gimplify: Fix ICE in collect_fallthrough_labels [PR122773]

In r16-4212 I had to tweak two spots in the gimplifier to ignore
gotos jumping to labels with the new VACUOUS_INIT_LABEL_P flag
(set by C++ FE when implementing goto/case interceptors with
extra .DEFERRED_INIT calls, so that jumps over vacuous initialization
are handled properly with the C++26 erroneous behavior requirements).
Except as the following testcase shows, the checks blindly assumed
that gimple_goto_dest operand is a LABEL_DECL, which is not the case
for computed jumps.

The following patch checks that gimple_goto_dest argument is a LABEL_DECL
before testing VACUOUS_INIT_LABEL_P flag on it.

2025-11-21  Jakub Jelinek  <jakub@redhat.com>

	PR middle-end/122773
	* gimplify.cc (collect_fallthrough_labels): Check whether
	gimple_goto_dest is a LABEL_DECL before testing VACUOUS_INIT_LABEL_P.
	(expand_FALLTHROUGH_r): Likewise.

	* gcc.dg/pr122773.c: New test.

diff --git a/gcc/gimplify.cc b/gcc/gimplify.cc
index d8725e4c5e203eeca59286c9dfb516559bf52770..d884e8b0d95755417dfd6e250cc98ddddf12ddd1 100644 (file)
--- a/gcc/gimplify.cc
+++ b/gcc/gimplify.cc
@@ -2673,6 +2673,7 @@ collect_fallthrough_labels (gimple_stmt_iterator *gsi_p,
          gsi_next (gsi_p);
        }
 
+      tree lab;
       /* Remember the last statement.  Skip labels that are of no interest
         to us.  */
       if (gimple_code (gsi_stmt (*gsi_p)) == GIMPLE_LABEL)
@@ -2691,7 +2692,9 @@ collect_fallthrough_labels (gimple_stmt_iterator *gsi_p,
        ;
       else if (flag_auto_var_init > AUTO_INIT_UNINITIALIZED
               && gimple_code (gsi_stmt (*gsi_p)) == GIMPLE_GOTO
-              && VACUOUS_INIT_LABEL_P (gimple_goto_dest (gsi_stmt (*gsi_p))))
+              && (lab = gimple_goto_dest (gsi_stmt (*gsi_p)))
+              && TREE_CODE (lab) == LABEL_DECL
+              && VACUOUS_INIT_LABEL_P (lab))
        ;
       else if (!is_gimple_debug (gsi_stmt (*gsi_p)))
        prev = gsi_stmt (*gsi_p);
@@ -2928,9 +2931,12 @@ expand_FALLTHROUGH_r (gimple_stmt_iterator *gsi_p, bool *handled_ops_p,
 
          gimple_stmt_iterator gsi2 = *gsi_p;
          stmt = gsi_stmt (gsi2);
+         tree lab;
          if (flag_auto_var_init > AUTO_INIT_UNINITIALIZED
              && gimple_code (stmt) == GIMPLE_GOTO
-             && VACUOUS_INIT_LABEL_P (gimple_goto_dest (stmt)))
+             && (lab = gimple_goto_dest (stmt))
+             && TREE_CODE (lab) == LABEL_DECL
+             && VACUOUS_INIT_LABEL_P (lab))
            {
              /* Handle for C++ artificial -ftrivial-auto-var-init=
                 sequences.  Those look like:

diff --git a/gcc/testsuite/gcc.dg/pr122773.c b/gcc/testsuite/gcc.dg/pr122773.c
new file mode 100644 (file)
index 0000000..a3860e9
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/pr122773.c
@@ -0,0 +1,25 @@
+/* PR middle-end/122773 */
+/* { dg-do compile } */
+/* { dg-options "-Wimplicit-fallthrough -O2 -ftrivial-auto-var-init=zero" } */
+
+void *l;
+int
+foo (int x)
+{
+  __label__ l1, l2, l3;
+  static void *l[] = { &&l1, &&l2, &&l3 };
+  switch (0)
+    {
+    case 0:
+      while (0)
+        ;
+      goto *l[x];
+    }
+  l1:
+  ++x;
+  l2:
+  ++x;
+  l3:
+  ++x;
+  return x;
+}