PR tree-optimization/71343: Optimize (X<<C)&(Y<<C) as (X&Y)<<C.

This patch is the first part of a solution to PR tree-optimization/71343,
a missed-optimization enhancement request where GCC fails to see that
(a<<2)+(b<<2) == a*4+b*4.

This piece is that (X<<C) op (Y<<C) can be simplified to (X op Y) << C,
for many binary operators, including AND, IOR, XOR, and (if overflow
isn't an issue) PLUS and MINUS.  Likewise, the right shifts (both logical
and arithmetic) and bit-wise logical operators can be simplified in a
similar fashion.  These all reduce the number of GIMPLE binary operations
from 3 to 2, by combining/eliminating a shift operation.

2022-08-15  Roger Sayle  <roger@nextmovesoftware.com>
	    Richard Biener  <rguenther@suse.de>

gcc/ChangeLog
	PR tree-optimization/71343
	* match.pd (op (lshift @0 @1) (lshift @2 @1)): Optimize the
	expression (X<<C) + (Y<<C) to (X+Y)<<C for multiple operators.
	(op (rshift @0 @1) (rshift @2 @1)): Likewise, simplify (X>>C)^(Y>>C)
	to (X^Y)>>C for binary logical operators, AND, IOR and XOR.

gcc/testsuite/ChangeLog
	PR tree-optimization/71343
	* gcc.dg/pr71343-1.c: New test case.

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