[llvm] r286233 - [VectorLegalizer] Expansion of CTLZ using CTPOP when possible

[Friedman, Eli via llvm-commits]

On 11/8/2016 6:10 AM, Simon Pilgrim via llvm-commits wrote:
> Author: rksimon
> Date: Tue Nov  8 08:10:28 2016
> New Revision: 286233
>
> URL: http://llvm.org/viewvc/llvm-project?rev=286233&view=rev
> Log:
> [VectorLegalizer] Expansion of CTLZ using CTPOP when possible
>
> This patch avoids scalarization of CTLZ by instead expanding to use CTPOP (ref: "Hacker's Delight") when the necessary operations are available.
>
> This also adds the necessary cost models for X86 SSE2 targets (the main beneficiary) to ensure vectorization only happens when its useful.
>
> Differential Revision: https://reviews.llvm.org/D25910
>
> Modified: llvm/trunk/test/CodeGen/X86/vec_ctbits.ll
> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/CodeGen/X86/vec_ctbits.ll?rev=286233&r1=286232&r2=286233&view=diff
> ==============================================================================
> --- llvm/trunk/test/CodeGen/X86/vec_ctbits.ll (original)
> +++ llvm/trunk/test/CodeGen/X86/vec_ctbits.ll Tue Nov  8 08:10:28 2016
> @@ -36,17 +36,42 @@ define <2 x i64> @footz(<2 x i64> %a) no
>   define <2 x i64> @foolz(<2 x i64> %a) nounwind {
>   ; CHECK-LABEL: foolz:
>   ; CHECK:       # BB#0:
> -; CHECK-NEXT:    movd %xmm0, %rax
> -; CHECK-NEXT:    bsrq %rax, %rax
> -; CHECK-NEXT:    xorq $63, %rax
> -; CHECK-NEXT:    movd %rax, %xmm1
> -; CHECK-NEXT:    pshufd {{.*#+}} xmm0 = xmm0[2,3,0,1]
> -; CHECK-NEXT:    movd %xmm0, %rax
> -; CHECK-NEXT:    bsrq %rax, %rax
> -; CHECK-NEXT:    xorq $63, %rax
> -; CHECK-NEXT:    movd %rax, %xmm0
> -; CHECK-NEXT:    punpcklqdq {{.*#+}} xmm1 = xmm1[0],xmm0[0]
> +; CHECK-NEXT:    movdqa %xmm0, %xmm1
> +; CHECK-NEXT:    psrlq $1, %xmm1
> +; CHECK-NEXT:    por %xmm0, %xmm1
> +; CHECK-NEXT:    movdqa %xmm1, %xmm0
> +; CHECK-NEXT:    psrlq $2, %xmm0
> +; CHECK-NEXT:    por %xmm1, %xmm0
> +; CHECK-NEXT:    movdqa %xmm0, %xmm1
> +; CHECK-NEXT:    psrlq $4, %xmm1
> +; CHECK-NEXT:    por %xmm0, %xmm1
> +; CHECK-NEXT:    movdqa %xmm1, %xmm0
> +; CHECK-NEXT:    psrlq $8, %xmm0
> +; CHECK-NEXT:    por %xmm1, %xmm0
> +; CHECK-NEXT:    movdqa %xmm0, %xmm1
> +; CHECK-NEXT:    psrlq $16, %xmm1
> +; CHECK-NEXT:    por %xmm0, %xmm1
>   ; CHECK-NEXT:    movdqa %xmm1, %xmm0
> +; CHECK-NEXT:    psrlq $32, %xmm0
> +; CHECK-NEXT:    por %xmm1, %xmm0
> +; CHECK-NEXT:    pcmpeqd %xmm1, %xmm1
> +; CHECK-NEXT:    pxor %xmm0, %xmm1
> +; CHECK-NEXT:    movdqa %xmm1, %xmm0
> +; CHECK-NEXT:    psrlq $1, %xmm0
> +; CHECK-NEXT:    pand {{.*}}(%rip), %xmm0
> +; CHECK-NEXT:    psubq %xmm0, %xmm1
> +; CHECK-NEXT:    movdqa {{.*#+}} xmm0 = [3689348814741910323,3689348814741910323]
> +; CHECK-NEXT:    movdqa %xmm1, %xmm2
> +; CHECK-NEXT:    pand %xmm0, %xmm2
> +; CHECK-NEXT:    psrlq $2, %xmm1
> +; CHECK-NEXT:    pand %xmm0, %xmm1
> +; CHECK-NEXT:    paddq %xmm2, %xmm1
> +; CHECK-NEXT:    movdqa %xmm1, %xmm2
> +; CHECK-NEXT:    psrlq $4, %xmm2
> +; CHECK-NEXT:    paddq %xmm1, %xmm2
> +; CHECK-NEXT:    pand {{.*}}(%rip), %xmm2
> +; CHECK-NEXT:    pxor %xmm0, %xmm0
> +; CHECK-NEXT:    psadbw %xmm2, %xmm0
>   ; CHECK-NEXT:    retq

This is going from 10 instructions to 35; it doesn't seem like an 
improvement.

-Eli

-- 
Employee of Qualcomm Innovation Center, Inc.
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