[issue4753] Faster opcode dispatch on gcc

[Paolo 'Blaisorblade' Giarrusso]

Paolo 'Blaisorblade' Giarrusso <p.giarrusso at gmail.com> added the comment:

> Same for CPU-specific tuning: I don't think we want to ship Python
with compiler flags which depend on the particular CPU being used.

I wasn't suggesting this - but since different CPUs have different
optimization rules, something like "oh, 20% performance slowdown on
PowerPC" or "on P4" is important to know (and yeah, configure options
are a good solution).

Which is the barrier for platform-specific tricks, as long as the code
is still portable? I'd like to experiment with __builtin_expect and with
manual alignment (through 'asm volatile(".p2align 4")' on x86/x86_64
with GAS - PPC might need a different alignment probably).

All hidden through macros to make it disappear on unsupported platforms,
without any configure option for them (there shouldn't be the need for
that).

> I doubt many people compile Python with icc, honestly.

Yep :-(. <rant>Why don't distributors do it?</rant> (First culprit might
be license/compatibility problems I guess, but the speedup would be
worth the time to fix the troubles IMHO).

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