Messages in this thread | | | Date | Fri, 9 Apr 2021 08:03:42 -0500 | From | Segher Boessenkool <> | Subject | Re: static_branch/jump_label vs branch merging |
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On Thu, Apr 08, 2021 at 06:52:18PM +0200, Peter Zijlstra wrote: > Is there *any* way in which we can have the compiler recognise that the > asm_goto only depends on its arguments and have it merge the branches > itself? > > I do realize that asm-goto being volatile this is a fairly huge ask, but > I figured I should at least raise the issue, if only to raise awareness.
"volatile" should not be an impediment to this at all, volatile means there is an unspecified side effect, nothing more, nothing less. But yes this currently does not work with GCC:
void f(int x) { if (x) asm volatile("ojee %0" :: "r"(x)); else asm volatile("ojee %0" :: "r"(x)); }
or even
static inline void h(int x) { asm volatile("ojee %0" :: "r"(x)); }
void f1(int x) { if (x) h(x); else h(x); }
which both emit silly machine code.
Segher
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