Remove remaining traces of AT&T assembly syntax #911
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compiler-builtins/src/mem/x86_64.rs
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| core::arch::asm!( | ||
| "repe movsb (%rsi), (%rdi)", | ||
| asm!( | ||
| "repe movsb [rdi], rsi", |
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In the original asm both rsi and rdi are dereferenced, here it’s only rdi. Is this still equivalent for some reason?
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I don't think it is. I fixed this.
| core::arch::asm!( | ||
| "repe movsb (%rsi), (%rdi)", | ||
| asm!( | ||
| "repe movsb [rdi], [rsi]", |
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| "repe movsb [rdi], [rsi]", | |
| "rep movsb [rdi], [rsi]", |
The repe mnemonic is for "repeat while equal" and only makes sense for the string comparison operations
https://www.felixcloutier.com/x86/rep:repe:repz:repne:repnz
(but the encoding is the same so I guess assemblers don't care)
| core::arch::asm!( | ||
| "repe stosb %al, (%rdi)", | ||
| asm!( | ||
| "repe stosb [rdi], al", |
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| "repe stosb [rdi], al", | |
| "rep stosb [rdi], al", |
| // We modify flags, but we restore it afterwards | ||
| options(att_syntax, nostack, preserves_flags) | ||
| options(nostack, preserves_flags) |
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This definitely shouldn't have preserves_flags. Flags are modified by each of add,sub,test. The comment refers to how std/cld are used to set/clear the direction flag, but that's separate since it must be cleared before exiting the inline assembly.
Actually, what is the point of the test instruction here? It only affects flags, and none of the subsequent instructions depend on any flags.
The current minimum LLVM version seems to be 18, way larger than required for resolving this FIXME.