[Bug libstdc++/59894] New: Force use of the default new/delete

["glisse at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=59894

            Bug ID: 59894
           Summary: Force use of the default new/delete
           Product: gcc
           Version: 4.9.0
            Status: UNCONFIRMED
          Severity: enhancement
          Priority: P3
         Component: libstdc++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: glisse at gcc dot gnu.org

Hello,

operator new and operator delete are hidden in libsupc++ so they can be easily
replaced, either directly in the code, or later by interposing a library. Doing
so has a cost, and I have seen people (and done it myself) providing a
definition in their code that was roughly equivalent to the standard one, just
so it could be inlined.

I wonder if we could provide a flag in libstdc++ so that if the user compiles
his code with -D_GLIBCXX_FORCE_DEFAULT_ALLOCATION (a better name would be
welcome), <new> defines inline versions of the operators. We might even want to
skip new_handler in that version, I am not sure.

I didn't think too long about the possible drawbacks, but defining the macro
would be a pretty clear message from the user that he takes full responsibility
for all the consequences.

(we are also using, in the same code, extern "C" __typeof(malloc) malloc
__attribute__((returns_nonnull)); so it really simplifies, but PR 59875 shows
that simplifying operator delete(0) would already be nice)

PR 59893 considers a different path using LTO to inline at link time the
definition from libsupc++.