Improve constexpr handling of other loop forms.

	* constexpr.c (breaks): Handle EXIT_EXPR.
	(cxx_eval_loop_expr): Handle COMPOUND_EXPR body.
	(cxx_eval_constant_expression): Handle EXIT_EXPR, improve handling
	of COMPOUND_EXPR.

From-SVN: r235218

gcc/cp/ChangeLog

 2016-04-19  Jason Merrill  <jason@redhat.com>
 
+	* constexpr.c (breaks): Handle EXIT_EXPR.
+	(cxx_eval_loop_expr): Handle COMPOUND_EXPR body.
+	(cxx_eval_constant_expression): Handle EXIT_EXPR, improve handling
+	of COMPOUND_EXPR.
+
 	PR c++/68206
 	PR c++/68530
 	* constexpr.c (potential_constant_expression_1): Handle LOOP_EXPR

gcc/cp/constexpr.c

@@ -3241,8 +3241,9 @@ static bool
 breaks (tree *jump_target)
 {
   return *jump_target
-    && TREE_CODE (*jump_target) == LABEL_DECL
-    && LABEL_DECL_BREAK (*jump_target);
+    && ((TREE_CODE (*jump_target) == LABEL_DECL
+	 && LABEL_DECL_BREAK (*jump_target))
+	|| TREE_CODE (*jump_target) == EXIT_EXPR);
 }
 
 static bool
@@ -3358,7 +3359,7 @@ cxx_eval_loop_expr (const constexpr_ctx *ctx, tree t,
       hash_set<tree> save_exprs;
       new_ctx.save_exprs = &save_exprs;
 
-      cxx_eval_statement_list (&new_ctx, body,
+      cxx_eval_constant_expression (&new_ctx, body, /*lval*/false,
 				    non_constant_p, overflow_p, jump_target);
 
       /* Forget saved values of SAVE_EXPRs.  */
@@ -3750,6 +3751,8 @@ cxx_eval_constant_expression (const constexpr_ctx *ctx, tree t,
 	    cxx_eval_constant_expression (ctx, op0,
 					  true, non_constant_p, overflow_p,
 					  jump_target);
+	    if (*non_constant_p)
+	      return t;
 	    op1 = TREE_OPERAND (t, 1);
 	    r = cxx_eval_constant_expression (ctx, op1,
 					      lval, non_constant_p, overflow_p,
@@ -4015,6 +4018,17 @@ cxx_eval_constant_expression (const constexpr_ctx *ctx, tree t,
 	}
       break;
 
+    case EXIT_EXPR:
+      {
+	tree cond = TREE_OPERAND (t, 0);
+	cond = cxx_eval_constant_expression (ctx, cond, /*lval*/false,
+					     non_constant_p, overflow_p);
+	VERIFY_CONSTANT (cond);
+	if (integer_nonzerop (cond))
+	  *jump_target = t;
+      }
+      break;
+
     case GOTO_EXPR:
       *jump_target = TREE_OPERAND (t, 0);
       gcc_assert (breaks (jump_target) || continues (jump_target));