https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99863
Jakub Jelinek <jakub at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
CC| |jakub at gcc dot gnu.org
--- Comment #10 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
I think the REG_DEAD note isn't the problem here.
At least, when I dump bb 2 in rest_of_handle_dse right before df_analyze call,
there is
(insn 6 3 7 2 (set (reg:CCZ 17 flags)
(compare:CCZ (reg/v:DI 203 [ y ])
(const_int 0 [0]))) "pr99863.c":14:12 8 {*cmpdi_ccno_1}
(nil))
(insn 7 6 8 2 (set (reg:QI 205)
(eq:QI (reg:CCZ 17 flags)
(const_int 0 [0]))) "pr99863.c":14:12 802 {*setcc_qi}
(expr_list:REG_DEAD (reg:CCZ 17 flags)
(nil)))
...
(insn 40 38 41 2 (set (reg:QI 220)
(ne:QI (reg:CCZ 17 flags)
(const_int 0 [0]))) "pr99863.c":15:11 802 {*setcc_qi}
(expr_list:REG_DEAD (reg:CCZ 17 flags)
(nil)))
but if I dump it right after df_analyze call, I see:
(insn 6 3 7 2 (set (reg:CCZ 17 flags)
(compare:CCZ (reg/v:DI 203 [ y ])
(const_int 0 [0]))) "pr99863.c":14:12 8 {*cmpdi_ccno_1}
(expr_list:REG_DEAD (reg/v:DI 203 [ y ])
(nil)))
(insn 7 6 8 2 (set (reg:QI 205)
(eq:QI (reg:CCZ 17 flags)
(const_int 0 [0]))) "pr99863.c":14:12 802 {*setcc_qi}
(nil))
...
(insn 40 38 41 2 (set (reg:QI 220)
(ne:QI (reg:CCZ 17 flags)
(const_int 0 [0]))) "pr99863.c":15:11 802 {*setcc_qi}
(expr_list:REG_DEAD (reg:CCZ 17 flags)
(nil)))
i.e. the problematic REG_DEAD note is gone and I think at this point DF knows
that CC is live there.
But replace_read has code to check for live hard regs, see
note_stores (this_insn, look_for_hardregs, regs_set);
in there etc.
