PR c++/70105: prevent nonsensical underline spew for macro expansions

diagnostic_show_locus can sometimes do the wrong thing when handling
expressions built up from macros.

PR c++/70105 (currently marked as a P3 regression) has an example of
a diagnostic where over 500 lines of irrelevant source are printed,
and underlined, giving >1000 lines of useless spew to stderr.

This patch adds extra sanitization to diagnostic-show-locus.c, so that
we only attempt to print underlines and secondary locations if such
locations are "sufficiently sane" relative to the primary location
of a diagnostic.

This "sufficiently sane" condition is implemented by a new helper
function compatible_locations_p, which requires such locations to
have the same macro expansion hierarchy as the primary location,
using linemap_macro_map_loc_unwind_toward_spelling, effectively
mimicing the expansion performed by LRK_SPELLING_LOCATION.

This may be too strong a condition, but it effectively fixes
PR c++/70105, without removing any underlines in my testing.

Successfully bootstrapped&regrtested in combination with the previous
patch on x86_64-pc-linux-gnu; adds 15 new PASS results to g++.sum
and 4 new PASS results to gcc.sum.

gcc/ChangeLog:
	PR c/68473
	PR c++/70105
	* diagnostic-show-locus.c (compatible_locations_p): New function.
	(layout::layout): Sanitize ranges using compatible_locations_p.

gcc/testsuite/ChangeLog:
	PR c/68473
	PR c++/70105
	* g++.dg/diagnostic/pr70105.C: New test.
	* gcc.dg/plugin/diagnostic-test-expressions-1.c (foo): New decl.
	(test_multiple_ordinary_maps): New test function.

libcpp/ChangeLog:
	PR c/68473
	PR c++/70105
	* line-map.c (linemap_macro_map_loc_unwind_toward_spelling): Move
	decl...
	* include/line-map.h
	(linemap_macro_map_loc_unwind_toward_spelling): ...here,
	converting from static to extern.

From-SVN: r234088

3 files changed, 18 insertions, 2 deletions

diff --git a/libcpp/ChangeLog b/libcpp/ChangeLog
index d583e98..19b9310 100644
--- a/libcpp/ChangeLog
+++ b/libcpp/ChangeLog
@@ -2,6 +2,16 @@
 
 	PR c/68473
 	PR c++/70105
+	* line-map.c (linemap_macro_map_loc_unwind_toward_spelling): Move
+	decl...
+	* include/line-map.h
+	(linemap_macro_map_loc_unwind_toward_spelling): ...here,
+	converting from static to extern.
+
+2016-03-09  David Malcolm  <dmalcolm@redhat.com>
+
+	PR c/68473
+	PR c++/70105
 	* include/line-map.h (source_range::debug): Delete.
 	(struct location_range): Update comment.  Replace
 	expanded_location fields "m_start", "m_finish", and "m_caret" with
diff --git a/libcpp/include/line-map.h b/libcpp/include/line-map.h
index 13cc6f8..292abce 100644
--- a/libcpp/include/line-map.h
+++ b/libcpp/include/line-map.h
@@ -1066,6 +1066,14 @@ int linemap_location_in_system_header_p (struct line_maps *,
 bool linemap_location_from_macro_expansion_p (const struct line_maps *,
 					      source_location);
 
+/* With the precondition that LOCATION is the locus of a token that is
+   an argument of a function-like macro MACRO_MAP and appears in the
+   expansion of MACRO_MAP, return the locus of that argument in the
+   context of the caller of MACRO_MAP.  */
+
+extern source_location linemap_macro_map_loc_unwind_toward_spelling
+  (line_maps *set, const line_map_macro *macro_map, source_location location);
+
 /* source_location values from 0 to RESERVED_LOCATION_COUNT-1 will
    be reserved for libcpp user as special values, no token from libcpp
    will contain any of those locations.  */
diff --git a/libcpp/line-map.c b/libcpp/line-map.c
index de6eafc..1fb634a 100644
--- a/libcpp/line-map.c
+++ b/libcpp/line-map.c
@@ -54,8 +54,6 @@ static const line_map_macro* linemap_macro_map_lookup (struct line_maps *,
 						       source_location);
 static source_location linemap_macro_map_loc_to_def_point
 (const line_map_macro *, source_location);
-static source_location linemap_macro_map_loc_unwind_toward_spelling
-(line_maps *set, const line_map_macro *, source_location);
 static source_location linemap_macro_map_loc_to_exp_point
 (const line_map_macro *, source_location);
 static source_location linemap_macro_loc_to_spelling_point