re PR tree-optimization/81396 (Optimization of reading Little-Endian 64-bit number with portable code has a regression)

	PR tree-optimization/81396
	* tree-ssa-math-opts.c (struct symbolic_number): Add n_ops field.
	(init_symbolic_number): Initialize it to 1.
	(perform_symbolic_merge): Add n_ops from both operands into the new
	n_ops.
	(find_bswap_or_nop): Don't consider n->n == cmpnop computations
	without base_addr as useless if they need more than one operation.
	(bswap_replace): Handle !bswap case for NULL base_addr.

	* gcc.dg/tree-ssa/pr81396.c: New test.

From-SVN: r250257