re PR rtl-optimization/27616 (Infinite loop at -O1 and above in RTL CSE)

re PR rtl-optimization/27616 (Infinite loop at -O1 and above in RTL CSE)

	PR rtl-optimization/27616
	* cse.c (table_size): New static variable.
	(new_basic_block): Initialize it to 0.
	(remove_from_table): Decrement it.
	(insert): Increment it.
	(fold_rtx_mem_1): New function, renamed from fold_rtx_mem.
	(fold_rtx_mem): Enforce a cap on the recursion depth.  Call
	fold_rtx_mem_1 if under the cap.
	(fold_rtx) <RTX_COMM_ARITH>: In the associative case, delay a little
	the lookup of the equivalent expression and test for equality of the
	first operand of the equivalent expression before in turn looking up
	an equivalent constant for the second operand.

From-SVN: r116683