https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94850
Richard Biener <rguenth at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
CC| |segher at gcc dot gnu.org
Component|rtl-optimization |target
Status|UNCONFIRMED |NEW
Last reconfirmed| |2020-04-29
Ever confirmed|0 |1
--- Comment #2 from Richard Biener <rguenth at gcc dot gnu.org> ---
Probably a missing combine helper or a non-canonical pattern. It looks like
(define_insn "x86_64_shrd"
[(set (match_operand:DI 0 "nonimmediate_operand" "+r*m")
(ior:DI (lshiftrt:DI (match_dup 0)
(match_operand:QI 2 "nonmemory_operand" "Jc"))
(ashift:DI (match_operand:DI 1 "register_operand" "r")
(minus:QI (const_int 64) (match_dup 2)))))
(clobber (reg:CC FLAGS_REG))]
it tries for example
Failed to match this instruction:
(parallel [
(set (reg:DI 93)
(ior:DI (ashift:DI (reg:DI 102)
(minus:QI (subreg:QI (reg:SI 95) 0)
(subreg:QI (reg/v:SI 92 [ x ]) 0)))
(reg:DI 97)))
(clobber (reg:CC 17 flags))
])
or
Failed to match this instruction:
(parallel [
(set (reg:DI 93)
(ior:DI (lshiftrt:DI (reg:DI 103)
(subreg:QI (reg/v:SI 92 [ x ]) 0))
(ashift:DI (reg:DI 102)
(subreg:QI (reg:SI 94) 0))))
(clobber (reg:CC 17 flags))
])
but the insn with basically four ops is likely too complex for combines
little mind. Ah here:
(set (reg:DI 93)
(ior:DI (lshiftrt:DI (reg:DI 103)
(subreg:QI (reg/v:SI 92 [ x ]) 0))
(ashift:DI (reg:DI 102)
(minus:QI (subreg:QI (reg:SI 95) 0)
(subreg:QI (reg/v:SI 92 [ x ]) 0)))))
but no (const 64) which is still separate here:
(insn 11 8 12 2 (set (reg:SI 95)
(const_int 64 [0x40])) "y.c":8:31 67 {*movsi_internal}
(nil))
not sure if combine could help out here by propagating constants?
