How many registers does an x86-64 CPU have? (2020)

Re:How many registers does an x86-64 CPU have? (2020) by cvoss on Saturday February 14, 2026 @11:33AM (#47015853)

With an increase in available registers, every value that a compiler might newly choose to keep in a register was a value that would previously have lived in the local stack frame anyway.

It's up to the compiler to decide how many registers it needs to preserve at a call. It's also up to the compiler to decide which registers shall be the call-clobbered ones. "None" is a valid choice here, if you wish.

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Re:How many registers does an x86-64 CPU have? (2020) by guenthert on Sunday February 15, 2026 @07:48AM (#47023267)

> It's up to the compiler to decide how many registers it needs to preserve at a call.

But the compiler is bound by the ABI, isn't it? (at least for externally visible entrance points / calls to sub routines external to the current compilation unit)

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Re:How many registers does an x86-64 CPU have? (2020) by cvoss on Sunday February 15, 2026 @01:43PM (#47026209)

Someone decides how to define the ABI too, and that is a free choice. CPU register count doesn't constrain this particular system design question.

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