On-demand locations within string-literals

gcc/c-family/ChangeLog:
	* c-common.c: Include "substring-locations.h".
	(get_cpp_ttype_from_string_type): New function.
	(g_string_concat_db): New global.
	(substring_loc::get_range): New method.
	* c-common.h (g_string_concat_db): New declaration.
	(class substring_loc): New class.
	* c-lex.c (lex_string): When concatenating strings, capture the
	locations of all tokens using a new obstack, and record the
	concatenation locations within g_string_concat_db.
	* c-opts.c (c_common_init_options): Construct g_string_concat_db
	on the ggc-heap.

gcc/ChangeLog:
	* input.c (string_concat::string_concat): New constructor.
	(string_concat_db::string_concat_db): New constructor.
	(string_concat_db::record_string_concatenation): New method.
	(string_concat_db::get_string_concatenation): New method.
	(string_concat_db::get_key_loc): New method.
	(class auto_cpp_string_vec): New class.
	(get_substring_ranges_for_loc): New function.
	(get_source_range_for_substring): New function.
	(get_num_source_ranges_for_substring): New function.
	(class selftest::lexer_test_options): New class.
	(struct selftest::lexer_test): New struct.
	(class selftest::ebcdic_execution_charset): New class.
	(selftest::ebcdic_execution_charset::s_singleton): New variable.
	(selftest::lexer_test::lexer_test): New constructor.
	(selftest::lexer_test::~lexer_test): New destructor.
	(selftest::lexer_test::get_token): New method.
	(selftest::assert_char_at_range): New function.
	(ASSERT_CHAR_AT_RANGE): New macro.
	(selftest::assert_num_substring_ranges): New function.
	(ASSERT_NUM_SUBSTRING_RANGES): New macro.
	(selftest::assert_has_no_substring_ranges): New function.
	(ASSERT_HAS_NO_SUBSTRING_RANGES): New macro.
	(selftest::test_lexer_string_locations_simple): New function.
	(selftest::test_lexer_string_locations_ebcdic): New function.
	(selftest::test_lexer_string_locations_hex): New function.
	(selftest::test_lexer_string_locations_oct): New function.
	(selftest::test_lexer_string_locations_letter_escape_1): New function.
	(selftest::test_lexer_string_locations_letter_escape_2): New function.
	(selftest::test_lexer_string_locations_ucn4): New function.
	(selftest::test_lexer_string_locations_ucn8): New function.
	(selftest::uint32_from_big_endian): New function.
	(selftest::test_lexer_string_locations_wide_string): New function.
	(selftest::uint16_from_big_endian): New function.
	(selftest::test_lexer_string_locations_string16): New function.
	(selftest::test_lexer_string_locations_string32): New function.
	(selftest::test_lexer_string_locations_u8): New function.
	(selftest::test_lexer_string_locations_utf8_source): New function.
	(selftest::test_lexer_string_locations_concatenation_1): New
	function.
	(selftest::test_lexer_string_locations_concatenation_2): New
	function.
	(selftest::test_lexer_string_locations_concatenation_3): New
	function.
	(selftest::test_lexer_string_locations_macro): New function.
	(selftest::test_lexer_string_locations_stringified_macro_argument):
	New function.
	(selftest::test_lexer_string_locations_non_string): New function.
	(selftest::test_lexer_string_locations_long_line): New function.
	(selftest::test_lexer_char_constants): New function.
	(selftest::input_c_tests): Call the new test functions once per
	case within the line_table test matrix.
	* input.h (struct string_concat): New struct.
	(struct location_hash): New struct.
	(class string_concat_db): New class.
	* substring-locations.h: New header.

gcc/testsuite/ChangeLog:
	* gcc.dg/plugin/diagnostic-test-string-literals-1.c: New file.
	* gcc.dg/plugin/diagnostic-test-string-literals-2.c: New file.
	* gcc.dg/plugin/diagnostic_plugin_test_string_literals.c: New file.
	* gcc.dg/plugin/plugin.exp (plugin_test_list): Add the above new files.

libcpp/ChangeLog:
	* charset.c (cpp_substring_ranges::cpp_substring_ranges): New
	constructor.
	(cpp_substring_ranges::~cpp_substring_ranges): New destructor.
	(cpp_substring_ranges::add_range): New method.
	(cpp_substring_ranges::add_n_ranges): New method.
	(_cpp_valid_ucn): Add "char_range" and "loc_reader" params; if
	they are non-NULL, read position information from *loc_reader
	and update char_range->m_finish accordingly.
	(convert_ucn): Add "char_range", "loc_reader", and "ranges"
	params.  If loc_reader is non-NULL, read location information from
	it, and update *ranges accordingly, using char_range.
	Conditionalize the conversion into tbuf on tbuf being non-NULL.
	(convert_hex): Likewise, conditionalizing the call to
	emit_numeric_escape on tbuf.
	(convert_oct): Likewise.
	(convert_escape): Add params "loc_reader" and "ranges".  If
	loc_reader is non-NULL, read location information from it, and
	update *ranges accordingly.  Conditionalize the conversion into
	tbuf on tbuf being non-NULL.
	(cpp_interpret_string): Rename to...
	(cpp_interpret_string_1): ...this, adding params "loc_readers" and
	"out".  Use "to" to conditionalize the initialization and usage of
	"tbuf", such as running the converter.  If "loc_readers" is
	non-NULL, use the instances within it, reading location
	information from them, and passing them to convert_escape; likewise
	write to "out" if loc_readers is non-NULL.  Check for leading
	quote and issue an error if it is not present.  Update boundary
	check from "== limit" to ">= limit" to protect against erroneous
	location values to calls that are not parsing string literals.
	(cpp_interpret_string): Reimplement in terms to
	cpp_interpret_string_1.
	(noop_error_cb): New function.
	(cpp_interpret_string_ranges): New function.
	(cpp_string_location_reader::cpp_string_location_reader): New
	constructor.
	(cpp_string_location_reader::get_next): New method.
	* include/cpplib.h (class cpp_string_location_reader): New class.
	(class cpp_substring_ranges): New class.
	(cpp_interpret_string_ranges): New prototype.
	* internal.h (_cpp_valid_ucn): Add params "char_range" and
	"loc_reader".
	* lex.c (forms_identifier_p): Pass NULL for new params to
	_cpp_valid_ucn.

From-SVN: r239175

14 files changed, 2286 insertions, 2 deletions

diff --git a/gcc/ChangeLog b/gcc/ChangeLog
index 10d7224..40ca18c 100644
--- a/gcc/ChangeLog
+++ b/gcc/ChangeLog
@@ -1,3 +1,61 @@
+2016-08-05  David Malcolm  <dmalcolm@redhat.com>
+
+	* input.c (string_concat::string_concat): New constructor.
+	(string_concat_db::string_concat_db): New constructor.
+	(string_concat_db::record_string_concatenation): New method.
+	(string_concat_db::get_string_concatenation): New method.
+	(string_concat_db::get_key_loc): New method.
+	(class auto_cpp_string_vec): New class.
+	(get_substring_ranges_for_loc): New function.
+	(get_source_range_for_substring): New function.
+	(get_num_source_ranges_for_substring): New function.
+	(class selftest::lexer_test_options): New class.
+	(struct selftest::lexer_test): New struct.
+	(class selftest::ebcdic_execution_charset): New class.
+	(selftest::ebcdic_execution_charset::s_singleton): New variable.
+	(selftest::lexer_test::lexer_test): New constructor.
+	(selftest::lexer_test::~lexer_test): New destructor.
+	(selftest::lexer_test::get_token): New method.
+	(selftest::assert_char_at_range): New function.
+	(ASSERT_CHAR_AT_RANGE): New macro.
+	(selftest::assert_num_substring_ranges): New function.
+	(ASSERT_NUM_SUBSTRING_RANGES): New macro.
+	(selftest::assert_has_no_substring_ranges): New function.
+	(ASSERT_HAS_NO_SUBSTRING_RANGES): New macro.
+	(selftest::test_lexer_string_locations_simple): New function.
+	(selftest::test_lexer_string_locations_ebcdic): New function.
+	(selftest::test_lexer_string_locations_hex): New function.
+	(selftest::test_lexer_string_locations_oct): New function.
+	(selftest::test_lexer_string_locations_letter_escape_1): New function.
+	(selftest::test_lexer_string_locations_letter_escape_2): New function.
+	(selftest::test_lexer_string_locations_ucn4): New function.
+	(selftest::test_lexer_string_locations_ucn8): New function.
+	(selftest::uint32_from_big_endian): New function.
+	(selftest::test_lexer_string_locations_wide_string): New function.
+	(selftest::uint16_from_big_endian): New function.
+	(selftest::test_lexer_string_locations_string16): New function.
+	(selftest::test_lexer_string_locations_string32): New function.
+	(selftest::test_lexer_string_locations_u8): New function.
+	(selftest::test_lexer_string_locations_utf8_source): New function.
+	(selftest::test_lexer_string_locations_concatenation_1): New
+	function.
+	(selftest::test_lexer_string_locations_concatenation_2): New
+	function.
+	(selftest::test_lexer_string_locations_concatenation_3): New
+	function.
+	(selftest::test_lexer_string_locations_macro): New function.
+	(selftest::test_lexer_string_locations_stringified_macro_argument):
+	New function.
+	(selftest::test_lexer_string_locations_non_string): New function.
+	(selftest::test_lexer_string_locations_long_line): New function.
+	(selftest::test_lexer_char_constants): New function.
+	(selftest::input_c_tests): Call the new test functions once per
+	case within the line_table test matrix.
+	* input.h (struct string_concat): New struct.
+	(struct location_hash): New struct.
+	(class string_concat_db): New class.
+	* substring-locations.h: New header.
+
 2016-08-05  Patrick Palka  <ppalka@gcc.gnu.org>
 
 	PR tree-optimization/72810
diff --git a/gcc/c-family/ChangeLog b/gcc/c-family/ChangeLog
index aed494a..d5cdfed 100644
--- a/gcc/c-family/ChangeLog
+++ b/gcc/c-family/ChangeLog
@@ -1,3 +1,17 @@
+2016-08-05  David Malcolm  <dmalcolm@redhat.com>
+
+	* c-common.c: Include "substring-locations.h".
+	(get_cpp_ttype_from_string_type): New function.
+	(g_string_concat_db): New global.
+	(substring_loc::get_range): New method.
+	* c-common.h (g_string_concat_db): New declaration.
+	(class substring_loc): New class.
+	* c-lex.c (lex_string): When concatenating strings, capture the
+	locations of all tokens using a new obstack, and record the
+	concatenation locations within g_string_concat_db.
+	* c-opts.c (c_common_init_options): Construct g_string_concat_db
+	on the ggc-heap.
+
 2016-07-29  Marek Polacek  <polacek@redhat.com>
 
 	PR c/71926
diff --git a/gcc/c-family/c-common.c b/gcc/c-family/c-common.c
index 27031b5..569f000 100644
--- a/gcc/c-family/c-common.c
+++ b/gcc/c-family/c-common.c
@@ -45,6 +45,7 @@ along with GCC; see the file COPYING3.  If not see
 #include "tree-iterator.h"
 #include "opts.h"
 #include "gimplify.h"
+#include "substring-locations.h"
 
 cpp_reader *parse_in;		/* Declared in c-pragma.h.  */
 
@@ -1098,6 +1099,67 @@ fix_string_type (tree value)
   TREE_STATIC (value) = 1;
   return value;
 }
+
+/* Given a string of type STRING_TYPE, determine what kind of string
+   token would give an equivalent execution encoding: CPP_STRING,
+   CPP_STRING16, or CPP_STRING32.  Return CPP_OTHER in case of error.
+   This may not be exactly the string token type that initially created
+   the string, since CPP_WSTRING is indistinguishable from the 16/32 bit
+   string type at this point.
+
+   This effectively reverses part of the logic in lex_string and
+   fix_string_type.  */
+
+static enum cpp_ttype
+get_cpp_ttype_from_string_type (tree string_type)
+{
+  gcc_assert (string_type);
+  if (TREE_CODE (string_type) != ARRAY_TYPE)
+    return CPP_OTHER;
+
+  tree element_type = TREE_TYPE (string_type);
+  if (TREE_CODE (element_type) != INTEGER_TYPE)
+    return CPP_OTHER;
+
+  int bits_per_character = TYPE_PRECISION (element_type);
+  switch (bits_per_character)
+    {
+    case 8:
+      return CPP_STRING;  /* It could have also been CPP_UTF8STRING.  */
+    case 16:
+      return CPP_STRING16;
+    case 32:
+      return CPP_STRING32;
+    }
+
+  return CPP_OTHER;
+}
+
+/* The global record of string concatentations, for use in
+   extracting locations within string literals.  */
+
+GTY(()) string_concat_db *g_string_concat_db;
+
+/* Attempt to determine the source range of the substring.
+   If successful, return NULL and write the source range to *OUT_RANGE.
+   Otherwise return an error message.  Error messages are intended
+   for GCC developers (to help debugging) rather than for end-users.  */
+
+const char *
+substring_loc::get_range (source_range *out_range) const
+{
+  gcc_assert (out_range);
+
+  enum cpp_ttype tok_type = get_cpp_ttype_from_string_type (m_string_type);
+  if (tok_type == CPP_OTHER)
+    return "unrecognized string type";
+
+  return get_source_range_for_substring (parse_in, g_string_concat_db,
+					 m_fmt_string_loc, tok_type,
+					 m_start_idx, m_end_idx,
+					 out_range);
+}
+
 
 /* Fold X for consideration by one of the warning functions when checking
    whether an expression has a constant value.  */
diff --git a/gcc/c-family/c-common.h b/gcc/c-family/c-common.h
index 8c80574..7b5da57 100644
--- a/gcc/c-family/c-common.h
+++ b/gcc/c-family/c-common.h
@@ -1110,6 +1110,35 @@ extern time_t cb_get_source_date_epoch (cpp_reader *pfile);
    __TIME__ can store.  */
 #define MAX_SOURCE_DATE_EPOCH HOST_WIDE_INT_C (253402300799)
 
+extern GTY(()) string_concat_db *g_string_concat_db;
+
+/* libcpp can calculate location information about a range of characters
+   within a string literal, but doing so is non-trivial.
+
+   This class encapsulates such a source location, so that it can be
+   passed around (e.g. within c-format.c).  It is effectively a deferred
+   call into libcpp.  If needed by a diagnostic, the actual source_range
+   can be calculated by calling the get_range method.  */
+
+class substring_loc
+{
+ public:
+  substring_loc (location_t fmt_string_loc, tree string_type,
+		 int start_idx, int end_idx)
+  : m_fmt_string_loc (fmt_string_loc), m_string_type (string_type),
+    m_start_idx (start_idx), m_end_idx (end_idx) {}
+
+  const char *get_range (source_range *out_range) const;
+
+  location_t get_fmt_string_loc () const { return m_fmt_string_loc; }
+
+ private:
+  location_t m_fmt_string_loc;
+  tree m_string_type;
+  int m_start_idx;
+  int m_end_idx;
+};
+
 /* In c-gimplify.c  */
 extern void c_genericize (tree);
 extern int c_gimplify_expr (tree *, gimple_seq *, gimple_seq *);
diff --git a/gcc/c-family/c-lex.c b/gcc/c-family/c-lex.c
index 8f33d86..4c7e385 100644
--- a/gcc/c-family/c-lex.c
+++ b/gcc/c-family/c-lex.c
@@ -1097,13 +1097,16 @@ lex_string (const cpp_token *tok, tree *valp, bool objc_string, bool translate)
   tree value;
   size_t concats = 0;
   struct obstack str_ob;
+  struct obstack loc_ob;
   cpp_string istr;
   enum cpp_ttype type = tok->type;
 
   /* Try to avoid the overhead of creating and destroying an obstack
      for the common case of just one string.  */
   cpp_string str = tok->val.str;
+  location_t init_loc = tok->src_loc;
   cpp_string *strs = &str;
+  location_t *locs = NULL;
 
   /* objc_at_sign_was_seen is only used when doing Objective-C string
      concatenation.  It is 'true' if we have seen an '@' before the
@@ -1142,16 +1145,21 @@ lex_string (const cpp_token *tok, tree *valp, bool objc_string, bool translate)
 	  else
 	    error ("unsupported non-standard concatenation of string literals");
 	}
+      /* FALLTHROUGH */
 
     case CPP_STRING:
       if (!concats)
 	{
 	  gcc_obstack_init (&str_ob);
+	  gcc_obstack_init (&loc_ob);
 	  obstack_grow (&str_ob, &str, sizeof (cpp_string));
+	  obstack_grow (&loc_ob, &init_loc, sizeof (location_t));
 	}
 
       concats++;
       obstack_grow (&str_ob, &tok->val.str, sizeof (cpp_string));
+      obstack_grow (&loc_ob, &tok->src_loc, sizeof (location_t));
+
       if (objc_string)
 	objc_at_sign_was_seen = false;
       goto retry;
@@ -1164,7 +1172,10 @@ lex_string (const cpp_token *tok, tree *valp, bool objc_string, bool translate)
   /* We have read one more token than we want.  */
   _cpp_backup_tokens (parse_in, 1);
   if (concats)
-    strs = XOBFINISH (&str_ob, cpp_string *);
+    {
+      strs = XOBFINISH (&str_ob, cpp_string *);
+      locs = XOBFINISH (&loc_ob, location_t *);
+    }
 
   if (concats && !objc_string && !in_system_header_at (input_location))
     warning (OPT_Wtraditional,
@@ -1176,6 +1187,12 @@ lex_string (const cpp_token *tok, tree *valp, bool objc_string, bool translate)
     {
       value = build_string (istr.len, (const char *) istr.text);
       free (CONST_CAST (unsigned char *, istr.text));
+      if (concats)
+	{
+	  gcc_assert (locs);
+	  gcc_assert (g_string_concat_db);
+	  g_string_concat_db->record_string_concatenation (concats + 1, locs);
+	}
     }
   else
     {
@@ -1227,7 +1244,10 @@ lex_string (const cpp_token *tok, tree *valp, bool objc_string, bool translate)
   *valp = fix_string_type (value);
 
   if (concats)
-    obstack_free (&str_ob, 0);
+    {
+      obstack_free (&str_ob, 0);
+      obstack_free (&loc_ob, 0);
+    }
 
   return objc_string ? CPP_OBJC_STRING : type;
 }
diff --git a/gcc/c-family/c-opts.c b/gcc/c-family/c-opts.c
index c11e7e7..0715b2e 100644
--- a/gcc/c-family/c-opts.c
+++ b/gcc/c-family/c-opts.c
@@ -216,6 +216,9 @@ c_common_init_options (unsigned int decoded_options_count,
   unsigned int i;
   struct cpp_callbacks *cb;
 
+  g_string_concat_db
+    = new (ggc_alloc <string_concat_db> ()) string_concat_db ();
+
   parse_in = cpp_create_reader (c_dialect_cxx () ? CLK_GNUCXX: CLK_GNUC89,
 				ident_hash, line_table);
   cb = cpp_get_callbacks (parse_in);
diff --git a/gcc/input.c b/gcc/input.c
index f91a702..d058b8a 100644
--- a/gcc/input.c
+++ b/gcc/input.c
@@ -1189,6 +1189,279 @@ dump_location_info (FILE *stream)
 				MAX_SOURCE_LOCATION + 1, UINT_MAX);
 }
 
+/* string_concat's constructor.  */
+
+string_concat::string_concat (int num, location_t *locs)
+  : m_num (num)
+{
+  m_locs = ggc_vec_alloc <location_t> (num);
+  for (int i = 0; i < num; i++)
+    m_locs[i] = locs[i];
+}
+
+/* string_concat_db's constructor.  */
+
+string_concat_db::string_concat_db ()
+{
+  m_table = hash_map <location_hash, string_concat *>::create_ggc (64);
+}
+
+/* Record that a string concatenation occurred, covering NUM
+   string literal tokens.  LOCS is an array of size NUM, containing the
+   locations of the tokens.  A copy of LOCS is taken.  */
+
+void
+string_concat_db::record_string_concatenation (int num, location_t *locs)
+{
+  gcc_assert (num > 1);
+  gcc_assert (locs);
+
+  location_t key_loc = get_key_loc (locs[0]);
+
+  string_concat *concat
+    = new (ggc_alloc <string_concat> ()) string_concat (num, locs);
+  m_table->put (key_loc, concat);
+}
+
+/* Determine if LOC was the location of the the initial token of a
+   concatenation of string literal tokens.
+   If so, *OUT_NUM is written to with the number of tokens, and
+   *OUT_LOCS with the location of an array of locations of the
+   tokens, and return true.  *OUT_LOCS is a borrowed pointer to
+   storage owned by the string_concat_db.
+   Otherwise, return false.  */
+
+bool
+string_concat_db::get_string_concatenation (location_t loc,
+					    int *out_num,
+					    location_t **out_locs)
+{
+  gcc_assert (out_num);
+  gcc_assert (out_locs);
+
+  location_t key_loc = get_key_loc (loc);
+
+  string_concat **concat = m_table->get (key_loc);
+  if (!concat)
+    return false;
+
+  *out_num = (*concat)->m_num;
+  *out_locs =(*concat)->m_locs;
+  return true;
+}
+
+/* Internal function.  Canonicalize LOC into a form suitable for
+   use as a key within the database, stripping away macro expansion,
+   ad-hoc information, and range information, using the location of
+   the start of LOC within an ordinary linemap.  */
+
+location_t
+string_concat_db::get_key_loc (location_t loc)
+{
+  loc = linemap_resolve_location (line_table, loc, LRK_SPELLING_LOCATION,
+				  NULL);
+
+  loc = get_range_from_loc (line_table, loc).m_start;
+
+  return loc;
+}
+
+/* Helper class for use within get_substring_ranges_for_loc.
+   An vec of cpp_string with responsibility for releasing all of the
+   str->text for each str in the vector.  */
+
+class auto_cpp_string_vec :  public auto_vec <cpp_string>
+{
+ public:
+  auto_cpp_string_vec (int alloc)
+    : auto_vec <cpp_string> (alloc) {}
+
+  ~auto_cpp_string_vec ()
+  {
+    /* Clean up the copies within this vec.  */
+    int i;
+    cpp_string *str;
+    FOR_EACH_VEC_ELT (*this, i, str)
+      free (const_cast <unsigned char *> (str->text));
+  }
+};
+
+/* Attempt to populate RANGES with source location information on the
+   individual characters within the string literal found at STRLOC.
+   If CONCATS is non-NULL, then any string literals that the token at
+   STRLOC  was concatenated with are also added to RANGES.
+
+   Return NULL if successful, or an error message if any errors occurred (in
+   which case RANGES may be only partially populated and should not
+   be used).
+
+   This is implemented by re-parsing the relevant source line(s).  */
+
+static const char *
+get_substring_ranges_for_loc (cpp_reader *pfile,
+			      string_concat_db *concats,
+			      location_t strloc,
+			      enum cpp_ttype type,
+			      cpp_substring_ranges &ranges)
+{
+  gcc_assert (pfile);
+
+  if (strloc == UNKNOWN_LOCATION)
+    return "unknown location";
+
+  /* If string concatenation has occurred at STRLOC, get the locations
+     of all of the literal tokens making up the compound string.
+     Otherwise, just use STRLOC.  */
+  int num_locs = 1;
+  location_t *strlocs = &strloc;
+  if (concats)
+    concats->get_string_concatenation (strloc, &num_locs, &strlocs);
+
+  auto_cpp_string_vec strs (num_locs);
+  auto_vec <cpp_string_location_reader> loc_readers (num_locs);
+  for (int i = 0; i < num_locs; i++)
+    {
+      /* Get range of strloc.  We will use it to locate the start and finish
+	 of the literal token within the line.  */
+      source_range src_range = get_range_from_loc (line_table, strlocs[i]);
+
+      if (src_range.m_start >= LINEMAPS_MACRO_LOWEST_LOCATION (line_table))
+	/* If the string is within a macro expansion, we can't get at the
+	   end location.  */
+	return "macro expansion";
+
+      if (src_range.m_start >= LINE_MAP_MAX_LOCATION_WITH_COLS)
+	/* If so, we can't reliably determine where the token started within
+	   its line.  */
+	return "range starts after LINE_MAP_MAX_LOCATION_WITH_COLS";
+
+      if (src_range.m_finish >= LINE_MAP_MAX_LOCATION_WITH_COLS)
+	/* If so, we can't reliably determine where the token finished within
+	   its line.  */
+	return "range ends after LINE_MAP_MAX_LOCATION_WITH_COLS";
+
+      expanded_location start
+	= expand_location_to_spelling_point (src_range.m_start);
+      expanded_location finish
+	= expand_location_to_spelling_point (src_range.m_finish);
+      if (start.file != finish.file)
+	return "range endpoints are in different files";
+      if (start.line != finish.line)
+	return "range endpoints are on different lines";
+      if (start.column > finish.column)
+	return "range endpoints are reversed";
+
+      int line_width;
+      const char *line = location_get_source_line (start.file, start.line,
+						   &line_width);
+      if (line == NULL)
+	return "unable to read source line";
+
+      /* Determine the location of the literal (including quotes
+	 and leading prefix chars, such as the 'u' in a u""
+	 token).  */
+      const char *literal = line + start.column - 1;
+      int literal_length = finish.column - start.column + 1;
+
+      gcc_assert (line_width >= (start.column - 1 + literal_length));
+      cpp_string from;
+      from.len = literal_length;
+      /* Make a copy of the literal, to avoid having to rely on
+	 the lifetime of the copy of the line within the cache.
+	 This will be released by the auto_cpp_string_vec dtor.  */
+      from.text = XDUPVEC (unsigned char, literal, literal_length);
+      strs.safe_push (from);
+
+      /* For very long lines, a new linemap could have started
+	 halfway through the token.
+	 Ensure that the loc_reader uses the linemap of the
+	 *end* of the token for its start location.  */
+      const line_map_ordinary *final_ord_map;
+      linemap_resolve_location (line_table, src_range.m_finish,
+				LRK_MACRO_EXPANSION_POINT, &final_ord_map);
+      location_t start_loc
+	= linemap_position_for_line_and_column (line_table, final_ord_map,
+						start.line, start.column);
+
+      cpp_string_location_reader loc_reader (start_loc, line_table);
+      loc_readers.safe_push (loc_reader);
+    }
+
+  /* Rerun cpp_interpret_string, or rather, a modified version of it.  */
+  const char *err = cpp_interpret_string_ranges (pfile, strs.address (),
+						 loc_readers.address (),
+						 num_locs, &ranges, type);
+  if (err)
+    return err;
+
+  /* Success: "ranges" should now contain information on the string.  */
+  return NULL;
+}
+
+/* Attempt to populate *OUT_RANGE with source location information on the
+   range of given characters within the string literal found at STRLOC.
+   START_IDX and END_IDX refer to offsets within the execution character
+   set.
+   If CONCATS is non-NULL, then any string literals that the token at
+   STRLOC was concatenated with are also considered.
+
+   This is implemented by re-parsing the relevant source line(s).
+
+   Return NULL if successful, or an error message if any errors occurred.
+   Error messages are intended for GCC developers (to help debugging) rather
+   than for end-users.  */
+
+const char *
+get_source_range_for_substring (cpp_reader *pfile,
+				string_concat_db *concats,
+				location_t strloc,
+				enum cpp_ttype type,
+				int start_idx, int end_idx,
+				source_range *out_range)
+{
+  gcc_checking_assert (start_idx >= 0);
+  gcc_checking_assert (end_idx >= 0);
+  gcc_assert (out_range);
+
+  cpp_substring_ranges ranges;
+  const char *err
+    = get_substring_ranges_for_loc (pfile, concats, strloc, type, ranges);
+  if (err)
+    return err;
+
+  if (start_idx >= ranges.get_num_ranges ())
+    return "start_idx out of range";
+  if (end_idx >= ranges.get_num_ranges ())
+    return "end_idx out of range";
+
+  out_range->m_start = ranges.get_range (start_idx).m_start;
+  out_range->m_finish = ranges.get_range (end_idx).m_finish;
+  return NULL;
+}
+
+/* As get_source_range_for_substring, but write to *OUT the number
+   of ranges that are available.  */
+
+const char *
+get_num_source_ranges_for_substring (cpp_reader *pfile,
+				     string_concat_db *concats,
+				     location_t strloc,
+				     enum cpp_ttype type,
+				     int *out)
+{
+  gcc_assert (out);
+
+  cpp_substring_ranges ranges;
+  const char *err
+    = get_substring_ranges_for_loc (pfile, concats, strloc, type, ranges);
+
+  if (err)
+    return err;
+
+  *out = ranges.get_num_ranges ();
+  return NULL;
+}
+
 #if CHECKING_P
 
 namespace selftest {
@@ -1541,6 +1814,1259 @@ test_lexer (const line_table_case &case_)
   cpp_destroy (parser);
 }
 
+/* Forward decls.  */
+
+struct lexer_test;
+class lexer_test_options;
+
+/* A class for specifying options of a lexer_test.
+   The "apply" vfunc is called during the lexer_test constructor.  */
+
+class lexer_test_options
+{
+ public:
+  virtual void apply (lexer_test &) = 0;
+};
+
+/* A struct for writing lexer tests.  */
+
+struct lexer_test
+{
+  lexer_test (const line_table_case &case_, const char *content,
+	      lexer_test_options *options);
+  ~lexer_test ();
+
+  const cpp_token *get_token ();
+
+  temp_source_file m_tempfile;
+  temp_line_table m_tmp_lt;
+  cpp_reader *m_parser;
+  string_concat_db m_concats;
+};
+
+/* Use an EBCDIC encoding for the execution charset, specifically
+   IBM1047-encoded (aka "EBCDIC 1047", or "Code page 1047").
+
+   This exercises iconv integration within libcpp.
+   Not every build of iconv supports the given charset,
+   so we need to flag this error and handle it gracefully.  */
+
+class ebcdic_execution_charset : public lexer_test_options
+{
+ public:
+  ebcdic_execution_charset () : m_num_iconv_errors (0)
+    {
+      gcc_assert (s_singleton == NULL);
+      s_singleton = this;
+    }
+  ~ebcdic_execution_charset ()
+    {
+      gcc_assert (s_singleton == this);
+      s_singleton = NULL;
+    }
+
+  void apply (lexer_test &test) FINAL OVERRIDE
+  {
+    cpp_options *cpp_opts = cpp_get_options (test.m_parser);
+    cpp_opts->narrow_charset = "IBM1047";
+
+    cpp_callbacks *callbacks = cpp_get_callbacks (test.m_parser);
+    callbacks->error = on_error;
+  }
+
+  static bool on_error (cpp_reader *pfile ATTRIBUTE_UNUSED,
+			int level ATTRIBUTE_UNUSED,
+			int reason ATTRIBUTE_UNUSED,
+			rich_location *richloc ATTRIBUTE_UNUSED,
+			const char *msgid, va_list *ap ATTRIBUTE_UNUSED)
+    ATTRIBUTE_FPTR_PRINTF(5,0)
+  {
+    gcc_assert (s_singleton);
+    /* Detect and record errors emitted by libcpp/charset.c:init_iconv_desc
+       when the local iconv build doesn't support the conversion.  */
+    if (strstr (msgid, "not supported by iconv"))
+      {
+	s_singleton->m_num_iconv_errors++;
+	return true;
+      }
+
+    /* Otherwise, we have an unexpected error.  */
+    abort ();
+  }
+
+  bool iconv_errors_occurred_p () const { return m_num_iconv_errors > 0; }
+
+ private:
+  static ebcdic_execution_charset *s_singleton;
+  int m_num_iconv_errors;
+};
+
+ebcdic_execution_charset *ebcdic_execution_charset::s_singleton;
+
+/* Constructor.  Override line_table with a new instance based on CASE_,
+   and write CONTENT to a tempfile.  Create a cpp_reader, and use it to
+   start parsing the tempfile.  */
+
+lexer_test::lexer_test (const line_table_case &case_, const char *content,
+			lexer_test_options *options) :
+  /* Create a tempfile and write the text to it.  */
+  m_tempfile (SELFTEST_LOCATION, ".c", content),
+  m_tmp_lt (case_),
+  m_parser (cpp_create_reader (CLK_GNUC99, NULL, line_table)),
+  m_concats ()
+{
+  if (options)
+    options->apply (*this);
+
+  cpp_init_iconv (m_parser);
+
+  /* Parse the file.  */
+  const char *fname = cpp_read_main_file (m_parser,
+					  m_tempfile.get_filename ());
+  ASSERT_NE (fname, NULL);
+}
+
+/* Destructor.  Verify that the next token in m_parser is EOF.  */
+
+lexer_test::~lexer_test ()
+{
+  location_t loc;
+  const cpp_token *tok;
+
+  tok = cpp_get_token_with_location (m_parser, &loc);
+  ASSERT_NE (tok, NULL);
+  ASSERT_EQ (tok->type, CPP_EOF);
+
+  cpp_finish (m_parser, NULL);
+  cpp_destroy (m_parser);
+}
+
+/* Get the next token from m_parser.  */
+
+const cpp_token *
+lexer_test::get_token ()
+{
+  location_t loc;
+  const cpp_token *tok;
+
+  tok = cpp_get_token_with_location (m_parser, &loc);
+  ASSERT_NE (tok, NULL);
+  return tok;
+}
+
+/* Verify that locations within string literals are correctly handled.  */
+
+/* Verify get_source_range_for_substring for token(s) at STRLOC,
+   using the string concatenation database for TEST.
+
+   Assert that the character at index IDX is on EXPECTED_LINE,
+   and that it begins at column EXPECTED_START_COL and ends at
+   EXPECTED_FINISH_COL (unless the locations are beyond
+   LINE_MAP_MAX_LOCATION_WITH_COLS, in which case don't check their
+   columns).  */
+
+static void
+assert_char_at_range (const location &loc,
+		      lexer_test& test,
+		      location_t strloc, enum cpp_ttype type, int idx,
+		      int expected_line, int expected_start_col,
+		      int expected_finish_col)
+{
+  cpp_reader *pfile = test.m_parser;
+  string_concat_db *concats = &test.m_concats;
+
+  source_range actual_range;
+  const char *err
+    = get_source_range_for_substring (pfile, concats, strloc, type,
+				      idx, idx, &actual_range);
+  if (should_have_column_data_p (strloc))
+    ASSERT_EQ_AT (loc, NULL, err);
+  else
+    {
+      ASSERT_STREQ_AT (loc,
+		       "range starts after LINE_MAP_MAX_LOCATION_WITH_COLS",
+		       err);
+      return;
+    }
+
+  int actual_start_line = LOCATION_LINE (actual_range.m_start);
+  ASSERT_EQ_AT (loc, expected_line, actual_start_line);
+  int actual_finish_line = LOCATION_LINE (actual_range.m_finish);
+  ASSERT_EQ_AT (loc, expected_line, actual_finish_line);
+
+  if (should_have_column_data_p (actual_range.m_start))
+    {
+      int actual_start_col = LOCATION_COLUMN (actual_range.m_start);
+      ASSERT_EQ_AT (loc, expected_start_col, actual_start_col);
+    }
+  if (should_have_column_data_p (actual_range.m_finish))
+    {
+      int actual_finish_col = LOCATION_COLUMN (actual_range.m_finish);
+      ASSERT_EQ_AT (loc, expected_finish_col, actual_finish_col);
+    }
+}
+
+/* Macro for calling assert_char_at_range, supplying SELFTEST_LOCATION for
+   the effective location of any errors.  */
+
+#define ASSERT_CHAR_AT_RANGE(LEXER_TEST, STRLOC, TYPE, IDX, EXPECTED_LINE, \
+			     EXPECTED_START_COL, EXPECTED_FINISH_COL)	\
+  assert_char_at_range (SELFTEST_LOCATION, (LEXER_TEST), (STRLOC), (TYPE), \
+			(IDX), (EXPECTED_LINE), (EXPECTED_START_COL), \
+			(EXPECTED_FINISH_COL))
+
+/* Verify get_num_source_ranges_for_substring for token(s) at STRLOC,
+   using the string concatenation database for TEST.
+
+   Assert that the token(s) at STRLOC contain EXPECTED_NUM_RANGES.  */
+
+static void
+assert_num_substring_ranges (const location &loc,
+			     lexer_test& test,
+			     location_t strloc,
+			     enum cpp_ttype type,
+			     int expected_num_ranges)
+{
+  cpp_reader *pfile = test.m_parser;
+  string_concat_db *concats = &test.m_concats;
+
+  int actual_num_ranges;
+  const char *err
+    = get_num_source_ranges_for_substring (pfile, concats, strloc, type,
+					   &actual_num_ranges);
+  if (should_have_column_data_p (strloc))
+    ASSERT_EQ_AT (loc, NULL, err);
+  else
+    {
+      ASSERT_STREQ_AT (loc,
+		       "range starts after LINE_MAP_MAX_LOCATION_WITH_COLS",
+		       err);
+      return;
+    }
+  ASSERT_EQ_AT (loc, expected_num_ranges, actual_num_ranges);
+}
+
+/* Macro for calling assert_num_substring_ranges, supplying
+   SELFTEST_LOCATION for the effective location of any errors.  */
+
+#define ASSERT_NUM_SUBSTRING_RANGES(LEXER_TEST, STRLOC, TYPE, \
+				    EXPECTED_NUM_RANGES)		\
+  assert_num_substring_ranges (SELFTEST_LOCATION, (LEXER_TEST), (STRLOC), \
+			       (TYPE), (EXPECTED_NUM_RANGES))
+
+
+/* Verify that get_num_source_ranges_for_substring for token(s) at STRLOC
+   returns an error (using the string concatenation database for TEST).  */
+
+static void
+assert_has_no_substring_ranges (const location &loc,
+				lexer_test& test,
+				location_t strloc,
+				enum cpp_ttype type,
+				const char *expected_err)
+{
+  cpp_reader *pfile = test.m_parser;
+  string_concat_db *concats = &test.m_concats;
+  cpp_substring_ranges ranges;
+  const char *actual_err
+    = get_substring_ranges_for_loc (pfile, concats, strloc,
+				    type, ranges);
+  if (should_have_column_data_p (strloc))
+    ASSERT_STREQ_AT (loc, expected_err, actual_err);
+  else
+    ASSERT_STREQ_AT (loc,
+		     "range starts after LINE_MAP_MAX_LOCATION_WITH_COLS",
+		     actual_err);
+}
+
+#define ASSERT_HAS_NO_SUBSTRING_RANGES(LEXER_TEST, STRLOC, TYPE, ERR)    \
+    assert_has_no_substring_ranges (SELFTEST_LOCATION, (LEXER_TEST), \
+				    (STRLOC), (TYPE), (ERR))
+
+/* Lex a simple string literal.  Verify the substring location data, before
+   and after running cpp_interpret_string on it.  */
+
+static void
+test_lexer_string_locations_simple (const line_table_case &case_)
+{
+  /* Digits 0-9 (with 0 at column 10), the simple way.
+     ....................000000000.11111111112.2222222223333333333
+     ....................123456789.01234567890.1234567890123456789
+     We add a trailing comment to ensure that we correctly locate
+     the end of the string literal token.  */
+  const char *content = "        \"0123456789\" /* not a string */\n";
+  lexer_test test (case_, content, NULL);
+
+  /* Verify that we get the expected token back, with the correct
+     location information.  */
+  const cpp_token *tok = test.get_token ();
+  ASSERT_EQ (tok->type, CPP_STRING);
+  ASSERT_TOKEN_AS_TEXT_EQ (test.m_parser, tok, "\"0123456789\"");
+  ASSERT_TOKEN_LOC_EQ (tok, test.m_tempfile.get_filename (), 1, 9, 20);
+
+  /* At this point in lexing, the quote characters are treated as part of
+     the string (they are stripped off by cpp_interpret_string).  */
+
+  ASSERT_EQ (tok->val.str.len, 12);
+
+  /* Verify that cpp_interpret_string works.  */
+  cpp_string dst_string;
+  const enum cpp_ttype type = CPP_STRING;
+  bool result = cpp_interpret_string (test.m_parser, &tok->val.str, 1,
+				      &dst_string, type);
+  ASSERT_TRUE (result);
+  ASSERT_STREQ ("0123456789", (const char *)dst_string.text);
+  free (const_cast <unsigned char *> (dst_string.text));
+
+  /* Verify ranges of individual characters.  This no longer includes the
+     quotes.  */
+  for (int i = 0; i <= 9; i++)
+    ASSERT_CHAR_AT_RANGE (test, tok->src_loc, type, i, 1,
+			  10 + i, 10 + i);
+
+  ASSERT_NUM_SUBSTRING_RANGES (test, tok->src_loc, type, 10);
+}
+
+/* As test_lexer_string_locations_simple, but use an EBCDIC execution
+   encoding.  */
+
+static void
+test_lexer_string_locations_ebcdic (const line_table_case &case_)
+{
+  /* EBCDIC support requires iconv.  */
+  if (!HAVE_ICONV)
+    return;
+
+  /* Digits 0-9 (with 0 at column 10), the simple way.
+     ....................000000000.11111111112.2222222223333333333
+     ....................123456789.01234567890.1234567890123456789
+     We add a trailing comment to ensure that we correctly locate
+     the end of the string literal token.  */
+  const char *content = "        \"0123456789\" /* not a string */\n";
+  ebcdic_execution_charset use_ebcdic;
+  lexer_test test (case_, content, &use_ebcdic);
+
+  /* Verify that we get the expected token back, with the correct
+     location information.  */
+  const cpp_token *tok = test.get_token ();
+  ASSERT_EQ (tok->type, CPP_STRING);
+  ASSERT_TOKEN_AS_TEXT_EQ (test.m_parser, tok, "\"0123456789\"");
+  ASSERT_TOKEN_LOC_EQ (tok, test.m_tempfile.get_filename (), 1, 9, 20);
+
+  /* At this point in lexing, the quote characters are treated as part of
+     the string (they are stripped off by cpp_interpret_string).  */
+
+  ASSERT_EQ (tok->val.str.len, 12);
+
+  /* The remainder of the test requires an iconv implementation that
+     can convert from UTF-8 to the EBCDIC encoding requested above.  */
+  if (use_ebcdic.iconv_errors_occurred_p ())
+    return;
+
+  /* Verify that cpp_interpret_string works.  */
+  cpp_string dst_string;
+  const enum cpp_ttype type = CPP_STRING;
+  bool result = cpp_interpret_string (test.m_parser, &tok->val.str, 1,
+				      &dst_string, type);
+  ASSERT_TRUE (result);
+  /* We should now have EBCDIC-encoded text, specifically
+     IBM1047-encoded (aka "EBCDIC 1047", or "Code page 1047").
+     The digits 0-9 are encoded as 240-249 i.e. 0xf0-0xf9.  */
+  ASSERT_STREQ ("\xf0\xf1\xf2\xf3\xf4\xf5\xf6\xf7\xf8\xf9",
+		(const char *)dst_string.text);
+  free (const_cast <unsigned char *> (dst_string.text));
+
+  /* Verify that we don't attempt to record substring location information
+     for such cases.  */
+  ASSERT_HAS_NO_SUBSTRING_RANGES
+    (test, tok->src_loc, type,
+     "execution character set != source character set");
+}
+
+/* Lex a string literal containing a hex-escaped character.
+   Verify the substring location data, before and after running
+   cpp_interpret_string on it.  */
+
+static void
+test_lexer_string_locations_hex (const line_table_case &case_)
+{
+  /* Digits 0-9, expressing digit 5 in ASCII as "\x35"
+     and with a space in place of digit 6, to terminate the escaped
+     hex code.
+     ....................000000000.111111.11112222.
+     ....................123456789.012345.67890123.  */
+  const char *content = "        \"01234\\x35 789\"\n";
+  lexer_test test (case_, content, NULL);
+
+  /* Verify that we get the expected token back, with the correct
+     location information.  */
+  const cpp_token *tok = test.get_token ();
+  ASSERT_EQ (tok->type, CPP_STRING);
+  ASSERT_TOKEN_AS_TEXT_EQ (test.m_parser, tok, "\"01234\\x35 789\"");
+  ASSERT_TOKEN_LOC_EQ (tok, test.m_tempfile.get_filename (), 1, 9, 23);
+
+  /* At this point in lexing, the quote characters are treated as part of
+     the string (they are stripped off by cpp_interpret_string).  */
+  ASSERT_EQ (tok->val.str.len, 15);
+
+  /* Verify that cpp_interpret_string works.  */
+  cpp_string dst_string;
+  const enum cpp_ttype type = CPP_STRING;
+  bool result = cpp_interpret_string (test.m_parser, &tok->val.str, 1,
+				      &dst_string, type);
+  ASSERT_TRUE (result);
+  ASSERT_STREQ ("012345 789", (const char *)dst_string.text);
+  free (const_cast <unsigned char *> (dst_string.text));
+
+  /* Verify ranges of individual characters.  This no longer includes the
+     quotes.  */
+  for (int i = 0; i <= 4; i++)
+    ASSERT_CHAR_AT_RANGE (test, tok->src_loc, type, i, 1, 10 + i, 10 + i);
+  ASSERT_CHAR_AT_RANGE (test, tok->src_loc, type, 5, 1, 15, 18);
+  for (int i = 6; i <= 9; i++)
+    ASSERT_CHAR_AT_RANGE (test, tok->src_loc, type, i, 1, 13 + i, 13 + i);
+
+  ASSERT_NUM_SUBSTRING_RANGES (test, tok->src_loc, type, 10);
+}
+
+/* Lex a string literal containing an octal-escaped character.
+   Verify the substring location data after running cpp_interpret_string
+   on it.  */
+
+static void
+test_lexer_string_locations_oct (const line_table_case &case_)
+{
+  /* Digits 0-9, expressing digit 5 in ASCII as "\065"
+     and with a space in place of digit 6, to terminate the escaped
+     octal code.
+     ....................000000000.111111.11112222.2222223333333333444
+     ....................123456789.012345.67890123.4567890123456789012  */
+  const char *content = "        \"01234\\065 789\" /* not a string */\n";
+  lexer_test test (case_, content, NULL);
+
+  /* Verify that we get the expected token back, with the correct
+     location information.  */
+  const cpp_token *tok = test.get_token ();
+  ASSERT_EQ (tok->type, CPP_STRING);
+  ASSERT_TOKEN_AS_TEXT_EQ (test.m_parser, tok, "\"01234\\065 789\"");
+
+  /* Verify that cpp_interpret_string works.  */
+  cpp_string dst_string;
+  const enum cpp_ttype type = CPP_STRING;
+  bool result = cpp_interpret_string (test.m_parser, &tok->val.str, 1,
+				      &dst_string, type);
+  ASSERT_TRUE (result);
+  ASSERT_STREQ ("012345 789", (const char *)dst_string.text);
+  free (const_cast <unsigned char *> (dst_string.text));
+
+  /* Verify ranges of individual characters.  This no longer includes the
+     quotes.  */
+  for (int i = 0; i < 5; i++)
+    ASSERT_CHAR_AT_RANGE (test, tok->src_loc, type, i, 1, 10 + i, 10 + i);
+  ASSERT_CHAR_AT_RANGE (test, tok->src_loc, type, 5, 1, 15, 18);
+  for (int i = 6; i <= 9; i++)
+    ASSERT_CHAR_AT_RANGE (test, tok->src_loc, type, i, 1, 13 + i, 13 + i);
+
+  ASSERT_NUM_SUBSTRING_RANGES (test, tok->src_loc, type, 10);
+}
+
+/* Test of string literal containing letter escapes.  */
+
+static void
+test_lexer_string_locations_letter_escape_1 (const line_table_case &case_)
+{
+  /* The string "\tfoo\\\nbar" i.e. tab, "foo", backslash, newline, bar.
+     .....................000000000.1.11111.1.1.11222.22222223333333
+     .....................123456789.0.12345.6.7.89012.34567890123456.  */
+  const char *content = ("        \"\\tfoo\\\\\\nbar\" /* non-str */\n");
+  lexer_test test (case_, content, NULL);
+
+  /* Verify that we get the expected tokens back.  */
+  const cpp_token *tok = test.get_token ();
+  ASSERT_EQ (tok->type, CPP_STRING);
+  ASSERT_TOKEN_AS_TEXT_EQ (test.m_parser, tok, "\"\\tfoo\\\\\\nbar\"");
+
+  /* Verify ranges of individual characters. */
+  /* "\t".  */
+  ASSERT_CHAR_AT_RANGE (test, tok->src_loc, CPP_STRING,
+			0, 1, 10, 11);
+  /* "foo". */
+  for (int i = 1; i <= 3; i++)
+    ASSERT_CHAR_AT_RANGE (test, tok->src_loc, CPP_STRING,
+			  i, 1, 11 + i, 11 + i);
+  /* "\\" and "\n".  */
+  ASSERT_CHAR_AT_RANGE (test, tok->src_loc, CPP_STRING,
+			4, 1, 15, 16);
+  ASSERT_CHAR_AT_RANGE (test, tok->src_loc, CPP_STRING,
+			5, 1, 17, 18);
+
+  /* "bar".  */
+  for (int i = 6; i <= 8; i++)
+    ASSERT_CHAR_AT_RANGE (test, tok->src_loc, CPP_STRING,
+			  i, 1, 13 + i, 13 + i);
+
+  ASSERT_NUM_SUBSTRING_RANGES (test, tok->src_loc, CPP_STRING, 9);
+}
+
+/* Another test of a string literal containing a letter escape.
+   Based on string seen in
+     printf ("%-%\n");
+   in gcc.dg/format/c90-printf-1.c.  */
+
+static void
+test_lexer_string_locations_letter_escape_2 (const line_table_case &case_)
+{
+  /* .....................000000000.1111.11.1111.22222222223.
+     .....................123456789.0123.45.6789.01234567890.  */
+  const char *content = ("        \"%-%\\n\" /* non-str */\n");
+  lexer_test test (case_, content, NULL);
+
+  /* Verify that we get the expected tokens back.  */
+  const cpp_token *tok = test.get_token ();
+  ASSERT_EQ (tok->type, CPP_STRING);
+  ASSERT_TOKEN_AS_TEXT_EQ (test.m_parser, tok, "\"%-%\\n\"");
+
+  /* Verify ranges of individual characters. */
+  /* "%-%".  */
+  for (int i = 0; i < 3; i++)
+    ASSERT_CHAR_AT_RANGE (test, tok->src_loc, CPP_STRING,
+			  i, 1, 10 + i, 10 + i);
+  /* "\n".  */
+  ASSERT_CHAR_AT_RANGE (test, tok->src_loc, CPP_STRING,
+			3, 1, 13, 14);
+
+  ASSERT_NUM_SUBSTRING_RANGES (test, tok->src_loc, CPP_STRING, 4);
+}
+
+/* Lex a string literal containing UCN 4 characters.
+   Verify the substring location data after running cpp_interpret_string
+   on it.  */
+
+static void
+test_lexer_string_locations_ucn4 (const line_table_case &case_)
+{
+  /* Digits 0-9, expressing digits 5 and 6 as Roman numerals expressed
+     as UCN 4.
+     ....................000000000.111111.111122.222222223.33333333344444
+     ....................123456789.012345.678901.234567890.12345678901234  */
+  const char *content = "        \"01234\\u2174\\u2175789\" /* non-str */\n";
+  lexer_test test (case_, content, NULL);
+
+  /* Verify that we get the expected token back, with the correct
+     location information.  */
+  const cpp_token *tok = test.get_token ();
+  ASSERT_EQ (tok->type, CPP_STRING);
+  ASSERT_TOKEN_AS_TEXT_EQ (test.m_parser, tok, "\"01234\\u2174\\u2175789\"");
+
+  /* Verify that cpp_interpret_string works.
+     The string should be encoded in the execution character
+     set.  Assuming that that is UTF-8, we should have the following:
+     -----------  ----  -----  -------  ----------------
+     Byte offset  Byte  Octal  Unicode  Source Column(s)
+     -----------  ----  -----  -------  ----------------
+     0            0x30         '0'      10
+     1            0x31         '1'      11
+     2            0x32         '2'      12
+     3            0x33         '3'      13
+     4            0x34         '4'      14
+     5            0xE2  \342   U+2174   15-20
+     6            0x85  \205    (cont)  15-20
+     7            0xB4  \264    (cont)  15-20
+     8            0xE2  \342   U+2175   21-26
+     9            0x85  \205    (cont)  21-26
+     10           0xB5  \265    (cont)  21-26
+     11           0x37         '7'      27
+     12           0x38         '8'      28
+     13           0x39         '9'      29
+     -----------  ----  -----  -------  ---------------.  */
+
+  cpp_string dst_string;
+  const enum cpp_ttype type = CPP_STRING;
+  bool result = cpp_interpret_string (test.m_parser, &tok->val.str, 1,
+				      &dst_string, type);
+  ASSERT_TRUE (result);
+  ASSERT_STREQ ("01234\342\205\264\342\205\265789",
+		(const char *)dst_string.text);
+  free (const_cast <unsigned char *> (dst_string.text));
+
+  /* Verify ranges of individual characters.  This no longer includes the
+     quotes.
+     '01234'.  */
+  for (int i = 0; i <= 4; i++)
+    ASSERT_CHAR_AT_RANGE (test, tok->src_loc, type, i, 1, 10 + i, 10 + i);
+  /* U+2174.  */
+  for (int i = 5; i <= 7; i++)
+    ASSERT_CHAR_AT_RANGE (test, tok->src_loc, type, i, 1, 15, 20);
+  /* U+2175.  */
+  for (int i = 8; i <= 10; i++)
+    ASSERT_CHAR_AT_RANGE (test, tok->src_loc, type, i, 1, 21, 26);
+  /* '789'.  */
+  for (int i = 11; i <= 13; i++)
+    ASSERT_CHAR_AT_RANGE (test, tok->src_loc, type, i, 1, 16 + i, 16 + i);
+
+  ASSERT_NUM_SUBSTRING_RANGES (test, tok->src_loc, type, 14);
+}
+
+/* Lex a string literal containing UCN 8 characters.
+   Verify the substring location data after running cpp_interpret_string
+   on it.  */
+
+static void
+test_lexer_string_locations_ucn8 (const line_table_case &case_)
+{
+  /* Digits 0-9, expressing digits 5 and 6 as Roman numerals as UCN 8.
+     ....................000000000.111111.1111222222.2222333333333.344444
+     ....................123456789.012345.6789012345.6789012345678.901234  */
+  const char *content = "        \"01234\\U00002174\\U00002175789\" /* */\n";
+  lexer_test test (case_, content, NULL);
+
+  /* Verify that we get the expected token back, with the correct
+     location information.  */
+  const cpp_token *tok = test.get_token ();
+  ASSERT_EQ (tok->type, CPP_STRING);
+  ASSERT_TOKEN_AS_TEXT_EQ (test.m_parser, tok,
+			   "\"01234\\U00002174\\U00002175789\"");
+
+  /* Verify that cpp_interpret_string works.
+     The UTF-8 encoding of the string is identical to that from
+     the ucn4 testcase above; the only difference is the column
+     locations.  */
+  cpp_string dst_string;
+  const enum cpp_ttype type = CPP_STRING;
+  bool result = cpp_interpret_string (test.m_parser, &tok->val.str, 1,
+				      &dst_string, type);
+  ASSERT_TRUE (result);
+  ASSERT_STREQ ("01234\342\205\264\342\205\265789",
+		(const char *)dst_string.text);
+  free (const_cast <unsigned char *> (dst_string.text));
+
+  /* Verify ranges of individual characters.  This no longer includes the
+     quotes.
+     '01234'.  */
+  for (int i = 0; i <= 4; i++)
+    ASSERT_CHAR_AT_RANGE (test, tok->src_loc, type, i, 1, 10 + i, 10 + i);
+  /* U+2174.  */
+  for (int i = 5; i <= 7; i++)
+    ASSERT_CHAR_AT_RANGE (test, tok->src_loc, type, i, 1, 15, 24);
+  /* U+2175.  */
+  for (int i = 8; i <= 10; i++)
+    ASSERT_CHAR_AT_RANGE (test, tok->src_loc, type, i, 1, 25, 34);
+  /* '789' at columns 35-37  */
+  for (int i = 11; i <= 13; i++)
+    ASSERT_CHAR_AT_RANGE (test, tok->src_loc, type, i, 1, 24 + i, 24 + i);
+
+  ASSERT_NUM_SUBSTRING_RANGES (test, tok->src_loc, type, 14);
+}
+
+/* Fetch a big-endian 32-bit value and convert to host endianness.  */
+
+static uint32_t
+uint32_from_big_endian (const uint32_t *ptr_be_value)
+{
+  const unsigned char *buf = (const unsigned char *)ptr_be_value;
+  return (((uint32_t) buf[0] << 24)
+	  | ((uint32_t) buf[1] << 16)
+	  | ((uint32_t) buf[2] << 8)
+	  | (uint32_t) buf[3]);
+}
+
+/* Lex a wide string literal and verify that attempts to read substring
+   location data from it fail gracefully.  */
+
+static void
+test_lexer_string_locations_wide_string (const line_table_case &case_)
+{
+  /* Digits 0-9.
+     ....................000000000.11111111112.22222222233333
+     ....................123456789.01234567890.12345678901234  */
+  const char *content = "       L\"0123456789\" /* non-str */\n";
+  lexer_test test (case_, content, NULL);
+
+  /* Verify that we get the expected token back, with the correct
+     location information.  */
+  const cpp_token *tok = test.get_token ();
+  ASSERT_EQ (tok->type, CPP_WSTRING);
+  ASSERT_TOKEN_AS_TEXT_EQ (test.m_parser, tok, "L\"0123456789\"");
+
+  /* Verify that cpp_interpret_string works, using CPP_WSTRING.  */
+  cpp_string dst_string;
+  const enum cpp_ttype type = CPP_WSTRING;
+  bool result = cpp_interpret_string (test.m_parser, &tok->val.str, 1,
+				      &dst_string, type);
+  ASSERT_TRUE (result);
+  /* The cpp_reader defaults to big-endian with
+     CHAR_BIT * sizeof (int) for the wchar_precision, so dst_string should
+     now be encoded as UTF-32BE.  */
+  const uint32_t *be32_chars = (const uint32_t *)dst_string.text;
+  ASSERT_EQ ('0', uint32_from_big_endian (&be32_chars[0]));
+  ASSERT_EQ ('5', uint32_from_big_endian (&be32_chars[5]));
+  ASSERT_EQ ('9', uint32_from_big_endian (&be32_chars[9]));
+  ASSERT_EQ (0, uint32_from_big_endian (&be32_chars[10]));
+  free (const_cast <unsigned char *> (dst_string.text));
+
+  /* We don't yet support generating substring location information
+     for L"" strings.  */
+  ASSERT_HAS_NO_SUBSTRING_RANGES
+    (test, tok->src_loc, type,
+     "execution character set != source character set");
+}
+
+/* Fetch a big-endian 16-bit value and convert to host endianness.  */
+
+static uint16_t
+uint16_from_big_endian (const uint16_t *ptr_be_value)
+{
+  const unsigned char *buf = (const unsigned char *)ptr_be_value;
+  return ((uint16_t) buf[0] << 8) | (uint16_t) buf[1];
+}
+
+/* Lex a u"" string literal and verify that attempts to read substring
+   location data from it fail gracefully.  */
+
+static void
+test_lexer_string_locations_string16 (const line_table_case &case_)
+{
+  /* Digits 0-9.
+     ....................000000000.11111111112.22222222233333
+     ....................123456789.01234567890.12345678901234  */
+  const char *content = "       u\"0123456789\" /* non-str */\n";
+  lexer_test test (case_, content, NULL);
+
+  /* Verify that we get the expected token back, with the correct
+     location information.  */
+  const cpp_token *tok = test.get_token ();
+  ASSERT_EQ (tok->type, CPP_STRING16);
+  ASSERT_TOKEN_AS_TEXT_EQ (test.m_parser, tok, "u\"0123456789\"");
+
+  /* Verify that cpp_interpret_string works, using CPP_STRING16.  */
+  cpp_string dst_string;
+  const enum cpp_ttype type = CPP_STRING16;
+  bool result = cpp_interpret_string (test.m_parser, &tok->val.str, 1,
+				      &dst_string, type);
+  ASSERT_TRUE (result);
+
+  /* The cpp_reader defaults to big-endian, so dst_string should
+     now be encoded as UTF-16BE.  */
+  const uint16_t *be16_chars = (const uint16_t *)dst_string.text;
+  ASSERT_EQ ('0', uint16_from_big_endian (&be16_chars[0]));
+  ASSERT_EQ ('5', uint16_from_big_endian (&be16_chars[5]));
+  ASSERT_EQ ('9', uint16_from_big_endian (&be16_chars[9]));
+  ASSERT_EQ (0, uint16_from_big_endian (&be16_chars[10]));
+  free (const_cast <unsigned char *> (dst_string.text));
+
+  /* We don't yet support generating substring location information
+     for L"" strings.  */
+  ASSERT_HAS_NO_SUBSTRING_RANGES
+    (test, tok->src_loc, type,
+     "execution character set != source character set");
+}
+
+/* Lex a U"" string literal and verify that attempts to read substring
+   location data from it fail gracefully.  */
+
+static void
+test_lexer_string_locations_string32 (const line_table_case &case_)
+{
+  /* Digits 0-9.
+     ....................000000000.11111111112.22222222233333
+     ....................123456789.01234567890.12345678901234  */
+  const char *content = "       U\"0123456789\" /* non-str */\n";
+  lexer_test test (case_, content, NULL);
+
+  /* Verify that we get the expected token back, with the correct
+     location information.  */
+  const cpp_token *tok = test.get_token ();
+  ASSERT_EQ (tok->type, CPP_STRING32);
+  ASSERT_TOKEN_AS_TEXT_EQ (test.m_parser, tok, "U\"0123456789\"");
+
+  /* Verify that cpp_interpret_string works, using CPP_STRING32.  */
+  cpp_string dst_string;
+  const enum cpp_ttype type = CPP_STRING32;
+  bool result = cpp_interpret_string (test.m_parser, &tok->val.str, 1,
+				      &dst_string, type);
+  ASSERT_TRUE (result);
+
+  /* The cpp_reader defaults to big-endian, so dst_string should
+     now be encoded as UTF-32BE.  */
+  const uint32_t *be32_chars = (const uint32_t *)dst_string.text;
+  ASSERT_EQ ('0', uint32_from_big_endian (&be32_chars[0]));
+  ASSERT_EQ ('5', uint32_from_big_endian (&be32_chars[5]));
+  ASSERT_EQ ('9', uint32_from_big_endian (&be32_chars[9]));
+  ASSERT_EQ (0, uint32_from_big_endian (&be32_chars[10]));
+  free (const_cast <unsigned char *> (dst_string.text));
+
+  /* We don't yet support generating substring location information
+     for L"" strings.  */
+  ASSERT_HAS_NO_SUBSTRING_RANGES
+    (test, tok->src_loc, type,
+     "execution character set != source character set");
+}
+
+/* Lex a u8-string literal.
+   Verify the substring location data after running cpp_interpret_string
+   on it.  */
+
+static void
+test_lexer_string_locations_u8 (const line_table_case &case_)
+{
+  /* Digits 0-9.
+     ....................000000000.11111111112.22222222233333
+     ....................123456789.01234567890.12345678901234  */
+  const char *content = "      u8\"0123456789\" /* non-str */\n";
+  lexer_test test (case_, content, NULL);
+
+  /* Verify that we get the expected token back, with the correct
+     location information.  */
+  const cpp_token *tok = test.get_token ();
+  ASSERT_EQ (tok->type, CPP_UTF8STRING);
+  ASSERT_TOKEN_AS_TEXT_EQ (test.m_parser, tok, "u8\"0123456789\"");
+
+  /* Verify that cpp_interpret_string works.  */
+  cpp_string dst_string;
+  const enum cpp_ttype type = CPP_STRING;
+  bool result = cpp_interpret_string (test.m_parser, &tok->val.str, 1,
+				      &dst_string, type);
+  ASSERT_TRUE (result);
+  ASSERT_STREQ ("0123456789", (const char *)dst_string.text);
+  free (const_cast <unsigned char *> (dst_string.text));
+
+  /* Verify ranges of individual characters.  This no longer includes the
+     quotes.  */
+  for (int i = 0; i <= 9; i++)
+    ASSERT_CHAR_AT_RANGE (test, tok->src_loc, type, i, 1, 10 + i, 10 + i);
+}
+
+/* Lex a string literal containing UTF-8 source characters.
+   Verify the substring location data after running cpp_interpret_string
+   on it.  */
+
+static void
+test_lexer_string_locations_utf8_source (const line_table_case &case_)
+{
+ /* This string literal is written out to the source file as UTF-8,
+    and is of the form "before mojibake after", where "mojibake"
+    is written as the following four unicode code points:
+       U+6587 CJK UNIFIED IDEOGRAPH-6587
+       U+5B57 CJK UNIFIED IDEOGRAPH-5B57
+       U+5316 CJK UNIFIED IDEOGRAPH-5316
+       U+3051 HIRAGANA LETTER KE.
+     Each of these is 3 bytes wide when encoded in UTF-8, whereas the
+     "before" and "after" are 1 byte per unicode character.
+
+     The numbering shown are "columns", which are *byte* numbers within
+     the line, rather than unicode character numbers.
+
+     .................... 000000000.1111111.
+     .................... 123456789.0123456.  */
+  const char *content = ("        \"before "
+			 /* U+6587 CJK UNIFIED IDEOGRAPH-6587
+			      UTF-8: 0xE6 0x96 0x87
+			      C octal escaped UTF-8: \346\226\207
+			    "column" numbers: 17-19.  */
+			 "\346\226\207"
+
+			 /* U+5B57 CJK UNIFIED IDEOGRAPH-5B57
+			      UTF-8: 0xE5 0xAD 0x97
+			      C octal escaped UTF-8: \345\255\227
+			    "column" numbers: 20-22.  */
+			 "\345\255\227"
+
+			 /* U+5316 CJK UNIFIED IDEOGRAPH-5316
+			      UTF-8: 0xE5 0x8C 0x96
+			      C octal escaped UTF-8: \345\214\226
+			    "column" numbers: 23-25.  */
+			 "\345\214\226"
+
+			 /* U+3051 HIRAGANA LETTER KE
+			      UTF-8: 0xE3 0x81 0x91
+			      C octal escaped UTF-8: \343\201\221
+			    "column" numbers: 26-28.  */
+			 "\343\201\221"
+
+			 /* column numbers 29 onwards
+			  2333333.33334444444444
+			  9012345.67890123456789. */
+			 " after\" /* non-str */\n");
+  lexer_test test (case_, content, NULL);
+
+  /* Verify that we get the expected token back, with the correct
+     location information.  */
+  const cpp_token *tok = test.get_token ();
+  ASSERT_EQ (tok->type, CPP_STRING);
+  ASSERT_TOKEN_AS_TEXT_EQ
+    (test.m_parser, tok,
+     "\"before \346\226\207\345\255\227\345\214\226\343\201\221 after\"");
+
+  /* Verify that cpp_interpret_string works.  */
+  cpp_string dst_string;
+  const enum cpp_ttype type = CPP_STRING;
+  bool result = cpp_interpret_string (test.m_parser, &tok->val.str, 1,
+				      &dst_string, type);
+  ASSERT_TRUE (result);
+  ASSERT_STREQ
+    ("before \346\226\207\345\255\227\345\214\226\343\201\221 after",
+     (const char *)dst_string.text);
+  free (const_cast <unsigned char *> (dst_string.text));
+
+  /* Verify ranges of individual characters.  This no longer includes the
+     quotes.
+     Assuming that both source and execution encodings are UTF-8, we have
+     a run of 25 octets in each.  */
+  for (int i = 0; i < 25; i++)
+    ASSERT_CHAR_AT_RANGE (test, tok->src_loc, type, i, 1, 10 + i, 10 + i);
+
+  ASSERT_NUM_SUBSTRING_RANGES (test, tok->src_loc, type, 25);
+}
+
+/* Test of string literal concatenation.  */
+
+static void
+test_lexer_string_locations_concatenation_1 (const line_table_case &case_)
+{
+  /* Digits 0-9.
+     .....................000000000.111111.11112222222222
+     .....................123456789.012345.67890123456789.  */
+  const char *content = ("        \"01234\" /* non-str */\n"
+			 "        \"56789\" /* non-str */\n");
+  lexer_test test (case_, content, NULL);
+
+  location_t input_locs[2];
+
+  /* Verify that we get the expected tokens back.  */
+  auto_vec <cpp_string> input_strings;
+  const cpp_token *tok_a = test.get_token ();
+  ASSERT_EQ (tok_a->type, CPP_STRING);
+  ASSERT_TOKEN_AS_TEXT_EQ (test.m_parser, tok_a, "\"01234\"");
+  input_strings.safe_push (tok_a->val.str);
+  input_locs[0] = tok_a->src_loc;
+
+  const cpp_token *tok_b = test.get_token ();
+  ASSERT_EQ (tok_b->type, CPP_STRING);
+  ASSERT_TOKEN_AS_TEXT_EQ (test.m_parser, tok_b, "\"56789\"");
+  input_strings.safe_push (tok_b->val.str);
+  input_locs[1] = tok_b->src_loc;
+
+  /* Verify that cpp_interpret_string works.  */
+  cpp_string dst_string;
+  const enum cpp_ttype type = CPP_STRING;
+  bool result = cpp_interpret_string (test.m_parser,
+				      input_strings.address (), 2,
+				      &dst_string, type);
+  ASSERT_TRUE (result);
+  ASSERT_STREQ ("0123456789", (const char *)dst_string.text);
+  free (const_cast <unsigned char *> (dst_string.text));
+
+  /* Simulate c-lex.c's lex_string in order to record concatenation.  */
+  test.m_concats.record_string_concatenation (2, input_locs);
+
+  location_t initial_loc = input_locs[0];
+
+  for (int i = 0; i <= 4; i++)
+    ASSERT_CHAR_AT_RANGE (test, initial_loc, type, i, 1, 10 + i, 10 + i);
+  for (int i = 5; i <= 9; i++)
+    ASSERT_CHAR_AT_RANGE (test, initial_loc, type, i, 2, 5 + i, 5 + i);
+
+  ASSERT_NUM_SUBSTRING_RANGES (test, initial_loc, type, 10);
+}
+
+/* Another test of string literal concatenation.  */
+
+static void
+test_lexer_string_locations_concatenation_2 (const line_table_case &case_)
+{
+  /* Digits 0-9.
+     .....................000000000.111.11111112222222
+     .....................123456789.012.34567890123456.  */
+  const char *content = ("        \"01\" /* non-str */\n"
+			 "        \"23\" /* non-str */\n"
+			 "        \"45\" /* non-str */\n"
+			 "        \"67\" /* non-str */\n"
+			 "        \"89\" /* non-str */\n");
+  lexer_test test (case_, content, NULL);
+
+  auto_vec <cpp_string> input_strings;
+  location_t input_locs[5];
+
+  /* Verify that we get the expected tokens back.  */
+  for (int i = 0; i < 5; i++)
+    {
+      const cpp_token *tok = test.get_token ();
+      ASSERT_EQ (tok->type, CPP_STRING);
+      input_strings.safe_push (tok->val.str);
+      input_locs[i] = tok->src_loc;
+    }
+
+  /* Verify that cpp_interpret_string works.  */
+  cpp_string dst_string;
+  const enum cpp_ttype type = CPP_STRING;
+  bool result = cpp_interpret_string (test.m_parser,
+				      input_strings.address (), 5,
+				      &dst_string, type);
+  ASSERT_TRUE (result);
+  ASSERT_STREQ ("0123456789", (const char *)dst_string.text);
+  free (const_cast <unsigned char *> (dst_string.text));
+
+  /* Simulate c-lex.c's lex_string in order to record concatenation.  */
+  test.m_concats.record_string_concatenation (5, input_locs);
+
+  location_t initial_loc = input_locs[0];
+
+  /* Within ASSERT_CHAR_AT_RANGE (actually assert_char_at_range), we can
+     detect if the initial loc is after LINE_MAP_MAX_LOCATION_WITH_COLS
+     and expect get_source_range_for_substring to fail.
+     However, for a string concatenation test, we can have a case
+     where the initial string is fully before LINE_MAP_MAX_LOCATION_WITH_COLS,
+     but subsequent strings can be after it.
+     Attempting to detect this within assert_char_at_range
+     would overcomplicate the logic for the common test cases, so
+     we detect it here.  */
+  if (should_have_column_data_p (input_locs[0])
+      && !should_have_column_data_p (input_locs[4]))
+    {
+      /* Verify that get_source_range_for_substring gracefully rejects
+	 this case.  */
+      source_range actual_range;
+      const char *err
+	= get_source_range_for_substring (test.m_parser, &test.m_concats,
+					  initial_loc, type, 0, 0,
+					  &actual_range);
+      ASSERT_STREQ ("range starts after LINE_MAP_MAX_LOCATION_WITH_COLS", err);
+      return;
+    }
+
+  for (int i = 0; i < 5; i++)
+    for (int j = 0; j < 2; j++)
+      ASSERT_CHAR_AT_RANGE (test, initial_loc, type, (i * 2) + j,
+			    i + 1, 10 + j, 10 + j);
+
+  ASSERT_NUM_SUBSTRING_RANGES (test, initial_loc, type, 10);
+}
+
+/* Another test of string literal concatenation, this time combined with
+   various kinds of escaped characters.  */
+
+static void
+test_lexer_string_locations_concatenation_3 (const line_table_case &case_)
+{
+  /* Digits 0-9, expressing digit 5 in ASCII as hex "\x35"
+     digit 6 in ASCII as octal "\066", concatenating multiple strings.  */
+  const char *content
+    /* .000000000.111111.111.1.2222.222.2.2233.333.3333.34444444444555
+       .123456789.012345.678.9.0123.456.7.8901.234.5678.90123456789012. */
+    = ("        \"01234\"  \"\\x35\"  \"\\066\"  \"789\" /* non-str */\n");
+  lexer_test test (case_, content, NULL);
+
+  auto_vec <cpp_string> input_strings;
+  location_t input_locs[4];
+
+  /* Verify that we get the expected tokens back.  */
+  for (int i = 0; i < 4; i++)
+    {
+      const cpp_token *tok = test.get_token ();
+      ASSERT_EQ (tok->type, CPP_STRING);
+      input_strings.safe_push (tok->val.str);
+      input_locs[i] = tok->src_loc;
+    }
+
+  /* Verify that cpp_interpret_string works.  */
+  cpp_string dst_string;
+  const enum cpp_ttype type = CPP_STRING;
+  bool result = cpp_interpret_string (test.m_parser,
+				      input_strings.address (), 4,
+				      &dst_string, type);
+  ASSERT_TRUE (result);
+  ASSERT_STREQ ("0123456789", (const char *)dst_string.text);
+  free (const_cast <unsigned char *> (dst_string.text));
+
+  /* Simulate c-lex.c's lex_string in order to record concatenation.  */
+  test.m_concats.record_string_concatenation (4, input_locs);
+
+  location_t initial_loc = input_locs[0];
+
+  for (int i = 0; i <= 4; i++)
+    ASSERT_CHAR_AT_RANGE (test, initial_loc, type, i, 1, 10 + i, 10 + i);
+  ASSERT_CHAR_AT_RANGE (test, initial_loc, type, 5, 1, 19, 22);
+  ASSERT_CHAR_AT_RANGE (test, initial_loc, type, 6, 1, 27, 30);
+  for (int i = 7; i <= 9; i++)
+    ASSERT_CHAR_AT_RANGE (test, initial_loc, type, i, 1, 28 + i, 28 + i);
+
+  ASSERT_NUM_SUBSTRING_RANGES (test, initial_loc, type, 10);
+}
+
+/* Test of string literal in a macro.  */
+
+static void
+test_lexer_string_locations_macro (const line_table_case &case_)
+{
+  /* Digits 0-9.
+     .....................0000000001111111111.22222222223.
+     .....................1234567890123456789.01234567890.  */
+  const char *content = ("#define MACRO     \"0123456789\" /* non-str */\n"
+			 "  MACRO");
+  lexer_test test (case_, content, NULL);
+
+  /* Verify that we get the expected tokens back.  */
+  const cpp_token *tok = test.get_token ();
+  ASSERT_EQ (tok->type, CPP_PADDING);
+
+  tok = test.get_token ();
+  ASSERT_EQ (tok->type, CPP_STRING);
+  ASSERT_TOKEN_AS_TEXT_EQ (test.m_parser, tok, "\"0123456789\"");
+
+  /* Verify ranges of individual characters.  We ought to
+     see columns within the macro definition.  */
+  for (int i = 0; i <= 9; i++)
+    ASSERT_CHAR_AT_RANGE (test, tok->src_loc, CPP_STRING,
+			  i, 1, 20 + i, 20 + i);
+
+  ASSERT_NUM_SUBSTRING_RANGES (test, tok->src_loc, CPP_STRING, 10);
+
+  tok = test.get_token ();
+  ASSERT_EQ (tok->type, CPP_PADDING);
+}
+
+/* Test of stringification of a macro argument.  */
+
+static void
+test_lexer_string_locations_stringified_macro_argument
+  (const line_table_case &case_)
+{
+  /* .....................000000000111111111122222222223.
+     .....................123456789012345678901234567890.  */
+  const char *content = ("#define MACRO(X) #X /* non-str */\n"
+			 "MACRO(foo)\n");
+  lexer_test test (case_, content, NULL);
+
+  /* Verify that we get the expected token back.  */
+  const cpp_token *tok = test.get_token ();
+  ASSERT_EQ (tok->type, CPP_PADDING);
+
+  tok = test.get_token ();
+  ASSERT_EQ (tok->type, CPP_STRING);
+  ASSERT_TOKEN_AS_TEXT_EQ (test.m_parser, tok, "\"foo\"");
+
+  /* We don't support getting the location of a stringified macro
+     argument.  Verify that it fails gracefully.  */
+  ASSERT_HAS_NO_SUBSTRING_RANGES (test, tok->src_loc, CPP_STRING,
+				  "cpp_interpret_string_1 failed");
+
+  tok = test.get_token ();
+  ASSERT_EQ (tok->type, CPP_PADDING);
+
+  tok = test.get_token ();
+  ASSERT_EQ (tok->type, CPP_PADDING);
+}
+
+/* Ensure that we are fail gracefully if something attempts to pass
+   in a location that isn't a string literal token.  Seen on this code:
+
+     const char a[] = " %d ";
+     __builtin_printf (a, 0.5);
+                       ^
+
+   when c-format.c erroneously used the indicated one-character
+   location as the format string location, leading to a read past the
+   end of a string buffer in cpp_interpret_string_1.  */
+
+static void
+test_lexer_string_locations_non_string (const line_table_case &case_)
+{
+  /* .....................000000000111111111122222222223.
+     .....................123456789012345678901234567890.  */
+  const char *content = ("         a\n");
+  lexer_test test (case_, content, NULL);
+
+  /* Verify that we get the expected token back.  */
+  const cpp_token *tok = test.get_token ();
+  ASSERT_EQ (tok->type, CPP_NAME);
+  ASSERT_TOKEN_AS_TEXT_EQ (test.m_parser, tok, "a");
+
+  /* At this point, libcpp is attempting to interpret the name as a
+     string literal, despite it not starting with a quote.  We don't detect
+     that, but we should at least fail gracefully.  */
+  ASSERT_HAS_NO_SUBSTRING_RANGES (test, tok->src_loc, CPP_STRING,
+				  "cpp_interpret_string_1 failed");
+}
+
+/* Ensure that we can read substring information for a token which
+   starts in one linemap and ends in another .  Adapted from
+   gcc.dg/cpp/pr69985.c.  */
+
+static void
+test_lexer_string_locations_long_line (const line_table_case &case_)
+{
+  /* .....................000000.000111111111
+     .....................123456.789012346789.  */
+  const char *content = ("/* A very long line, so that we start a new line map.  */\n"
+			 "     \"0123456789012345678901234567890123456789"
+			 "0123456789012345678901234567890123456789"
+			 "0123456789012345678901234567890123456789"
+			 "0123456789\"\n");
+
+  lexer_test test (case_, content, NULL);
+
+  /* Verify that we get the expected token back.  */
+  const cpp_token *tok = test.get_token ();
+  ASSERT_EQ (tok->type, CPP_STRING);
+
+  if (!should_have_column_data_p (line_table->highest_location))
+    return;
+
+  /* Verify ranges of individual characters.  */
+  ASSERT_NUM_SUBSTRING_RANGES (test, tok->src_loc, CPP_STRING, 130);
+  for (int i = 0; i < 130; i++)
+    ASSERT_CHAR_AT_RANGE (test, tok->src_loc, CPP_STRING,
+			  i, 2, 7 + i, 7 + i);
+}
+
+/* Test of lexing char constants.  */
+
+static void
+test_lexer_char_constants (const line_table_case &case_)
+{
+  /* Various char constants.
+     .....................0000000001111111111.22222222223.
+     .....................1234567890123456789.01234567890.  */
+  const char *content = ("         'a'\n"
+			 "        u'a'\n"
+			 "        U'a'\n"
+			 "        L'a'\n"
+			 "         'abc'\n");
+  lexer_test test (case_, content, NULL);
+
+  /* Verify that we get the expected tokens back.  */
+  /* 'a'.  */
+  const cpp_token *tok = test.get_token ();
+  ASSERT_EQ (tok->type, CPP_CHAR);
+  ASSERT_TOKEN_AS_TEXT_EQ (test.m_parser, tok, "'a'");
+
+  unsigned int chars_seen;
+  int unsignedp;
+  cppchar_t cc = cpp_interpret_charconst (test.m_parser, tok,
+					  &chars_seen, &unsignedp);
+  ASSERT_EQ (cc, 'a');
+  ASSERT_EQ (chars_seen, 1);
+
+  /* u'a'.  */
+  tok = test.get_token ();
+  ASSERT_EQ (tok->type, CPP_CHAR16);
+  ASSERT_TOKEN_AS_TEXT_EQ (test.m_parser, tok, "u'a'");
+
+  /* U'a'.  */
+  tok = test.get_token ();
+  ASSERT_EQ (tok->type, CPP_CHAR32);
+  ASSERT_TOKEN_AS_TEXT_EQ (test.m_parser, tok, "U'a'");
+
+  /* L'a'.  */
+  tok = test.get_token ();
+  ASSERT_EQ (tok->type, CPP_WCHAR);
+  ASSERT_TOKEN_AS_TEXT_EQ (test.m_parser, tok, "L'a'");
+
+  /* 'abc' (c-char-sequence).  */
+  tok = test.get_token ();
+  ASSERT_EQ (tok->type, CPP_CHAR);
+  ASSERT_TOKEN_AS_TEXT_EQ (test.m_parser, tok, "'abc'");
+}
 /* A table of interesting location_t values, giving one axis of our test
    matrix.  */
 
@@ -1599,6 +3125,27 @@ input_c_tests ()
 	  /* Run all tests for the given case within the test matrix.  */
 	  test_accessing_ordinary_linemaps (c);
 	  test_lexer (c);
+	  test_lexer_string_locations_simple (c);
+	  test_lexer_string_locations_ebcdic (c);
+	  test_lexer_string_locations_hex (c);
+	  test_lexer_string_locations_oct (c);
+	  test_lexer_string_locations_letter_escape_1 (c);
+	  test_lexer_string_locations_letter_escape_2 (c);
+	  test_lexer_string_locations_ucn4 (c);
+	  test_lexer_string_locations_ucn8 (c);
+	  test_lexer_string_locations_wide_string (c);
+	  test_lexer_string_locations_string16 (c);
+	  test_lexer_string_locations_string32 (c);
+	  test_lexer_string_locations_u8 (c);
+	  test_lexer_string_locations_utf8_source (c);
+	  test_lexer_string_locations_concatenation_1 (c);
+	  test_lexer_string_locations_concatenation_2 (c);
+	  test_lexer_string_locations_concatenation_3 (c);
+	  test_lexer_string_locations_macro (c);
+	  test_lexer_string_locations_stringified_macro_argument (c);
+	  test_lexer_string_locations_non_string (c);
+	  test_lexer_string_locations_long_line (c);
+	  test_lexer_char_constants (c);
 
 	  num_cases_tested++;
 	}
diff --git a/gcc/input.h b/gcc/input.h
index d51f950..c17e440 100644
--- a/gcc/input.h
+++ b/gcc/input.h
@@ -95,4 +95,39 @@ void dump_location_info (FILE *stream);
 
 void diagnostics_file_cache_fini (void);
 
+struct GTY(()) string_concat
+{
+  string_concat (int num, location_t *locs);
+
+  int m_num;
+  location_t * GTY ((atomic)) m_locs;
+};
+
+struct location_hash : int_hash <location_t, UNKNOWN_LOCATION> { };
+
+class GTY(()) string_concat_db
+{
+ public:
+  string_concat_db ();
+  void record_string_concatenation (int num, location_t *locs);
+
+  bool get_string_concatenation (location_t loc,
+				 int *out_num,
+				 location_t **out_locs);
+
+ private:
+  static location_t get_key_loc (location_t loc);
+
+  /* For the fields to be private, we must grant access to the
+     generated code in gtype-desc.c.  */
+
+  friend void ::gt_ggc_mx_string_concat_db (void *x_p);
+  friend void ::gt_pch_nx_string_concat_db (void *x_p);
+  friend void ::gt_pch_p_16string_concat_db (void *this_obj, void *x_p,
+					     gt_pointer_operator op,
+					     void *cookie);
+
+  hash_map <location_hash, string_concat *> *m_table;
+};
+
 #endif
diff --git a/gcc/substring-locations.h b/gcc/substring-locations.h
new file mode 100644
index 0000000..274ebbe
--- /dev/null
+++ b/gcc/substring-locations.h
@@ -0,0 +1,30 @@
+/* Source locations within string literals.
+   Copyright (C) 2016 Free Software Foundation, Inc.
+
+This file is part of GCC.
+
+GCC is free software; you can redistribute it and/or modify it under
+the terms of the GNU General Public License as published by the Free
+Software Foundation; either version 3, or (at your option) any later
+version.
+
+GCC is distributed in the hope that it will be useful, but WITHOUT ANY
+WARRANTY; without even the implied warranty of MERCHANTABILITY or
+FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+for more details.
+
+You should have received a copy of the GNU General Public License
+along with GCC; see the file COPYING3.  If not see
+<http://www.gnu.org/licenses/>.  */
+
+#ifndef GCC_SUBSTRING_LOCATIONS_H
+#define GCC_SUBSTRING_LOCATIONS_H
+
+extern const char *get_source_range_for_substring (cpp_reader *pfile,
+						   string_concat_db *concats,
+						   location_t strloc,
+						   enum cpp_ttype type,
+						   int start_idx, int end_idx,
+						   source_range *out_range);
+
+#endif /* ! GCC_SUBSTRING_LOCATIONS_H */
diff --git a/gcc/testsuite/ChangeLog b/gcc/testsuite/ChangeLog
index 25af783..997efac 100644
--- a/gcc/testsuite/ChangeLog
+++ b/gcc/testsuite/ChangeLog
@@ -1,3 +1,10 @@
+2016-08-05  David Malcolm  <dmalcolm@redhat.com>
+
+	* gcc.dg/plugin/diagnostic-test-string-literals-1.c: New file.
+	* gcc.dg/plugin/diagnostic-test-string-literals-2.c: New file.
+	* gcc.dg/plugin/diagnostic_plugin_test_string_literals.c: New file.
+	* gcc.dg/plugin/plugin.exp (plugin_test_list): Add the above new files.
+
 2016-08-05  Patrick Palka  <ppalka@gcc.gnu.org>
 
 	PR tree-optimization/72810
diff --git a/gcc/testsuite/gcc.dg/plugin/diagnostic-test-string-literals-1.c b/gcc/testsuite/gcc.dg/plugin/diagnostic-test-string-literals-1.c
new file mode 100644
index 0000000..82689b4
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/plugin/diagnostic-test-string-literals-1.c
@@ -0,0 +1,211 @@
+/* { dg-do compile } */
+/* { dg-options "-O -fdiagnostics-show-caret" } */
+
+/* This is a collection of unittests for ranges within string literals,
+   using diagnostic_plugin_test_string_literals, which handles
+   "__emit_string_literal_range" by generating a warning at the given
+   subset of a string literal.
+
+   The indices are 0-based.  It's easiest to verify things using string
+   literals that are runs of 0-based digits (to avoid having to count
+   characters).
+
+   LITERAL is a const void * to allow testing the various kinds of wide
+   string literal, rather than just const char *.  */
+
+extern void __emit_string_literal_range (const void *literal,
+					 int start_idx, int end_idx);
+
+void
+test_simple_string_literal (void)
+{
+  __emit_string_literal_range ("0123456789", /* { dg-warning "range" } */
+			       6, 7);
+/* { dg-begin-multiline-output "" }
+   __emit_string_literal_range ("0123456789",
+                                       ^~
+   { dg-end-multiline-output "" } */
+}
+
+void
+test_concatenated_string_literal (void)
+{
+  __emit_string_literal_range ("01234" "56789", /* { dg-warning "range" } */
+			       3, 6);
+/* { dg-begin-multiline-output "" }
+   __emit_string_literal_range ("01234" "56789",
+                                    ^~~~~~~
+   { dg-end-multiline-output "" } */
+}
+
+void
+test_multiline_string_literal (void)
+{
+  __emit_string_literal_range ("01234" /* { dg-warning "range" } */
+                               "56789",
+                               3, 6);
+/* { dg-begin-multiline-output "" }
+   __emit_string_literal_range ("01234"
+                                    ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+                                "56789",
+                                ~~~  
+   { dg-end-multiline-output "" } */
+  /* FIXME: why does the above need two trailing spaces?  */
+}
+
+/* Tests of various unicode encodings.
+
+   Digits 0 through 9 are unicode code points:
+      U+0030 DIGIT ZERO
+      ...
+      U+0039 DIGIT NINE
+   However, these are not always valid as UCN (see the comment in
+   libcpp/charset.c:_cpp_valid_ucn).
+
+   Hence we need to test UCN using an alternative unicode
+   representation of numbers; let's use Roman numerals,
+   (though these start at one, not zero):
+      U+2170 SMALL ROMAN NUMERAL ONE
+      ...
+      U+2174 SMALL ROMAN NUMERAL FIVE  ("v")
+      U+2175 SMALL ROMAN NUMERAL SIX   ("vi")
+      ...
+      U+2178 SMALL ROMAN NUMERAL NINE.  */
+
+void
+test_hex (void)
+{
+  /* Digits 0-9, expressing digit 5 in ASCII as "\x35"
+     and with a space in place of digit 6, to terminate the escaped
+     hex code.  */
+  __emit_string_literal_range ("01234\x35 789", /* { dg-warning "range" } */
+			       3, 7);
+/* { dg-begin-multiline-output "" }
+   __emit_string_literal_range ("01234\x35 789"
+                                    ^~~~~~~~
+   { dg-end-multiline-output "" } */
+}
+
+void
+test_oct (void)
+{
+  /* Digits 0-9, expressing digit 5 in ASCII as "\065"
+     and with a space in place of digit 6, to terminate the escaped
+     octal code.  */
+  __emit_string_literal_range ("01234\065 789", /* { dg-warning "range" } */
+			       3, 7);
+/* { dg-begin-multiline-output "" }
+   __emit_string_literal_range ("01234\065 789"
+                                    ^~~~~~~~
+   { dg-end-multiline-output "" } */
+}
+
+void
+test_multiple (void)
+{
+  /* Digits 0-9, expressing digit 5 in ASCII as hex "\x35"
+     digit 6 in ASCII as octal "\066", concatenating multiple strings.  */
+  __emit_string_literal_range ("01234"  "\x35"  "\066"  "789", /* { dg-warning "range" } */
+			       3, 8);
+/* { dg-begin-multiline-output "" }
+   __emit_string_literal_range ("01234"  "\x35"  "\066"  "789",
+                                    ^~~~~~~~~~~~~~~~~~~~~~~~
+   { dg-end-multiline-output "" } */
+}
+
+void
+test_ucn4 (void)
+{
+  /* Digits 0-9, expressing digits 5 and 6 as Roman numerals expressed
+     as UCN 4.
+     The resulting string is encoded as UTF-8.  Most of the digits are 1 byte
+     each, but digits 5 and 6 are encoded with 3 bytes each.
+     Hence to underline digits 4-7 we need to underling using bytes 4-11 in
+     the UTF-8 encoding.  */
+  __emit_string_literal_range ("01234\u2174\u2175789", /* { dg-warning "range" } */
+			       4, 11);
+/* { dg-begin-multiline-output "" }
+   __emit_string_literal_range ("01234\u2174\u2175789",
+                                     ^~~~~~~~~~~~~~
+   { dg-end-multiline-output "" } */
+}
+
+void
+test_ucn8 (void)
+{
+  /* Digits 0-9, expressing digits 5 and 6 as Roman numerals as UCN 8.
+     The resulting string is the same as as in test_ucn4 above, and hence
+     has the same UTF-8 encoding, and so we again need to underline bytes
+     4-11 in the UTF-8 encoding in order to underline digits 4-7.  */
+  __emit_string_literal_range ("01234\U00002174\U00002175789", /* { dg-warning "range" } */
+			       4, 11);
+/* { dg-begin-multiline-output "" }
+   __emit_string_literal_range ("01234\U00002174\U00002175789",
+                                     ^~~~~~~~~~~~~~~~~~~~~~
+   { dg-end-multiline-output "" } */
+}
+
+void
+test_u8 (void)
+{
+  /* Digits 0-9.  */
+  __emit_string_literal_range (u8"0123456789", /* { dg-warning "range" } */
+			       4, 7);
+/* { dg-begin-multiline-output "" }
+   __emit_string_literal_range (u8"0123456789",
+                                       ^~~~
+   { dg-end-multiline-output "" } */
+}
+
+void
+test_u (void)
+{
+  /* Digits 0-9.  */
+  __emit_string_literal_range (u"0123456789", /* { dg-error "unable to read substring range: execution character set != source character set" } */
+			       4, 7);
+/* { dg-begin-multiline-output "" }
+   __emit_string_literal_range (u"0123456789",
+                                ^~~~~~~~~~~~~
+   { dg-end-multiline-output "" } */
+}
+
+void
+test_U (void)
+{
+  /* Digits 0-9.  */
+  __emit_string_literal_range (U"0123456789", /* { dg-error "unable to read substring range: execution character set != source character set" } */
+			       4, 7);
+/* { dg-begin-multiline-output "" }
+   __emit_string_literal_range (U"0123456789",
+                                ^~~~~~~~~~~~~
+   { dg-end-multiline-output "" } */
+}
+
+void
+test_L (void)
+{
+  /* Digits 0-9.  */
+  __emit_string_literal_range (L"0123456789", /* { dg-error "unable to read substring range: execution character set != source character set" } */
+			       4, 7);
+/* { dg-begin-multiline-output "" }
+   __emit_string_literal_range (L"0123456789",
+                                ^~~~~~~~~~~~~
+   { dg-end-multiline-output "" } */
+}
+
+void
+test_macro (void)
+{
+#define START "01234"  /* { dg-warning "range" } */
+  __emit_string_literal_range (START
+                               "56789",
+                               3, 6);
+/* { dg-begin-multiline-output "" }
+ #define START "01234"
+                   ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+   __emit_string_literal_range (START
+   ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+                                "56789",
+                                ~~~
+   { dg-end-multiline-output "" } */
+}
diff --git a/gcc/testsuite/gcc.dg/plugin/diagnostic-test-string-literals-2.c b/gcc/testsuite/gcc.dg/plugin/diagnostic-test-string-literals-2.c
new file mode 100644
index 0000000..7851c02
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/plugin/diagnostic-test-string-literals-2.c
@@ -0,0 +1,53 @@
+/* { dg-do compile } */
+
+/* See the notes in diagnostic-test-string-literals-1.c.
+   This test case has caret-printing disabled.  */
+
+extern void __emit_string_literal_range (const void *literal,
+					 int start_idx, int end_idx);
+/* Test of a stringified macro argument, by itself.  */
+
+void
+test_stringified_token_1 (int x)
+{
+#define STRINGIFY(EXPR) #EXPR
+
+  __emit_string_literal_range (STRINGIFY(x > 0), /* { dg-error "unable to read substring range: macro expansion" } */
+                               0, 4);
+
+#undef STRINGIFY
+}
+
+/* Test of a stringified token within a concatenation.  */
+
+void
+test_stringized_token_2 (int x)
+{
+#define EXAMPLE(EXPR, START_IDX, END_IDX)			\
+  do {								\
+    __emit_string_literal_range ("  before " #EXPR " after \n",	\
+				 START_IDX, END_IDX);		\
+  } while (0)
+
+  EXAMPLE(x > 0, 1, 6);
+  /* { dg-error "unable to read substring range: cpp_interpret_string_1 failed" "" { target *-*-* } 28 } */
+
+#undef EXAMPLE
+}
+
+/* Test of a doubly-stringified macro argument (by itself).  */
+
+void
+test_stringified_token_3 (int x)
+{
+#define XSTR(s) STR(s)
+#define STR(s) #s
+#define FOO 123456789
+  __emit_string_literal_range (XSTR (FOO), /* { dg-error "unable to read substring range: macro expansion" } */
+                               2, 3);
+
+#undef XSTR
+#undef STR
+#undef FOO
+}
+
diff --git a/gcc/testsuite/gcc.dg/plugin/diagnostic_plugin_test_string_literals.c b/gcc/testsuite/gcc.dg/plugin/diagnostic_plugin_test_string_literals.c
new file mode 100644
index 0000000..d44612a
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/plugin/diagnostic_plugin_test_string_literals.c
@@ -0,0 +1,212 @@
+/* This plugin uses the diagnostics code to verify tracking of source code
+   locations within string literals.  */
+/* { dg-options "-O" } */
+
+#include "gcc-plugin.h"
+#include "config.h"
+#include "system.h"
+#include "coretypes.h"
+#include "tm.h"
+#include "tree.h"
+#include "stringpool.h"
+#include "toplev.h"
+#include "basic-block.h"
+#include "hash-table.h"
+#include "vec.h"
+#include "ggc.h"
+#include "basic-block.h"
+#include "tree-ssa-alias.h"
+#include "internal-fn.h"
+#include "gimple-fold.h"
+#include "tree-eh.h"
+#include "gimple-expr.h"
+#include "is-a.h"
+#include "gimple.h"
+#include "gimple-iterator.h"
+#include "tree.h"
+#include "tree-pass.h"
+#include "intl.h"
+#include "plugin-version.h"
+#include "c-family/c-common.h"
+#include "diagnostic.h"
+#include "context.h"
+#include "print-tree.h"
+#include "cpplib.h"
+#include "c-family/c-pragma.h"
+
+int plugin_is_GPL_compatible;
+
+/* A custom pass for printing string literal location information.  */
+
+const pass_data pass_data_test_string_literals =
+{
+  GIMPLE_PASS, /* type */
+  "test_string_literals", /* name */
+  OPTGROUP_NONE, /* optinfo_flags */
+  TV_NONE, /* tv_id */
+  PROP_ssa, /* properties_required */
+  0, /* properties_provided */
+  0, /* properties_destroyed */
+  0, /* todo_flags_start */
+  0, /* todo_flags_finish */
+};
+
+class pass_test_string_literals : public gimple_opt_pass
+{
+public:
+  pass_test_string_literals(gcc::context *ctxt)
+    : gimple_opt_pass(pass_data_test_string_literals, ctxt)
+  {}
+
+  /* opt_pass methods: */
+  bool gate (function *) { return true; }
+  virtual unsigned int execute (function *);
+
+}; // class pass_test_string_literals
+
+/* Determine if STMT is a call with NUM_ARGS arguments to a function
+   named FUNCNAME.
+   If so, return STMT as a gcall *.  Otherwise return NULL.  */
+
+static gcall *
+check_for_named_call (gimple *stmt,
+		      const char *funcname, unsigned int num_args)
+{
+  gcc_assert (funcname);
+
+  gcall *call = dyn_cast <gcall *> (stmt);
+  if (!call)
+    return NULL;
+
+  tree fndecl = gimple_call_fndecl (call);
+  if (!fndecl)
+    return NULL;
+
+  if (strcmp (IDENTIFIER_POINTER (DECL_NAME (fndecl)), funcname))
+    return NULL;
+
+  if (gimple_call_num_args (call) != num_args)
+    {
+      error_at (stmt->location, "expected number of args: %i (got %i)",
+		num_args, gimple_call_num_args (call));
+      return NULL;
+    }
+
+  return call;
+}
+
+/* Emit a warning covering SRC_RANGE, with the caret at the start of
+   SRC_RANGE.  */
+
+static void
+emit_warning (source_range src_range)
+{
+  location_t loc
+    = make_location (src_range.m_start, src_range.m_start, src_range.m_finish);
+  warning_at (loc, 0, "range %i:%i-%i:%i",
+	      LOCATION_LINE (src_range.m_start),
+	      LOCATION_COLUMN (src_range.m_start),
+	      LOCATION_LINE (src_range.m_finish),
+	      LOCATION_COLUMN (src_range.m_finish));
+}
+
+/* Support code for verifying that we are correctly tracking ranges
+   within string literals, for use by diagnostic-test-string-literals-*.c.
+   Emit a warning showing the range of a string literal, for each call to
+   a function named "__emit_string_literal_range".
+   The initial argument should be a string literal; arguments 2 and 3
+   should be integer constants, giving the range within the string
+   to be printed.  */
+
+static void
+test_string_literals (gimple *stmt)
+{
+  gcall *call = check_for_named_call (stmt, "__emit_string_literal_range", 3);
+  if (!call)
+    return;
+
+  /* We expect an ADDR_EXPR with a STRING_CST inside it for the
+     initial arg.  */
+  tree t_addr_string = gimple_call_arg (call, 0);
+  if (TREE_CODE (t_addr_string) != ADDR_EXPR)
+    {
+      error_at (call->location, "string literal required for arg 1");
+      return;
+    }
+
+  tree t_string = TREE_OPERAND (t_addr_string, 0);
+  if (TREE_CODE (t_string) != STRING_CST)
+    {
+      error_at (call->location, "string literal required for arg 1");
+      return;
+    }
+
+  tree t_start_idx = gimple_call_arg (call, 1);
+  if (TREE_CODE (t_start_idx) != INTEGER_CST)
+    {
+      error_at (call->location, "integer constant required for arg 2");
+      return;
+    }
+  int start_idx = TREE_INT_CST_LOW (t_start_idx);
+
+  tree t_end_idx = gimple_call_arg (call, 2);
+  if (TREE_CODE (t_end_idx) != INTEGER_CST)
+    {
+      error_at (call->location, "integer constant required for arg 3");
+      return;
+    }
+  int end_idx = TREE_INT_CST_LOW (t_end_idx);
+
+  /* A STRING_CST doesn't have a location, but the ADDR_EXPR does.  */
+  location_t strloc = EXPR_LOCATION (t_addr_string);
+  source_range src_range;
+  substring_loc substr_loc (strloc, TREE_TYPE (t_string),
+			    start_idx, end_idx);
+  const char *err = substr_loc.get_range (&src_range);
+  if (err)
+    error_at (strloc, "unable to read substring range: %s", err);
+  else
+    emit_warning (src_range);
+}
+
+/* Call test_string_literals on every statement within FUN.  */
+
+unsigned int
+pass_test_string_literals::execute (function *fun)
+{
+  gimple_stmt_iterator gsi;
+  basic_block bb;
+
+  FOR_EACH_BB_FN (bb, fun)
+    for (gsi = gsi_start_bb (bb); !gsi_end_p (gsi); gsi_next (&gsi))
+      {
+	gimple *stmt = gsi_stmt (gsi);
+	test_string_literals (stmt);
+      }
+
+  return 0;
+}
+
+/* Entrypoint for the plugin.  Create and register the custom pass.  */
+
+int
+plugin_init (struct plugin_name_args *plugin_info,
+	     struct plugin_gcc_version *version)
+{
+  struct register_pass_info pass_info;
+  const char *plugin_name = plugin_info->base_name;
+  int argc = plugin_info->argc;
+  struct plugin_argument *argv = plugin_info->argv;
+
+  if (!plugin_default_version_check (version, &gcc_version))
+    return 1;
+
+  pass_info.pass = new pass_test_string_literals (g);
+  pass_info.reference_pass_name = "ssa";
+  pass_info.ref_pass_instance_number = 1;
+  pass_info.pos_op = PASS_POS_INSERT_AFTER;
+  register_callback (plugin_name, PLUGIN_PASS_MANAGER_SETUP, NULL,
+		     &pass_info);
+
+  return 0;
+}
diff --git a/gcc/testsuite/gcc.dg/plugin/plugin.exp b/gcc/testsuite/gcc.dg/plugin/plugin.exp
index faebb75..715038a 100644
--- a/gcc/testsuite/gcc.dg/plugin/plugin.exp
+++ b/gcc/testsuite/gcc.dg/plugin/plugin.exp
@@ -70,6 +70,9 @@ set plugin_test_list [list \
 	  diagnostic-test-expressions-1.c } \
     { diagnostic_plugin_show_trees.c \
 	  diagnostic-test-show-trees-1.c } \
+    { diagnostic_plugin_test_string_literals.c \
+	  diagnostic-test-string-literals-1.c \
+	  diagnostic-test-string-literals-2.c } \
     { location_overflow_plugin.c \
 	  location-overflow-test-1.c \
 	  location-overflow-test-2.c } \