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c: Fix location for _Pragma tokens [PR97498] 

The handling of #pragma GCC diagnostic uses input_location, which is not always
as precise as needed; in particular the relative location of some tokens and a
_Pragma directive will crucially determine whether a given diagnostic is enabled
or suppressed in the desired way. PR97498 shows how the C frontend ends up with
input_location pointing to the beginning of the line containing a _Pragma()
directive, resulting in the wrong behavior if the diagnostic to be modified
pertains to some tokens found earlier on the same line. This patch fixes that by
addressing two issues:

    a) libcpp was not assigning a valid location to the CPP_PRAGMA token
    generated by the _Pragma directive.
    b) C frontend was not setting input_location to something reasonable.

With this change, the C frontend is able to change input_location to point to
the _Pragma token as needed.

This is just a two-line fix (one for each of a) and b)), the testsuite changes
were needed only because the location on the tested warnings has been somewhat
improved, so the tests need to look for the new locations.

gcc/c/ChangeLog:

	PR preprocessor/97498
	* c-parser.c (c_parser_pragma): Set input_location to the
	location of the pragma, rather than the start of the line.

libcpp/ChangeLog:

	PR preprocessor/97498
	* directives.c (destringize_and_run): Override the location of
	the CPP_PRAGMA token from a _Pragma directive to the location of
	the expansion point, as is done for the tokens lexed from it.

gcc/testsuite/ChangeLog:

	PR preprocessor/97498
	* c-c++-common/pr97498.c: New test.
	* gcc.dg/pragma-message.c: Adapt for improved warning locations.

(cherry picked from commit 0587cef3d7)
This commit is contained in:
Lewis Hyatt 2022-07-09 16:12:21 -04:00
parent a221c4b8e5
commit 8d783f0f69
4 changed files with 11 additions and 3 deletions
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1
gcc/c/c-parser.c
View File

@ -12328,6 +12328,7 @@ c_parser_pragma (c_parser *parser, enum pragma_context context, bool *if_p)
unsigned int id;
const char *construct = NULL;
input_location = c_parser_peek_token (parser)->location;
id = c_parser_peek_token (parser)->pragma_kind;
gcc_assert (id != PRAGMA_NONE);

4
gcc/testsuite/c-c++-common/pr97498.c Normal file
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@ -0,0 +1,4 @@
/* { dg-do compile } */
/* { dg-additional-options "-Wunused-function" } */
#pragma GCC diagnostic ignored "-Wunused-function"
static void f() {} _Pragma("GCC diagnostic error \"-Wunused-function\"") /* { dg-bogus "-Wunused-function" } */

8
gcc/testsuite/gcc.dg/pragma-message.c
View File

@ -42,9 +42,11 @@
#pragma message ("Okay " THREE) /* { dg-message "Okay 3" } */
/* Create a TODO() that prints a message on compilation. */
#define DO_PRAGMA(x) _Pragma (#x)
#define TODO(x) DO_PRAGMA(message ("TODO - " #x))
TODO(Okay 4) /* { dg-message "TODO - Okay 4" } */
#define DO_PRAGMA(x) _Pragma (#x) /* { dg-line pragma_loc1 } */
#define TODO(x) DO_PRAGMA(message ("TODO - " #x)) /* { dg-line pragma_loc2 } */
TODO(Okay 4) /* { dg-message "in expansion of macro 'TODO'" } */
/* { dg-message "TODO - Okay 4" "test4.1" { target *-*-* } pragma_loc1 } */
/* { dg-message "in expansion of macro 'DO_PRAGMA'" "test4.2" { target *-*-* } pragma_loc2 } */
#if 0
#pragma message ("Not printed")

1
libcpp/directives.c
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@ -1887,6 +1887,7 @@ destringize_and_run (cpp_reader *pfile, const cpp_string *in,
maxcount = 50;
toks = XNEWVEC (cpp_token, maxcount);
toks[0] = pfile->directive_result;
toks[0].src_loc = expansion_loc;
do
{