(try_combine): When removing REG_UNUSED note, update reg_n_deaths.

Likewise, when making new REG_DEAD notes for distribute_notes.
(remove_death, move_deaths): Update reg_n_deaths.
(distribute_notes): When placing second REG_DEAD or REG_UNUSED note or
ignoring such a note, update reg_n_deaths.

(simplify_comparison, case ASHIFT): Fix typo.

(try_combine): The insns made by a DEFINE_SPLIT might contain a PARALLEL and
the call to recog_for_combine might add it.


(combine_instructions): Clear significant_valid at end of combine pass for
a function.
(find_split_point, case MEM): See if first operand of the PLUS that makes
up an address is complex.
(subst): Add missing arg to recursive calls when IF_THEN_ELSE is an arg
of an operator.
(subst, case IF_THEN_ELSE): Generalize code to propagate comparison result
into arms by using known_cond.
If an arm is the first operand of the comparison, make it the true arm.
Remove unneeded comparison when arms are identical.
Try to convert IF_THEN_ELSE to ABS, (neg (abs X)), [US]MIN, [US]MAX.
Convert (if_then_else (ne A 0) (OP X C) X) to (OP X (mult A C)).
(subst, case SET): If we don't have conditional moves, convert IF_THEN_ELSE
into logical operations.
(subst, case AND): Always make conditional moves, even if we don't support
them on the machine.
(known_cond, extended_count): New functions.
(gen_binary): For commutative operations, put constant last.

From-SVN: r2182