[PATCH] tree-cfg: Fix up gimple_merge_blocks FORCED_LABEL handling [PR99034]

[Jakub Jelinek]

Hi!

The verifiers require that DECL_NONLOCAL or EH_LANDING_PAD_NR
labels are always the first label if there is more than one label.

When merging blocks, we don't honor that though.
On the following testcase, we try to merge blocks:
<bb 13> [count: 0]:
<L2>:
S::~S (&s);

and
<bb 15> [count: 0]:
<L0>:
resx 1

where <L2> is landing pad and <L0> is FORCED_LABEL.  And the code puts
the FORCED_LABEL before the landing pad label, violating the verification
requirements.

The following patch fixes it by moving the FORCED_LABEL after the
DECL_NONLOCAL or EH_LANDING_PAD_NR label if it is the first label.

Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk?

2021-02-19  Jakub Jelinek  <jakub@redhat.com>

	PR ipa/99034
	* tree-cfg.c (gimple_merge_blocks): If bb a starts with eh landing
	pad or non-local label, put FORCED_LABELs from bb b after that label
	rather than before it.

	* g++.dg/opt/pr99034.C: New test.

--- gcc/tree-cfg.c.jj	2021-02-18 16:20:57.053826485 +0100
+++ gcc/tree-cfg.c	2021-02-18 19:15:48.436526437 +0100
@@ -2124,7 +2124,17 @@ gimple_merge_blocks (basic_block a, basi
 	  if (FORCED_LABEL (label))
 	    {
 	      gimple_stmt_iterator dest_gsi = gsi_start_bb (a);
-	      gsi_insert_before (&dest_gsi, stmt, GSI_NEW_STMT);
+	      tree first_label = NULL_TREE;
+	      if (!gsi_end_p (dest_gsi))
+		if (glabel *first_label_stmt
+		    = dyn_cast <glabel *> (gsi_stmt (dest_gsi)))
+		  first_label = gimple_label_label (first_label_stmt);
+	      if (first_label
+		  && (DECL_NONLOCAL (first_label)
+		      || EH_LANDING_PAD_NR (first_label) != 0))
+		gsi_insert_after (&dest_gsi, stmt, GSI_NEW_STMT);
+	      else
+		gsi_insert_before (&dest_gsi, stmt, GSI_NEW_STMT);
 	    }
 	  /* Other user labels keep around in a form of a debug stmt.  */
 	  else if (!DECL_ARTIFICIAL (label) && MAY_HAVE_DEBUG_BIND_STMTS)
--- gcc/testsuite/g++.dg/opt/pr99034.C.jj	2021-02-18 19:05:27.205347304 +0100
+++ gcc/testsuite/g++.dg/opt/pr99034.C	2021-02-18 19:07:32.352973196 +0100
@@ -0,0 +1,23 @@
+// PR ipa/99034
+// { dg-do compile }
+// { dg-options "-O2" }
+
+void *b[5];
+void foo (void);
+struct S { ~S (); };
+
+static inline void
+__attribute__((always_inline))
+bar (int d)
+{
+  S s;
+  while (d)
+    foo ();
+}
+
+void
+baz (void)
+{
+  bar (2);
+  __builtin_setjmp (b);
+}

	Jakub