cppinit.c (cpp_create_reader, [...]): Warn about trigraphs unless explicity set or -trigraphs.

	* cppinit.c (cpp_create_reader, post_options): Warn about
	trigraphs unless explicity set or -trigraphs.
	* cpplex.c (warn_in_comment): New.
	(_cpp_process_line_notes): Better handling of -Wtrigraphs.
	(_cpp_skip_block_comment): Add call to _cpp_process_line_notes.
	* doc/cppopts.texi, doc/cpp.texi: Update.
testsuite:
	* gcc.dg/cpp/Wtrigraphs.c: Update.
	* gcc.dg/cpp/Wtrigraphs-2.c: New tests.

From-SVN: r66459

2 files changed, 25 insertions, 18 deletions

diff --git a/gcc/doc/cpp.texi b/gcc/doc/cpp.texi
index cf962c4..173e341 100644
--- a/gcc/doc/cpp.texi
+++ b/gcc/doc/cpp.texi
@@ -293,16 +293,18 @@ obsolete systems that lack some of C's punctuation to use C@.  For
 example, @samp{??/} stands for @samp{\}, so @t{'??/n'} is a character
 constant for a newline.
 
-Trigraphs are not popular and many compilers implement them incorrectly.
-Portable code should not rely on trigraphs being either converted or
-ignored.  If you use the @option{-Wall} or @option{-Wtrigraphs} options,
-GCC will warn you when a trigraph would change the meaning of your
-program if it were converted.
-
-In a string constant, you can prevent a sequence of question marks from
-being confused with a trigraph by inserting a backslash between the
-question marks.  @t{"(??\?)"} is the string @samp{(???)}, not
-@samp{(?]}.  Traditional C compilers do not recognize this idiom.
+Trigraphs are not popular and many compilers implement them
+incorrectly.  Portable code should not rely on trigraphs being either
+converted or ignored.  With @option{-Wtrigraphs} GCC will warn you
+when a trigraph may change the meaning of your program if it were
+converted.  @xref{Wtrigraphs}.
+
+In a string constant, you can prevent a sequence of question marks
+from being confused with a trigraph by inserting a backslash between
+the question marks, or by separating the string literal at the
+trigraph and making use of string literal concatenation.  @t{"(??\?)"}
+is the string @samp{(???)}, not @samp{(?]}.  Traditional C compilers
+do not recognize these idioms.
 
 The nine trigraphs and their replacements are
 
diff --git a/gcc/doc/cppopts.texi b/gcc/doc/cppopts.texi
index 9212c80..490905a 100644
--- a/gcc/doc/cppopts.texi
+++ b/gcc/doc/cppopts.texi
@@ -69,10 +69,12 @@ use @option{-o} to specify the output file.
 
 @item -Wall
 @opindex Wall
-Turns on all optional warnings which are desirable for normal code.  At
-present this is @option{-Wcomment} and @option{-Wtrigraphs}.  Note that
-many of the preprocessor's warnings are on by default and have no
-options to control them.
+Turns on all optional warnings which are desirable for normal code.
+At present this is @option{-Wcomment}, @option{-Wtrigraphs},
+@option{-Wmultichar} and a warning about integer promotion causing a
+change of sign in @code{#if} expressions.  Note that many of the
+preprocessor's warnings are on by default and have no options to
+control them.
 
 @item -Wcomment
 @itemx -Wcomments
@@ -84,10 +86,13 @@ comment, or whenever a backslash-newline appears in a @samp{//} comment.
 
 @item -Wtrigraphs
 @opindex Wtrigraphs
-Warn if any trigraphs are encountered.  This option used to take effect
-only if @option{-trigraphs} was also specified, but now works
-independently.  Warnings are not given for trigraphs within comments, as
-they do not affect the meaning of the program.
+@anchor{Wtrigraphs}
+Warn if any trigraphs that may change the meaning of a program are
+encountered.  This option is in effect unless trigraphs are turned on,
+and is implied by @option{-Wall}.  With the exception of a trigraph
+that would form an escaped newline, warnings are not given for
+trigraphs within comments as they do not affect the meaning of the
+program.
 
 @item -Wtraditional
 @opindex Wtraditional