[FFmpeg-devel] [PATCH 07/12] mips/aacdec: remove uses of mips32r2 specific ext instructions
Nedeljko.Babic at imgtec.com
Wed Mar 4 11:07:33 CET 2015
>> >Removing these removes the dependency of this code on mips32r2 which would
>> >allow it to be used on processors which have FPU instructions, but not r2
>> >instructions (like the mips64el debian port for instance).
>> I would be more comfortable if there were two instances of this code: one for
>> mips32r2 and one for mips32 so advantages of using mips32r2 instructions
>> (however small here) are left intact.
>> On the other hand, since this doesn't change much number of instructions used
>> (adding at maximum around 100 instructions overall if I am not mistaking) I
>> am ok with this.
>Well I can't see how 'ext' can ever be faster than 'and' (it does more
>work) so most of these should be no slower anyway. For VMUL4S my version
>has 2 extra instructions in it so it could be a bit slower. Does this
>#if seem ok?
I never said that 'ext' is faster than 'and'.
This code was written so that the pipeline stalls are eliminated (or reduced to a minimum).
Taking this in consideration it is not important which instruction is faster overall.
Maybe I was not clear, but I said that I am ok with your first patch.
It is true that you only have 2 extra instructions in VMUL4S and I don't have a problem with that.
Regarding your question about #if, this is even better than original patch from my point of view,
but you should use HAVE_MIPS32R2 in this case.
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