MIPS16: Implement `code_readable` function attribute.

Support for __attribute__ ((code_readable)).  Takes up to one argument of
"yes", "no", "pcrel".  This will change the code readability setting for just
that function.  If no argument is supplied, then the setting is 'yes'.

gcc/ChangeLog:

	* config/mips/mips.cc (enum mips_code_readable_setting):New enmu.
	(mips_handle_code_readable_attr):New static function.
	(mips_get_code_readable_attr):New static enum function.
	(mips_set_current_function):Set the code_readable mode.
	(mips_option_override):Same as above.
	* doc/extend.texi:Document code_readable.

gcc/testsuite/ChangeLog:

	* gcc.target/mips/code-readable-attr-1.c: New test.
	* gcc.target/mips/code-readable-attr-2.c: New test.
	* gcc.target/mips/code-readable-attr-3.c: New test.
	* gcc.target/mips/code-readable-attr-4.c: New test.
	* gcc.target/mips/code-readable-attr-5.c: New test.

1 files changed, 17 insertions, 0 deletions

diff --git a/gcc/doc/extend.texi b/gcc/doc/extend.texi
index cdbd4b3..e01e244 100644
--- a/gcc/doc/extend.texi
+++ b/gcc/doc/extend.texi
@@ -5670,6 +5670,23 @@ command line (@pxref{MIPS Options}).
 This function attribute instructs the compiler to generate a hazard barrier
 return that clears all execution and instruction hazards while returning,
 instead of generating a normal return instruction.
+
+@item code_readable
+@cindex @code{code_readable} function attribute, MIPS
+For MIPS targets that support PC-relative addressing modes, this attribute
+can be used to control how an object is addressed.  The attribute takes
+a single optional argument:
+
+@table @samp
+@item no
+The function should not read the instruction stream as data.
+@item yes
+The function can read the instruction stream as data.
+@item pcrel
+The function can read the instruction stream in a pc-relative mode.
+@end table
+
+If there is no argument supplied, the default of @code{"yes"} applies.
 @end table
 
 @node MSP430 Function Attributes