c++: Fix up mangling of function/block scope static structured bindings [PR111069]

c++: Fix up mangling of function/block scope static structured bindings [PR111069]

As can be seen on the testcase, we weren't correctly mangling
static/thread_local structured bindings (C++20 feature) at function/block
scope.  The following patch fixes that by using what write_local_name
does for those cases (note, structured binding mandling doesn't use the
standard path because it needs to pass a list of all the identifiers in
the structured binding to the mangling).  In addition to that it fixes
mangling of various helpers which use write_guarded_name (_ZGV*, _ZTH*,
_ZTW*) and kills find_decomp_unqualified_name which for the local names
would be too hard to implement and uses write_guarded_name for structured
binding related _ZGR* names as well.

All the mangled names on the first testcase match now clang++ and my
expectations.
Because the old mangled names were plain wrong (they mangled the same as
structured binding at global scope and resulted in assembly errors if there
was more than one static structured binding with the same identifiers in
the same (or another) function, I think we don't need to play with another
mangling ABI level which turns on/off the old broken way.

In addition to that the patch starts to emit abi-tags into the mangle_decomp
produced names when needed and emits a -Wabi warning for that as well.
To make that work, I had to move cp_maybe_mangle_decomp calls from before
cp_finish_decl into a middle of cp_finish_decl after type is deduced and
maybe_commonize_var (which also had to be changed not to ignore structured
bindings) is called but before anything might need a mangled name for the
decl, so a new cp_decomp structure is passed to cp_finish_decl; various
other structured binding related functions have been changed to pass
pointer to that around instead of passing a tree and unsigned int separately.

On decomp9.C, there is a
_ZZ3barI1TB3quxEivEDC1o1pEB3qux
(g++) vs.
_ZZ3barI1TB3quxEivEDC1o1pE
(clang++) mangling difference, but that seems to be a clang++ bug and happens
also with normal static block vars, doesn't need structured bindings.

2023-09-01  Jakub Jelinek  <jakub@redhat.com>

	PR c++/111069
gcc/
	* common.opt (fabi-version=): Document version 19.
	* doc/invoke.texi (-fabi-version=): Likewise.
gcc/c-family/
	* c-opts.cc (c_common_post_options): Change latest_abi_version to 19.
gcc/cp/
	* cp-tree.h (determine_local_discriminator): Add NAME argument with
	NULL_TREE default.
	(struct cp_decomp): New type.
	(cp_finish_decl): Add DECOMP argument defaulted to nullptr.
	(cp_maybe_mangle_decomp): Remove declaration.
	(cp_finish_decomp): Add cp_decomp * argument, remove tree and unsigned
	args.
	(cp_convert_range_for): Likewise.
	* decl.cc (determine_local_discriminator): Add NAME argument, use it
	if non-NULL, otherwise compute it the old way.
	(maybe_commonize_var): Don't return early for structured bindings.
	(cp_finish_decl): Add DECOMP argument, if non-NULL, call
	cp_maybe_mangle_decomp.
	(cp_maybe_mangle_decomp): Make it static with a forward declaration.
	Call determine_local_discriminator.  Replace FIRST and COUNT arguments
	with DECOMP argument.
	(cp_finish_decomp): Replace FIRST and COUNT arguments with DECOMP
	argument.
	* mangle.cc (find_decomp_unqualified_name): Remove.
	(write_unqualified_name): Don't call find_decomp_unqualified_name.
	(mangle_decomp): Handle mangling of static function/block scope
	structured bindings.  Don't call decl_mangling_context twice.  Call
	check_abi_tags, call write_abi_tags for abi version >= 19 and emit
	-Wabi warnings if needed.
	(write_guarded_var_name): Handle structured bindings.
	(mangle_ref_init_variable): Use write_guarded_var_name.
	* parser.cc (cp_parser_range_for): Adjust do_range_for_auto_deduction
	and cp_convert_range_for callers.
	(do_range_for_auto_deduction): Replace DECOMP_FIRST_NAME and
	DECOMP_CNT arguments with DECOMP.  Adjust cp_finish_decomp caller.
	(cp_convert_range_for): Replace DECOMP_FIRST_NAME and
	DECOMP_CNT arguments with DECOMP.  Don't call cp_maybe_mangle_decomp,
	adjust cp_finish_decl and cp_finish_decomp callers.
	(cp_parser_decomposition_declaration): Don't call
	cp_maybe_mangle_decomp, adjust cp_finish_decl and cp_finish_decomp
	callers.
	(cp_convert_omp_range_for): Adjust do_range_for_auto_deduction
	and cp_finish_decomp callers.
	(cp_finish_omp_range_for): Don't call cp_maybe_mangle_decomp,
	adjust cp_finish_decl and cp_finish_decomp callers.
	* pt.cc (tsubst_omp_for_iterator): Adjust tsubst_decomp_names
	caller.
	(tsubst_decomp_names): Replace FIRST and CNT arguments with DECOMP.
	(tsubst_expr): Don't call cp_maybe_mangle_decomp, adjust
	tsubst_decomp_names, cp_finish_decl, cp_finish_decomp and
	cp_convert_range_for callers.
gcc/testsuite/
	* g++.dg/cpp2a/decomp8.C: New test.
	* g++.dg/cpp2a/decomp9.C: New test.
	* g++.dg/abi/macro0.C: Expect __GXX_ABI_VERSION 1019 rather than
	1018.