Exophase (exophase.delete@this.gmail.com) on August 17, 2012 9:30 am wrote:
[snip]
> That assembly coders can often make use of a lot of registers
> isn't just because they're finding more use than a compiler would (or are
> wasting registers) but because they've chosen to target critical
> functions.

Assembly programmers also tend to have more aliasing information than a compiler (of C source code).

I suspect that most code is compiled using the standard ABI even for internal functions. (In my ignorant opinion, even library functions could have more customized interfaces, publishing such as part of the major version interface of the library.)

Does gcc even support using a calling interface other than the standard ABI, even with link-time optimization?

[snip]
> On the other hand, I've encountered programs that see a
> 15-20% performance delta from x86-32 to x86-64, for instance
> the emulator cores in bsnes. AFAIK this code doesn't use a lot of pointer heavy
> data structures so it's less penalized by the increase in pointer size. However
> it does heavily use software context switches for co-routines.

Thank you for that information.