[Bug inline-asm/97708] Inline asm does not use the local register asm specified with register ... asm() as input

[jakub at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=97708

--- Comment #17 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
It is all documented exactly in the place you've linked:

Then use the local variable for the asm operand and specify any constraint
letter that matches the register
^^^^^^^^^^^^^^^^^^^^^^^^^

The g constraint letter does not match that register.