Add intrinsic for Option::Some(_) offset#109095

llogiq · 2023-03-13T20:40:16Z

This replaces the prior hacky calculation with an option_some_offset intrinsic that directly gets the offset from the type layout.

cc @scottmcm #108545

rustbot · 2023-03-13T20:40:24Z

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rustbot · 2023-03-13T20:40:28Z

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If this PR contains changes to any rust-lang/rust public library APIs then please comment with @rustbot label +T-libs-api -T-libs to tag it appropriately. If this PR contains changes to any unstable APIs please edit the PR description to add a link to the relevant API Change Proposal or create one if you haven't already. If you're unsure where your change falls no worries, just leave it as is and the reviewer will take a look and make a decision to forward on if necessary.

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cc @rust-lang/miri

oli-obk · 2023-03-13T21:15:10Z

library/core/src/intrinsics.rs

Please re-add the FIXME from the hacky libstd impl here, so we remember to nuke this intrinsic in the future

the8472 · 2023-03-13T21:27:41Z

library/core/src/option.rs

0 should be the safest choice here.

llogiq · 2023-03-14T07:41:14Z

I'm a bit confused about the error. I had included the const-unstable feature in library/core/src/lib.rs, but it appears to be required whenever the const is actually instantiated? That to me looks like a bug in the feature gate check. Should I simply make the intrinsic const-stable?

oli-obk · 2023-03-14T07:50:06Z

Should I simply make the intrinsic const-stable?

if the intrinsic is used from stable code, then yes, you need to make it stable.

Noratrieb · 2023-03-14T10:27:22Z

library/core/src/intrinsics.rs

Can you add the intrinsics to the main extern "rust-intrinsic" block instead and just cfg the fn directly?

RalfJung · 2023-03-14T16:35:15Z

compiler/rustc_codegen_ssa/src/mir/intrinsic.rs

Why not use variant.fields.offset(0)? I am not sure if the bug! here is truly unreachable. Layouts can take very surprising shapes sometimes.

RalfJung · 2023-03-14T16:35:27Z

compiler/rustc_codegen_ssa/src/mir/intrinsic.rs

I think this will ICE on Option<!>.

Oh, a test for Option<Never> would be a good add, regardless of implementation 👍

RalfJung · 2023-03-14T16:36:02Z

compiler/rustc_const_eval/src/interpret/intrinsics.rs

I think we should avoid duplicating this code.

Ok, where to put it then?

RalfJung · 2023-03-14T16:38:12Z

I'm a bit confused about the error. I had included the const-unstable feature in library/core/src/lib.rs, but it appears to be required whenever the const is actually instantiated? That to me looks like a bug in the feature gate check. Should I simply make the intrinsic const-stable?

Const stability checking is fully recursive, unlike the usual library stability checking. We want to avoid accidentally stably exposing the behavior of some unstable function / intrinsic at compile time.

scottmcm

I think this probably needs some updates before it can land, but I'm usually just a libs reviewer, so this should go to someone better equipped to evaluate the right way to do this in the compiler.

r? compiler

library/core/src/intrinsics.rs

llogiq · 2023-03-15T09:44:30Z

Closing this in favor of a offset_payload_ptr-intrinsic based solution.

…ce, r=eholk move Option::as_slice to intrinsic `@scottmcm` suggested on rust-lang#109095 I use a direct approach of unpacking the operation in MIR lowering, so here's the implementation. cc `@nikic` as this should hopefully unblock rust-lang#107224 (though perhaps other changes to the prior implementation, which I left for bootstrapping, are needed).

…ce, r=eholk move Option::as_slice to intrinsic ``@scottmcm`` suggested on rust-lang#109095 I use a direct approach of unpacking the operation in MIR lowering, so here's the implementation. cc ``@nikic`` as this should hopefully unblock rust-lang#107224 (though perhaps other changes to the prior implementation, which I left for bootstrapping, are needed).

…ce, r=eholk move Option::as_slice to intrinsic ```@scottmcm``` suggested on rust-lang#109095 I use a direct approach of unpacking the operation in MIR lowering, so here's the implementation. cc ```@nikic``` as this should hopefully unblock rust-lang#107224 (though perhaps other changes to the prior implementation, which I left for bootstrapping, are needed).

…ce, r=eholk move Option::as_slice to intrinsic ````@scottmcm```` suggested on rust-lang#109095 I use a direct approach of unpacking the operation in MIR lowering, so here's the implementation. cc ````@nikic```` as this should hopefully unblock rust-lang#107224 (though perhaps other changes to the prior implementation, which I left for bootstrapping, are needed).

rustbot assigned scottmcm Mar 13, 2023

rustbot added S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. T-compiler Relevant to the compiler team, which will review and decide on the PR/issue. T-libs Relevant to the library team, which will review and decide on the PR/issue. labels Mar 13, 2023

llogiq mentioned this pull request Mar 13, 2023

Tracking Issue for option_as_slice #108545

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oli-obk reviewed Mar 13, 2023

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0 should be the safest choice here.

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Noratrieb reviewed Mar 14, 2023

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llogiq force-pushed the option-some-offset-intrinsic branch from da1a88c to 86bc827 Compare March 14, 2023 12:24

RalfJung reviewed Mar 14, 2023

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Add intrinsic for Option::Some(_) offset

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llogiq force-pushed the option-some-offset-intrinsic branch from 86bc827 to a5ac44e Compare March 14, 2023 17:13

scottmcm reviewed Mar 14, 2023

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rustbot assigned michaelwoerister and petrochenkov and unassigned scottmcm Mar 14, 2023

scottmcm unassigned petrochenkov Mar 14, 2023

scottmcm mentioned this pull request Mar 14, 2023

Upgrade to LLVM 16 #107224

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llogiq closed this Mar 15, 2023

llogiq deleted the option-some-offset-intrinsic branch March 15, 2023 09:44

llogiq mentioned this pull request Mar 15, 2023

move Option::as_slice to intrinsic #109179

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michaelwoerister removed their assignment Mar 17, 2023

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llogiq commented Mar 13, 2023 •

edited by scottmcm

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