[FFmpeg-devel] [PATCH] avutil: disable arch specific intmath routines if optimizations are disabled

[Hendrik Leppkes]

On Tue, Feb 16, 2016 at 4:00 PM, Yu Xiaolei <dreifachstein at gmail.com> wrote:
> On Tue, Feb 16, 2016 at 9:01 PM, Michael Niedermayer <michael at niedermayer.cc
>> wrote:
>
>> On Tue, Feb 16, 2016 at 02:40:10PM +0800, Xiaolei Yu wrote:
>> > Current intmath routines for arm require inter-procedure constant
>> propagation
>> > and fail to compile when optimizations are disabled.
>> > ---
>> >  configure           | 1 +
>> >  libavutil/intmath.h | 2 ++
>> >  2 files changed, 3 insertions(+)
>>
>> on arm without opts and this patch i get
>> src/libavcodec/arm/aac.h: In function ‘VMUL4S’:
>> src/libavcodec/arm/aac.h:102:5: error: can't find a register in class
>> ‘LO_REGS’ while reloading ‘asm’
>> src/libavcodec/arm/aac.h:102:5: error: ‘asm’ operand has impossible
>> constraints
>> make: *** [libavcodec/aacdec.o] Error 1
>>
>>
> This error seems unrelated to the patch, but I am not sure as I am only
> building some selected codecs.
> Can you build again without the patch?
>
> Without the patch I get:
> In file included from src/libavutil/intmath.h:30:0,
>                  from src/libavutil/common.h:106,
>                  from src/libavutil/avutil.h:288,
>                  from src/libavutil/samplefmt.h:24,
>                  from src/libavcodec/avcodec.h:31,
>                  from src/libavcodec/internal.h:33,
>                  from src/libavcodec/h264_direct.c:28:
> src/libavutil/arm/intmath.h: In function 'get_scale_factor':
> src/libavutil/arm/intmath.h:69:5: warning: asm operand 2 probably doesn't
> match constraints
>      __asm__ ("ssat %0, %2, %1" : "=r"(x) : "r"(a), "i"(p+1));
>      ^
> src/libavutil/arm/intmath.h:69:5: error: impossible constraint in 'asm'
>
> on x86 build passes with and without the patch here
>> with what compiler is this needed ?
>>
>>
> Yes, x86 builds fine without this patch. But the underlying problem is not
> arch specific and may be encountered in other inline asm. I think current
> patch is more consistent if we consider these routines as manual
> optimizations.
>

--disable-optimization is just meant to disable compiler optimizations
so that debugging is easier, its not meant to disable any kind of
hand-written ASM, this may even be a target of the debugging in some
cases.
If one wanted to get rid of all ASM, there are other options for that.

- Hendrik