Enum rustc_codegen_llvm::abi::PassMode

pub enum PassMode {
    Ignore,
    Direct(ArgAttributes),
    Pair(ArgAttributes, ArgAttributes),
    Cast {
        pad_i32: bool,
        cast: Box<CastTarget, Global>,
    },
    Indirect {
        attrs: ArgAttributes,
        meta_attrs: Option<ArgAttributes>,
        on_stack: bool,
    },
}

Variants

Ignore

Ignore the argument.

The argument is either uninhabited or a ZST.

Direct(ArgAttributes)

Pass the argument directly.

The argument has a layout abi of Scalar or Vector. Unfortunately due to past mistakes, in rare cases on wasm, it can also be Aggregate. This is bad since it leaks LLVM implementation details into the ABI. (Also see https://github.com/rust-lang/rust/issues/115666.)

Pair(ArgAttributes, ArgAttributes)

Pass a pair’s elements directly in two arguments.

The argument has a layout abi of ScalarPair.

Cast

Fields

pad_i32: bool

cast: Box<CastTarget, Global>

Pass the argument after casting it. See the CastTarget docs for details. The bool indicates if a Reg::i32() dummy argument is emitted before the real argument.

Indirect

Fields

attrs: ArgAttributes

meta_attrs: Option<ArgAttributes>

on_stack: bool

Pass the argument indirectly via a hidden pointer. The meta_attrs value, if any, is for the metadata (vtable or length) of an unsized argument. (This is the only mode that supports unsized arguments.) on_stack defines that the value should be passed at a fixed stack offset in accordance to the ABI rather than passed using a pointer. This corresponds to the byval LLVM argument attribute (using the Rust type of this argument). on_stack cannot be true for unsized arguments, i.e., when meta_attrs is Some.

Layout

Note: Most layout information is completely unstable and may even differ between compilations. The only exception is types with certain repr(...) attributes. Please see the Rust Reference's “Type Layout” chapter for details on type layout guarantees.

Size: 40 bytes

Size for each variant:

• Ignore: 0 bytes
• Direct: 23 bytes
• Pair: 39 bytes
• Cast: 15 bytes
• Indirect: 39 bytes