[C++ Patch] Tweak check_previous_goto_1 to emit hard errors instead of permerrors in some cases

[Paolo Carlini]

Hi,

over the years we reworked and improved the code in decl.c checking 
gotos quite a bit. Lately, in some specific unsafe cases, identify_goto 
issues upfront an error instead of a permerror, whereas it used to 
always issue a permerror. Over the last weeks a few colleagues of mine 
noticed that we don't do that, escalating a permerror to a plain error, 
in a case which is certainly unsafe - decl_jump_unsafe returns 2 - thus, 
if the user passes -fpermissive we end up emitting assembly completely 
missing labels. The straightforward patchlet below passes testing on 
x86_64-linux.

Thanks, Paolo.

/////////////////////

/cp
2018-08-09  Paolo Carlini  <paolo.carl...@oracle.com>

        * decl.c (check_previous_goto_1): When decl_jump_unsafe returns 2
        emit an error instead of a permerror.

/testsuite
2018-08-09  Paolo Carlini  <paolo.carl...@oracle.com>

        * g++.dg/init/goto3.C: Adjust for error intead of permerror.
Index: cp/decl.c
===================================================================
--- cp/decl.c   (revision 263443)
+++ cp/decl.c   (working copy)
@@ -3191,7 +3191,8 @@ check_previous_goto_1 (tree decl, cp_binding_level
          if (!identified)
            {
              complained = identify_goto (decl, input_location, locus,
-                                         DK_PERMERROR);
+                                         problem > 1
+                                         ? DK_ERROR : DK_PERMERROR);
              identified = 1;
            }
          if (complained)
Index: testsuite/g++.dg/init/goto3.C
===================================================================
--- testsuite/g++.dg/init/goto3.C       (revision 263443)
+++ testsuite/g++.dg/init/goto3.C       (working copy)
@@ -15,11 +15,11 @@ adapt_parameters_next_iteration(void)
     case VAR_NONE: break;
 
     case VAR_DELTA:
-        int trunc_n_ants = 0;
+        int trunc_n_ants = 0;  // { dg-message "initialization" }
         n_ants += trunc_n_ants;
         break;
-    case VAR_SWITCH:
+    case VAR_SWITCH:  // { dg-error "jump" }
         break;
-      default: break;
+      default: break;  // { dg-error "jump" }
     }
 }