On Fri, 12 Apr 2019, Jakub Jelinek wrote:
> Hi!
>
> In the following testcase, we have initially during RTL expansion a call
> which can throw, followed by fallthrough into an empty block with two
> similar predecessors (both calling the same function) and with a fallthrough
> into an empty block with no successors (__builtin_unreachable).
> That last block is optimized away soon and in the cfglayout mode we have
> a bb with no successors that has a BARRIER in BB_FOOTER. During cfg cleanup
> during combine we actually optimize away even that other empty bb with no
> successors, but end up not putting a BARRIER into BB_FOOTER of the bb with a
> call. There is in the following hunk in try_optimize_cfg code to handle
> that, but a) it assumes a BARRIER has to be the first in BB_FOOTER, which
> as all other spots I've found don't assume, even for the non-cfglayout
> mode a few lines below we call get_last_bb_insn which walks the following
> insn chain (note, this isn't a problem on this exact testcase though)
> and b) punt if e->src bb already has non-NULL BB_FOOTER (that is what
> breaks this testcase - the testcase has a NOTE_INSN_DELETED_LABEL in
> BB_FOOTER, but of course no BARRIER, we don't add one here and later on
> when outof_cfglayout we ICE because there is no BARRIER after a bb that
> doesn't fall thru). Apparently there is a function which can handle
> adding a barrier, both into an empty BB_FOOTER as well as when there is
> a BB_FOOTER, but doesn't contain a BARRIER in there.
>
> So, this patch fixes both issues.
>
> Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk?
LGTM.
Richard.
> 2019-04-12 Jakub Jelinek <ja...@redhat.com>
>
> PR rtl-optimization/90026
> * cfgcleanup.c (try_optimize_cfg): When removing empty bb with no
> successors, look for BARRIERs inside of the whole BB_FOOTER chain
> rather than just at the start of it. If e->src BB_FOOTER is not NULL
> in cfglayout mode, use emit_barrier_after_bb.
>
> * g++.dg/opt/pr90026.C: New test.
>
> --- gcc/cfgcleanup.c.jj 2019-03-09 09:25:11.743785011 +0100
> +++ gcc/cfgcleanup.c 2019-04-11 11:30:52.967173100 +0200
> @@ -2712,23 +2712,23 @@ try_optimize_cfg (int mode)
>
> if (current_ir_type () == IR_RTL_CFGLAYOUT)
> {
> - if (BB_FOOTER (b)
> - && BARRIER_P (BB_FOOTER (b)))
> + rtx_insn *insn;
> + for (insn = BB_FOOTER (b);
> + insn; insn = NEXT_INSN (insn))
> + if (BARRIER_P (insn))
> + break;
> + if (insn)
> FOR_EACH_EDGE (e, ei, b->preds)
> - if ((e->flags & EDGE_FALLTHRU)
> - && BB_FOOTER (e->src) == NULL)
> + if ((e->flags & EDGE_FALLTHRU))
> {
> - if (BB_FOOTER (b))
> + if (BB_FOOTER (b)
> + && BB_FOOTER (e->src) == NULL)
> {
> BB_FOOTER (e->src) = BB_FOOTER (b);
> BB_FOOTER (b) = NULL;
> }
> else
> - {
> - start_sequence ();
> - BB_FOOTER (e->src) = emit_barrier ();
> - end_sequence ();
> - }
> + emit_barrier_after_bb (e->src);
> }
> }
> else
> --- gcc/testsuite/g++.dg/opt/pr90026.C.jj 2019-04-11 12:40:14.508840308
> +0200
> +++ gcc/testsuite/g++.dg/opt/pr90026.C 2019-04-11 12:39:43.431352423
> +0200
> @@ -0,0 +1,24 @@
> +// PR rtl-optimization/90026
> +// { dg-do compile }
> +// { dg-options "-fnon-call-exceptions -ftracer -O2 -w" }
> +
> +typedef __SIZE_TYPE__ size_t;
> +struct S { int *b; ~S () { delete b; } };
> +void bar ();
> +char c[sizeof (int)];
> +
> +void *
> +operator new (size_t, void *)
> +{
> + __builtin_unreachable ();
> +}
> +
> +void
> +foo ()
> +{
> + S a;
> + if (a.b)
> + a.b = new int ();
> + bar ();
> + new (c) int ();
> +}
>
> Jakub
>
--
Richard Biener <rguent...@suse.de>
SUSE Linux GmbH, Maxfeldstrasse 5, 90409 Nuernberg, Germany;
GF: Felix Imendörffer, Mary Higgins, Sri Rasiah; HRB 21284 (AG Nürnberg)
