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RE: [PATCH] [Aarch64] Optimize subtract in shift counts


> On Aarc64 SHIFT_COUNT_TRUNCATED is only true if SIMD code generation
> is disabled. This is because the simd instructions can be used for
> shifting but they do not truncate the shift count.

In that case, the change isn't safe!  Consider if the value was
negative, for example.  Yes, it's technically undefined, but I'm not
sure I'd want to rely on that.


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