Design meeting: Float semantics (RFC 3514)

[traviscross]

Summary

We'll meet to discuss float semantics.

Background reading

• add float semantics RFC rfcs#3514

About this issue

This issue corresponds to a lang-team design meeting proposal. It corresponds to a possible topic of discussion that may be scheduled for deeper discussion during one of our design meetings.

cc @RalfJung

[pnkfelix]

(the reason I cc'ed this issue from rust-lang/rust#124364 is that I wanted to ensure that this comment from Ralf does not get overlooked in that meeting: rust-lang/rust#124364 (comment); some relevant quotes below.)

If LLVM assumes float operations are deterministic then indeed it must not do any const-folding that differs from the effective runtime behavior.

Non-deterministic NaNs can cause miscompilations.

[RalfJung]

Non-deterministic NaNs can cause miscompilations.

This part got fixed in llvm/llvm-project#90942.