[C/C++ PATCH] Fix bogus warning with -Wswitch-unreachable (PR c/71249)

[Marek Polacek]

Martin S. noticed that cc1plus bogusly warns on the following test.  That's
because I didn't realize that GIMPLE_BINDs might be nested in C++ so we need to
look through them, and only then get the first statement in the seq.

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

2016-05-24  Marek Polacek  <pola...@redhat.com>

        PR c/71249
        * gimplify.c (gimplify_switch_expr): Look into the innermost lexical
        scope.

        * c-c++-common/Wswitch-unreachable-2.c: New test.

diff --git gcc/gimplify.c gcc/gimplify.c
index 6473544..5c5e9d6 100644
--- gcc/gimplify.c
+++ gcc/gimplify.c
@@ -1605,8 +1605,9 @@ gimplify_switch_expr (tree *expr_p, gimple_seq *pre_p)
          && switch_body_seq != NULL)
        {
          gimple_seq seq = switch_body_seq;
-         if (gimple_code (switch_body_seq) == GIMPLE_BIND)
-           seq = gimple_bind_body (as_a <gbind *> (switch_body_seq));
+         /* Look into the innermost lexical scope.  */
+         while (gimple_code (seq) == GIMPLE_BIND)
+           seq = gimple_bind_body (as_a <gbind *> (seq));
          gimple *stmt = gimple_seq_first_stmt (seq);
          enum gimple_code code = gimple_code (stmt);
          if (code != GIMPLE_LABEL && code != GIMPLE_TRY)
diff --git gcc/testsuite/c-c++-common/Wswitch-unreachable-2.c 
gcc/testsuite/c-c++-common/Wswitch-unreachable-2.c
index e69de29..8f57392 100644
--- gcc/testsuite/c-c++-common/Wswitch-unreachable-2.c
+++ gcc/testsuite/c-c++-common/Wswitch-unreachable-2.c
@@ -0,0 +1,18 @@
+/* PR c/71249 */
+/* { dg-do compile } */
+
+int
+f (int i)
+{
+  switch (i)
+    {
+      {
+       int j;
+      foo:
+       return i; /* { dg-bogus "statement will never be executed" } */
+      };
+    case 3:
+      goto foo;
+    }
+  return i;
+}

        Marek