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swresample/resample: Properly empty MMX state 

There is a x86-32 MMXEXT implementation for resampling
planar 16bit data. multiple_resample() therefore calls
emms_c() if it thinks that this needed. And this is bad:

1. It is a maintenance nightmare because changes to the
x86 resample DSP code would necessitate changes to the check
whether to call emms_c().
2. The return value of av_get_cpu_flags() does not tell
whether the MMX DSP functions are in use, as they could
have been overridden by av_force_cpu_flags().
3. The MMX DSP functions will never be overridden in case of
an x86-32 build with --disable-sse2. In this scenario lots of
resampling tests (like swr-resample_exact_lin_async-s16p-8000-48000)
fail because the cpuflags indicate that SSE2 is available
(presuming that the test is run on a CPU with SSE2).
4. The check includes a call to av_get_cpu_flags(). This is not
optimized away for arches other than x86-32.
5. The check takes about as much time as emms_c() itself,
making it pointless.

This commit therefore removes the check and calls emms_c()
unconditionally (it is a no-op for non-x86).

Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@outlook.com>
This commit is contained in:
Andreas Rheinhardt 2022-06-11 23:25:14 +02:00
parent ff07492cd8
commit 55fc2c5a89
1 changed files with 1 additions and 5 deletions
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6
libswresample/resample.c
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@ -452,9 +452,6 @@ static int set_compensation(ResampleContext *c, int sample_delta, int compensati
static int multiple_resample(ResampleContext *c, AudioData *dst, int dst_size, AudioData *src, int src_size, int *consumed){
int i;
int av_unused mm_flags = av_get_cpu_flags();
int need_emms = c->format == AV_SAMPLE_FMT_S16P && ARCH_X86_32 &&
(mm_flags & (AV_CPU_FLAG_MMX2 | AV_CPU_FLAG_SSE2)) == AV_CPU_FLAG_MMX2;
int64_t max_src_size = (INT64_MAX/2 / c->phase_count) / c->src_incr;
if (c->compensation_distance)
@ -500,8 +497,7 @@ static int multiple_resample(ResampleContext *c, AudioData *dst, int dst_size, A
}
}
if(need_emms)
emms_c();
emms_c();
if (c->compensation_distance) {
c->compensation_distance -= dst_size;