[Bug middle-end/69542] New: [6 Regression] -fcompare-debug failure in simplify-rtx.c on i?86 since r232905

[jakub at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=69542

            Bug ID: 69542
           Summary: [6 Regression] -fcompare-debug failure in
                    simplify-rtx.c on i?86 since r232905
           Product: gcc
           Version: 6.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: middle-end
          Assignee: unassigned at gcc dot gnu.org
          Reporter: jakub at gcc dot gnu.org
  Target Milestone: ---

r232905 breaks bootstrap on i686-linux, with miscompare of simplify-rtx.o.
I'm still reducing testcase for this, but have bisected it to this commit
already.
Guess either the
 if (regno >= FIRST_PSEUDO_REGISTER && reg->subreg_p)
680                      bitmap_set_bit (&subreg_regs, regno);
or perhaps the whole set_bb_regs function should not be called for DEBUG_INSNs.
I think it shouldn't contain any type != OP_IN regs anyway, nor REG_DEAD notes.