[gcc r11-8583] libcpp: location comparison within macro [PR100796]

[Jason Merrill <jason@gcc.gnu.org>]

https://gcc.gnu.org/g:bb2e908638758097e261bca1a4825d171a18af9c

commit r11-8583-gbb2e908638758097e261bca1a4825d171a18af9c
Author: Jason Merrill <jason@redhat.com>
Date:   Mon Jun 14 17:37:43 2021 -0400

    libcpp: location comparison within macro [PR100796]
    
    The patch for 96391 changed linemap_compare_locations to give up on
    comparing locations from macro expansions if we don't have column
    information.  But in this testcase, the BOILERPLATE macro is multiple lines
    long, so we do want to compare locations within the macro.  So this patch
    moves the LINE_MAP_MAX_LOCATION_WITH_COLS check inside the block, to use it
    for failing gracefully.
    
            PR c++/100796
            PR preprocessor/96391
    
    libcpp/ChangeLog:
    
            * line-map.c (linemap_compare_locations): Only use comparison with
            LINE_MAP_MAX_LOCATION_WITH_COLS to avoid abort.
    
    gcc/testsuite/ChangeLog:
    
            * g++.dg/plugin/location-overflow-test-pr100796.c: New test.
            * g++.dg/plugin/plugin.exp: Run it.

Diff:
---
 .../plugin/location-overflow-test-pr100796.c       | 25 ++++++++++++++++++++++
 libcpp/line-map.c                                  | 20 +++++++++--------
 gcc/testsuite/g++.dg/plugin/plugin.exp             |  3 ++-
 3 files changed, 38 insertions(+), 10 deletions(-)

diff --git a/gcc/testsuite/g++.dg/plugin/location-overflow-test-pr100796.c b/gcc/testsuite/g++.dg/plugin/location-overflow-test-pr100796.c
new file mode 100644
index 00000000000..7fa964c07e5
--- /dev/null
+++ b/gcc/testsuite/g++.dg/plugin/location-overflow-test-pr100796.c
@@ -0,0 +1,25 @@
+// PR c++/100796
+// { dg-additional-options "-Wsuggest-override -fplugin-arg-location_overflow_plugin-value=0x60000001" }
+// Passing LINE_MAP_MAX_LOCATION_WITH_COLS meant we stopped distinguishing between lines in a macro.
+
+#define DO_PRAGMA(text)           _Pragma(#text)
+#define WARNING_PUSH              DO_PRAGMA(GCC diagnostic push)
+#define WARNING_POP               DO_PRAGMA(GCC diagnostic pop)
+#define WARNING_DISABLE(text)     DO_PRAGMA(GCC diagnostic ignored text)
+#define NO_OVERRIDE_WARNING       WARNING_DISABLE("-Wsuggest-override")
+
+#define BOILERPLATE				\
+  WARNING_PUSH					\
+  NO_OVERRIDE_WARNING				\
+  void f();					\
+  WARNING_POP
+
+struct B
+{
+  virtual void f();
+};
+
+struct D: B
+{
+  BOILERPLATE
+};
diff --git a/libcpp/line-map.c b/libcpp/line-map.c
index a03d6760a8e..1a6902acdb7 100644
--- a/libcpp/line-map.c
+++ b/libcpp/line-map.c
@@ -1421,23 +1421,25 @@ linemap_compare_locations (line_maps *set,
 
   if (l0 == l1
       && pre_virtual_p
-      && post_virtual_p
-      && l0 <= LINE_MAP_MAX_LOCATION_WITH_COLS)
+      && post_virtual_p)
     {
       /* So pre and post represent two tokens that are present in a
 	 same macro expansion.  Let's see if the token for pre was
 	 before the token for post in that expansion.  */
-      unsigned i0, i1;
       const struct line_map *map =
 	first_map_in_common (set, pre, post, &l0, &l1);
 
       if (map == NULL)
-	/* This should not be possible.  */
-	abort ();
-
-      i0 = l0 - MAP_START_LOCATION (map);
-      i1 = l1 - MAP_START_LOCATION (map);
-      return i1 - i0;
+	/* This should not be possible while we have column information, but if
+	   we don't, the tokens could be from separate macro expansions on the
+	   same line.  */
+	gcc_assert (l0 > LINE_MAP_MAX_LOCATION_WITH_COLS);
+      else
+	{
+	  unsigned i0 = l0 - MAP_START_LOCATION (map);
+	  unsigned i1 = l1 - MAP_START_LOCATION (map);
+	  return i1 - i0;
+	}
     }
 
   if (IS_ADHOC_LOC (l0))
diff --git a/gcc/testsuite/g++.dg/plugin/plugin.exp b/gcc/testsuite/g++.dg/plugin/plugin.exp
index 5cd4b4bff90..74e12df207c 100644
--- a/gcc/testsuite/g++.dg/plugin/plugin.exp
+++ b/gcc/testsuite/g++.dg/plugin/plugin.exp
@@ -73,7 +73,8 @@ set plugin_test_list [list \
 	  ../../gcc.dg/plugin/diagnostic-test-string-literals-3.c \
 	  ../../gcc.dg/plugin/diagnostic-test-string-literals-4.c } \
     { ../../gcc.dg/plugin/location_overflow_plugin.c \
-	  location-overflow-test-pr96391.c } \
+	  location-overflow-test-pr96391.c \
+          location-overflow-test-pr100796.c } \
     { show_template_tree_color_plugin.c \
     	  show-template-tree-color.C \
     	  show-template-tree-color-labels.C \