re PR c++/772 (Statement expressions issues)

	PR c/772
	PR c/17913
	* c-tree.h (C_DECL_UNJUMPABLE_STMT_EXPR,
	C_DECL_UNDEFINABLE_STMT_EXPR, struct c_label_list, struct
	c_label_context, label_context_stack): New.
	* c-decl.c (define_label): Check for jumps into statement
	expressions.  Add label to list of defined labels.
	(start_function): Push context on label_context_stack.
	(finish_function): Pop context from label_context_stack.
	* c-typeck.c (label_context_stack): New.
	(c_finish_goto_label): Check for jumps into statement
	expressions.  Add label to list of jumped to labels.
	(struct c_switch): Add blocked_stmt_expr.
	(c_start_case): Initialize it.
	(do_case): Check it.
	(c_finish_case): Verify !blocked_stmt_expr.
	(c_begin_stmt_expr):  Push context on label_context_stack.
	Increment blocked_stmt_expr.  Mark labels jumped to from outside
	as undefinable.
	(c_finish_stmt_expr): December blocked_stmt_expr.  Mark labels
	defined in the statement expression and no longer jumpable to.
	Mark labels jumped to from just outside the statement expression
	as again definable.  Pop context from label_context_stack.
	* doc/extend.texi (Statement Exprs): Update.

objc:
	* objc-act.c (objc_start_function): Push context on
	label_context_stack.

testsuite:
	* gcc.dg/stmt-expr-label-1.c, gcc.dg/stmt-expr-label-2.c,
	gcc.dg/stmt-expr-label-3.c : New tests.
	* gcc.c-torture/execute/medce-2.c: Remove.

From-SVN: r97273

1 files changed, 23 insertions, 0 deletions

diff --git a/gcc/doc/extend.texi b/gcc/doc/extend.texi
index f09338f..02a03ec 100644
--- a/gcc/doc/extend.texi
+++ b/gcc/doc/extend.texi
@@ -187,6 +187,29 @@ work with C++.  (Note that some versions of the GNU C Library contained
 header files using statement-expression that lead to precisely this
 bug.)
 
+Jumping into a statement expression with @code{goto} or using a
+@code{switch} statement outside the statement expression with a
+@code{case} or @code{default} label inside the statement expression is
+not permitted.  Jumping into a statement expression with a computed
+@code{goto} (@pxref{Labels as Values}) yields undefined behavior.
+Jumping out of a statement expression is permitted, but if the
+statement expression is part of a larger expression then it is
+unspecified which other subexpressions of that expression have been
+evaluated except where the language definition requires certain
+subexpressions to be evaluated before or after the statement
+expression.  In any case, as with a function call the evaluation of a
+statement expression is not interleaved with the evaluation of other
+parts of the containing expression.  For example,
+
+@smallexample
+  foo (), ((@{ bar1 (); goto a; 0; @}) + bar2 ()), baz();
+@end smallexample
+
+@noindent
+will call @code{foo} and @code{bar1} and will not call @code{baz} but
+may or may not call @code{bar2}.  If @code{bar2} is called, it will be
+called after @code{foo} and before @code{bar1}
+
 @node Local Labels
 @section Locally Declared Labels
 @cindex local labels