Re:ARM or x86? ISA Doesn’t Matter
by audunw on Monday May 15, 2023 @07:48AM
(#35946686)
> However, fixed length instructions decrease code density, which asks more of the instruction cache.
The problem is that x86 has a lot of legacy that wastes the potential gain of variable length encoding. If I remember correctly, the code density of 64-bit x86 isn't really significantly better than 64-bit ARM, despite ARM dropping support for Thumb.
RISC-V is going to be interesting in that regard because with the latest revisions of the compressed instruction format, it can potentially beat both ARM and x86 on real-world code density, while still being easier to decode.
The problem is that x86 has a lot of legacy that wastes the potential gain of variable length encoding. If I remember correctly, the code density of 64-bit x86 isn't really significantly better than 64-bit ARM, despite ARM dropping support for Thumb.
RISC-V is going to be interesting in that regard because with the latest revisions of the compressed instruction format, it can potentially beat both ARM and x86 on real-world code density, while still being easier to decode.