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by snvzz
868 days ago
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>In the other hand, I am not fond of the ABI register names Why? They're simple substitution, and very helpful with following ABI. >and the pseudo-instructions involving mini-compilation. Again, why? These aren't specific to the assembler used, but rather, defined in the specification itself. This means they are reliable, and will always be there for as long as you use a RISC-V compliant assembler. They are thus also the register names you will see in disassembler output, debuggers and other tools. Also, you might be interested in this new RVA22+V board[0]. 0. https://forum.banana-pi.org/t/leading-the-future-of-computin... |
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For example `li` gets expanded by the assembler into `liu` and `addi` which on larger RISC-V cores get recognised and fused back into a single op. Using `xori` instead of `addi` would have had the same result but wouldn't get fused.
Next, some idioms get recognised and automatically assembled into "compressed" 16-bit instructions to save space. For example "mv rd,rs" and "addi rd, rs, 0" both get assembled into "c.mv rd,rs". And on a larger RISC-V core, "c.mv" could be only a register rename in the decoder, thus taking 0 cycles.