https://gcc.gnu.org/bugzilla/show_bug.cgi?id=120284
Jakub Jelinek <jakub at gcc dot gnu.org> changed:
What |Removed |Added
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CC| |jakub at gcc dot gnu.org
--- Comment #6 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
(In reply to Huiba Li from comment #3)
> And actually, I don't need the input register to be the same as the output
> register. All I need here is making x both input and output to the assembly.
> So in theory, should it also be OK to write ```asm volatile("" : "=r"(x) :
> "r"(x))```?
In that case you need to use "movq %1, %0" in the asm to actually copy the
value, because the constraints don't guarantee it is the same register, it can
very well be a different one.
By using "0" or "+r" you require that the input and output use the same
register and so don't need to copy anything.
