Ping?
In case there isn't immediate approval for the patch proper (I suppose
different parts will require review by different subsystem maintainers),
I'd appreciate at least community and language lawyers buy-in (or
turn-down) for the new feature hereby proposed for C-family languages,
namely, attribute exalias("symbol_name") as a means to have symbol_name
output as a same-linkage alias for functions, variables, and for C++
class types' RTTI symbols.
Thanks in advance,
On Aug 7, 2020, Alexandre Oliva <ol...@adacore.com> wrote:
Since last week's patchlet, I've delayed the creation of the exalias
decls, improved the merging of attributes, minimizing
interface/visibility updates, found a better way to assign exaliases to
nested explicit instantiations, even after enabling aliases to
already-defined types, so now I'm reasonably happy with the patch.
This patch introduces an attribute to add extra aliases to a symbol
when its definition is output. The main goal is to ease interfacing
C++ with Ada, as C++ mangled names have to be named, and in some cases
(e.g. when using stdint.h typedefs in function arguments) the symbol
names may vary across platforms.
The attribute is usable in C and C++, presumably in all C-family
languages. It can be attached to global variables and functions. In
C++, it can also be attached to namespace-scoped variables and
functions, static data members, member functions, explicit
instantiations and specializations of template functions, members and
classes. When applied to constructors or destructor, additional
exaliases with _Base and _Del suffixes are defined for variants other
than complete-object ones.
Applying the attribute to class types is only valid in C++, and the
effect is to attach the alias to the RTTI object associated with the
class type.
While working on this, I noticed C++ didn't merge attributes of extern
local declarations with those of the namespace-scoped declaration.
I've added code to merge the attributes if there is a namespace-scoped
declaration, but if there isn't one, there won't be any merging, and
the effects are noticeable, as in the added attr-weak-1.C. I'm also
slightly concerned that an earlier local decl would go out of sync if
a subsequent local decl, say within the same or even in another
function, introduces additional attributes in the global decl.
Regstrapped on x86_64-linux-gnu. Ok to install?
(The newly-introduced attr-weak-1.c passes in C, but is marked as XFAIL
for C++, so it gets an XPASS in C; I could move it to some C++-only
subtree, or drop it altogether and file a PR instead)
for gcc/ChangeLog
* attribs.c: Include cgraph.h.
(decl_attributes): Allow late introduction of exalias in
types.
(create_exalias_decl, create_exalias_decls): New.
* attribs.h: Declare them.
(FOR_EACH_EXALIAS): New macro.
* cgraph.c (cgraph_node::create): Create exalias decls.
* varpool.c (varpool_node::get_create): Create exalias decls.
* cgraph.h (symtab_node::remap_exalias_target): New.
* symtab.c (symtab_node::remap_exalias_target): Define.
* cgraphunit.c (cgraph_node::analyze): Create alias_target
node if needed.
(analyze_functions): Fixup visibility of implicit alias only
after its node is analyzed.
* doc/extend.texi (exalias): Document for variables, functions
and types.
for gcc/ada/ChangeLog
* doc/gnat_rm/interfacing_to_other_languages.rst: Mention
attribute exalias to give RTTI symbols mnemonic names.
* doc/gnat_ugn/the_gnat_compilation_model.rst: Mention
attribute exalias. Fix incorrect ref to C1 ctor variant.
for gcc/c-family/ChangeLog
* c-ada-spec.c (pp_asm_name): Use first exalias if available.
* c-attribs.c (handle_exalias_attribute): New.
(c_common_attribute_table): Add exalias.
(handle_copy_attribute): Do not copy exalias.
* c-decl.c (duplicate_decls): Remap exalias target.
for gcc/cp/ChangeLog
* class.c (copy_fndecl_with_name): Move/adjust exalias to
cdtor variants.
(build_cdtor_clones): Drop exalias from primary variant.
* cp-tree.h (update_exalias_interface, update_tinfo_exalias):
Declare.
* decl.c (duplicate_decls): Remap exalias target.
(grokfndecl): Tentatively create exalias decls after adding
attributes in e.g. a template member function explicit
instantiation.
* decl2.c (cplus_decl_attributes): Update tinfo exalias.
(copy_interface, update_exalias_interface): New.
(determine_visibility): Update exalias interface.
(tentative_decl_linkage, import_export_decl): Likewise.
* name-lookup.c: Include target.h and cgraph.h.
(set_local_extern_decl_linkage): Merge attributes with a
namespace-scoped decl if one is found. Remap exalias
targets, and drop exaliases from the local decl.
* optimize.c (maybe_clone_body): Only copy attributes if they
haven't been copied yet. Update exalias interface.
* rtti.c: Include attribs.h and cgraph.h.
(get_tinfo_decl): Copy exalias attributes from type to tinfo
decl. Create exalias decls.
(update_tinfo_exalias): New.
for gcc/testsuite/ChangeLog
* c-c++-common/attr-weak-1.c: New, xfailed.
* c-c++-common/torture/attr-exalias-1.c: New.
* c-c++-common/torture/attr-exalias-2.c: New.
* c-c++-common/torture/attr-exalias-3.c: New.
* c-c++-common/torture/attr-exalias-4.c: New.
* g++.dg/torture/attr-exalias-1.C: New.
* g++.dg/torture/attr-exalias-2.C: New.
* g++.dg/torture/attr-exalias-3.C: New.
* g++.dg/torture/attr-exalias-4.C: New.
https://gcc.gnu.org/pipermail/gcc-patches/2020-August/551614.html
