bbpart: Fix up ICE on asm goto [PR108596]

On the following testcase we have asm goto in hot block with 2 successors,
one cold to which it both falls through and has one of the label
pointing to it and another hot successor with another label.

Now, during bbpart we want to ensure that no blocks from one partition fall
through into a block in a different partition.  fix_up_fall_thru_edges
does that by temporarily clearing the EDGE_CROSSING on the fallthrough edge,
calling force_nonfallthru and then depending on whether it created a new
bb either set EDGE_CROSSING on the single successor edge from the new bb
(the new bb is kept in the same partition as the predecessor block), or
if no new bb has been created setting EDGE_CROSSING back on the fallthru
edge which has been forced non-EDGE_FALLTHRU.
For asm goto this doesn't always work, force_nonfallthru can create a new bb
and change the fallthrough edge to point to that, but if the original
fallthru destination block has its label referenced among the asm goto
labels, it will create a new non-fallthru edge for the label(s).
But because we've temporarily cheated and cleared EDGE_CROSSING on the edge,
it is cleared on the new edge as well, then the caller sees we've created
a new bb and just sets EDGE_CROSSING on the single fallthru edge from the
new bb.  But the direct edge from cur_bb to fallthru edge's destination
isn't handled and fails afterwards consistency checks, because it crosses
partitions.

The following patch notes the case and sets EDGE_CROSSING on that edge too.

2023-01-31  Jakub Jelinek  <jakub@redhat.com>

	PR rtl-optimization/108596
	* bb-reorder.cc (fix_up_fall_thru_edges): Handle the case where cur_bb
	ends with asm goto and has a crossing fallthrough edge to the same bb
	that contains at least one of its labels by restoring EDGE_CROSSING
	flag even on possible edge from cur_bb to new_bb successor.

	* gcc.c-torture/compile/pr108596.c: New test.

(cherry picked from commit 603a6fbcaac1e80aa90d1d26318c881a53473066)

2 files changed, 46 insertions, 1 deletions

diff --git a/gcc/bb-reorder.cc b/gcc/bb-reorder.cc
index d20ccb83aa6..2c194aa9055 100644
--- a/gcc/bb-reorder.cc
+++ b/gcc/bb-reorder.cc
@@ -1998,6 +1998,7 @@ fix_up_fall_thru_edges (void)
 		     becomes EDGE_CROSSING.  */
 
 		  fall_thru->flags &= ~EDGE_CROSSING;
+		  unsigned old_count = EDGE_COUNT (cur_bb->succs);
 		  basic_block new_bb = force_nonfallthru (fall_thru);
 
 		  if (new_bb)
@@ -2009,7 +2010,25 @@ fix_up_fall_thru_edges (void)
 		      gcc_assert (BB_PARTITION (new_bb)
                                   == BB_PARTITION (cur_bb));
 
-		      single_succ_edge (new_bb)->flags |= EDGE_CROSSING;
+		      edge e = single_succ_edge (new_bb);
+		      e->flags |= EDGE_CROSSING;
+		      if (EDGE_COUNT (cur_bb->succs) > old_count)
+			{
+			  /* If asm goto has a crossing fallthrough edge
+			     and at least one of the labels to the same bb,
+			     force_nonfallthru can result in the fallthrough
+			     edge being redirected and a new edge added for the
+			     label or more labels to e->dest.  As we've
+			     temporarily cleared EDGE_CROSSING flag on the
+			     fallthrough edge, we need to restore it again.
+			     See PR108596.  */
+			  rtx_insn *j = BB_END (cur_bb);
+			  gcc_checking_assert (JUMP_P (j)
+					       && asm_noperands (PATTERN (j)));
+			  edge e2 = find_edge (cur_bb, e->dest);
+			  if (e2)
+			    e2->flags |= EDGE_CROSSING;
+			}
 		    }
 		  else
 		    {
diff --git a/gcc/testsuite/gcc.c-torture/compile/pr108596.c b/gcc/testsuite/gcc.c-torture/compile/pr108596.c
new file mode 100644
index 00000000000..4de6c49d7ce
--- /dev/null
+++ b/gcc/testsuite/gcc.c-torture/compile/pr108596.c
@@ -0,0 +1,26 @@
+/* PR rtl-optimization/108596 */
+
+__attribute__((__cold__)) void foo (void);
+void bar (void);
+
+void
+baz (void)
+{
+  asm goto ("" : : : : l1, l0);
+  goto l0;
+l1:
+  bar ();
+l0:
+  foo ();
+}
+
+void
+qux (void)
+{
+  asm goto ("" : : : : l1, l0);
+  __builtin_unreachable ();
+l1:
+  bar ();
+l0:
+  foo ();
+}