match.pd: Simplify popcount(X&Y)+popcount(X|Y) as popcount(X)+popcount(Y)

match.pd: Simplify popcount(X&Y)+popcount(X|Y) as popcount(X)+popcount(Y)

This patch teaches match.pd to simplify popcount(X&Y)+popcount(X|Y) as
popcount(X)+popcount(Y), and the related simplifications that
popcount(X)+popcount(Y)-popcount(X&Y) is popcount(X|Y).  As surprising
as it might seem, this idiom is common in cheminformatics codes
(for Tanimoto coefficient calculations).

2023-05-11  Roger Sayle  <roger@nextmovesoftware.com>

gcc/ChangeLog
	* match.pd <popcount optimizations>: Simplify popcount(X|Y) +
	popcount(X&Y) as popcount(X)+popcount(Y).  Likewise, simplify
	popcount(X)+popcount(Y)-popcount(X&Y) as popcount(X|Y), and
	vice versa.

gcc/testsuite/ChangeLog
	* gcc.dg/fold-popcount-8.c: New test case.
	* gcc.dg/fold-popcount-9.c: Likewise.
	* gcc.dg/fold-popcount-10.c: Likewise.