c: Implement C2Y N3355 - Named Loops [PR117022]

The following patch implements the C2Y N3355 - Named Loops paper.

I've tried to implement it lazily, rather than proactively e.g. push
labels to a vector just in case the following statement is iteration
statement, switch statement or one of the loop pragmas followed by
iteration statement the patch just notes the last statement in
cur_stmt_list if any before c_parser_label/c_parser_all_labels and
passes it down to the iteration/switch statement parsing routines,
which then search backward for LABEL_EXPRs before they reach the given
stop statement.

The patch then adds one extra argument to
{FOR,WHILE,DO,BREAK,CONTINUE,SWITCH}_STMT, which is set to a canonical
name LABEL_DECL (the last named label before the construct).
If one just refers to the innermost construct with a fancy name,
it is in the end parsed the same as break/continue without an identifier
(i.e. NULL_TREE argument), and if a loop or switch has name(s) but
break/continue to that isn't used, the name is set to NULL_TREE.
At c-gimplify.cc time the name is then pushed into a hash map mapping
it to a pair of labels.

I've implemented it also for ObjC foreach loops (which have break/continue
handled during parsing, not during c-gimplify.cc).

As for OpenMP/OpenACC, the patch right now pretends no OpenMP loop
has a name, until something different is decided in the standard.
As shown in the testcases, most break identifier/continue identifier
cases aren't really useful in OpenMP code, a break identifier or
continue identifier jumping out of an OpenMP region is certainly invalid
(such regions have to be single entry single exit, so escaping it
through goto/break lab/continue lab violates that), similarly break
is disallowed in the innermost OpenMP nested loop, just continue
is allowed, so the only thing that would make sense for OpenMP (second
gomp testcase) would be allowing to give name to the innermost
loop in OpenMP canonical loop nest (except that labels aren't allowed
in the syntax right now in between the loops) and only continue to
that label.  For collapse(1) loops that would be a label before
the #pragma or [[omp::directive (parallel for)]] etc.  And of course,
what already works fine in the patch is break/continue to non-OpenMP loops
nested in OpenMP loops.

2024-10-12  Jakub Jelinek  <jakub@redhat.com>

	PR c/117022
gcc/c-family/
	* c-common.def (FOR_STMT, WHILE_STMT, DO_STMT, BREAK_STMT,
	CONTINUE_STMT, SWITCH_STMT): Add an extra operand, *_NAME
	and document it.
	* c-common.h (bc_hash_map_t): New typedef.
	(struct bc_state): Add bc_hash_map member.
	(WHILE_NAME, DO_NAME, FOR_NAME, BREAK_NAME, CONTINUE_NAME,
	SWITCH_STMT_NAME): Define.
	* c-pretty-print.cc (c_pretty_printer::statement): Print
	BREAK_STMT or CONTINUE_STMT operand if any.
	* c-gimplify.cc (bc_hash_map): New static variable.
	(note_named_bc, release_named_bc): New functions.
	(save_bc_state): Save and clear bc_hash_map.
	(restore_bc_state): Assert NULL and restore bc_hash_map.
	(genericize_c_loop): Add NAME argument, call note_named_bc
	and release_named_bc if non-NULL around the body walk.
	(genericize_for_stmt, genericize_while_stmt, genericize_do_stmt):
	Adjust callers of it.
	(genericize_switch_stmt): Rename break_block variable to blab.
	Call note_named_bc and release_named_bc if SWITCH_STMT_NAME is
	non-NULL around the body walk.
	(genericize_continue_stmt): Handle non-NULL CONTINUE_NAME.
	(genericize_break_stmt): Handle non-NULL BREAK_NAME.
	(c_genericize): Delete and clear bc_hash_map.
gcc/c/
	* c-tree.h: Implement C2Y N3355 - Named loops.
	(C_DECL_LOOP_NAME, C_DECL_SWITCH_NAME, C_DECL_LOOP_SWITCH_NAME_VALID,
	C_DECL_LOOP_SWITCH_NAME_USED, IN_NAMED_STMT): Define.
	(c_get_loop_names, c_release_loop_names, c_finish_bc_name): Declare.
	(c_start_switch): Add NAME argument.
	(c_finish_bc_stmt): Likewise.
	* c-lang.h (struct language_function): Add loop_names and
	loop_names_hash members.
	* c-parser.cc (c_parser_external_declaration,
	c_parser_declaration_or_fndef, c_parser_struct_or_union_specifier,
	c_parser_parameter_declaration): Adjust c_parser_pragma caller.
	(get_before_labels): New function.
	(c_parser_compound_statement_nostart): Call get_before_labels when
	needed, adjust c_parser_pragma and c_parser_statement_after_labels
	callers.
	(c_parser_statement): Call get_before_labels first and pass it to
	c_parser_statement_after_labels.
	(c_parser_bc_name): New function.
	(c_parser_statement_after_labels): Add BEFORE_LABELS argument.  Pass
	it down to c_parser_switch_statement, c_parser_while_statement,
	c_parser_do_statement, c_parser_for_statement and c_parser_pragma.
	Call c_parser_bc_name for RID_BREAK and RID_CONTINUE and pass it as
	another argument to c_finish_bc_stmt.
	(c_parser_if_body, c_parser_else_body): Call get_before_labels
	early and pass it to c_parser_statement_after_labels.
	(c_parser_switch_statement): Add BEFORE_LABELS argument.  Call
	c_get_loop_names, if named, pass switch_name to c_start_switch,
	mark it valid and set IN_NAMED_STMT bit in in_statement before
	parsing body, otherwise clear IN_NAMED_STMT bit before that parsing.
	Run c_release_loop_names at the end.
	(c_parser_while_statement, c_parser_do_statement,
	c_parser_for_statement): Add BEFORE_LABELS argument.  Call
	c_get_loop_names, if named, mark it valid and set IN_NAMED_STMT bit
	in in_statement before parsing body, otherwise clear IN_NAMED_STMT
	before that parsing, arrange for the loop name if used to be
	another *_STMT argument.
	(c_parser_objc_class_instance_variables,
	c_parser_objc_methodprotolist): Adjust c_parser_pragma callers.
	(c_parser_pragma): Add BEFORE_LABELS argument.  Pass it down to
	c_parser_for_statement, c_parser_while_statement or
	c_parser_do_statement.
	(c_parser_omp_loop_nest, c_maybe_parse_omp_decl): Adjust
	c_parser_pragma callers.
	* c-decl.cc (loop_names, loop_names_hash): New static variables.
	(add_stmt): Set STATEMENT_LIST_HAS_LABEL after push_stmt_list rather
	than before it.
	(c_push_function_context): Save and clear loop_names and
	loop_names_hash.
	(c_pop_function_context): Release or delete, restore and clear
	loop_names and loop_names_hash.
	(c_get_loop_names, c_release_loop_names, c_finish_bc_name): New
	functions.
	* c-typeck.cc (c_start_switch): Add SWITCH_NAME argument, pass it down
	to build_stmt.
	(c_finish_bc_stmt): Add NAME argument.  Mark of IN_NAMED_STMT bit
	of in_statement in swtiches.  Use label for IN_OBJC_FOREACH only if
	name is NULL.  If name is non-NULL and C_DECL_LOOP_NAME and
	C_DECL_SWITCH_NAME are both set, assume outer ObjC foreach and
	dig labels from DECL_CHAIN of name.  Pass NAME to build_stmt
	otherwise.
gcc/cp/
	* semantics.cc (begin_while_stmt, begin_do_stmt, begin_for_stmt,
	finish_break_stmt, finish_continue_stmt, begin_switch_stmt): Pass
	another NULL_TREE to build_stmt calls.
gcc/testsuite/
	* gcc.dg/c23-named-loops-1.c: New test.
	* gcc.dg/c23-named-loops-5.c: New test.
	* gcc.dg/c2y-named-loops-1.c: New test.
	* gcc.dg/c2y-named-loops-2.c: New test.
	* gcc.dg/c2y-named-loops-4.c: New test.
	* gcc.dg/c2y-named-loops-5.c: New test.
	* gcc.dg/c2y-named-loops-6.c: New test.
	* gcc.dg/c2y-named-loops-7.c: New test.
	* gcc.dg/gnu99-named-loops-1.c: New test.
	* gcc.dg/gnu99-named-loops-2.c: New test.
	* gcc.dg/gnu99-named-loops-3.c: New test.
	* gcc.dg/gnu99-named-loops-4.c: New test.
	* gcc.dg/gnu2y-named-loops-3.c: New test.
	* gcc.dg/gomp/named-loops-1.c: New test.
	* gcc.dg/gomp/named-loops-2.c: New test.
	* objc.dg/named-loops-1.m: New test.