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Summary

Stabilize the -C overflow-checks command line argument.

Motivation

This is an easy way to turn on overflow checks in release builds without otherwise turning on debug assertions, via the -C debug-assertions flag. In stable Rust today you can't get one without the other.

Users can use the -C overflow-checks flag from their Cargo config to turn on overflow checks for an entire application.

This flag, which accepts values of 'yes'/'no', 'on'/'off', is being renamed from force-overflow-checks because the force doesn't add anything that the 'yes'/'no'

Detailed design

This is a stabilization RFC. The only steps will be to move force-overflow-checks from -Z to -C, renaming it to overflow-checks, and making it stable.

Drawbacks

It's another rather ad-hoc flag for modifying code generation.

Like other such flags, this applies to the entire code unit, regardless of monomorphizations. This means that code generation for a single function can be diferent based on which code unit its instantiated in.

Alternatives

The flag could instead be tied to crates such that any time code from that crate is inlined/monomorphized it turns on overflow checks.

We might also want a design that provides per-function control over overflow checks.

Unresolved questions

Cargo might also add a profile option like

[profile.dev]
overflow-checks = true

This may also be accomplished by Cargo's pending support for passing arbitrary flags to rustc.