In 2023 it's not a 1-2% performance penalty anymore and certainly not for most use cases. Only if the 15th register is critical for performance on an x86_64 CPU.
Certain workloads might suffer more, but most will certainly suffer less than a 1-2% hit.
Using any of the higher 8 registers on an x86_64 requires an opcode prefix and makes your instruction 1 byte longer. There is still a small reward for avoiding r8-r15.
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This is very hyperbolic and inaccurate.
In 2023 it's not a 1-2% performance penalty anymore and certainly not for most use cases. Only if the 15th register is critical for performance on an x86_64 CPU.
Certain workloads might suffer more, but most will certainly suffer less than a 1-2% hit.
Using any of the higher 8 registers on an x86_64 requires an opcode prefix and makes your instruction 1 byte longer. There is still a small reward for avoiding r8-r15.
very allegorical