Re: [PATCH V2 3/5] OpenMP: C++ support for imperfectly-nested loops

[Jakub Jelinek <jakub@redhat.com>]

On Sun, Jul 23, 2023 at 04:15:19PM -0600, Sandra Loosemore wrote:
> OpenMP 5.0 removed the restriction that multiple collapsed loops must
> be perfectly nested, allowing "intervening code" (including nested
> BLOCKs) before or after each nested loop.  In GCC this code is moved
> into the inner loop body by the respective front ends.
> 
> This patch changes the C++ front end to use recursive descent parsing
> on nested loops within an "omp for" construct, rather than an
> iterative approach, in order to preserve proper nesting of compound
> statements.  Preserving cleanups (destructors) for class objects
> declared in intervening code and loop initializers complicates moving
> the former into the body of the loop; this is handled by parsing the
> entire construct before reassembling any of it.
> 
> gcc/cp/ChangeLog
> 	* cp-tree.h (cp_convert_omp_range_for): Adjust declaration.
> 	* parser.cc (struct omp_for_parse_data): New.
> 	(cp_parser_postfix_expression): Diagnose calls to OpenMP runtime
> 	in intervening code.
> 	(check_omp_intervening_code): New.
> 	(cp_parser_statement_seq_opt): Special-case nested loops, blocks,
> 	and other constructs for OpenMP loops.
> 	(cp_parser_iteration_statement): Reject loops in intervening code.
> 	(cp_parser_omp_for_loop_init): Expand comments and tweak the
> 	interface slightly to better distinguish input/output parameters.
> 	(cp_convert_omp_range_for): Likewise.
> 	(cp_parser_omp_loop_nest): New, split from cp_parser_omp_for_loop
> 	and largely rewritten.  Add more comments.
> 	(insert_structured_blocks): New.
> 	(find_structured_blocks): New.
> 	(struct sit_data, substitute_in_tree_walker, substitute_in_tree):
> 	New.
> 	(fixup_blocks_walker): New.
> 	(cp_parser_omp_for_loop): Rewrite to use recursive descent instead
> 	of a loop.  Add logic to reshuffle the bits of code collected
> 	during parsing so intervening code gets moved to the loop body.
> 	(cp_parser_omp_loop): Remove call to finish_omp_for_block, which
> 	is now redundant.
> 	(cp_parser_omp_simd): Likewise.
> 	(cp_parser_omp_for): Likewise.
> 	(cp_parser_omp_distribute): Likewise.
> 	(cp_parser_oacc_loop): Likewise.
> 	(cp_parser_omp_taskloop): Likewise.
> 	(cp_parser_pragma): Reject OpenMP pragmas in intervening code.
> 	* parser.h (struct cp_parser): Add omp_for_parse_state field.
> 	* pt.cc (tsubst_omp_for_iterator): Adjust call to
> 	cp_convert_omp_range_for.
> 	* semantics.cc (finish_omp_for): Try harder to preserve location
> 	of loop variable init expression for use in diagnostics.
> 	(struct fofb_data, finish_omp_for_block_walker): New.
> 	(finish_omp_for_block): Allow variables to be bound in a BIND_EXPR
> 	nested inside BIND instead of directly in BIND itself.
> 
> gcc/testsuite/ChangeLog
> 	* c-c++-common/goacc/tile-2.c: Adjust expected error patterns.
> 	* g++.dg/gomp/attrs-imperfect1.C: New test.
> 	* g++.dg/gomp/attrs-imperfect2.C: New test.
> 	* g++.dg/gomp/attrs-imperfect3.C: New test.
> 	* g++.dg/gomp/attrs-imperfect4.C: New test.
> 	* g++.dg/gomp/attrs-imperfect5.C: New test.
> 	* g++.dg/gomp/pr41967.C: Adjust expected error patterns.
> 	* g++.dg/gomp/tpl-imperfect-gotos.C: New test.
> 	* g++.dg/gomp/tpl-imperfect-invalid-scope.C: New test.
> 
> libgomp/ChangeLog
> 	* testsuite/libgomp.c++/attrs-imperfect1.C: New test.
> 	* testsuite/libgomp.c++/attrs-imperfect2.C: New test.
> 	* testsuite/libgomp.c++/attrs-imperfect3.C: New test.
> 	* testsuite/libgomp.c++/attrs-imperfect4.C: New test.
> 	* testsuite/libgomp.c++/attrs-imperfect5.C: New test.
> 	* testsuite/libgomp.c++/attrs-imperfect6.C: New test.
> 	* testsuite/libgomp.c++/imperfect-class-1.C: New test.
> 	* testsuite/libgomp.c++/imperfect-class-2.C: New test.
> 	* testsuite/libgomp.c++/imperfect-class-3.C: New test.
> 	* testsuite/libgomp.c++/imperfect-destructor.C: New test.
> 	* testsuite/libgomp.c++/imperfect-template-1.C: New test.
> 	* testsuite/libgomp.c++/imperfect-template-2.C: New test.
> 	* testsuite/libgomp.c++/imperfect-template-3.C: New test.

Ok (though, if the c-c++-common tests are tweaked in the C patch,
this patch needs to undo that).

	Jakub