[x264-devel] Re: problem with X264 over Itanium - IA64

[Henri-Pierre Charles]

Hello,

On 4/20/06, Guillaume POIRIER <poirierg at gmail.com> wrote:
> What kind of optimizations do you have in mind?

My main focus are low level optimization, ILP, but we are also interested
on multithreading and memory access.

> I suppose GCC has some pragmas to force aligment by using padding...

Well, not really. It has -Wpadded which give hints like :

./common/common.h:215: warning: padding struct size to alignment boundary
./common/common.h:262: warning: padding struct to align 'nal'
./common/common.h:264: warning: padding struct to align 'p_bitstream'
./common/common.h:328: warning: padding struct size to alignment boundary
./common/common.h:449: warning: padding struct size to alignment boundary
./common/common.h:404: warning: padding struct to align 'type'
./common/common.h:449: warning: padding struct to align 'pic'
./common/common.h:493: warning: padding struct size to alignment boundary
./common/common.h:534: warning: padding struct to align 'i_sqe_global'
./common/common.h:283: warning: padding struct to align 'sps'
./common/common.h:300: warning: padding struct to align 'sh'
./common/common.h:338: warning: padding struct to align 'fref0'
./common/common.h:340: warning: padding struct to align 'fref1'
./common/common.h:573: warning: padding struct size to alignment boundary

But without actual knowledge on the code, it's a little bit difficult.

On what documentation is based the x264 encoder (if any :-) ?

> Among the platforms supported by x264 is the PPC64, which, like most
> RISC cpu (like Sparc), has strong aligment restrictions, so I'm
> surprised that you experience unaligned access problems and PPC64
> users don't (but maybe it's because no userland app runs in 64bits
> mode on PPC64, like on early Sparc64).
> x86-64 is a special case as all aligment is allowed.

Yes, but maybe, on the ppc, the alignment problems are done at the
altivec level ? (I am unable to compile x264 on ppc/macos without
-faltivec, is it possible ?)


H-P Charles

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