[Bug c/90181] Feature request: provide a way to explicitly select specific named registers in constraints

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=90181

--- Comment #8 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
I thought there was another bug which was asking for something similar that I
did not link here yet.  It had a reference to a syntax something like {"r1"}. 
But I can't find it right now.