The lambda capture path in finish_id_expression wasn't calling mark_used
like the other paths.
Tested x86_64-pc-linux-gnu, applying to trunk and 4.6.
commit 0aceb42a8ba7bde23447d6ae74c8615721a40952
Author: Jason Merrill <ja...@redhat.com>
Date: Mon Aug 29 11:23:56 2011 -0400
PR c++/50224
* semantics.c (finish_id_expression): Mark captured variables used.
diff --git a/gcc/cp/semantics.c b/gcc/cp/semantics.c
index 5deb2eb..07f53b5 100644
--- a/gcc/cp/semantics.c
+++ b/gcc/cp/semantics.c
@@ -2949,6 +2949,9 @@ finish_id_expression (tree id_expression,
tree lambda_expr = NULL_TREE;
tree initializer = convert_from_reference (decl);
+ /* Mark it as used now even if the use is ill-formed. */
+ mark_used (decl);
+
/* Core issue 696: "[At the July 2009 meeting] the CWG expressed
support for an approach in which a reference to a local
[constant] automatic variable in a nested class or lambda body
diff --git a/gcc/testsuite/g++.dg/cpp0x/lambda/lambda-use2.C b/gcc/testsuite/g++.dg/cpp0x/lambda/lambda-use2.C
new file mode 100644
index 0000000..695a0b4
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp0x/lambda/lambda-use2.C
@@ -0,0 +1,11 @@
+// PR c++/50224
+// { dg-options "-std=c++0x -Wunused-parameter" }
+
+struct T;
+
+void m(T& t) // ERROR here
+{
+ [&]{
+ t; // ``t`` is referenced here
+ };
+}
