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> the impact of x86 decoding was not that major at a point, I suspect it has increased with time Can you elaborate why decode would become more problematic ove
by ClumsyPilot 5y ago
> the impact of x86 decoding was not that major at a point, I suspect it has increased with time
Can you elaborate why decode would become more problematic over time?
- vlovich123 5y agoif I recall correctly ARM instructions are fixed length. You can start deciding instructions on parallel at the same time (ie right after you fetch). X86 uses variable length instructions. Decoding the next instruction requires the previous one to be decoded (think decompression vs reading fixed records). Hopefully I got that right. Now in theory Intel and AMD do employ tricks to optimize x86 decode. If I recall this correctly, they decide opportunistically several possible paths simultaneously and start speculatively executing the ones that turn out to be valid instructions. Likely this works pretty well (+ the variable length means better utilization of the code cache).