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?
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
