Add a codegen test for comparisons of 2-tuples of primitives #108156
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| // CHECK-LABEL: @check_lt_via_cmp | ||
| // CHECK-SAME: (i16 noundef %[[A0:.+]], i16 noundef %[[A1:.+]], i16 noundef %[[B0:.+]], i16 noundef %[[B1:.+]]) | ||
| #[no_mangle] | ||
| pub fn check_lt_via_cmp(a: TwoTuple, b: TwoTuple) -> bool { |
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Ah, interesting check_lt_via_cmp passed on LLVM 15, but not LLVM 14. Will bump the version needed.
EDIT: Done.
The operators are all overridden in full for tuples, so those parts pass easily, but they're worth pinning. Going via `Ord::cmp`, though, doesn't optimize away for anything but `cmp`+`is_le`. So this leaves `FIXME`s in the tests for the others.
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Looks like I might as well just land this via #108157 instead; closing. |
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…dtolnay Use `partial_cmp` to implement tuple `lt`/`le`/`ge`/`gt` In today's implementation, `(A, B)::gt` contains calls to *both* `A::eq` *and* `A::gt`. That's fine for primitives, but for things like `String`s it's kinda weird -- `(String, usize)::gt` has a call to both `bcmp` and `memcmp` (<https://rust.godbolt.org/z/7jbbPMesf>) because when `bcmp` says the `String`s aren't equal, it turns around and calls `memcmp` to find out which one's bigger. This PR changes the implementation to instead implement `(A, …, C, Z)::gt` using `A::partial_cmp`, `…::partial_cmp`, `C::partial_cmp`, and `Z::gt`. (And analogously for `lt`, `le`, and `ge`.) That way expensive comparisons don't need to be repeated. Technically this is an observable change on stable, so I've marked it `needs-fcp` + `T-libs-api` and will r? rust-lang/libs-api I'm hoping that this will be non-controversial, however, since it's very similar to the observable changes that were made to the derives (rust-lang#81384 rust-lang#98655) -- like those, this only changes behaviour if a type overrode behaviour in a way inconsistent with the rules for the various traits involved. (The first commit here is rust-lang#108156, adding the codegen test, which I used to make sure this doesn't regress behaviour for primitives.) Zulip conversation about this change: <https://rust-lang.zulipchat.com/#narrow/stream/219381-t-libs/topic/.60.3E.60.20on.20Tuples/near/328392927>.
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[no compiler nor library changes]
The operators are all overridden in full for tuples, so those parts pass easily, but they're worth pinning.
Going via
Ord::cmp, though, doesn't optimize away for anything butcmp+is_le. So this leavesFIXMEs in the tests for the others, referencing #106107.(I was using this to test whether using Clang's IR pattern for C++20's
<=>optimized any better, so figured I might as well check it in for anyone else looking to investigate similar stuff.)