match.pd: Optimize ctz/popcount/parity/ffs on extended argument [PR112566]

ctz(ext(X)) is the same as ctz(X) in the UB on zero case (or could be also
in the 2 argument case on large BITINT_TYPE by preserving the argument, not
implemented in this patch),
popcount(zext(X)) is the same as popcount(X),
parity(zext(X)) is the same as parity(X),
parity(sext(X)) is the same as parity(X) provided the bit difference between
the extended and unextended types is even,
ffs(ext(X)) is the same as ffs(X).

The following patch optimizes those in match.pd if those are beneficial
(always in the large BITINT_TYPE case, or if the narrower type has optab
and the wider doesn't, or the wider is larger than word and narrower is
one of the standard argument sizes (tested just int and long long, as
long is on most targets same bitsize as one of those two).

Joseph in the PR mentioned that ctz(narrow(X)) is the same as ctz(X)
if UB on 0, but that can be handled incrementally (and would need different
decisions when it is profitable).
And clz(zext(X)) is clz(X) + bit_difference, but not sure we want to change
that in match.pd at all, perhaps during insn selection?

2023-11-17  Jakub Jelinek  <jakub@redhat.com>

	PR tree-optimization/112566
	PR tree-optimization/83171
	* match.pd (ctz(ext(X)) -> ctz(X), popcount(zext(X)) -> popcount(X),
	parity(ext(X)) -> parity(X), ffs(ext(X)) -> ffs(X)): New
	simplifications.
	( __builtin_ffs (X) == 0 -> X == 0): Use FFS rather than
	BUILT_IN_FFS BUILT_IN_FFSL BUILT_IN_FFSLL BUILT_IN_FFSIMAX.

	* gcc.dg/pr112566-1.c: New test.
	* gcc.dg/pr112566-2.c: New test.
	* gcc.target/i386/pr78057.c (foo): Pass another long long argument
	and use it in __builtin_ia32_*zcnt_u64 instead of the int one.