[llvm] r371518 - [InstCombine] Use SimplifyFMulInst to simplify multiply in fma.

[Philip Reames via llvm-commits]

Wait, is this correct?  I thought that FMA had different rounding 
behavior than fadd/fmul.  Is it legal to take the simplified mul and 
simple feed it as an operand to a fadd?

Or is there some guard outside the diff which makes this correct?

Philip

On 9/10/19 6:10 AM, Florian Hahn via llvm-commits wrote:
> Author: fhahn
> Date: Tue Sep 10 06:10:28 2019
> New Revision: 371518
>
> URL: http://llvm.org/viewvc/llvm-project?rev=371518&view=rev
> Log:
> [InstCombine] Use SimplifyFMulInst to simplify multiply in fma.
>
> This allows us to fold fma's that multiply with 0.0. Also, the
> multiply by 1.0 case is handled there as well. The fneg/fabs cases
> are not handled by SimplifyFMulInst, so we need to keep them.
>
> Reviewers: spatel, anemet, lebedev.ri
>
> Reviewed By: spatel
>
> Differential Revision: https://reviews.llvm.org/D67351
>
> 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=371518&r1=371517&r2=371518&view=diff
> ==============================================================================
> --- llvm/trunk/lib/Transforms/InstCombine/InstCombineCalls.cpp (original)
> +++ llvm/trunk/lib/Transforms/InstCombine/InstCombineCalls.cpp Tue Sep 10 06:10:28 2019
> @@ -2258,9 +2258,11 @@ Instruction *InstCombiner::visitCallInst
>         return II;
>       }
>   
> -    // fma x, 1, z -> fadd x, z
> -    if (match(Src1, m_FPOne())) {
> -      auto *FAdd = BinaryOperator::CreateFAdd(Src0, II->getArgOperand(2));
> +    // Try to simplify the underlying FMul.
> +    if (Value *V = SimplifyFMulInst(II->getArgOperand(0), II->getArgOperand(1),
> +                                    II->getFastMathFlags(),
> +                                    SQ.getWithInstruction(II))) {
> +      auto *FAdd = BinaryOperator::CreateFAdd(V, II->getArgOperand(2));
>         FAdd->copyFastMathFlags(II);
>         return FAdd;
>       }
>
> Modified: llvm/trunk/test/Transforms/InstCombine/fma.ll
> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/InstCombine/fma.ll?rev=371518&r1=371517&r2=371518&view=diff
> ==============================================================================
> --- llvm/trunk/test/Transforms/InstCombine/fma.ll (original)
> +++ llvm/trunk/test/Transforms/InstCombine/fma.ll Tue Sep 10 06:10:28 2019
> @@ -372,8 +372,7 @@ define float @fmuladd_x_1_z_fast(float %
>   define <2 x double> @fmuladd_a_0_b(<2 x double> %a, <2 x double> %b) {
>   ; CHECK-LABEL: @fmuladd_a_0_b(
>   ; CHECK-NEXT:  entry:
> -; CHECK-NEXT:    [[RES:%.*]] = call nnan nsz <2 x double> @llvm.fmuladd.v2f64(<2 x double> [[A:%.*]], <2 x double> zeroinitializer, <2 x double> [[B:%.*]])
> -; CHECK-NEXT:    ret <2 x double> [[RES]]
> +; CHECK-NEXT:    ret <2 x double> [[B:%.*]]
>   ;
>   entry:
>     %res = call nnan nsz <2 x double> @llvm.fmuladd.v2f64(<2 x double> %a, <2 x double> zeroinitializer, <2 x double> %b)
> @@ -383,8 +382,7 @@ entry:
>   define <2 x double> @fmuladd_0_a_b(<2 x double> %a, <2 x double> %b) {
>   ; CHECK-LABEL: @fmuladd_0_a_b(
>   ; CHECK-NEXT:  entry:
> -; CHECK-NEXT:    [[RES:%.*]] = call nnan nsz <2 x double> @llvm.fmuladd.v2f64(<2 x double> [[A:%.*]], <2 x double> zeroinitializer, <2 x double> [[B:%.*]])
> -; CHECK-NEXT:    ret <2 x double> [[RES]]
> +; CHECK-NEXT:    ret <2 x double> [[B:%.*]]
>   ;
>   entry:
>     %res = call nnan nsz <2 x double> @llvm.fmuladd.v2f64(<2 x double> zeroinitializer, <2 x double> %a, <2 x double> %b)
> @@ -407,8 +405,7 @@ declare <2 x double> @llvm.fmuladd.v2f64
>   define <2 x double> @fma_a_0_b(<2 x double> %a, <2 x double> %b) {
>   ; CHECK-LABEL: @fma_a_0_b(
>   ; CHECK-NEXT:  entry:
> -; CHECK-NEXT:    [[RES:%.*]] = call nnan nsz <2 x double> @llvm.fma.v2f64(<2 x double> [[A:%.*]], <2 x double> zeroinitializer, <2 x double> [[B:%.*]])
> -; CHECK-NEXT:    ret <2 x double> [[RES]]
> +; CHECK-NEXT:    ret <2 x double> [[B:%.*]]
>   ;
>   entry:
>     %res = call nnan nsz <2 x double> @llvm.fma.v2f64(<2 x double> %a, <2 x double> zeroinitializer, <2 x double> %b)
> @@ -418,8 +415,7 @@ entry:
>   define <2 x double> @fma_0_a_b(<2 x double> %a, <2 x double> %b) {
>   ; CHECK-LABEL: @fma_0_a_b(
>   ; CHECK-NEXT:  entry:
> -; CHECK-NEXT:    [[RES:%.*]] = call nnan nsz <2 x double> @llvm.fma.v2f64(<2 x double> [[A:%.*]], <2 x double> zeroinitializer, <2 x double> [[B:%.*]])
> -; CHECK-NEXT:    ret <2 x double> [[RES]]
> +; CHECK-NEXT:    ret <2 x double> [[B:%.*]]
>   ;
>   entry:
>     %res = call nnan nsz <2 x double> @llvm.fma.v2f64(<2 x double> zeroinitializer, <2 x double> %a, <2 x double> %b)
> @@ -440,8 +436,7 @@ entry:
>   define <2 x double> @fma_sqrt(<2 x double> %a, <2 x double> %b) {
>   ; CHECK-LABEL: @fma_sqrt(
>   ; CHECK-NEXT:  entry:
> -; CHECK-NEXT:    [[SQRT:%.*]] = call fast <2 x double> @llvm.sqrt.v2f64(<2 x double> [[A:%.*]])
> -; CHECK-NEXT:    [[RES:%.*]] = call fast <2 x double> @llvm.fma.v2f64(<2 x double> [[SQRT]], <2 x double> [[SQRT]], <2 x double> [[B:%.*]])
> +; CHECK-NEXT:    [[RES:%.*]] = fadd fast <2 x double> [[A:%.*]], [[B:%.*]]
>   ; CHECK-NEXT:    ret <2 x double> [[RES]]
>   ;
>   entry:
>
>
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