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, 26 insertions, 0 deletions

diff --git a/gcc/input.c b/gcc/input.c
index bbb6abb..3e67314 100644
--- a/gcc/input.c
+++ b/gcc/input.c
@@ -1699,6 +1699,22 @@ test_accessing_ordinary_linemaps (const line_table_case &case_)
       ASSERT_EQ (7, map->m_column_and_range_bits - map->m_range_bits);
     }
 
+  /* Example of a line that will eventually be seen to be longer
+     than LINE_MAP_MAX_COLUMN_NUMBER; the initially seen width is
+     below that.  */
+  linemap_line_start (line_table, 5, 2000);
+
+  location_t loc_start_of_very_long_line
+    = linemap_position_for_column (line_table, 2000);
+  location_t loc_too_wide
+    = linemap_position_for_column (line_table, 4097);
+  location_t loc_too_wide_2
+    = linemap_position_for_column (line_table, 4098);
+
+  /* ...and back to a sane line length.  */
+  linemap_line_start (line_table, 6, 100);
+  location_t loc_sane_again = linemap_position_for_column (line_table, 10);
+
   linemap_add (line_table, LC_LEAVE, false, NULL, 0);
 
   /* Multiple files.  */
@@ -1714,6 +1730,16 @@ test_accessing_ordinary_linemaps (const line_table_case &case_)
   assert_loceq ("foo.c", 2, 17, loc_d);
   assert_loceq ("foo.c", 3, 700, loc_e);
   assert_loceq ("foo.c", 4, 100, loc_back_to_short);
+
+  /* In the very wide line, the initial location should be fully tracked.  */
+  assert_loceq ("foo.c", 5, 2000, loc_start_of_very_long_line);
+  /* ...but once we exceed LINE_MAP_MAX_COLUMN_NUMBER column-tracking should
+     be disabled.  */
+  assert_loceq ("foo.c", 5, 0, loc_too_wide);
+  assert_loceq ("foo.c", 5, 0, loc_too_wide_2);
+  /*...and column-tracking should be re-enabled for subsequent lines.  */
+  assert_loceq ("foo.c", 6, 10, loc_sane_again);
+
   assert_loceq ("bar.c", 1, 150, loc_f);
 
   ASSERT_FALSE (is_location_from_builtin_token (loc_a));