[FFmpeg-devel] [PATCH 06/10] avfilter/avgblur_vulkan: call av_vkfmt_from_pixfmt only one time

[Wu, Jianhua]

Andreas Rheinhardt wrote:
> 
> Wu Jianhua:
> > There is a loop in av_vkfmt_from_pixfmt. And, even though some
> > compilers will optimize it when the optimization option is on, to
> > consider more situations, just call the function only one time here.
> >
> > Signed-off-by: Wu Jianhua <jianhua.wu at intel.com>
> > ---
> 
> What compilers optimize this? And how? After all, this function is not marked
> as const.

When there is some same operations in the codes the compiler will help the
developer to reuse the same result when the optimization is on, like -O3 options
in GCC. However the -O# was not used, the function would be called again and
again. And I check the assembly codes, it did. If someone compiled with the
optimizations, this commit didn't changed anything in assembly codes. But it
did help when there is no optimizations compiling.

I am more prefer this way to just call the function only one time literally. I am
not sure if anybody like this so I put it on the back of the patch set. And I check
this function and it did return a const VkFormat * that supposed to
mean we should not change the content.

Thanks,
Jianhua

> 
> >  libavfilter/vf_avgblur_vulkan.c | 10 +++++++---
> >  1 file changed, 7 insertions(+), 3 deletions(-)
> >
> > diff --git a/libavfilter/vf_avgblur_vulkan.c
> > b/libavfilter/vf_avgblur_vulkan.c index 243e932f35..080a8b1b63 100644
> > --- a/libavfilter/vf_avgblur_vulkan.c
> > +++ b/libavfilter/vf_avgblur_vulkan.c
> > @@ -210,6 +210,10 @@ static int process_frames(AVFilterContext *avctx,
> AVFrame *out_f, AVFrame *tmp_f
> >      AVVkFrame *in = (AVVkFrame *)in_f->data[0];
> >      AVVkFrame *tmp = (AVVkFrame *)tmp_f->data[0];
> >      AVVkFrame *out = (AVVkFrame *)out_f->data[0];
> > +
> > +    const VkFormat *input_formats = av_vkfmt_from_pixfmt(s-
> >vkctx.input_format);
> > +    const VkFormat *output_formats =
> > + av_vkfmt_from_pixfmt(s->vkctx.output_format);
> > +
> >      int planes = av_pix_fmt_count_planes(s->vkctx.output_format);
> >
> >      /* Update descriptors and init the exec context */ @@ -219,17
> > +223,17 @@ static int process_frames(AVFilterContext *avctx, AVFrame
> *out_f, AVFrame *tmp_f
> >      for (int i = 0; i < planes; i++) {
> >          RET(ff_vk_create_imageview(avctx, s->exec, &s-
> >input_images[i].imageView,
> >                                     in->img[i],
> > -                                   av_vkfmt_from_pixfmt(s->vkctx.input_format)[i],
> > +                                   input_formats[i],
> >                                     ff_comp_identity_map));
> >
> >          RET(ff_vk_create_imageview(avctx, s->exec, &s-
> >tmp_images[i].imageView,
> >                                     tmp->img[i],
> > -                                   av_vkfmt_from_pixfmt(s->vkctx.output_format)[i],
> > +                                   output_formats[i],
> >                                     ff_comp_identity_map));
> >
> >          RET(ff_vk_create_imageview(avctx, s->exec, &s-
> >output_images[i].imageView,
> >                                     out->img[i],
> > -                                   av_vkfmt_from_pixfmt(s->vkctx.output_format)[i],
> > +                                   output_formats[i],
> >                                     ff_comp_identity_map));
> >
> >          s->input_images[i].imageLayout =
> > VK_IMAGE_LAYOUT_SHADER_READ_ONLY_OPTIMAL;
> >
> 
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