[PATCH] PR tree-optimization/94026: Simplify (X>>8)&6 != 0 as X&1536 != 0.

This patch implements the missed optimization described in PR 94026,
where a the shift can be eliminated from the sequence of a shift,
followed by a bit-wise AND followed by an equality/inequality test.
Specifically, ((X << C1) & C2) cmp C3 into (X & (C2 >> C1)) cmp (C3 >> C1)
and likewise ((X >> C1) & C2) cmp C3 into (X & (C2 << C1)) cmp (C3 << C1)
where cmp is == or !=, and C1, C2 and C3 are integer constants.
The example in the subject line is taken from the hot function
self_atari from the Go program Leela (in SPEC CPU 2017).

2022-06-27  Roger Sayle  <roger@nextmovesoftware.com>

gcc/ChangeLog
	PR tree-optimization/94026
	* match.pd (((X << C1) & C2) eq/ne C3): New simplification.
	(((X >> C1) & C2) eq/ne C3): Likewise.

gcc/testsuite/ChangeLog
	PR tree-optimization/94026
	* gcc.dg/pr94026.c: New test case.

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