https://gcc.gnu.org/bugzilla/show_bug.cgi?id=82692
--- Comment #4 from Uroš Bizjak <ubizjak at gmail dot com> ---
(In reply to Segher Boessenkool from comment #3)
> The combine output you showed is _not_ succeeding though? "matched"
> just means the rtx was recog()'ed; not that it was actually replaced.
FAOD, this is the sequence before combine:
--cut here--
(insn 7 6 8 2 (set (reg:CCFPU 17 flags)
(compare:CCFPU (reg:DF 95)
(reg/v:DF 91 [ x ]))) "pr82692.c":9 52 {*cmpiudf}
(expr_list:REG_DEAD (reg:DF 95)
(expr_list:REG_EQUAL (compare:CCFPU (const_double:DF 0.0 [0x0.0p+0])
(reg/v:DF 91 [ x ]))
(nil))))
(insn 8 7 9 2 (set (reg:QI 94)
(unlt:QI (reg:CCFPU 17 flags)
(const_int 0 [0]))) "pr82692.c":9 664 {*setcc_qi}
(expr_list:REG_DEAD (reg:CCFPU 17 flags)
(nil)))
(insn 9 8 10 2 (set (reg:CCZ 17 flags)
(compare:CCZ (reg:QI 94)
(const_int 0 [0]))) "pr82692.c":9 1 {*cmpqi_ccno_1}
(expr_list:REG_DEAD (reg:QI 94)
(nil)))
(jump_insn 10 9 32 2 (set (pc)
(if_then_else (eq (reg:CCZ 17 flags)
(const_int 0 [0]))
(label_ref:DI 34)
(pc))) "pr82692.c":9 668 {*jcc}
(expr_list:REG_DEAD (reg:CCZ 17 flags)
(int_list:REG_BR_PROB 182536112 (nil)))
-> 34)
--cut here--
which is converted by combine pass to:
--cut here--
(note 7 6 8 2 NOTE_INSN_DELETED)
(note 8 7 9 2 NOTE_INSN_DELETED)
(insn 9 8 10 2 (set (reg:CCFP 17 flags)
(compare:CCFP (reg:DF 95)
(reg/v:DF 91 [ x ]))) "pr82692.c":9 50 {*cmpidf}
(expr_list:REG_DEAD (reg:DF 95)
(nil)))
(jump_insn 10 9 32 2 (set (pc)
(if_then_else (ge (reg:CCFP 17 flags)
(const_int 0 [0]))
(label_ref:DI 34)
(pc))) "pr82692.c":9 668 {*jcc}
(expr_list:REG_DEAD (reg:CCZ 17 flags)
(int_list:REG_BR_PROB 182536112 (nil)))
-> 34)
--cut here--
UNLT compare (CCFPUmode) has been converted to GE compare (CCFPmode). This is
not correct as far as traps are concerned, since UNLT doesn't trap on qNaN,
while GE does.
