Where do arguments come from?
On the GC ABI, the first integer argument arrives in r3. That's the same register the return value goes back in. The overlap has a funny consequence: a few functions give the compiler nothing to emit beyond the return instruction.
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One blr, and that's a whole valid function. Further integer and pointer arguments stack up in r4, r5, r6, and so on through r10. Floats play by different rules, riding in f1–f8 without consuming an integer slot.
When the assembly is only a blr with nothing touching r3, ask yourself: what would the input and output have to be for no work to be needed at all?
Your task
Write identity, taking an int x, to reproduce the assembly above.