https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108826
Andrew Pinski <pinskia at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Keywords| |missed-optimization
Last reconfirmed| |2023-02-16
Status|UNCONFIRMED |NEW
Ever confirmed|0 |1
--- Comment #4 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Trying 13, 14, 15 -> 16:
13: r84:DI=r83:DI+0xc8
REG_DEAD r83:DI
14: r85:DI=r84:DI<<0x2
REG_DEAD r84:DI
15: r86:DI=r72:DI+r85:DI
REG_DEAD r85:DI
16: r76:DI=sign_extend([r86:DI])
REG_DEAD r86:DI
Failed to match this instruction:
(set (reg:DI 76 [ _5 ])
(sign_extend:DI (mem:SI (plus:DI (plus:DI (mult:DI (reg:DI 83)
(const_int 4 [0x4]))
(reg/f:DI 72 [ _nettle_aes_decrypt_T.0_1 ]))
(const_int 800 [0x320])) [2
_nettle_aes_decrypt_T.0_1->table[2][_4]+0 S4 A32])))
Failed to match this instruction:
(set (reg/f:DI 86)
(plus:DI (ashift:DI (reg:DI 83)
(const_int 2 [0x2]))
(reg/f:DI 72 [ _nettle_aes_decrypt_T.0_1 ])))
So combine does know how to combine all 4 instructions and produce the plus 800
there. But then it goes and splits it up and fails. I can't remember if there
is 4->3 splitting or just 4->2 .
