[SR-11857] Swift fails to optimise repeated force unwraps of the same variable. #54266
Description
| Previous ID | SR-11857 |
| Radar | rdar://problem/57494816 |
| Original Reporter | @Lukasa |
| Type | Bug |
Environment
Linux Swift 5.1
Additional Detail from JIRA
| Votes | 0 |
| Component/s | Compiler |
| Labels | Bug, Performance |
| Assignee | None |
| Priority | Medium |
md5: 263a33d97196a85107a6e2fdad176491
Issue Description:
When holding on to an optional local variable, Swift is unable to infer that if one force unwrap of that variable succeeds, all others must succeed as well. There are some potentially invalidating operations that would prevent this optimisation (e.g. calling a mutating function on the Optional), but in simple cases this should be entirely safe to optimise.
Here is a compiler explorer link with an example of the bug in the decodeLoop function.