* 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
