Fold ctz(-x) and ctz(abs(x)) as ctz(x) in match.pd.

Fold ctz(-x) and ctz(abs(x)) as ctz(x) in match.pd.

The subject line pretty much says it all; the count-trailing-zeros function
of -X and abs(X) produce the same result as count-trailing-zeros of X.
This transformation eliminates a negation which may potentially overflow
with an equivalent expression that doesn't [much like the analogous
abs(-X) simplification in match.pd].

I'd noticed this -X equivalence, which isn't mentioned in Hacker's Delight,
investigating whether ranger's non_zero_bits can help determine whether
an integer variable may be converted to a floating point type exactly
(without raising FE_INEXACT), but it turns out this observation isn't
novel, as (disappointingly) LLVM already performs this same folding.

2024-07-27  Roger Sayle  <roger@nextmovesoftware.com>
	    Andrew Pinski  <quic_apinski@quicinc.com>

gcc/ChangeLog
	* match.pd (ctz (-X) => ctz (X)): New simplification.
	(ctz (abs (X)) => ctz (X)): Likewise.

gcc/testsuite/ChangeLog
	* gcc.dg/fold-ctz-1.c: New test case.
	* gcc.dg/fold-ctz-2.c: Likewise.