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rustc should output a loop in the IR for initializing arrays #5491

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thestinger opened this issue Mar 22, 2013 · 1 comment
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rustc should output a loop in the IR for initializing arrays #5491

thestinger opened this issue Mar 22, 2013 · 1 comment
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I-slow Issue: Problems and improvements with respect to performance of generated code.

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@thestinger
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At the moment [1, ..256] creates 2 * 256 instructions. LLVM will optimize it back to a loop or a memset, but it would better to start with that in the first place and rely on the unrolling heuristics for small loops (which may or not be enabled right now).
@thestinger
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Closing in favour of #4694.

oli-obk pushed a commit to oli-obk/rust that referenced this issue May 2, 2020
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Auto merge of rust-lang#5491 - smklein:borrowed_box, r=flip1995
2efc2d6 
Fix issue rust-lang#2907.

Update the "borrow box" lint to avoid recommending the following
conversion:

```
  // Old
  pub fn f(&mut Box<T>) {...}

  // New
  pub fn f(&mut T) {...}
```

Given a mutable reference to a box, functions may want to change
"which" object the Box is pointing at.

This change avoids recommending removing the "Box" parameter
for mutable references.

changelog: Don't trigger [`borrow_box`] lint on `&mut Box` references
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@thestinger