target.h (struct gcc_target): Add mode_rep_extended.

	* target.h (struct gcc_target): Add mode_rep_extended.
	* rtlanal.c (num_sign_bit_copies_in_rep): New global.
	(init_num_sign_bit_copies_in_rep): Initialize it using
	mode_rep_extended.
	(truncate_to_mode): Use it.
	(init_rtlanal): Call init_num_sign_bit_copies_in_rep.
	* targhooks.h (default_mode_rep_extended): Declare it.
	* targhooks.c (default_mode_rep_extended): Define it.
	* target-def.h (TARGET_MODE_REP_EXTENDED): New macro.  Default to
	default_mode_rep_extended.
	(TARGET_INITIALIZER): Include it.
	* doc/tm.texi (Misc): Document it.
	* config/mips/mips.c (TARGET_TRUNCATED_TO_MODE): Override it.
	(mips_truncated_to_mode): New function.

From-SVN: r112998

1 files changed, 28 insertions, 0 deletions

diff --git a/gcc/doc/tm.texi b/gcc/doc/tm.texi
index 9ee6a83..639e9e9 100644
--- a/gcc/doc/tm.texi
+++ b/gcc/doc/tm.texi
@@ -9143,6 +9143,34 @@ If this is the case, making @code{TRULY_NOOP_TRUNCATION} return 0 in
 such cases may improve things.
 @end defmac
 
+@deftypefn {Target Hook} int TARGET_MODE_REP_EXTENDED (enum machine_mode @var{mode}, enum machine_mode @var{rep_mode})
+The representation of an intergral mode can be such that the values
+are always extended to a wider integral mode.  Return
+@code{SIGN_EXTEND} if values of @var{mode} are represented in
+sign-extended form to @var{rep_mode}.  Return @code{UNKNOWN}
+otherwise.  (Currently, none of the targets use zero-extended
+representation this way so unlike @code{LOAD_EXTEND_OP},
+@code{TARGET_MODE_REP_EXTENDED} is expected to return either
+@code{SIGN_EXTEND} or @code{UNKNOWN}.  Also no target extends
+@var{mode} to @var{mode_rep} so that @var{mode_rep} is not the next
+widest integral mode and currently we take advantage of this fact.)
+
+Similarly to @code{LOAD_EXTEND_OP} you may return a non-@code{UNKNOWN}
+value even if the extension is not performed on certain hard registers
+as long as for the @code{REGNO_REG_CLASS} of these hard registers
+@code{CANNOT_CHANGE_MODE_CLASS} returns nonzero.
+
+Note that @code{TARGET_MODE_REP_EXTENDED} and @code{LOAD_EXTEND_OP}
+describe two related properties.  If you define
+@code{TARGET_MODE_REP_EXTENDED (mode, word_mode)} you probably also want
+to define @code{LOAD_EXTEND_OP (mode)} to return the same type of
+extension.
+
+In order to enforce the representation of @code{mode},
+@code{TRULY_NOOP_TRUNCATION} should return false when truncating to
+@code{mode}.
+@end deftypefn
+
 @defmac STORE_FLAG_VALUE
 A C expression describing the value returned by a comparison operator
 with an integral mode and stored by a store-flag instruction