I've added an initial "Porting to GCC 4.9" page at http://gcc.gnu.org/gcc-4.9/porting_to.html
So far it only contains a couple of C++ changes that caused some failures during mass rebuilds, other additions are welcome.
--- /dev/null 2014-02-20 09:50:47.841935984 +0000 +++ porting_to.html 2014-03-04 22:25:55.001566175 +0000 @@ -0,0 +1,114 @@ +<html> + +<head> +<title>Porting to GCC 4.9</title> +</head> + +<body> +<h1>Porting to GCC 4.9</h1> + +<p> +The GCC 4.9 release series differs from previous GCC releases in more +than the usual list of +<a href="http://gcc.gnu.org/gcc-4.9/changes.html";>changes</a>. Some of +these are a result of bug fixing, and some old behaviors have been +intentionally changed in order to support new standards, or relaxed +in standards-conforming ways to facilitate compilation or runtime +performance. Some of these changes are not visible to the naked eye +and will not cause problems when updating from older versions. +</p> + +<p> +However, some of these changes are visible, and can cause grief to +users porting to GCC 4.9. This document is an effort to identify major +issues and provide clear solutions in a quick and easily searched +manner. Additions and suggestions for improvement are welcome. +</p> + +<!-- +<h2>General issues</h2> +--> + +<!-- +<h3>New warnings</h3> +--> + +<!-- +<h2>C language issues</h2> +--> + +<h2>C++ language issues</h2> + +<h3>Shadowing name of exception in catch clause now rejected</h3> + +<p> GCC by default no longer accepts code such as: </p> + +<pre><code> + try { + // ... + } catch (const E& e) { + int e = 0; + } +</code></pre> + +<p>This example now gives the following diagnostic:</p> + +<pre> +e.cc:8:9: error: redeclaration of ‘int e’ [-fpermissive] + int e = 0; + ^ +e.cc:7:21: note: ‘const E& e’ previously declared here + } catch (const E& e) { + ^ +</pre> + +<p> +The standard says the example is ill-formed, so GCC was changed to reject it +for <a href="http://gcc.gnu.org/bugzilla/show_bug.cgi?id=31952";>PR 31952</a>. + +To fix the error either rename one of the variables or use an additional +nested scope for the second one. +</p> + +<h3>Default arguments on redeclaration of member function of class template no rejected</h3> + +<p> GCC by default no longer accepts code such as: </p> + +<pre><code> + template<class T> + struct A + { + void f(int); + }; + + template<class T> + void A<T>::f(int i=0) { } +</code></pre> + +<p>This example now gives the following diagnostic:</p> + +<pre> +r.cc:8:21: error: redeclaration of ‘void A<T>::f(int)’ may not have default arguments [-fpermissive] +</pre> + +<p> +The standard says the example is ill-formed, so GCC was changed to reject it. + +To fix the error the default argument must appear when the member function +is first declared. +</p> + +<!-- +<h3>Java issues</h3> +--> + +<h3>Links</h3> + +<p> +Matthias Klose, + <a href="http://gcc.gnu.org/ml/gcc/2014-01/msg00237.html";>Debian test rebuild on x86_64-linux-gnu with trunk 20140118</a> +</p> + +</body> +</html> +
