https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109414
Jeffrey A. Law <law at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Resolution|--- |FIXED
Status|UNCONFIRMED |RESOLVED
CC| |law at gcc dot gnu.org
--- Comment #5 from Jeffrey A. Law <law at gcc dot gnu.org> ---
These code generation inefficiences have been fixed. I didn't bisect, but I
would hazard a guess it was Jivan's work on exposing the widening nature of the
32 bit operations and extracting the result via a promoted subreg.
ie, for the first example we now generate this during expand:
(insn 2 5 3 2 (set (reg/v:DI 136 [ x ])
(reg:DI 10 a0 [ x ])) "j.c":1:26 -1
(nil))
(insn 3 2 4 2 (set (reg/v:DI 137 [ n ])
(reg:DI 11 a1 [ n ])) "j.c":1:26 -1
(nil))
(note 4 3 7 2 NOTE_INSN_FUNCTION_BEG)
(insn 7 4 8 2 (set (reg:DI 140)
(sign_extend:DI (plus:SI (subreg/s/u:SI (reg/v:DI 136 [ x ]) 0)
(const_int 1 [0x1])))) "j.c":2:12 -1
(nil))
(insn 8 7 9 2 (set (reg:SI 139)
(subreg/s/u:SI (reg:DI 140) 0)) "j.c":2:12 -1
(expr_list:REG_EQUAL (plus:SI (subreg/s/u:SI (reg/v:DI 136 [ x ]) 0)
(const_int 1 [0x1]))
(nil)))
(insn 9 8 10 2 (set (reg:DI 141)
(xor:DI (reg/v:DI 137 [ n ])
(subreg:DI (reg:SI 139) 0))) "j.c":2:17 -1
(nil))
(insn 10 9 11 2 (set (reg:DI 142)
(sign_extend:DI (subreg:SI (reg:DI 141) 0))) "j.c":2:17 discrim 1 -1
(nil))
(insn 11 10 15 2 (set (reg:DI 135 [ <retval> ])
(reg:DI 142)) "j.c":2:17 discrim 1 -1
(nil))
(insn 15 11 16 2 (set (reg/i:DI 10 a0)
(reg:DI 135 [ <retval> ])) "j.c":3:1 -1
(nil))
(insn 16 15 0 2 (use (reg/i:DI 10 a0)) "j.c":3:1 -1
(nil))
Which is much easier for combine to analyze and prove the trailing sign
extension is unnecessary.
