[FFmpeg-cvslog] r24926 - trunk/libavcodec/x86/vp56dsp.asm

[Måns Rullgård]

Reimar D?ffinger <Reimar.Doeffinger at gmx.de> writes:

> On Thu, Aug 26, 2010 at 09:27:55PM +0100, M?ns Rullg?rd wrote:
>> Reimar D?ffinger <Reimar.Doeffinger at gmx.de> writes:
>> > But in case I was unclear, I actually managed to construct
>> > a case (of course very artificial) that shows the issue
>> > _in principle_ even with non-broken/ancient compilers.
>> >
>> > extern long j;
>> > extern char *array;
>> > int test(void)
>> > {
>> >   int i;
>> >   int s;
>> >   for (i = 0; i < j; i++)
>> >       s += array[i];
>> >   return s;
>> > }
>> > int test2(void)
>> > {
>> >   unsigned i;
>> >   int s;
>> >   for (i = 0; i < j; i++)
>> >       s += array[i];
>> >   return s;
>> > }
>> > int test3(void)
>> > {
>> >   unsigned long i;
>> >   int s;
>> >   for (i = 0; i < j; i++)
>> >       s += array[i];
>> >   return s;
>> > }
>> >
>> > Compiled on PowerPC 64 the three loops are:
>> > .L3:
>> >         lbzx 0,9,11
>> >         addi 11,11,1
>> >         add 0,0,3
>> >         extsw 3,0
>> >         bdnz .L3
>> >
>> > .L9:
>> >         lbzx 9,10,11
>> >         addi 0,11,1
>> >         rldicl 11,0,0,32
>> >         add 9,9,3
>> >         cmpd 7,11,8
>> >         extsw 3,9
>> >         blt 7,.L9
>> >
>> > .L14:
>> >         lbzx 0,9,11
>> >         addi 11,11,1
>> >         add 0,0,3
>> >         extsw 3,0
>> >         bdnz .L14
>> 
>> Yes, the compiler did badly with the 32-bit unsigned counter.  What
>> is that supposed to prove?
>
> That it seems like PPC64 also does not have a 32x32->32 addition

It doesn't have _unsigned_ 32-bit addition.

> and just like for x86 a register-size type is the easiest way
> to tell the compiler that no, we really don't care about the

No, the signed 32-bit and unsigned 64-bit gave exactly the same code.
Why do you call one of them easier?

-- 
M?ns Rullg?rd
mans at mansr.com