re PR c++/44609 (Invalid template code causes infinite loop of error messages)

PR c++/44609
	* cp-tree.h (struct tinst_level): Add errors field.
	* pt.c (neglectable_inst_p, limit_bad_template_recurson): New.
	(push_tinst_level): Don't start another decl in that case.
	(reopen_tinst_level): Adjust errors field.
	* decl2.c (cp_write_global_declarations): Don't complain about
	undefined inline if its template was defined.
	* mangle.c (mangle_decl_string): Handle failure from push_tinst_level.

From-SVN: r176176

gcc/cp/ChangeLog

@@ -1,3 +1,14 @@
+2011-07-11  Jason Merrill  <jason@redhat.com>
+
+	PR c++/44609
+	* cp-tree.h (struct tinst_level): Add errors field.
+	* pt.c (neglectable_inst_p, limit_bad_template_recurson): New.
+	(push_tinst_level): Don't start another decl in that case.
+	(reopen_tinst_level): Adjust errors field.
+	* decl2.c (cp_write_global_declarations): Don't complain about
+	undefined inline if its template was defined.
+	* mangle.c (mangle_decl_string): Handle failure from push_tinst_level.
+
 2011-07-10  Jason Merrill  <jason@redhat.com>
 
 	PR c++/49691

gcc/cp/cp-tree.h

@@ -4679,6 +4679,9 @@ struct GTY((chain_next ("%h.next"))) tinst_level {
   /* The location where the template is instantiated.  */
   location_t locus;
 
+  /* errorcount+sorrycount when we pushed this level.  */
+  int errors;
+
   /* True if the location is in a system header.  */
   bool in_system_header_p;
 };

gcc/cp/decl2.c

@@ -3950,10 +3950,10 @@ cp_write_global_declarations (void)
 	     #pragma interface, etc.) we decided not to emit the
 	     definition here.  */
 	  && !DECL_INITIAL (decl)
-	  /* An explicit instantiation can be used to specify
-	     that the body is in another unit. It will have
-	     already verified there was a definition.  */
-	  && !DECL_EXPLICIT_INSTANTIATION (decl))
+	  /* Don't complain if the template was defined.  */
+	  && !(DECL_TEMPLATE_INSTANTIATION (decl)
+	       && DECL_INITIAL (DECL_TEMPLATE_RESULT
+				(template_for_substitution (decl)))))
 	{
 	  warning (0, "inline function %q+D used but never defined", decl);
 	  /* Avoid a duplicate warning from check_global_declaration_1.  */

gcc/cp/mangle.c

@@ -3106,11 +3106,11 @@ mangle_decl_string (const tree decl)
   if (DECL_LANG_SPECIFIC (decl) && DECL_USE_TEMPLATE (decl))
     {
       struct tinst_level *tl = current_instantiation ();
-      if (!tl || tl->decl != decl)
+      if ((!tl || tl->decl != decl)
+	  && push_tinst_level (decl))
 	{
 	  template_p = true;
 	  saved_fn = current_function_decl;
-	  push_tinst_level (decl);
 	  current_function_decl = NULL_TREE;
 	}
     }

gcc/cp/pt.c

@@ -7499,6 +7499,36 @@ uses_template_parms_level (tree t, int level)
 				 /*include_nondeduced_p=*/true);
 }
 
+/* Returns TRUE iff INST is an instantiation we don't need to do in an
+   ill-formed translation unit, i.e. a variable or function that isn't
+   usable in a constant expression.  */
+
+static inline bool
+neglectable_inst_p (tree d)
+{
+  return (DECL_P (d)
+	  && !(TREE_CODE (d) == FUNCTION_DECL ? DECL_DECLARED_CONSTEXPR_P (d)
+	       : decl_maybe_constant_var_p (d)));
+}
+
+/* Returns TRUE iff we should refuse to instantiate DECL because it's
+   neglectable and instantiated from within an erroneous instantiation.  */
+
+static bool
+limit_bad_template_recurson (tree decl)
+{
+  struct tinst_level *lev = current_tinst_level;
+  int errs = errorcount + sorrycount;
+  if (lev == NULL || errs == 0 || !neglectable_inst_p (decl))
+    return false;
+
+  for (; lev; lev = lev->next)
+    if (neglectable_inst_p (lev->decl))
+      break;
+
+  return (lev && errs > lev->errors);
+}
+
 static int tinst_depth;
 extern int max_tinst_depth;
 #ifdef GATHER_STATISTICS
@@ -7532,9 +7562,16 @@ push_tinst_level (tree d)
       return 0;
     }
 
+  /* If the current instantiation caused problems, don't let it instantiate
+     anything else.  Do allow deduction substitution and decls usable in
+     constant expressions.  */
+  if (limit_bad_template_recurson (d))
+    return 0;
+
   new_level = ggc_alloc_tinst_level ();
   new_level->decl = d;
   new_level->locus = input_location;
+  new_level->errors = errorcount+sorrycount;
   new_level->in_system_header_p = in_system_header;
   new_level->next = current_tinst_level;
   current_tinst_level = new_level;
@@ -7578,6 +7615,8 @@ reopen_tinst_level (struct tinst_level *level)
 
   current_tinst_level = level;
   pop_tinst_level ();
+  if (current_tinst_level)
+    current_tinst_level->errors = errorcount+sorrycount;
   return level->decl;
 }
 

gcc/testsuite/ChangeLog

@@ -1,3 +1,8 @@
+2011-07-11  Jason Merrill  <jason@redhat.com>
+
+	PR c++/44609
+	* g++.dg/template/recurse3.C: New.
+
 2011-07-11  Jakub Jelinek  <jakub@redhat.com>
 
 	PR debug/49676

gcc/testsuite/g++.dg/template/recurse3.C

@@ -0,0 +1,14 @@
+// PR c++/44609
+// { dg-options -ftemplate-depth=10 }
+
+template<int N>
+void f()
+{
+  0 = 0;			// { dg-error "lvalue required" }
+  f<N+1>();			// { dg-bogus "instantiation depth" }
+}
+
+int main()
+{
+  f<0>();
+}