[Bug bootstrap/44469] [4.5/4.6 Regression] internal compiler error: in fixup_reorder_chain, at cfglayout.c:797

["jakub at gcc dot gnu dot org" <gcc-bugzilla at gcc dot gnu dot org>]

------- Comment #3 from jakub at gcc dot gnu dot org  2010-06-09 13:55 -------
There are more issues:
1) cleanup_barriers seems to do weird things with these empty bbs from
__builtin_unreachable (), I guess it shouldn't reorder anything if prev is a
LABEL_P
2) the reason why this compiles fine on x86_64 seems to be in different bb
reordering.  On arm the empty bb is reordered after the condjump, which means
its label is deleted by /* Remove code labels no longer used.  */ in
try_optimize_cfg and then the block is trivially empty.  On x86_64 we don't
ICE, but generate useless code:
        movl    (%rdi), %eax
        testl   %eax, %eax
        je      .L2
        cmpl    $1, %eax
        jne     .L3
        movq    %rdi, %rsi
.L2:
        xorl    %eax, %eax
        cmpb    $0, (%rsi)
        sete    %al
        ret
.L3:
        .cfi_endproc

I'd say we shouldn't try to delete just trivially_empty_bb_p's, but also ones
that before the bb note also have labels and after it nothing or only
DEBUG_INSNs, but we should delete only if we actually succeed adjusting the
jump insn at the end of the earlier block.


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=44469