Fortran: Add OpenMP's assume(s) directives

Fortran: Add OpenMP's assume(s) directives

libgomp/ChangeLog:

	* libgomp.texi (OpenMP 5.1 Impl. Status): Mark 'assume' as 'Y'.

gcc/fortran/ChangeLog:

	* dump-parse-tree.cc (show_omp_assumes): New.
	(show_omp_clauses, show_namespace): Call it.
	(show_omp_node, show_code_node): Handle OpenMP ASSUME.
	* gfortran.h (enum gfc_statement): Add ST_OMP_ASSUME,
	ST_OMP_END_ASSUME, ST_OMP_ASSUMES and ST_NOTHING.
	(gfc_exec_op): Add EXEC_OMP_ASSUME.
	(gfc_omp_assumptions): New struct.
	(gfc_get_omp_assumptions): New XCNEW #define.
	(gfc_omp_clauses, gfc_namespace): Add assume member.
	(gfc_resolve_omp_assumptions): New prototype.
	* match.h (gfc_match_omp_assume, gfc_match_omp_assumes): New.
	* openmp.cc (omp_code_to_statement): Forward declare.
	(enum gfc_omp_directive_kind, struct gfc_omp_directive): New.
	(gfc_free_omp_clauses): Free assume member and its struct data.
	(enum omp_mask2): Add OMP_CLAUSE_ASSUMPTIONS.
	(gfc_omp_absent_contains_clause): New.
	(gfc_match_omp_clauses): Call it; optionally use passed
	omp_clauses argument.
	(omp_verify_merge_absent_contains, gfc_match_omp_assume,
	 gfc_match_omp_assumes, gfc_resolve_omp_assumptions): New.
	(resolve_omp_clauses): Call the latter.
	(gfc_resolve_omp_directive, omp_code_to_statement): Handle
	EXEC_OMP_ASSUME.
	* parse.cc (decode_omp_directive): Parse OpenMP ASSUME(S).
	(next_statement, parse_executable, parse_omp_structured_block):
	Handle ST_OMP_ASSUME.
	(case_omp_decl): Add ST_OMP_ASSUMES.
	(gfc_ascii_statement): Handle Assumes, optional return
	string without '!$OMP '/'!$ACC ' prefix.
	* parse.h (gfc_ascii_statement): Add optional bool arg to prototype.
	* resolve.cc (gfc_resolve_blocks, gfc_resolve_code): Add
	EXEC_OMP_ASSUME.
	(gfc_resolve): Resolve ASSUMES directive.
	* symbol.cc (gfc_free_namespace): Free omp_assumes member.
	* st.cc (gfc_free_statement): Handle EXEC_OMP_ASSUME.
	* trans-openmp.cc (gfc_trans_omp_directive): Likewise.
	* trans.cc (trans_code): Likewise.

gcc/testsuite/ChangeLog:

	* gfortran.dg/gomp/assume-1.f90: New test.
	* gfortran.dg/gomp/assume-2.f90: New test.
	* gfortran.dg/gomp/assumes-1.f90: New test.
	* gfortran.dg/gomp/assumes-2.f90: New test.