> Now that we have a way of explicitly marking a variable as dead, we > can use that to indicate the end of a temporary's lifetime by adding > it as a cleanup for that temporary. Since gimple_push_cleanup still > deals in trees I needed to tweak a couple of places to avoid trying > to treat a clobber as a real CONSTRUCTOR, but the changes were small. > > One somewhat surprising thing that showed up as a result of this > change were some failures in the libstdc++ testsuite. When I > investigated, I found that the tests were relying on temporaries > living longer than they should: > > > const int& x = std::max(1, 2); > > Since std::max takes its arguments by const reference and returns one > of them, x ends up as a dangling reference to the temporary > containing 2, which dies at the end of the declaration-statement. > This patch breaks the testcase because now the temporary stack slots > get reused by the next statement, so by the time we look at x it no > longer points to a 2. I've fixed the tests by removing the references > on the variables.
Interesting. Thanks for the heads up. This should definitely be mentioned in 4.7/porting_to.html. -benjamin
