[Bug rtl-optimization/60043] -fschedule-insns2 breaks anti-dependency

["abel at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=60043

--- Comment #5 from Andrey Belevantsev <abel at gcc dot gnu.org> ---
(In reply to Richard Biener from comment #4)
> Hmm, oops.  The testcase has a true dependence ... ;)  Still, isn't the
> code in sched_analyze_2 wrong?  Or are pending_mems all before 't'?

Yes (to second question :).  The analysis code roughly works like this
(sched_analyze is the entry point):

- process insns one by one in a bb/ebb doing two things in parallel:

  o mark reads/writes to registers, writes/reads to mems of this insn in
various fields of the deps context; and
  o find dependencies between this insn reads/writes of registers/memory and
previously noted reads/writes of the same register or memory from the deps
context.

So the pending_mem read/write will always happen before the currently
processing insn mem read/write.