PR preprocessor/53463 - Fix system header detection for built-in macro tokens

The location for a built-in macro token is BUILTIN_LOCATION.  When we
see that location value, we cannot know if that token was used in a
system header or not.  And that can trigger some unwanted warnings on
e.g, the use of __LONG_LONG_MAX__ built-in macro in system headers
when we compile with -pedantic, like in the test case accompanying
this patch.

In that case, I think we ought to step-up to see where the built-in
macro has been expanded, until we see a location that is not for a
built-in macro.  Then we can check if the resulting location is in a
system header or not.

Now that we step up to the location of first non-built-in-macro token,
it appeared that for
testsuite/c-c++-common/dfp/convert-int-saturate.c, G++ then fails to
emit the warning in:

    volatile unsigned int usi;
    int
    main ()
    {
      usi = DEC32_MAX;  /* { dg-warning "overflow in implicit constant conversion" } */
     ...
    }

Because DEC32_MAX is defined in the system header float.h as a
built-in macro:

    #define DEC32_MAX	__DEC32_MAX__

And during the parsing of the assignment expression that should have
led to the warning above, input_location is set to the location for
the DEC32_MAX, which is actually the location for the built-in
__DECL32_MAX_EXP.

A possible fix is to use the location of the "=" operator as the
default location for assignment expressions.  This is what the patch
does.

I had to adjust a couple of tests to arrange for this.

Bootstrapped and tested on x86_64-unknown-linux-gnu against trunk.

libcpp/

	PR preprocessor/53463
	* line-map.c (linemap_location_in_system_header_p): For built-in
	macro tokens, check the first expansion point location for that is
	not for a token coming from a built-in macro.

gcc/cp/

	PR preprocessor/53463
	* parser.c (cp_parser_assignment_expression): Use the location
	for the LHS as the default location for the expression.

gcc/testsuite/

	PR preprocessor/53463
	* g++.dg/cpp/limits.C: New test.
	* g++.dg/parse/error19.C: Adjust.
	* g++.dg/warn/Wconversion-real-integer2.C: Likewise.
	* g++.dg/warn/pr35635.C: Likewise.
	* g++.old-deja/g++.pt/assign1.C: Likewise.

From-SVN: r188203

1 files changed, 6 insertions, 1 deletions

diff --git a/gcc/cp/parser.c b/gcc/cp/parser.c
index 16139d6..2afcbc0 100644
--- a/gcc/cp/parser.c
+++ b/gcc/cp/parser.c
@@ -7481,6 +7481,7 @@ cp_parser_assignment_expression (cp_parser* parser, bool cast_p,
 	  if (assignment_operator != ERROR_MARK)
 	    {
 	      bool non_constant_p;
+	      location_t saved_input_location;
 
 	      /* Parse the right-hand side of the assignment.  */
 	      tree rhs = cp_parser_initializer_clause (parser, &non_constant_p);
@@ -7493,11 +7494,15 @@ cp_parser_assignment_expression (cp_parser* parser, bool cast_p,
 	      if (cp_parser_non_integral_constant_expression (parser,
 							      NIC_ASSIGNMENT))
 		return error_mark_node;
-	      /* Build the assignment expression.  */
+	      /* Build the assignment expression.  Its default
+		 location is the location of the '=' token.  */
+	      saved_input_location = input_location;
+	      input_location = loc;
 	      expr = build_x_modify_expr (loc, expr,
 					  assignment_operator,
 					  rhs,
 					  tf_warning_or_error);
+	      input_location = saved_input_location;
 	    }
 	}
     }