[C++ PATCH] Fix ICE with statement expression (PR c++/71728)

[Jakub Jelinek]

Hi!

It is true that parsing should make sure that GOTO_EXPRs (other than
break/continue) aren't allowed in constant expression contexts, but
potential_constant_expression_1 may be called (with tf_none) also
on arbitrary code either for warning purposes, or (very recent change)
also in cp_fully_fold, usually from maybe_constant_value.

So asserting they don't appear doesn't work.

Fixed thusly, alternatively we could assert that (flags & tf_error) == 0
before returning false.

Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk/6.2?

2016-07-21  Jakub Jelinek  <ja...@redhat.com>

        PR c++/71728
        * constexpr.c (potential_constant_expression_1) <case GOTO_EXPR>:
        Replace assert with test, return false if the goto isn't break
        or continue.  Formatting fix.

        * g++.dg/other/pr71728.C: New test.

--- gcc/cp/constexpr.c.jj       2016-07-21 08:59:50.000000000 +0200
+++ gcc/cp/constexpr.c  2016-07-21 12:05:16.828618186 +0200
@@ -5289,10 +5289,12 @@ potential_constant_expression_1 (tree t,
     case GOTO_EXPR:
       {
        tree *target = &TREE_OPERAND (t, 0);
-       /* Gotos representing break and continue are OK; we should have
-          rejected other gotos in parsing.  */
-       gcc_assert (breaks (target) || continues (target));
-       return true;
+       /* Gotos representing break and continue are OK.  */
+       if (breaks (target) || continues (target))
+         return true;
+       if (flags & tf_error)
+         error ("%<goto%> is not a constant-expression");
+       return false;
       }
 
     default:
@@ -5300,7 +5302,7 @@ potential_constant_expression_1 (tree t,
        return false;
 
       sorry ("unexpected AST of kind %s", get_tree_code_name (TREE_CODE (t)));
-      gcc_unreachable();
+      gcc_unreachable ();
       return false;
     }
 #undef RECUR
--- gcc/testsuite/g++.dg/other/pr71728.C.jj     2016-07-21 12:13:31.686461551 
+0200
+++ gcc/testsuite/g++.dg/other/pr71728.C        2016-07-21 12:14:46.974524876 
+0200
@@ -0,0 +1,11 @@
+// PR c++/71728
+// { dg-do compile }
+// { dg-options "-std=gnu++14 -Wall" }
+
+int
+foo ()
+{
+  if (({ goto test; test: 1; }) != 1)
+    return 1;
+  return 2;
+}

        Jakub