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Rollup merge of #108416 - pat-nel87:Issue-107957-black_box_docs, r=jyn514

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black_box doc corrections for clarification - Issue #107957

Made a complete pass through the docs to help resolve https://github.com/rust-lang/rust/issues/107957

No code changes, just documentation

`@rustbot` label +T-libs-api -T-libs
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jyn 2023-04-26 01:55:49 -05:00 • committed by GitHub
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9
library/core/src/hint.rs
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@ -217,17 +217,14 @@ pub fn spin_loop() {
/// Note however, that `black_box` is only (and can only be) provided on a "best-effort" basis. The
/// extent to which it can block optimisations may vary depending upon the platform and code-gen
/// backend used. Programs cannot rely on `black_box` for *correctness*, beyond it behaving as the
/// identity function.
/// identity function. As such, it **must not be relied upon to control critical program behavior.**
/// This _immediately_ precludes any direct use of this function for cryptographic or security
/// purposes.
///
/// [`std::convert::identity`]: crate::convert::identity
///
/// # When is this useful?
///
/// First and foremost: `black_box` does _not_ guarantee any exact behavior and, in some cases, may
/// do nothing at all. As such, it **must not be relied upon to control critical program behavior.**
/// This _immediately_ precludes any direct use of this function for cryptographic or security
/// purposes.
///
/// While not suitable in those mission-critical cases, `black_box`'s functionality can generally be
/// relied upon for benchmarking, and should be used there. It will try to ensure that the
/// compiler doesn't optimize away part of the intended test code based on context. For