Optimize offset_from_unsigned result bounds

[SomeFlyingThing]

Hint that result cannot be larger than isize max

[rustbot]

r? @jieyouxu

rustbot has assigned @jieyouxu.
They will have a look at your PR within the next two weeks and either review your PR or reassign to another reviewer.

Use r? to explicitly pick a reviewer

Why was this reviewer chosen?

The reviewer was selected based on:

• Owners of files modified in this PR: compiler
• compiler expanded to 75 candidates
• Random selection from 18 candidates

[jieyouxu]

r? libs

[clarfonthey]

Seems reasonable. For lack of any niche-type APIs that represent this, it should be okay to add this assumption.

@bors r+

[rust-bors]

📌 Commit 7dbde06 has been approved by clarfonthey

It is now in the queue for this repository.

[JonathanBrouwer]

💔 I suspect this PR failed tests as part of a rollup
@bors r-

After fixing the problem, consider running a try job for the failed job before re-approving.

Link to failure: #161089 (comment)

@bors try jobs=test-various

[rust-bors]

This pull request was unapproved.

This PR was contained in a rollup (#161092), which was unapproved.

View changes since this unapproval

[rust-bors]

💔 Test for f4b1164 failed: CI. Failed job:

• try - test-various (web logs, enhanced plaintext logs)

[clarfonthey]

Not sure if spurious, will have to take a closer look later.

[clarfonthey]

@rustbot review

[clarfonthey]

Finally getting back to this, confused why it passed CI in the PR but not on the rollup, but this is indeed a real issue. Running locally I also have a failure for the test that failed, tests/codegen-llvm/lib-optimizations/append-elements.rs.

So, @rustbot author

[rustbot]

Reminder, once the PR becomes ready for a review, use @rustbot ready.