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Currently the `asm!` macro supports raw (thin) pointers as operands, and references as input operands. As discussed in Zulip (https://rust-lang.zulipchat.com/#narrow/channel/213817-t-lang/topic/.60NonNull.60s.20as.20register.20operand.20values.20of.20asm.21/with/629100221), it would be acceptable to extend support to fundamental types with the same ABI as raw pointers. This commit adds support for (thin) `NonNull` pointer inputs. The reason for not allowing `NonNull` outputs is that the `asm!` code has no way to explicitly assert that the safety invariant of `NonNull` is preserved.
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re: that Zulip discussion, Amanieu was critical of this idea in its unqualified form and as our de facto expert in inline r? @Amanieu |
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LGTM, but this needs a positive codegen test. The current tests all fail and never reach codegen. |
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Currently the
asm!macro supports raw (thin) pointers as operands, and references as input operands. As discussed in Zulip, it seems reasonable to extend support to fundamental types with the same ABI as raw pointers. This commit adds support for (thin)NonNullpointer inputs. The reason for not allowingNonNulloutputs is that theasm!code has no way to explicitly assert that the safety invariant ofNonNullis preserved.Support for
Box<T>andOptional<NonNull<T>>seems a bit more debatable, so that's left as future work (which might require more than a FCP).I'll make the existing error messages dependent on whether the operand is allowed specifically as an input in a subsequent PR (because it also affects references). Right now the message is a bit too general.