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| author | Guillaume Gomez <guillaume1.gomez@gmail.com> | 2020-10-20 21:46:40 +0200 |
|---|---|---|
| committer | GitHub <noreply@github.com> | 2020-10-20 21:46:40 +0200 |
| commit | ad218f9bb92cbeb9bf21c319d7a04eb47cfdb56e (patch) | |
| tree | 4b6316897ba0a9f989ad4207ff2117087dad70be | |
| parent | a8a424f4aad4444a89f1d40d97ef9da824f7d015 (diff) | |
| parent | 2705caed8afbf41e1d0ae5e88a70a92687a1a5da (diff) | |
| download | rust-ad218f9bb92cbeb9bf21c319d7a04eb47cfdb56e.tar.gz rust-ad218f9bb92cbeb9bf21c319d7a04eb47cfdb56e.zip | |
Rollup merge of #78144 - bugadani:elements-nodrop, r=oli-obk
Don't update `entries` in `TypedArena` if T does not need drop As far as I can tell, `entries` is only used when dropping `TypedArenaChunk`s and their contents. It is already ignored there, if T is not `mem::needs_drop`, this PR just skips updating it's value. You can see `TypedArenaChunk` ignoring the entry count in L71. The reasoning is similar to what you can find in `DroplessArena`. r? @oli-obk
| -rw-r--r-- | compiler/rustc_arena/src/lib.rs | 8 |
1 files changed, 6 insertions, 2 deletions
diff --git a/compiler/rustc_arena/src/lib.rs b/compiler/rustc_arena/src/lib.rs index 34736b820e9..1a85a46ed74 100644 --- a/compiler/rustc_arena/src/lib.rs +++ b/compiler/rustc_arena/src/lib.rs @@ -217,8 +217,12 @@ impl<T> TypedArena<T> { let mut chunks = self.chunks.borrow_mut(); let mut new_cap; if let Some(last_chunk) = chunks.last_mut() { - let used_bytes = self.ptr.get() as usize - last_chunk.start() as usize; - last_chunk.entries = used_bytes / mem::size_of::<T>(); + // If a type is `!needs_drop`, we don't need to keep track of how many elements + // the chunk stores - the field will be ignored anyway. + if mem::needs_drop::<T>() { + let used_bytes = self.ptr.get() as usize - last_chunk.start() as usize; + last_chunk.entries = used_bytes / mem::size_of::<T>(); + } // If the previous chunk's len is less than HUGE_PAGE // bytes, then this chunk will be least double the previous |