https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100378
Andrew Pinski <pinskia at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Last reconfirmed| |2021-05-02
Status|UNCONFIRMED |NEW
Ever confirmed|0 |1
--- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Trying 2 -> 6:
2: r94:DI=r96:DI
REG_DEAD r96:DI
6: r95:SI=sign_extend(r94:DI#0)
REG_DEAD r94:DI
Failed to match this instruction:
(set (reg:SI 95 [ s ])
(ashiftrt:SI (subreg:SI (ashift:DI (reg:DI 96)
(const_int 16 [0x10])) 0)
(const_int 16 [0x10])))
So what is happening is now combine is inserting an extra mov from x0 to a new
register 96 and when it does the combine, it does it badly not into what it was
before:
(insn 6 3 11 2 (set (reg:SI 95 [ s ])
(sign_extend:SI (subreg:HI (reg/v:DI 94 [ s ]) 0))) "t8877.c":6:37 111
{*extendhisi2_aarch64}
(expr_list:REG_DEAD (reg/v:DI 94 [ s ])
(nil)))
Confirmed. I thought there was a dup of this bug somewhere but I cannot find
it.
