------- Comment #22 from rguenth at gcc dot gnu dot org 2010-06-19 12:58
-------
(In reply to comment #21)
> This is the inline (after preprocessor)
>
> I guess the many asm meta commands confuse the heuristic. Maybe it could
> be fixed to ignore such commands.
>
> static inline void rdtsc_barrier(void)
> {
> asm volatile ("661:\n\t"
".byte 0x66,0x66,0x90\n"
"\n
662:\n"
".section .altinstructions,\"a\"\n"
" " ".balign 8" " " "\n"
" " ".quad" " " "661b\n"
" " ".quad" " " "663f\n"
" .byte " "(3*32+17)" "\n"
" .byte 662b-661b\n"
" .byte 664f-663f\n"
" .byte 0xff + (664f-663f) - (662b-661b)\n"
> ".previous\n"
".section .altinstr_replacement, \"ax\"\n"
"663:\n
\t" "mfence" "\n664:\n"
".previous" : : : "memory");
that's 16 lines alone and the call stmt removal doens't result in so
much code-saving that the code size would not increase (which is what
-Os is about - do _not_ increase code-size, not do increase it only
a little). If I read the above asm correctly it will result in a
single instruction? We could add support for annotating asm()s
with a size, though that's probably just another source of possible
errors.
The size estimation used is final.c:asm_str_count(), it is currently
not architecture specific.
It could be improved to disregard vertical space and label-only
lines (though even that is tricky to do with respect to the various
assemblers we try to support).
--
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=44129
