https://gcc.gnu.org/bugzilla/show_bug.cgi?id=117047
--- Comment #45 from GCC Commits <cvs-commit at gcc dot gnu.org> --- The master branch has been updated by Jakub Jelinek <ja...@gcc.gnu.org>: https://gcc.gnu.org/g:8c15a6cefa0d1f8ec12701af1f528f473c33ff6b commit r15-7770-g8c15a6cefa0d1f8ec12701af1f528f473c33ff6b Author: Jakub Jelinek <ja...@redhat.com> Date: Sat Mar 1 11:22:27 2025 +0100 ggc: Avoid using ATTRIBUTE_MALLOC for allocations that need finalization [PR117047] As analyzed by Andrew/David/Richi/Sam in the PR, the reason for the libgccjit ICE is that there are GC allocations with finalizers and we still mark ggc_internal_{,cleared_}alloc with ATTRIBUTE_MALLOC, which to the optimizers hints that nothing will actually read the state of the objects when they get out of lifetime. The finalizer actually inspects those though. What actually happens in the testcases is that on tree expr_size = TYPE_SIZE (expr->get_type ()->as_tree ()); we see that expr->get_type () was allocated using something with malloc attribute but it doesn't escape and only the type size from it is queried, so there is no need to store other members of it. Except that it does escape in the GC internals. Normal GC allocations are fine, they don't look at the data in the allocated objects on "free", but the ones with finalizers actually call a function on that object and expect the data to be in there. So that we don't lose ATTRIBUTE_MALLOC for the common case when no finalization is needed, the following patch uses the approach used e.g. for glibc error function which can sometimes be noreturn but at other times just return normally. If possible, it uses __attribute__((alias ("..."))) to add an alias to the function, where one is without ATTRIBUTE_MALLOC and one (with _no_dtor suffix) is with ATTRIBUTE_MALLOC (note, as this is C++ and I didn't want to hardcode particular mangling I used an extern "C" function with 2 aliases to it), and otherwise adds a wrapper (for the ggc-page/ggc-common case with noinline attribute if possible, for ggc-none that doesn't matter because ggc-none doesn't support finalizers). The *_no_dtor aliases/wrappers are then used in inline functions which pass unconditional NULL, 0 as the f/s pair. 2025-03-01 Jakub Jelinek <ja...@redhat.com> PR jit/117047 * acinclude.m4 (gcc_CHECK_ATTRIBUTE_ALIAS): New. * configure.ac: Add gcc_CHECK_ATTRIBUTE_ALIAS. * ggc.h (ggc_internal_alloc): Remove ATTRIBUTE_MALLOC from overload with finalizer pointer. Call ggc_internal_alloc_no_dtor in inline overload without finalizer pointer. (ggc_internal_alloc_no_dtor): Declare. (ggc_internal_cleared_alloc): Remove ATTRIBUTE_MALLOC from overload with finalizer pointer. Call ggc_internal_cleared_alloc_no_dtor in inline overload without finalizer pointer. (ggc_internal_cleared_alloc_no_dtor): Declare. (ggc_alloc): Call ggc_internal_alloc_no_dtor if no finalization is needed. (ggc_alloc_no_dtor): Call ggc_internal_alloc_no_dtor. (ggc_cleared_alloc): Call ggc_internal_cleared_alloc_no_dtor if no finalization is needed. (ggc_vec_alloc): Call ggc_internal_alloc_no_dtor if no finalization is needed. (ggc_cleared_vec_alloc): Call ggc_internal_cleared_alloc_no_dtor if no finalization is needed. * ggc-page.cc (ggc_internal_alloc): If HAVE_ATTRIBUTE_ALIAS, turn overload with finalizer into alias to ggc_internal_alloc_ and rename it to ... (ggc_internal_alloc_): ... this, make it extern "C". (ggc_internal_alloc_no_dtor): New alias if HAVE_ATTRIBUTE_ALIAS, otherwise new noinline wrapper. * ggc-common.cc (ggc_internal_cleared_alloc): If HAVE_ATTRIBUTE_ALIAS, turn overload with finalizer into alias to ggc_internal_alloc_ and rename it to ... (ggc_internal_cleared_alloc_): ... this, make it extern "C". (ggc_internal_cleared_alloc_no_dtor): New alias if HAVE_ATTRIBUTE_ALIAS, otherwise new noinline wrapper. * ggc-none.cc (ggc_internal_alloc): If HAVE_ATTRIBUTE_ALIAS, turn overload with finalizer into alias to ggc_internal_alloc_ and rename it to ... (ggc_internal_alloc_): ... this, make it extern "C". (ggc_internal_alloc_no_dtor): New alias if HAVE_ATTRIBUTE_ALIAS, otherwise new wrapper. (ggc_internal_cleared_alloc): If HAVE_ATTRIBUTE_ALIAS, turn overload with finalizer into alias to ggc_internal_alloc_ and rename it to ... (ggc_internal_cleared_alloc_): ... this, make it extern "C". (ggc_internal_cleared_alloc_no_dtor): New alias if HAVE_ATTRIBUTE_ALIAS, otherwise new wrapper. * genmatch.cc (ggc_internal_cleared_alloc, ggc_free): Formatting fix. (ggc_internal_cleared_alloc_no_dtor): Define. * config.in: Regenerate. * configure: Regenerate.
