Inline assembly

asm block

asm is a low-level syntax for directly inserting instructions of the target architecture.

fun read_value() -> i64 {
    var result: i64 = 0;
    asm {
        "mov rax, 123"
        out("rax") result
    }

    return result;
}

String literals within a block are passed as an assembly instruction list.

input and output

var result: i64 = 0;
asm {
    "mov rax, rdi"
    in("rdi") 123
    out("rax") result
}

• in("reg") expression wires the value Wave to the input operand.
• out("reg") target writes the output value to the assignable Wave target.
• Register names can be written as strings or identifiers.

Input operands can include variables, integer/string literals, &identifier, deref identifier, and negative numbers.

clobber

If a block changes a register or memory state other than an explicit output, it is recorded in clobber(...).

asm {
    "nop"
    clobber("rax", "rcx", "memory")
}

Check when using

• The instruction syntax must match the target architecture and the LLVM inline assembly contract.
• Do not arbitrarily destroy registers that must be preserved according to the calling convention.
• For blocks that read or write memory, declare clobber, including memory.
• If possible, isolate architecture-specific asm behind a small function.

The behavior and portability of inline assembly are not guaranteed by language type alone.

Learning and Example Range

Practice with the full program · Standard library