riscv64: Add bitmanip extension flags #5847
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afonso360
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jameysharp
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Feb 21, 2023
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I'm taking your word for it regarding which instructions are associated with which extensions. Given that, this looks correct to me!
I especially appreciate that you added descriptions to the has_* flags with a little more detail about what names like bkb actually mean.
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This PR clarifies our bit manipulation set of ISA flags.
It seems that our current "B" extension is the full set of instructions defined in the Bit-Manipulation spec (pdf). However we should be querying each extension individually since some processors may not implement all of them.
Additionally it may cause confusion with the currently reserved B extension defined in Chapter 19 of the ISA (pdf). These are unrelated and there is no connection between "B" and the various extensions defined in the Bit-Manipulation spec.
As an example, the SiFive U74 implements only a subset of these (Zbb, Zba) so it wouldn't qualify for most of these optimizations previously, despite most of them only needing Zbb.