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.



git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/trunk@244292 138bc75d-0d04-0410-961f-82ee72b054a4

8 files changed, 84 insertions, 2 deletions

diff --git a/gcc/ChangeLog b/gcc/ChangeLog
index d0c53d066ea..ff8dac4eddd 100644
--- a/gcc/ChangeLog
+++ b/gcc/ChangeLog
@@ -1,3 +1,10 @@
+2017-01-10  David Malcolm  <dmalcolm@redhat.com>
+
+	PR c++/77949
+	* input.c (selftest::test_accessing_ordinary_linemaps): Verify
+	that we correctly handle column numbers greater than
+	LINE_MAP_MAX_COLUMN_NUMBER.
+
 2017-01-10  Martin Sebor  <msebor@redhat.com>
 
 	PR tree-optimization/78775
diff --git a/gcc/cp/ChangeLog b/gcc/cp/ChangeLog
index 25f5a85db92..892651a7eeb 100644
--- a/gcc/cp/ChangeLog
+++ b/gcc/cp/ChangeLog
@@ -1,3 +1,10 @@
+2017-01-10  David Malcolm  <dmalcolm@redhat.com>
+
+	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.
+
 2017-01-10  Jason Merrill  <jason@redhat.com>
 
 	FI 20, decomposition declaration with parenthesized initializer.
diff --git a/gcc/cp/parser.c b/gcc/cp/parser.c
index 45173131ee9..7b3ee30345e 100644
--- a/gcc/cp/parser.c
+++ b/gcc/cp/parser.c
@@ -22164,7 +22164,10 @@ cp_parser_class_specifier_1 (cp_parser* parser)
 	  next_loc = linemap_position_for_loc_and_offset (line_table, loc, 1);
 
 	rich_location richloc (line_table, next_loc);
-	richloc.add_fixit_insert_before (next_loc, ";");
+
+	/* If we successfully offset the location, suggest the fix-it.  */
+	if (next_loc != loc)
+	  richloc.add_fixit_insert_before (next_loc, ";");
 
 	if (CLASSTYPE_DECLARED_CLASS (type))
 	  error_at_rich_loc (&richloc,
diff --git a/gcc/input.c b/gcc/input.c
index bbb6abb8878..3e67314932a 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));
diff --git a/gcc/testsuite/ChangeLog b/gcc/testsuite/ChangeLog
index f8cba4221ab..59a2fcfbef4 100644
--- a/gcc/testsuite/ChangeLog
+++ b/gcc/testsuite/ChangeLog
@@ -1,3 +1,8 @@
+2017-01-10  David Malcolm  <dmalcolm@redhat.com>
+
+	PR c++/77949
+	* g++.dg/diagnostic/pr77949.C: New test case.
+
 2017-01-10  Martin Sebor  <msebor@redhat.com>
 
 	PR tree-optimization/78775
diff --git a/gcc/testsuite/g++.dg/diagnostic/pr77949.C b/gcc/testsuite/g++.dg/diagnostic/pr77949.C
new file mode 100644
index 00000000000..0d8b333a2ad
--- /dev/null
+++ b/gcc/testsuite/g++.dg/diagnostic/pr77949.C
@@ -0,0 +1,7 @@
+// Ensure that no fix-it hints are emitted
+// { dg-options "-fdiagnostics-parseable-fixits" }
+
+/* Very long line, where a missing semicolon would be suggested for
+   insertion at column 4097.  */
+class test {                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                   }   
+// { dg-error "0: expected .;. after class definition" "" { target *-*-* } .-1 }
diff --git a/libcpp/ChangeLog b/libcpp/ChangeLog
index 082291d5648..208e1d52e6f 100644
--- a/libcpp/ChangeLog
+++ b/libcpp/ChangeLog
@@ -1,3 +1,13 @@
+2017-01-10  David Malcolm  <dmalcolm@redhat.com>
+
+	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.
+
 2017-01-07  David Malcolm  <dmalcolm@redhat.com>
 
 	PR c++/72803
diff --git a/libcpp/line-map.c b/libcpp/line-map.c
index b410c00e367..949489eb1a1 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 =