[llvm] r295353 - InstCombine: Canonicalize fast fmuladd to fmul + fadd

[Philip Reames via llvm-commits]

Can you explain this one a bit?  On the surface this seems a bit strange.

Philip


On 02/16/2017 10:46 AM, Matt Arsenault via llvm-commits wrote:
> Author: arsenm
> Date: Thu Feb 16 12:46:24 2017
> New Revision: 295353
>
> URL: http://llvm.org/viewvc/llvm-project?rev=295353&view=rev
> Log:
> InstCombine: Canonicalize fast fmuladd to fmul + fadd
>
> Modified:
>      llvm/trunk/lib/Transforms/InstCombine/InstCombineCalls.cpp
>      llvm/trunk/test/Transforms/InstCombine/fma.ll
>
> Modified: llvm/trunk/lib/Transforms/InstCombine/InstCombineCalls.cpp
> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/InstCombine/InstCombineCalls.cpp?rev=295353&r1=295352&r2=295353&view=diff
> ==============================================================================
> --- llvm/trunk/lib/Transforms/InstCombine/InstCombineCalls.cpp (original)
> +++ llvm/trunk/lib/Transforms/InstCombine/InstCombineCalls.cpp Thu Feb 16 12:46:24 2017
> @@ -2044,8 +2044,21 @@ Instruction *InstCombiner::visitCallInst
>         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);
>   
>
> Modified: llvm/trunk/test/Transforms/InstCombine/fma.ll
> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/InstCombine/fma.ll?rev=295353&r1=295352&r2=295353&view=diff
> ==============================================================================
> --- llvm/trunk/test/Transforms/InstCombine/fma.ll (original)
> +++ llvm/trunk/test/Transforms/InstCombine/fma.ll Thu Feb 16 12:46:24 2017
> @@ -78,7 +78,8 @@ define float @fmuladd_fneg_x_fneg_y(floa
>   }
>   
>   ; 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 @@ define float @fmuladd_fabs_x_fabs_x(floa
>   }
>   
>   ; 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 @@ define float @fma_k_y_z_fast(float %y, f
>   }
>   
>   ; 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
>
>
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