openmp: Add OpenMP assume, assumes and begin/end assumes support

openmp: Add OpenMP assume, assumes and begin/end assumes support

The following patch implements OpenMP 5.1
 #pragma omp assume
 #pragma omp assumes
and
 #pragma omp begin assumes
 #pragma omp end assumes
directive support for C and C++.  Currently it doesn't remember
anything from the assumption clauses for later, so is mainly
to support the directives and diagnose errors in their use.
If the recently posted C++23 [[assume (cond)]]; support makes it
in, the intent is that this can be easily adjusted at least for
the #pragma omp assume directive with holds clause(s) to use
the same infrastructure.  Now, C++23 portable assumptions are slightly
different from OpenMP 5.1 assumptions' holds clause in that C++23
assumption holds just where it appears, while OpenMP 5.1 assumptions
hold everywhere in the scope of the directive.  For assumes
directive which can appear at file or namespace scope it is the whole
TU and everything that functions from there call at runtime, for
begin assumes/end assumes pair all the functions in between those
directives and everything they call and for assume directive the
associated (currently structured) block.  I have no idea how to
represents such holds to be usable for optimizers, except to
make
 #pragma omp assume holds (cond)
block;
expand essentially to
[[assume (cond)]];
block;
or
[[assume (cond)]];
block;
[[assume (cond)]];
for now.  Except for holds clause, the other assumptions are
OpenMP related, I'd say we should brainstorm where it would be
useful to optimize based on such information (I guess e.g. in target
regions it easily could) and only when we come up with something
like that think about how to propagate the assumptions to the optimizers.

2022-09-27  Jakub Jelinek  <jakub@redhat.com>

gcc/c-family/
	* c-pragma.h (enum pragma_kind): Add PRAGMA_OMP_ASSUME,
	PRAGMA_OMP_ASSUMES and PRAGMA_OMP_BEGIN.  Rename
	PRAGMA_OMP_END_DECLARE_TARGET to PRAGMA_OMP_END.
	* c-pragma.cc (omp_pragmas): Add assumes and begin.
	For end rename PRAGMA_OMP_END_DECLARE_TARGET to PRAGMA_OMP_END.
	(omp_pragmas_simd): Add assume.
	* c-common.h (c_omp_directives): Declare.
	* c-omp.cc (omp_directives): Rename to ...
	(c_omp_directives): ... this.  No longer static.  Uncomment
	assume, assumes, begin assumes and end assumes entries.
	In end declare target entry rename PRAGMA_OMP_END_DECLARE_TARGET
	to PRAGMA_OMP_END.
	(c_omp_categorize_directive): Adjust for omp_directives to
	c_omp_directives renaming.
gcc/c/
	* c-lang.h (current_omp_begin_assumes): Declare.
	* c-parser.cc: Include bitmap.h.
	(c_parser_omp_end_declare_target): Rename to ...
	(c_parser_omp_end): ... this.  Handle also end assumes.
	(c_parser_omp_begin, c_parser_omp_assumption_clauses,
	c_parser_omp_assumes, c_parser_omp_assume): New functions.
	(c_parser_translation_unit): Also diagnose #pragma omp begin assumes
	without corresponding #pragma omp end assumes.
	(c_parser_pragma): Use %s in may only be used at file scope
	diagnostics to decrease number of translatable messages.  Handle
	PRAGMA_OMP_BEGIN and PRAGMA_OMP_ASSUMES.  Handle PRAGMA_OMP_END
	rather than PRAGMA_OMP_END_DECLARE_TARGET and call c_parser_omp_end
	for it rather than c_parser_omp_end_declare_target.
	(c_parser_omp_construct): Handle PRAGMA_OMP_ASSUME.
	* c-decl.cc (current_omp_begin_assumes): Define.
gcc/cp/
	* cp-tree.h (struct omp_begin_assumes_data): New type.
	(struct saved_scope): Add omp_begin_assumes member.
	* parser.cc: Include bitmap.h.
	(cp_parser_omp_assumption_clauses, cp_parser_omp_assume,
	cp_parser_omp_assumes, cp_parser_omp_begin): New functions.
	(cp_parser_omp_end_declare_target): Rename to ...
	(cp_parser_omp_end): ... this.  Handle also end assumes.
	(cp_parser_omp_construct): Handle PRAGMA_OMP_ASSUME.
	(cp_parser_pragma): Handle PRAGMA_OMP_ASSUME, PRAGMA_OMP_ASSUMES
	and PRAGMA_OMP_BEGIN.  Handle PRAGMA_OMP_END rather than
	PRAGMA_OMP_END_DECLARE_TARGET and call cp_parser_omp_end
	for it rather than cp_parser_omp_end_declare_target.
	* pt.cc (apply_late_template_attributes): Also temporarily clear
	omp_begin_assumes.
	* semantics.cc (finish_translation_unit): Also diagnose
	#pragma omp begin assumes without corresponding
	#pragma omp end assumes.
gcc/testsuite/
	* c-c++-common/gomp/assume-1.c: New test.
	* c-c++-common/gomp/assume-2.c: New test.
	* c-c++-common/gomp/assume-3.c: New test.
	* c-c++-common/gomp/assumes-1.c: New test.
	* c-c++-common/gomp/assumes-2.c: New test.
	* c-c++-common/gomp/assumes-3.c: New test.
	* c-c++-common/gomp/assumes-4.c: New test.
	* c-c++-common/gomp/begin-assumes-1.c: New test.
	* c-c++-common/gomp/begin-assumes-2.c: New test.
	* c-c++-common/gomp/begin-assumes-3.c: New test.
	* c-c++-common/gomp/begin-assumes-4.c: New test.
	* c-c++-common/gomp/declare-target-6.c: New test.
	* g++.dg/gomp/attrs-1.C (bar): Add n1 and n2 arguments, add
	tests for assume directive.
	* g++.dg/gomp/attrs-2.C (bar): Likewise.
	* g++.dg/gomp/attrs-9.C: Add n1 and n2 variables, add tests for
	begin assumes directive.
	* g++.dg/gomp/attrs-15.C: New test.
	* g++.dg/gomp/attrs-16.C: New test.
	* g++.dg/gomp/attrs-17.C: New test.