On Sat, Jan 14, 2017 at 09:47:41PM -0700, Jeff Law wrote:
> > PR target/72749
> > * cfgrtl.c (rtl_split_edge): Also patch jump insns that jump to the
> > fallthrough.
> > * haifa-sched.c (dump_insn_stream): Don't crash if there is a label
> > in the currently scheduled RTL fragment.
> So presumably the semantics in this case can only mean one thing -- both
> the fallthru and the jump have to go to the same place after splitting.
> Right? ISTM that ought to be documented in rtl_split_edge somewhere.
We could call patch_jump_insn in *all* cases, except for simple jumps
it does
gcc_assert (JUMP_LABEL (insn) == old_label);
which is a useful check (for the other callers), and patch_jump_insn
isn't a very cheap routine to call anyway, better not do it too often.
> In this case is the edge a fallthru or branch edge?
Both! You get only one edge if both jump targets are the same.
> And, no we don't make any guarantee about degenerate jumps -- a jump
> with a side effect in particular can easily survive. I wouldn't be
> surprised if there's various bugs lurking for cases where we have a
> degenerate jump like that. It's just not common enough to have been
> heavily exercised.
>
> Patch with PATTERN fix is OK.
Thanks, I'll commit it tomorrow.
Segher
