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https://github.com/rust-lang/rust
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649e80184b
This makes sure that &[] is just as efficient as indirecting through unsafe code (from_raw_parts). No new stable guarantee is intended about whether or not we do this, this is just an optimization. Co-authored-by: Ralf Jung <post@ralfj.de>
27 lines
1,015 B
Rust
27 lines
1,015 B
Rust
//@ run-pass
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#[repr(align(4))]
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struct Foo;
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static FOO: Foo = Foo;
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fn main() {
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// There's no stable guarantee that these are true.
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// However, we want them to be true so that our LLVM IR and runtime are a bit faster:
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// a constant address is cheap and doesn't result in relocations in comparison to a "real"
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// global somewhere in the data section.
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let x: &'static () = &();
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assert_eq!(x as *const () as usize, 1);
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let x: &'static Foo = &Foo;
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assert_eq!(x as *const Foo as usize, 4);
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// The exact addresses returned by these library functions are not necessarily stable guarantees
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// but for now we assert that we're still matching.
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assert_eq!(<Vec<i32>>::new().as_ptr(), <&[i32]>::default().as_ptr());
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assert_eq!(<Box<[i32]>>::default().as_ptr(), (&[]).as_ptr());
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// statics must have a unique address (see https://github.com/rust-lang/rust/issues/18297, not
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// clear whether this is a stable guarantee)
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assert_ne!(&FOO as *const Foo as usize, 4);
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}
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