Messages in this thread | | | Subject | Re: [PATCH 7/8] i386: bitops: Kill needless usage of __asm__ __volatile__ | From | Nicholas Miell <> | Date | Mon, 23 Jul 2007 14:48:28 -0700 |
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On Mon, 2007-07-23 at 23:30 +0200, Andi Kleen wrote: > > gcc also tries to count the number of instructions, to guess how large in > > bytes the asm block is, as it could make a difference for near vs short > > jumps, etc. > > Are you sure? I doubt it. It would need a full asm parser to do this > properly and then even it could be wrong > (e.g. when the sections are switched like Linux does extensively) > > gcc doesn't have such a parser. > > Also on x86 gcc doesn't need to care about long/short anyways because > the assembler takes care of this and the other instructions who cared > about this (loop) isn't generated anymore. > > You're probably confusing it with some other compiler, who sometimes > do this. e.g. the Microsoft inline asm syntax requires assembler parsing > in the compiler. > > > I wonder it it also affects the instruction count the inline heuristics > > use? > > AFAIK it counts like one operand. > > -Andi
GCC counts newlines and semicolons and uses that number as the likely instruction count.
See asm_insn_count() in gcc/gcc/final.c
-- Nicholas Miell <nmiell@comcast.net>
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