[Bug inline-asm/39847] 16 symbolic register names generates error: more than 30 operands in 'asm'

[d at teklibre dot com]

------- Comment #9 from d at teklibre dot com  2009-04-22 17:24 -------
Pinskia:

It is going to take me a long time to address these issues piecemeal, so...

0) I will build gcc-4.4 and try that. I will also make the 1 line patch to it
to try increasing the number of asm params, and try that. I would prefer that
someone with more guts inside the guts of gcc do the latter, I fear I would
rapidly end up over my head. Is it a magic number or just a stupid default?

re 1) I am using -mtune=core2 -O3 which is correct. 

I note, that in looking at the generated code today, without that and with -O2,
using the non-sse version (just doubles), -O2 generates the following code
sequence for    

left [0] += icoeff * filter->buffer [data_index];
left [1] += icoeff * filter->buffer [data_index+1];

 - where left[0] and icoeff are doubles, filter->buffer[data_index] is a float

movss  (%r11),%xmm0
cvtps2pd %xmm0,%xmm0; cvtss2sd would be more correct and faster on most x86_64
arches prior to the k10 and core2.
... mult and add elided, second line elided ... 

(-O3 -mtune will do a cvtss2sd (%r9), %xmm0 which is better)

converting this into the SSE2 equivalent can't be expressed in the intrinsics
(requires an explicit, separate, load & cast). Doing it as inline assembly
ended up generating extra leas, would not get scheduled well, and stuff like
that. 

... like I said, it will take me a while to discuss this piecemeal and going to
0) is the right thing. 


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=39847