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From: "jakub at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug target/65496] ICE: in maybe_record_trace_start, at dwarf2cfi.c:2318 with -O3 -fsched2-use-superblocks -mavx512dq --param=max-pending-list-length=0
Date: Fri, 20 Mar 2015 18:10:00 -0000
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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?