https://gcc.gnu.org/bugzilla/show_bug.cgi?id=86763
Uroš Bizjak <ubizjak at gmail dot com> changed:
What |Removed |Added
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CC|uros at gcc dot gnu.org |ubizjak at gmail dot com
Component|target |rtl-optimization
--- Comment #5 from Uroš Bizjak <ubizjak at gmail dot com> ---
(In reply to Richard Biener from comment #3)
> see how the compare is moved very far away from the branch possibly across
> flag clobbering insns (rep movsq?). Target sounds good.
Scheduler (sched2) pass is moving the compare:
(insn 21 17 22 2 (set (reg:CCZ 17 flags)
(compare:CCZ (mem/c:DI (plus:DI (reg/f:DI 7 sp)
(const_int 8 [0x8])) [1 MEM[(struct Msg &)&t].id+0 S8 A64])
(const_int 1001 [0x3e9]))) "t4.cpp":32 12 {*cmpdi_1}
(nil))
in front of rep movsd:
(insn 11 10 12 2 (parallel [
(set (reg:DI 2 cx [92])
(const_int 0 [0]))
(set (reg/f:DI 5 di [90])
(plus:DI (ashift:DI (reg:DI 2 cx [92])
(const_int 3 [0x3]))
(reg/f:DI 5 di [90])))
(set (reg/f:DI 4 si [91])
(plus:DI (ashift:DI (reg:DI 2 cx [92])
(const_int 3 [0x3]))
(reg/f:DI 4 si [91])))
(set (mem/c:BLK (reg/f:DI 5 di [90]) [7 MEM[(struct T *)&t]+0 S232
A128])
(mem/c:BLK (reg/f:DI 4 si [91]) [7 MEM[(struct T *)&D.2891]+0
S232 A128]))
(use (reg:DI 2 cx [92]))
]) "t4.cpp":31 993 {*rep_movdi_rex64}
(expr_list:REG_UNUSED (reg:DI 2 cx [92])
(nil)))
Scheduler doesn't notice that rep movsd target overlaps compare operand.
Looks like rtl-optimization (scheduler) to me.
