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  <jakub@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.

0 files changed, 0 insertions, 0 deletions