This patch is another piece of preparation for C2x attributes support.

C2x attributes require unbounded lookahead in the parser, because the
token sequence '[[' that starts a C2x attribute is also valid in
Objective-C in some of the same contexts, so it is necessary to see
whether the matching ']]' are consecutive tokens or not to determine
whether those tokens start an attribute.

Unbounded lookahead means lexing an unbounded number of tokens before
they are parsed.  c_lex_one_token does various context-sensitive
processing of tokens that cannot be done at that lookahead time,
because it depends on information (such as whether particular
identifiers are typedefs) that may be different at the time it is
relevant than at the time the lookahead is needed (recall that more or
less arbitrary C code, including declarations and statements, can
appear inside expressions in GNU C).

Most of that context-sensitive processing is not a problem, simply
because it is not needed for lookahead purposes so can be deferred
until the tokens lexed during lookahead are parsed.  However, the
earliest piece of context-sensitive processing is the handling of
string literals based on flags passed to c_lex_with_flags, which
determine whether adjacent literals are concatenated and whether
translation to the execution character set occurs.

Because the choice of whether to translate to the execution character
set is context-sensitive, this means that unbounded lookahead requires
the C parser to move to the approach used by the C++ parser, where
string literals are generally not translated or concatenated from
within c_lex_with_flags, but only later in the parser once it knows
whether translation is needed.  (Translation requires the tokens in
their form before concatenation.)

Thus, this patch makes that change to the C parser.  Flags in the
parser are still used for two special cases similar to C++: the
handling of an initial #pragma pch_preprocess, and arranging for
strings inside attributes not to be translated (the latter is made
more logically correct by saving and restoring the flags, as in the
C++ parser, rather than assuming that the state outside the attribute
was always to translate string literals, which might not be the case
in corner cases involving declarations and attributes inside
attributes).

The consequent change to pragma_lex to use c_parser_string_literal
makes it disallow wide strings and disable translation in that
context, which also follows C++ and is more logically correct than the
previous state without special handling in that regard.  Translation
to the execution character set is always disabled when string
constants are handled in the GIMPLE parser.

Although the handling of strings is now a lot closer to that in C++,
there are still some differences, in particular regarding the handling
of locations.  See c-c++-common/Wformat-pr88257.c, which has different
expected multiline diagnostic output for C and C++, for example; I'm
not sure whether the C or C++ output is better there (C++ has a more
complete range than C, C mentions a macro definition location that C++
doesn't), but I tried to keep the locations the same as those
previously used by the C front end, as far as possible, to minimize
the testsuite changes needed, rather than possibly making them closer
to those used with C++.

The only changes needed for tests of user-visible diagnostics were for
the wording of one diagnostic changing to match C++ (as a consequence
of having a check for wide strings based on a flag in a general
string-handling function rather than in a function specific to asm).
However, although locations are extremely similar to what they were
before, I couldn't make them completely identical in all cases.  (My
understanding of the implementation reason for the differences is as
follows: lex_string uses src_loc from each cpp_token; the C parser is
using the virtual location from cpp_get_token_with_location as called
by c_lex_with_flags, and while passing that through
linemap_resolve_location with LRK_MACRO_DEFINITION_LOCATION, as this
patch does, produces something very close to what lex_string uses,
it's not completely identical in some cases.)

This results in changes being needed to two of the gcc.dg/plugin tests
that use a plugin to test details of how string locations are handled.
Because the tests being changed are for ICEs and the only change is to
the details of the particular non-user-visible error that code gives
in cases it can't handle (one involving __FILE__, one involving a
string literal from stringizing), I think it's OK to change that
non-user-visible error and that the new errors are no worse than the
old ones.  So these particular errors are now different for C and C++
(some other messages in those tests already had differences between C
and C++).

Bootstrapped with no regressions on x86_64-pc-linux-gnu.

gcc/c:
	* c-parser.c (c_parser): Remove lex_untranslated_string.  Add
	lex_joined_string and translate_strings_p.
	(c_lex_one_token): Pass 0 or C_LEX_STRING_NO_JOIN to
	c_lex_with_flags.
	(c_parser_string_literal): New function.
	(c_parser_static_assert_declaration_no_semi): Use
	c_parser_string_literal.  Do not set lex_untranslated_string.
	(c_parser_asm_string_literal): Use c_parser_string_literal.
	(c_parser_simple_asm_expr): Do not set lex_untranslated_string.
	(c_parser_gnu_attributes): Set and restore translate_strings_p
	instead of lex_untranslated_string.
	(c_parser_asm_statement): Do not set lex_untranslated_string.
	(c_parser_asm_operands): Likewise.
	(c_parser_has_attribute_expression): Set and restore
	translate_strings_p instead of lex_untranslated_string.
	(c_parser_postfix_expression): Use c_parser_string_literal.
	(pragma_lex): Likewise.
	(c_parser_pragma_pch_preprocess): Set lex_joined_string.
	(c_parse_file): Set translate_strings_p.
	* gimple-parser.c (c_parser_gimple_postfix_expression)
	(c_parser_gimple_or_rtl_pass_list): Use c_parser_string_literal.
	* c-parser.c (c_parser_string_literal): Declare function.

gcc/testsuite:
	* gcc.dg/asm-wide-1.c, gcc.dg/diagnostic-token-ranges.c,
	gcc.dg/plugin/diagnostic-test-string-literals-1.c,
	gcc.dg/plugin/diagnostic-test-string-literals-2.c: Update expected
	diagnostics.

From-SVN: r277903