| commit | 79d246112dc95bbd67848f7546f3fd1aca516b82 | [log] [tgz] |
|---|---|---|
| author | bors <bors@rust-lang.org> | Fri Mar 08 02:01:51 2024 +0000 |
| committer | bors <bors@rust-lang.org> | Fri Mar 08 02:01:51 2024 +0000 |
| tree | 680d94c32d7ab3997e17fb2f692da58ba1204e97 | |
| parent | 9823f173150baf893b2491513466ac024ae63e40 [diff] | |
| parent | e349900339fc5ff512828aee9fddf87995e5e347 [diff] |
Auto merge of #122048 - erikdesjardins:inbounds, r=oli-obk Use GEP inbounds for ZST and DST field offsets ZST field offsets have been non-`inbounds` since I made [this old layout change](https://github.com/rust-lang/rust/pull/73453/files#diff-160634de1c336f2cf325ff95b312777326f1ab29fec9b9b21d5ee9aae215ecf5). Before that, they would have been `inbounds` due to using `struct_gep`. Using `inbounds` for ZSTs likely doesn't matter for performance, but I'd like to remove the special case. DST field offsets have been non-`inbounds` since the alignment-aware DST field offset computation was first [implemented](https://github.com/erikdesjardins/rust/commit/a2557d472e570559caf18d9b042cd941f5002398#diff-04fd352da30ca186fe0bb71cc81a503d1eb8a02ca17a3769e1b95981cd20964aR1188) in 1.6 (back then `GEPi()` would be used for `inbounds`), but I don't think there was any reason for it. Split out from #121577 / #121665. r? `@oli-obk` cc `@RalfJung` -- is there some weird situation where field offsets can't be `inbounds`? Note that it's fine for `inbounds` offsets to be one-past-the-end, so it's okay even if there's a ZST as the last field in the layout: > The base pointer has an in bounds address of an allocated object, which means that it points into an allocated object, or to its end. [(link)](https://llvm.org/docs/LangRef.html#getelementptr-instruction) For https://github.com/rust-lang/unsafe-code-guidelines/issues/93, zero-offset GEP is (now) always `inbounds`: > Note that getelementptr with all-zero indices is always considered to be inbounds, even if the base pointer does not point to an allocated object. [(link)](https://llvm.org/docs/LangRef.html#getelementptr-instruction)
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