Fix issues with unrepresentable column numbers (PR c++/77949)

PR c++/77949 identifies an ICE when the C++ frontend attempts to emit a
fix-it hint inserting a missing semicolon at column 4097 of a source file.

This column value exceeds LINE_MAP_MAX_COLUMN_NUMBER and hence isn't
representable using a location_t.

Attempting to do so leads to these problems, which this patch fixes:

(a) when encountering a column number > LINE_MAP_MAX_COLUMN_NUMBER we
create a new linemap with m_column_and_range_bits == 0, but
linemap_position_for_column doesn't check for this, and hence can emit
a bogus location_t value that's calculated relative to the previous
linemap start, but which will be decoded relative to the new linemap,
leading to very large incorrect line values.

(b) when encountering a column number that can't be represented, and
for which the linemap was pre-existing, the code would hit this assertion:
  if (linemap_assert_fails (column < (1u << map->m_column_and_range_bits)))
around a bail-out condition.  The patch replaces this assertion with a
simple conditional, to stop the ICE when this occurs, and fixes the
bit count (effective column bits, vs column+range bits)

(c) the C++ frontend wasn't checking for failure of
linemap_position_for_loc_and_offset when considering emitting the fix-it
hint.  The patch adds a conditional, so that no fix-it hint is emitted
if the location is bogus.

gcc/cp/ChangeLog:
	PR c++/77949
	* parser.c (cp_parser_class_specifier_1): Only suggest inserting
	a missing semicolon if we have a valid insertion location for
	the fix-it hint.

gcc/ChangeLog:
	PR c++/77949
	* input.c (selftest::test_accessing_ordinary_linemaps): Verify
	that we correctly handle column numbers greater than
	LINE_MAP_MAX_COLUMN_NUMBER.

gcc/testsuite/ChangeLog:
	PR c++/77949
	* g++.dg/diagnostic/pr77949.C: New test case.

libcpp/ChangeLog:
	PR c++/77949
	* line-map.c (linemap_position_for_column): When calling
	linemap_start_line, detect if a new linemap was created with
	0 column bits, and bail out early if this is the case.
	(linemap_position_for_loc_and_offset): Replace overzealous
	linemap_assert_fails with a simple conditional; use correct
	bit count.

From-SVN: r244292

1 files changed, 18 insertions, 1 deletions

diff --git a/libcpp/line-map.c b/libcpp/line-map.c
index b410c00..949489e 100644
--- a/libcpp/line-map.c
+++ b/libcpp/line-map.c
@@ -816,8 +816,22 @@ linemap_position_for_column (struct line_maps *set, unsigned int to_column)
 	}
       else
 	{
+	  /* Otherwise, attempt to start a new line that can hold TO_COLUMN,
+	     with some space to spare.  This may or may not lead to a new
+	     linemap being created.  */
 	  line_map_ordinary *map = LINEMAPS_LAST_ORDINARY_MAP (set);
 	  r = linemap_line_start (set, SOURCE_LINE (map, r), to_column + 50);
+	  map = LINEMAPS_LAST_ORDINARY_MAP (set);
+	  if (map->m_column_and_range_bits == 0)
+	    {
+	      /* ...then the linemap has column-tracking disabled,
+		 presumably due to exceeding either
+		 LINE_MAP_MAX_LOCATION_WITH_COLS (overall) or
+		 LINE_MAP_MAX_COLUMN_NUMBER (within this line).
+		 Return the start of the linemap, which encodes column 0, for
+		 the whole line.  */
+	      return r;
+	    }
 	}
     }
   line_map_ordinary *map = LINEMAPS_LAST_ORDINARY_MAP (set);
@@ -905,7 +919,10 @@ linemap_position_for_loc_and_offset (struct line_maps *set,
     }
 
   column += column_offset;
-  if (linemap_assert_fails (column < (1u << map->m_column_and_range_bits)))
+
+  /* Bail out if the column is not representable within the existing
+     linemap.  */
+  if (column >= (1u << (map->m_column_and_range_bits - map->m_range_bits)))
     return loc;
 
   source_location r =