[x264-devel] [PATCHv2 2/6] arm: Don't use vcmp.f64 for testing for an all-zeros register

[Janne Grunau]

On 2016-11-16 10:56:14 +0200, Martin Storsjö wrote:
> On iOS, vcmp.f64 can behave as if the register was zero, if the
> register (interpreted as a f64), was a denormal number.
> 
> The vcmp.f64 (and other VFP instructions) will trap to the kernel
> (which is supposed to implement the FP operation, which it apparently
> doesn't do properly on iOS) if the value is a denormal. If this happens,
> the whole comparison ends up way more costly.
> ---
> Updated to use lr as temp register.
> ---
>  common/arm/deblock-a.S | 10 ++++++----
>  1 file changed, 6 insertions(+), 4 deletions(-)
> 
> diff --git a/common/arm/deblock-a.S b/common/arm/deblock-a.S
> index d781828..41306e2 100644
> --- a/common/arm/deblock-a.S
> +++ b/common/arm/deblock-a.S
> @@ -211,8 +211,8 @@ endfunc
>      vclt.u8         q13, q4,  q14   @ < (alpha >> 2) + 2 if_2
>      vand            q12, q7,  q6    @ if_1
>      vshrn.u16       d28, q12,  #4
> -    vcmp.f64        d28, #0
> -    vmrs            APSR_nzcv, FPSCR
> +    vmov            r2,  lr,  d28
> +    orrs            r2,  r2,  lr
>      beq             9f
>  
>      sub             sp,  sp,  #32
> @@ -325,6 +325,7 @@ endfunc
>  .endm
>  
>  function x264_deblock_v_luma_intra_neon
> +    push            {lr}
>      vld1.64         {d0, d1},  [r0,:128], r1
>      vld1.64         {d2, d3},  [r0,:128], r1
>      vld1.64         {d4, d5},  [r0,:128], r1
> @@ -348,10 +349,11 @@ function x264_deblock_v_luma_intra_neon
>      vst1.64         {d4, d5},  [r0,:128]
>  9:
>      align_pop_regs
> -    bx              lr
> +    pop             {pc}
>  endfunc
>  
>  function x264_deblock_h_luma_intra_neon
> +    push            {lr}
>      sub             r0,  r0,  #4
>      vld1.64         {d22}, [r0], r1
>      vld1.64         {d20}, [r0], r1
> @@ -397,7 +399,7 @@ function x264_deblock_h_luma_intra_neon
>      vst1.64         {d7},  [r0], r1
>  9:
>      align_pop_regs
> -    bx              lr
> +    pop             {pc}
>  endfunc
>  
>  .macro h264_loop_filter_chroma

ok

Janne