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mark borrowed pointer parameters without a named lifetime as nocapture #6751

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thestinger opened this issue May 26, 2013 · 4 comments
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mark borrowed pointer parameters without a named lifetime as nocapture #6751

thestinger opened this issue May 26, 2013 · 4 comments
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A-lifetimes Area: Lifetimes / regions A-LLVM Area: Code generation parts specific to LLVM. Both correctness bugs and optimization-related issues. I-slow Issue: Problems and improvements with respect to performance of generated code.

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@thestinger
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From the LLVM documentation:

nocapture
This indicates that the callee does not make any copies of the pointer that outlive the callee itself. This is not a valid attribute for return values.

@nikomatsakis: is this a sane optimization? it seems so
@nikomatsakis
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Yes, this should be valid.

@Aatch
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Aatch commented May 29, 2013

We could do this, but it is worth nothing that the LLVM optimizations are able to infer this most of the time.

@pnkfelix
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visiting for triage, email from 2013 sep 09.

Seems like a potentially simple thing to try out, see how it goes.

(one potential caveat is that if we did just rely on LLVM optimizations to infer this, then we wouldn't have to worry about the nocapture marking getting invalidated by unsafe code. Of course unsafe code probably shouldn't be capturing the values of borrowed pointers anyway...)

@thestinger
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It looks like nocapture might end up being how escape analysis will be implemented in LLVM, so this will get more important.

@emberian emberian mentioned this issue Mar 18, 2014
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bors added a commit that referenced this issue Mar 27, 2014
@bors
auto merge of #13001 : cmr/rust/unnamed-lifetime-nocapture, r=nikomat…
25e5238 
…sakis

Closes #6751
flip1995 pushed a commit to flip1995/rust that referenced this issue Oct 6, 2022
@bors
Auto merge of rust-lang#9484 - Xaeroxe:clamping-without-clamp, r=Alex…
64243c6 
…endoo

Implement `manual_clamp` lint

Fixes rust-lang#9477
Fixes rust-lang#6751

Identifies common patterns where usage of the `clamp` function would be more succinct and clear, and suggests using the `clamp` function instead.

changelog: [`manual_clamp`]: Implement manual_clamp lint
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A-lifetimes Area: Lifetimes / regions A-LLVM Area: Code generation parts specific to LLVM. Both correctness bugs and optimization-related issues. I-slow Issue: Problems and improvements with respect to performance of generated code.
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rustc: mark references w/anonymous lifetime nocapture
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@nikomatsakis @pnkfelix @Aatch @thestinger