[FFmpeg-devel] [PATCH] Extra build options for ALS (and others)

[Thilo Borgmann]

M?ns Rullg?rd schrieb:
> Thilo Borgmann <thilo.borgmann at googlemail.com> writes:
> 
>> Hi,
>>
>> recently the need for an extra build option for the ALS decoder arose.
> 
> Is it impossible to achieve the desired outcome with some combination
> of always_inline, noinline, and flatten attributes?

No. See [PATCH] Split reading and decoding of blocks in ALS.

Although I've managed to have the functions from the alsdec.c inlined
manually according to the grep'ed output of the assembler code, it seems
like it is not enough to manually inline functions from within that .c
file only using these technique.

> 
>> It seems like we are lacking a possibility for this or I have not found
>> it... hints, discussion or better approaches welcome.
>>
>> The applied patch extends the implicit build rule for the object file,
>> allowing to define extra compiler/linker/etc. options per file.
> 
> We've never had a need for this before, so there is no clean way of
> doing it.  I'll have to think about how to do it properly, but first
> answer the question above.

In some way there is something like that already. In libavcodec/Makefile
there is a block which is also extending the implicit rule that way:

ifdef CONFIG_MPEGAUDIO_HP
$(SUBDIR)mpegaudio_tablegen$(HOSTEXESUF): HOSTCFLAGS += -DFRAC_BITS=23
$(SUBDIR)mpegaudio_tablegen.ho: CPPFLAGS += -DFRAC_BITS=23
else
$(SUBDIR)mpegaudio_tablegen$(HOSTEXESUF): HOSTCFLAGS += -DFRAC_BITS=15
$(SUBDIR)mpegaudio_tablegen.ho: CPPFLAGS += -DFRAC_BITS=15
endif

That way is also suggested by the GNU make documentation:
"... You would want to write a rule for foo.o with no command lines if
you need to specify additional prerequisites, such as header files, that
the implicit rule cannot supply."
from:
http://www.gnu.org/software/make/manual/html_node/Using-Implicit.html#Using-Implicit

> 
>> Regards,
>> Thilo
>> Index: libavcodec/Makefile
>> ===================================================================
>> --- libavcodec/Makefile	(Revision 20627)
>> +++ libavcodec/Makefile	(Arbeitskopie)
>> @@ -%ld,%ld +%ld,%ld @@
>>  SKIPHEADERS-$(CONFIG_VDPAU)            += vdpau.h
>>  SKIPHEADERS-$(CONFIG_XVMC)             += xvmc.h
>>
>> +# extra build options
>> +$(SUBDIR)alsdec.o: CFLAGS += -finline-limit=4096
> 
> This will break with many non-gcc compilers.

I think it might be feasible to adopt this to the compiler in use, not?
How many compilers do we care for in such a sense?
We might even check for "-finline-limit" in the configure script to use
it at least with gcc or accept 10% slowdown on "unsupported" compilers...

-Thilo