[Bug target/55181] [5/6/7 Regression] Expensive shift loop where a bit-testing instruction could be used

[gjl at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=55181

--- Comment #17 from Georg-Johann Lay <gjl at gcc dot gnu.org> ---
For now and for avr, hacked around the issue by supplying a pattern for the
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