[Bug target/70008] [ARM] Reverse subtract with carry can be generated in thumb2 mode

[rearnsha at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=70008

--- Comment #1 from Richard Earnshaw <rearnsha at gcc dot gnu.org> ---
Huh?  The attribute

   (set_attr "arch" "*,a")

Should disable the second alternative for Thumb.