[Bug middle-end/84071] [7/8 regression] nonzero_bits1 of subreg incorrect

[ebotcazou at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=84071

--- Comment #7 from Eric Botcazou <ebotcazou at gcc dot gnu.org> ---
The problem is that reg_nonzero_bits_for_combine returns 0xffff for (reg:HI
121) when queried for SImode after:

(insn 10 7 11 2 (set (subreg:SI (reg:HI 121) 0)
        (sign_extend:SI (mem/c:HI (plus:SI (reg/f:SI 103 afp)
                    (const_int 4 [0x4])) [1 u+0 S2 A32]))) 171
{*arm_extendhisi2_v6}