECK-NEXT:    [[FMULADD:%.*]] = fadd fast float [[TMP1]], [[Z:%.*]]
+; CHECK-NEXT:    [[FMULADD:%.*]] = call fast float @llvm.fmuladd.f32(float [[X:%.*]], float [[Y:%.*]], float [[Z:%.*]])
 ; CHECK-NEXT:    ret float [[FMULADD]]
 ;
   %x.fneg = fneg float %x
@@ -285,8 +283,7 @@ define float @fmuladd_fabs_x_fabs_x(float %x, float %z) {
 
 define float @fmuladd_fabs_x_fabs_x_fast(float %x, float %z) {
 ; CHECK-LABEL: @fmuladd_fabs_x_fabs_x_fast(
-; CHECK-NEXT:    [[TMP1:%.*]] = fmul fast float [[X:%.*]], [[X]]
-; CHECK-NEXT:    [[FMULADD:%.*]] = fadd fast float [[TMP1]], [[Z:%.*]]
+; CHECK-NEXT:    [[FMULADD:%.*]] = call fast float @llvm.fmuladd.f32(float [[X:%.*]], float [[X]], float [[Z:%.*]])
 ; CHECK-NEXT:    ret float [[FMULADD]]
 ;
   %x.fabs = call float @llvm.fabs.f32(float %x)
@@ -312,10 +309,10 @@ define float @fma_k_y_z_fast(float %y, float %z) {
   ret float %fma
 }
 
+; Treat fmuladd like an fma intrinsic
 define float @fmuladd_k_y_z_fast(float %y, float %z) {
 ; CHECK-LABEL: @fmuladd_k_y_z_fast(
-; CHECK-NEXT:    [[TMP1:%.*]] = fmul fast float [[Y:%.*]], 4.000000e+00
-; CHECK-NEXT:    [[FMULADD:%.*]] = fadd fast float [[TMP1]], [[Z:%.*]]
+; CHECK-NEXT:    [[FMULADD:%.*]] = call fast float @llvm.fmuladd.f32(float [[Y:%.*]], float 4.000000e+00, float [[Z:%.*]])
 ; CHECK-NEXT:    ret float [[FMULADD]]
 ;
   %fmuladd = call fast float @llvm.fmuladd.f32(float 4.0, float %y, float %z)