In this problem report, the compiler is fed a (bogus) translation unit
in which some literals contain bytes whose value is zero.  The
preprocessor detects that and proceeds to emit diagnostics for that
king of bogus literals.  But then when the diagnostics machinery
re-reads the input file again to display the bogus literals with a
caret, it attempts to calculate the length of each of the lines it got
using fgets.  The line length calculation is done using strlen.  But
that doesn't work well when the content of the line can have several
zero bytes.  The result is that the read_line never sees the end of
the line because strlen repeatedly reports that the line ends before
the end-of-line character; so read_line thinks its buffer for reading
the line is too small; it thus increases the buffer, leading to a huge
memory consumption and disaster.

Here is what this patch does.

location_get_source_line is modified to return the length of a source
line that can now contain bytes with zero value.
diagnostic_show_locus() is then modified to consider that a line can
have characters of value zero, and so just shows a white space when
instructed to display one of these characters.

Additionally location_get_source_line is modified to avoid re-reading
each and every line from the beginning of the file until it reaches
the line number N that it is instructed to get; this was leading to
annoying quadratic behaviour when reading adjacent lines near the end
of (big) files.  So a cache is now associated to the file opened in
text mode.  When the content of the file is read, that content is
stashed in the file cache.  That file cache is searched for line
delimiters.  A number of line positions are saved in the cache and a
number of file caches are kept in memory.  That way when
location_get_source_line is asked to read line N + 1, it just has to
start reading from line N that it has already read.

libcpp/ChangeLog:

	* include/line-map.h (linemap_get_file_highest_location): Declare
	new function.
	* line-map.c (linemap_get_file_highest_location): Define it.

gcc/ChangeLog:

	* input.h (location_get_source_line): Take an additional line_size
	parameter.
	(void diagnostics_file_cache_fini): Declare new function.
	* input.c (struct fcache): New type.
	(fcache_tab_size, fcache_buffer_size, fcache_line_record_size):
	New static constants.
	(diagnostic_file_cache_init, total_lines_num)
	(lookup_file_in_cache_tab, evicted_cache_tab_entry)
	(add_file_to_cache_tab, lookup_or_add_file_to_cache_tab)
	(needs_read, needs_grow, maybe_grow, read_data, maybe_read_data)
	(get_next_line, read_next_line, goto_next_line, read_line_num):
	New static function definitions.
	(diagnostic_file_cache_fini): New function.
	(location_get_source_line): Take an additional output line_len
	parameter.  Re-write using lookup_or_add_file_to_cache_tab and
	read_line_num.
	* diagnostic.c (diagnostic_finish): Call
	diagnostic_file_cache_fini.
	(adjust_line): Take an additional input parameter for the length
	of the line, rather than calculating it with strlen.
	(diagnostic_show_locus): Adjust the use of
	location_get_source_line and adjust_line with respect to their new
	signature.  While displaying a line now, do not stop at the first
	null byte.  Rather, display the zero byte as a space and keep
	going until we reach the size of the line.
	* Makefile.in: Add vec.o to OBJS-libcommon

gcc/testsuite/ChangeLog:

	* c-c++-common/cpp/warning-zero-in-literals-1.c: New test file.

Signed-off-by: Dodji Seketeli <dodji@seketeli.org>

From-SVN: r206957