Mar 15, 2017 · What xzr gives us, however - in addition to a dummy register as per @InfinitelyManic's answer - is access to a zero-valued operand without having to load and occupy a real register. This has the dual benefit of one less instruction, and …

May 1, 2020 · The ARM Reference manual writes Xn when XZR can be used and Xn|SP when SP can be used. See the introduction to §5 “A64 INSTRUCTION SET.” See the introduction to §5 “A64 INSTRUCTION SET.” Some mnemonics have multiple forms such that both a form with an Xn operand and one with an Xn|SP operand are available.

When XZR is used, the field says something like <Xn> and the text just says “general-purpose register.” You need to know which instruction you are decoding to know whether to decode XZR or SP. And note that there are some times multiple instructions sharing the same mnemonic.

Sep 20, 2018 · The zero register xzr resp. wzr is a cute design trick in the Aarch64 ISA. It's register number is 31, just as the stack pointer sp resp. wsp. Depending on the context, register number 31 refers to one of them. This cute trick allows the Aarch64 ISA to …

Nov 19, 2018 · It is supposed XZR can be used in any register field of ARMv8 ISA, but when I try use in indexed addressing for load/store intruction, I always obtain errors: ex2.s:3: Error: integer 64-bit register

Apr 3, 2023 · The tricky thing here is ARM64's encoding convention that "register 31" is XZR in some instruction and SP in others, chosen according to which they thought would be more useful for that particular instruction. Unfortunately it seems like the usual flag-setting instructions made the choice that doesn't work for us. –

Apr 13, 2017 · For the sake of avoiding spoon-feeding, I wrote a LEGv8 program that finds Fibonacci sequence using recursion

Nov 13, 2018 · XZR is the zero register and its value is always zero. The XZR and the SP share are identified by the same number (31), that is why an ORR instruction cannot be used when the SP is the destination or an operand. Instead the ADD instruction is used. MOVZ and MOVK. These two instructions are sometimes used one after the other.

Dec 9, 2022 · add-immediate with xzr is impossible, since the same syntax compilers use for adding 1 (add reg, reg, #1) doesn't assemble if XZR is the source register. For some instructions, like add-immediate, that register number is the stack pointer, not the zero register, so xzr isn't encodeable. That makes sense; there are instructions that can get a ...

Dec 3, 2019 · XZR is an alias for a register that always returns 0 and can't be changed to anything but 0. It's new in AArch64, but other RISCs like MIPS have always had a zero register. It's new in AArch64, but other RISCs like MIPS have always had a zero register.