simplify-rtx: Simplify trunc of and of shiftrt

simplify-rtx: Simplify trunc of and of shiftrt

If we have

	(truncate:M1 (and:M2 (lshiftrt:M2 (x:M2) C) C2))

we can write it instead as

	(and:M1 (lshiftrt:M1 (truncate:M1 (x:M2)) C) C2)

(if that is valid, of course), which has smaller modes for the
binary ops, and the truncate can often simplify further (if "x"
is a register, for example).

	* gcc/simplify-rtx.c (simplify_truncation): Simplify TRUNCATE
	of AND of [LA]SHIFTRT.

From-SVN: r230164