https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65496
Jakub Jelinek <jakub at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
CC| |rth at gcc dot gnu.org
--- Comment #2 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
And the problem is that with these weirdo scheduling options the scheduler
schedules the
(insn/f:TI 620 60 37 2 (set (reg:DI 39 r10)
(plus:DI (reg/f:DI 7 sp)
(const_int 8 [0x8]))) pr65496.c:3 214 {*leadi}
(nil))
instruction before the shrink-wrapping conditional jump:
(jump_insn:TI 38 45 43 2 (set (pc)
(if_then_else (eq (reg:CCZ 17 flags)
(const_int 0 [0]))
(label_ref:DI 645)
(pc))) pr65496.c:4 613 {*jcc_1}
(expr_list:REG_DEAD (reg:CCZ 17 flags)
(int_list:REG_BR_PROB 900 (nil)))
-> 645)
At the end of the function we have:
(insn/f:TI 641 640 645 40 (set (reg/f:DI 7 sp)
(plus:DI (reg:DI 39 r10)
(const_int -8 [0xfffffffffffffff8]))) pr65496.c:6 214 {*leadi}
(expr_list:REG_DEAD (reg:DI 39 r10)
(expr_list:REG_CFA_DEF_CFA (plus:DI (reg/f:DI 7 sp)
(const_int 8 [0x8]))
(nil))))
(code_label 645 641 644 41 106 "" [1 uses])
(note 644 645 663 41 [bb 41] NOTE_INSN_BASIC_BLOCK)
(jump_insn 663 644 643 41 (parallel [
(simple_return)
(unspec [
(const_int 0 [0])
] UNSPEC_REP)
]) pr65496.c:6 682 {simple_return_internal_long}
(nil))
(barrier 643 663 355)
And the problem is that because the r10 = rsp + 8 frame related instruction is
moved before the shrink-wrapping jump we assume CFA is in r10 + 0, but before
fallthru into the return we have a CFA restore note to use r8 + 8 again as CFA
(not really needed in this case, but desirable for the case when the r10 = rsp
+ 8 instruction isn't moved.
Richard, any thoughts what to do about this? Avoid scheduling frame related
instructions across conditional jumps? Something else?
