OpenMP: C++ front end support for "begin declare variant"

2025-11-22T17:05:22+00:00
This patch implements C++ support for the "begin declare variant"
construct.  The OpenMP specification is hazy on interaction of this
feature with C++ language features.  Variant functions in classes are
supported but must be defined as members in the class definition,
using an unqualified name for the base function which also must be
present in that class.  Similarly variant functions in a namespace can
only be defined in that namespace using an unqualified name for a base
function already declared in that namespace.  Variants for template
functions or inside template classes seem to (mostly) work.

gcc/c-family/ChangeLog
	* c-omp.cc (c_omp_directives): Uncomment "begin declare variant"
	and "end declare variant".

gcc/cp/ChangeLog
	* cp-tree.h (struct cp_omp_declare_variant_attr): New.
	(struct saved_scope): Add omp_declare_variant_attribute field.
	* decl.cc (omp_declare_variant_finalize_one): Add logic to inject
	"this" parameter for method calls.
	* parser.cc (cp_parser_skip_to_pragma_omp_end_declare_variant): New.
	(cp_parser_translation_unit): Handle leftover "begin declare variant"
	functions.
	(omp_start_variant_function): New.
	(omp_finish_variant_function): New.
	(omp_maybe_record_variant_base): New.
	(cp_parser_init_declarator): Handle variant functions.
	(cp_parser_class_specifier): Handle deferred lookup of base functions
	when the entire class has been seen.
	(cp_parser_member_declaration): Handle variant functions.
	(cp_finish_omp_declare_variant): Merge context selectors if in
	a "begin declare variant" block.
	(cp_parser_omp_begin): Match "omp begin declare variant".  Adjust
	error messages.
	(cp_parser_omp_end): Match "omp end declare variant".
	* parser.h (struct omp_begin_declare_variant_map_entry): New.
	(struct cp_parser): Add omp_begin_declare_variant_map field.
	* semantics.cc (finish_translation_unit): Detect unmatched
	"omp begin declare variant".

gcc/testsuite/ChangeLog
	* g++.dg/gomp/delim-declare-variant-1.C: New.
	* g++.dg/gomp/delim-declare-variant-2.C: New.
	* g++.dg/gomp/delim-declare-variant-3.C: New.
	* g++.dg/gomp/delim-declare-variant-4.C: New.
	* g++.dg/gomp/delim-declare-variant-5.C: New.
	* g++.dg/gomp/delim-declare-variant-6.C: New.
	* g++.dg/gomp/delim-declare-variant-7.C: New.
	* g++.dg/gomp/delim-declare-variant-40.C: New.
	* g++.dg/gomp/delim-declare-variant-41.C: New.
	* g++.dg/gomp/delim-declare-variant-50.C: New.
	* g++.dg/gomp/delim-declare-variant-51.C: New.
	* g++.dg/gomp/delim-declare-variant-52.C: New.
	* g++.dg/gomp/delim-declare-variant-70.C: New.
	* g++.dg/gomp/delim-declare-variant-71.C: New.

libgomp/
	* testsuite/libgomp.c++/bdv_module1.C: New.
	* testsuite/libgomp.c++/bdv_module1_main.C: New.
	* testsuite/libgomp.c++/bdv_module2.C: New.
	* testsuite/libgomp.c++/bdv_module2_impl.C: New.
	* testsuite/libgomp.c++/bdv_module2_main.C: New.
	* testsuite/libgomp.c++/bdv_module3.C: New.
	* testsuite/libgomp.c++/bdv_module3_impl.C: New.
	* testsuite/libgomp.c++/bdv_module3_main.C: New.
	* testsuite/libgomp.c++/delim-declare-variant-1.C: New.
	* testsuite/libgomp.c++/delim-declare-variant-2.C: New.
	* testsuite/libgomp.c++/delim-declare-variant-7.C: New.

Co-Authored-By: Julian Brown 
Co-Authored-By: waffl3x
gcc.git/libgomp/testsuite/libgomp.c++/bdv_module2.C, branch master

OpenMP: C++ front end support for "begin declare variant"
