[PATCH] [AArch64] Multiply-Negate operation not lowered to mneg in AArch64

[James Molloy]

Hi Karthik,

This all looks fine to me.

Cheers,

James

On Mon Dec 22 2014 at 11:58:41 AM Karthik Bhat <kv.bhat at samsung.com> wrote:

> Hi t.p.northover,
>
> Hi All,
> The below code-
>
> int a,b,c;
> void fn() {
>   c = -(a*b);
> }
>
> when compiled on AArch64 bit with -O3 generates the assembly as follows-
>
> fn:                                     // @fn
> // BB#0:
>         adrp    x8, a
>         adrp    x9, b
>         ldr     w8, [x8, :lo12:a]
>         ldr     w9, [x9, :lo12:b]
>         neg      w8, w8
>         mul      w8, w9, w8
>         adrp    x9, c
>         str     w8, [x9, :lo12:c]
>         ret
>
> the neg and mul operation can be combined to mneg in AArch64. Gcc combines
> the above to mneg instruction.
> Added a patch in llvm to do the same.
>
> Post patch the following assembly is generated-
> fn:                                     // @fn
> // BB#0:
>         adrp    x8, a
>         adrp    x9, b
>         ldr     w8, [x8, :lo12:a]
>         ldr     w9, [x9, :lo12:b]
>         mneg     w8, w8, w9
>         adrp    x9, c
>         str     w8, [x9, :lo12:c]
>         ret
>
> Please let me know if this is good to commit.
>
> Thanks and Regards
> Karthik Bhat
>
> REPOSITORY
>   rL LLVM
>
> http://reviews.llvm.org/D6754
>
> Files:
>   lib/Target/AArch64/AArch64InstrInfo.td
>   test/CodeGen/AArch64/dp-3source.ll
>
> Index: lib/Target/AArch64/AArch64InstrInfo.td
> ===================================================================
> --- lib/Target/AArch64/AArch64InstrInfo.td
> +++ lib/Target/AArch64/AArch64InstrInfo.td
> @@ -657,6 +657,10 @@
>            (MSUBWrrr GPR32:$Rn, GPR32:$Rm, WZR)>;
>  def : Pat<(i64 (ineg (mul GPR64:$Rn, GPR64:$Rm))),
>            (MSUBXrrr GPR64:$Rn, GPR64:$Rm, XZR)>;
> +def : Pat<(i32 (mul (ineg GPR32:$Rn), GPR32:$Rm)),
> +          (MSUBWrrr GPR32:$Rn, GPR32:$Rm, WZR)>;
> +def : Pat<(i64 (mul (ineg GPR64:$Rn), GPR64:$Rm)),
> +          (MSUBXrrr GPR64:$Rn, GPR64:$Rm, XZR)>;
>  } // AddedComplexity = 7
>
>  let AddedComplexity = 5 in {
> Index: test/CodeGen/AArch64/dp-3source.ll
> ===================================================================
> --- test/CodeGen/AArch64/dp-3source.ll
> +++ test/CodeGen/AArch64/dp-3source.ll
> @@ -161,3 +161,18 @@
>  ; CHECK: umnegl {{x[0-9]+}}, {{w[0-9]+}}, {{w[0-9]+}}
>    ret i64 %res
>  }
> +
> + at a = common global i32 0, align 4
> + at b = common global i32 0, align 4
> + at c = common global i32 0, align 4
> +
> +define void @test_mneg(){
> +; CHECK-LABEL: test_mneg:
> +  %1 = load i32* @a, align 4
> +  %2 = load i32* @b, align 4
> +  %3 = sub i32 0, %1
> +  %4 = mul i32 %2, %3
> +  store i32 %4, i32* @c, align 4
> +; CHECK: mneg {{w[0-9]+}}, {{w[0-9]+}}, {{w[0-9]+}}
> +  ret void
> +}
>
> EMAIL PREFERENCES
>   http://reviews.llvm.org/settings/panel/emailpreferences/
> _______________________________________________
> llvm-commits mailing list
> llvm-commits at cs.uiuc.edu
> http://lists.cs.uiuc.edu/mailman/listinfo/llvm-commits
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.llvm.org/pipermail/llvm-commits/attachments/20141222/769b7451/attachment.html>