I'm unsure what the root cause of this is, and have been unable to reproduce it in a minimal project for many months, but every so often trig functions such as sin/cos/sin_cos will produce NaN values on perfectly valid inputs, only when using the Windows GNU toolchains.

In a project I have these lines:

let (sin_phi, cos_phi) = phi.sin_cos();

assert!(!sin_phi.is_nan(), "SIN {} {}", sin_phi, phi);
assert!(!cos_phi.is_nan(), "COS {} {}", cos_phi, phi);

which panics with this message:

thread 'main' panicked at 'SIN NaN -0.044661168'

on nightly-x86_64-pc-windows-gnu (1.40.0-nightly (3a9abe3f0 2019-10-15))

The program is complex but deterministic, and produces no such issues on the Windows MSVC toolchains.

This occurs with no RUSTFLAGS, and with the Cargo.toml config of:

[profile.dev]
debug = true
opt-level = 3
incremental = false
debug-assertions = true
codegen-units = 32

Then it's the same as #53254 and I think there is no point in keeping it open.

This is (mostly?) packed_simd bug and should be fixed there, upstream tracking issue: https://github.com/rust-lang-nursery/packed_simd/issues/72