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Have the ARM AArch64 designers ever commented on this? They intentionally left out any kind of compressed instructions, and certainly Apple at least cares a lot

• deleted 5y ago
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• klelatti 5y ago
  Try this at 34:30 - from Arm’s architecture lead Richard Grisenthwaite. Earlier he says that several leading micro architects think that mixing 16 bit and 32 bit instructions (Thumb2) was the worst thing that Arm ever did. https://m.soundcloud.com/university-of-cambridge/a-history-of-the-arm-architecture-and-the-lessons-learned-while-building-it https://m.soundcloud.com/university-of-cambridge/a-history-o...
  • brucehoult 5y ago
    He explicitly specifies that those micro-architects are at companies OTHER than ARM. His own opinion appears to be that the worst thing ARM ever did was T2EE, designed for JIT compilers and compilers for dynamic languages. He says that by the time the chips came out compiler technology had advanced to the point that it was no longer useful and no one else used it. A couple of other points picked up in the talk: - He reverses Hennessy and Patterson wrt SPARC and MIPS. - A64 effort started in 2007. So it took 5 years to freeze/publishing, the same as RISC-V. - A64 architects thought code density is no longer important. Some people definitely disagree with that. At the time they probably thought amd64 was the only competition and matching/beating that was good enough. - he seems to be regretting the 2nd operand shift because it fell naturally out of the 1985 micro-architecture, but it's a burden now. And yet it was included in A64 -- presumably because the initial processor pipelines had it anyway, because they supported A32. But now we have A64-only CPUs. - LL/SC was the wrong thing to do.