Hello,

I followed the advice in this discussion:
https://gcc.gnu.org/ml/gcc-patches/2014-04/msg00269.html

and here is a new patch. I made an effort to isolate a path in at least 
one subcase so it doesn't look too strange that the warning is in this 
file. Computing the dominance info just to tweak the warning message may 
be a bit excessive. I kept the same option as the front-ends, I don't know 
if we want a different one, or maybe a Wmaybe-... version. There will be 
cases where we get a duplicate warning from -Wtarget-lifetime in fortran, 
but none in the testsuite, and I would rather have 2 warnings than miss 
such broken code. The uninit-G testcase is about initialization, not 
returning, so I am changing that, even if it is unnecessary with the 
current version of the patch (only activated at -O2).

Bootstrap+testsuite (--enable-languages=all,obj-c++,ada,go) on 
x86_64-unknown-linux-gnu.

(by the way, contrib/compare_tests is confused when I use all languages, 
it prints "comm: file 1 is not in sorted order" and tons of spurious 
differences)

2014-06-23  Marc Glisse  <marc.glisse@inria.fr>

 	PR c++/60517
gcc/c/
 	* c-typeck.c (c_finish_return): Return 0 instead of the address of
 	a local variable.
gcc/cp/
 	* typeck.c (maybe_warn_about_returning_address_of_local): Return
 	whether it is returning the address of a local variable.
 	(check_return_expr): Return 0 instead of the address of a local
 	variable.
gcc/c-family/
 	* c.opt (-Wreturn-local-addr): Move to common.opt.
gcc/
 	* common.opt (-Wreturn-local-addr): Moved from c.opt.
 	* gimple-ssa-isolate-paths.c: Include diagnostic-core.h.
 	(isolate_path): New argument to avoid inserting a trap.
 	(find_implicit_erroneous_behaviour): Handle returning the address
 	of a local variable.
 	(find_explicit_erroneous_behaviour): Likewise.
 	(gimple_ssa_isolate_erroneous_paths): Calculate dominance info.
gcc/testsuite/
 	* c-c++-common/addrtmp.c: New file.
 	* c-c++-common/uninit-G.c: Adapt.

-- 
Marc Glisse