https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96176
Jakub Jelinek <jakub at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
CC| |jakub at gcc dot gnu.org
--- Comment #1 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
The zero extension is initially there because the builtin has the arguments
promoted. Normally combine would fix this up:
(insn 10 7 11 2 (set (reg:SI 88 [ new_val ])
(zero_extend:SI (subreg:QI (reg:SI 93) 0))) "pr96176.c":3:5 143
{*zero_extendqisi2}
(expr_list:REG_DEAD (reg:SI 93)
(nil)))
(insn 11 10 0 2 (parallel [
(set (reg:QI 89)
(unspec_volatile:QI [
(mem/v:QI (reg/v/f:DI 83 [ addr ]) [-1 S1 A8])
(reg/v:QI 84 [ old_val ])
(subreg:QI (reg:SI 88 [ new_val ]) 0)
(const_int 0 [0])
] UNSPECV_CMPXCHG))
(set (mem/v:QI (reg/v/f:DI 83 [ addr ]) [-1 S1 A8])
(unspec_volatile:QI [
(const_int 0 [0])
] UNSPECV_CMPXCHG))
(set (reg:CCZ 17 flags)
(unspec_volatile:CCZ [
(const_int 0 [0])
] UNSPECV_CMPXCHG))
]) "pr96176.c":3:5 6114 {atomic_compare_and_swapqi_1}
(expr_list:REG_DEAD (reg:SI 88 [ new_val ])
(expr_list:REG_DEAD (reg/v:QI 84 [ old_val ])
(expr_list:REG_DEAD (reg/v/f:DI 83 [ addr ])
(expr_list:REG_UNUSED (reg:QI 89)
(expr_list:REG_UNUSED (reg:CCZ 17 flags)
(nil)))))))
but it fails:
Trying 10 -> 11:
10: r88:SI=zero_extend(r93:SI#0)
REG_DEAD r93:SI
11: {r89:QI=unspec/v[[r83:DI],r84:QI,r88:SI#0,0] 90;[r83:DI]=unspec/v[0]
90;flags:CCZ=unspec/v[0] 90;}
REG_DEAD r88:SI
REG_DEAD r84:QI
REG_DEAD r83:DI
REG_UNUSED r89:QI
REG_UNUSED flags:CCZ
Failed to match this instruction:
(parallel [
(set (reg:QI 89)
(unspec_volatile:QI [
(mem/v:QI (reg/v/f:DI 83 [ addr ]) [-1 S1 A8])
(reg/v:QI 84 [ old_val ])
(subreg:QI (reg:SI 93) 0)
(const_int 0 [0])
] UNSPECV_CMPXCHG))
(set (mem/v:QI (reg/v/f:DI 83 [ addr ]) [-1 S1 A8])
(unspec_volatile:QI [
(const_int 0 [0])
] UNSPECV_CMPXCHG))
(set (reg:CCZ 17 flags)
(unspec_volatile:CCZ [
(const_int 0 [0])
] UNSPECV_CMPXCHG))
])
due to the MEM_VOLATILE_P and volatile_ok not being true during combine.
But we can do something about it during expansion.
