[llvm] r292784 - [InstCombine][X86] MULDQ/MULUDQ undef -> zero

[Simon Pilgrim via llvm-commits]

I added constant folding support which currently handles the 1 undef case, but I can move it into the early out very easily.

David - I’ll investigate whether moving this to constant folding is viable.

Cheers, Simon.

> On 24 Jan 2017, at 02:11, Craig Topper <craig.topper at gmail.com> wrote:
> 
> Shouldn't it be if either is undef return 0?
> 
> Generic mul does this
> 
>   // X * undef -> 0
> 
> ~Craig
> 
> On Mon, Jan 23, 2017 at 4:07 AM, Simon Pilgrim via llvm-commits <llvm-commits at lists.llvm.org <mailto:llvm-commits at lists.llvm.org>> wrote:
> Author: rksimon
> Date: Mon Jan 23 06:07:32 2017
> New Revision: 292784
> 
> URL: http://llvm.org/viewvc/llvm-project?rev=292784&view=rev <http://llvm.org/viewvc/llvm-project?rev=292784&view=rev>
> Log:
> [InstCombine][X86] MULDQ/MULUDQ undef -> zero
> 
> Match generic mul behaviour so that <X x i64> multiply and muldq/muludq pattern act the same
> 
> Modified:
>     llvm/trunk/lib/Transforms/InstCombine/InstCombineCalls.cpp
>     llvm/trunk/test/Transforms/InstCombine/x86-muldq.ll
> 
> Modified: llvm/trunk/lib/Transforms/InstCombine/InstCombineCalls.cpp
> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/InstCombine/InstCombineCalls.cpp?rev=292784&r1=292783&r2=292784&view=diff <http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/InstCombine/InstCombineCalls.cpp?rev=292784&r1=292783&r2=292784&view=diff>
> ==============================================================================
> --- llvm/trunk/lib/Transforms/InstCombine/InstCombineCalls.cpp (original)
> +++ llvm/trunk/lib/Transforms/InstCombine/InstCombineCalls.cpp Mon Jan 23 06:07:32 2017
> @@ -515,9 +515,9 @@ static Value *simplifyX86muldq(const Int
>    Value *Arg1 = II.getArgOperand(1);
>    Type *ResTy = II.getType();
> 
> -  // muldq/muludq(undef, undef) -> undef
> +  // muldq/muludq(undef, undef) -> zero (matches generic mul behavior)
>    if (isa<UndefValue>(Arg0) && isa<UndefValue>(Arg1))
> -    return UndefValue::get(ResTy);
> +    return ConstantAggregateZero::get(ResTy);
> 
>    return nullptr;
>  }
> 
> Modified: llvm/trunk/test/Transforms/InstCombine/x86-muldq.ll
> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/InstCombine/x86-muldq.ll?rev=292784&r1=292783&r2=292784&view=diff <http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/InstCombine/x86-muldq.ll?rev=292784&r1=292783&r2=292784&view=diff>
> ==============================================================================
> --- llvm/trunk/test/Transforms/InstCombine/x86-muldq.ll (original)
> +++ llvm/trunk/test/Transforms/InstCombine/x86-muldq.ll Mon Jan 23 06:07:32 2017
> @@ -7,7 +7,7 @@
> 
>  define <2 x i64> @undef_pmuludq_128(<4 x i32> %a0, <4 x i32> %a1) {
>  ; CHECK-LABEL: @undef_pmuludq_128(
> -; CHECK-NEXT:    ret <2 x i64> undef
> +; CHECK-NEXT:    ret <2 x i64> zeroinitializer
>  ;
>    %1 = call <2 x i64> @llvm.x86.sse2.pmulu.dq(<4 x i32> undef, <4 x i32> undef)
>    ret <2 x i64> %1
> @@ -15,7 +15,7 @@ define <2 x i64> @undef_pmuludq_128(<4 x
> 
>  define <4 x i64> @undef_pmuludq_256(<8 x i32> %a0, <8 x i32> %a1) {
>  ; CHECK-LABEL: @undef_pmuludq_256(
> -; CHECK-NEXT:    ret <4 x i64> undef
> +; CHECK-NEXT:    ret <4 x i64> zeroinitializer
>  ;
>    %1 = call <4 x i64> @llvm.x86.avx2.pmulu.dq(<8 x i32> undef, <8 x i32> undef)
>    ret <4 x i64> %1
> @@ -23,7 +23,7 @@ define <4 x i64> @undef_pmuludq_256(<8 x
> 
>  define <8 x i64> @undef_pmuludq_512(<16 x i32> %a0, <16 x i32> %a1) {
>  ; CHECK-LABEL: @undef_pmuludq_512(
> -; CHECK-NEXT:    ret <8 x i64> undef
> +; CHECK-NEXT:    ret <8 x i64> zeroinitializer
>  ;
>    %1 = call <8 x i64> @llvm.x86.avx512.pmulu.dq.512(<16 x i32> undef, <16 x i32> undef)
>    ret <8 x i64> %1
> @@ -31,7 +31,7 @@ define <8 x i64> @undef_pmuludq_512(<16
> 
>  define <2 x i64> @undef_pmuldq_128(<4 x i32> %a0, <4 x i32> %a1) {
>  ; CHECK-LABEL: @undef_pmuldq_128(
> -; CHECK-NEXT:    ret <2 x i64> undef
> +; CHECK-NEXT:    ret <2 x i64> zeroinitializer
>  ;
>    %1 = call <2 x i64> @llvm.x86.sse41.pmuldq(<4 x i32> undef, <4 x i32> undef)
>    ret <2 x i64> %1
> @@ -39,7 +39,7 @@ define <2 x i64> @undef_pmuldq_128(<4 x
> 
>  define <4 x i64> @undef_pmuldq_256(<8 x i32> %a0, <8 x i32> %a1) {
>  ; CHECK-LABEL: @undef_pmuldq_256(
> -; CHECK-NEXT:    ret <4 x i64> undef
> +; CHECK-NEXT:    ret <4 x i64> zeroinitializer
>  ;
>    %1 = call <4 x i64> @llvm.x86.avx2.pmul.dq(<8 x i32> undef, <8 x i32> undef)
>    ret <4 x i64> %1
> @@ -47,7 +47,7 @@ define <4 x i64> @undef_pmuldq_256(<8 x
> 
>  define <8 x i64> @undef_pmuldq_512(<16 x i32> %a0, <16 x i32> %a1) {
>  ; CHECK-LABEL: @undef_pmuldq_512(
> -; CHECK-NEXT:    ret <8 x i64> undef
> +; CHECK-NEXT:    ret <8 x i64> zeroinitializer
>  ;
>    %1 = call <8 x i64> @llvm.x86.avx512.pmul.dq.512(<16 x i32> undef, <16 x i32> undef)
>    ret <8 x i64> %1
> 
> 
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