[FFmpeg-devel] [Ffmpeg-devel] [PATCH] detect support for 10 operands in configure

Loren Merritt lorenm
Thu Feb 12 20:13:24 CET 2009

On Thu, 12 Feb 2009, Diego Biurrun wrote:
> On Thu, Feb 12, 2009 at 03:49:33AM +0000, Loren Merritt wrote:
>> On Wed, 11 Feb 2009, Diego Biurrun wrote:
>>> Loren, this reminds me: I think you wrote some Vorbis (?) optimization
>>> that broke on gcc 2.95 and which you eventually reverted.  I think the
>>> reason was this problem.  Maybe you can restore it now.
>> There's r5964, but that was removed with my fft overhaul.
> Umm, the code is still there.  What exactly do you mean?

Oops, I saw one of the asm blocks replaced and didn't notice the other 
However, it is not a question of HAVE_TEN_OPERANDS. That asm used only 5
operands, and the problem was that gcc<4 failed to find 5 registers for 
them. (Because it doesn't know how to spill ebx or ebp, nor does it know 
how to spill one operand to free up a temp register to compute another.)

I could put fft_3dn under (HAVE_7REGS || GCC4).
I could write the loop part in inline asm, and put fft_3dn under HAVE_7REGS.
I could force-disable frame-pointer and pic on fft_3dn.
I could move the loop to yasm, which isn't all that different insofar as 
it also ignores frame-pointer and pic.
Or I could laugh at x86 for having too few registers, and ignore it.

--Loren Merritt

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