combine: Improve change_zero_ext (fixes PR71847)

combine: Improve change_zero_ext (fixes PR71847)

This improves a few things in change_zero_ext.  Firstly, it should use
the passed in pattern in recog_for_combine, not the pattern of the insn
(they are not the same if the whole pattern was replaced).  Secondly,
it handled zero_ext of a subreg, but with hard registers we do not get
a subreg, instead the mode of the reg is changed.  So this handles that.
Thirdly, after changing a zero_ext to an AND, the resulting RTL may become
non-canonical, like (ior (ashift ..) (and ..)); the AND should be first,
it is commutative.  And lastly, zero_extract as a set_dest wasn't handled
at all, but now it is.

This fixes the testcase in PR71847, and improves code generation in some
other edge cases too.

	PR target/71847
	* combine.c (change_zero_ext): Handle zero_ext of hard registers.
	Swap commutative operands in new RTL if needed.  Handle zero_ext
	in the set_dest.
	(recog_for_combine): Pass *pnewpat to change_zero_ext instead of
	PATTERN (insn).

From-SVN: r241664