re PR rtl-optimization/33927 (replace_read in dse.c could handle cases where GET_MODE_CLASS (read_mode) != GET_MODE_CLASS (store_mode) (and the size is the same))

gcc/
	PR rtl-optimization/33927
	* Makefile.in (dse.o): Depend on $(TM_P_H).
	* expr.h (extract_low_bits): Declare.
	* expmed.c (extract_low_bits): New function.
	* rtlhooks.c (gen_lowpart_general): Generalize SUBREG handling.
	* dse.c: Include tm_p.h.
	(find_shift_sequence): Remove the read_reg argument and return the
	read value.  Emit the instructions instead of returning them.
	Iterate on new_mode rather than calculating it each time.
	Check MODES_TIEABLE_P.  Use simplify_gen_subreg to convert the
	source to NEW_MODE and extract_low_bits to convert the shifted
	value to READ_MODE.
	(replace_read): Allow the load and store to have different mode
	classes.  Use extract_low_bits when SHIFT == 0.  Create the shift
	or extraction instructions before trying the replacement.  Update
	dump-file code accordingly, avoiding use of REGNO (store_info->rhs).

gcc/testsuite/
	* gcc.target/mips/dse-1.c: Add checks for zeros.

From-SVN: r133452