Add `CastKind::Transmute` to MIR #108442

scottmcm · 2023-02-25T02:36:10Z

~~Nothing actually produces it in this commit, so I don't know how to test it, but it also means it shouldn't be possible for it to break anything.~~

Includes lowering transmute calls to it, so it's used.

Zulip Conversation: https://rust-lang.zulipchat.com/#narrow/stream/189540-t-compiler.2Fwg-mir-opt/topic/Good.20first.20isssue/near/321849610

rustbot · 2023-02-25T02:36:15Z

Failed to set assignee to JakobDegen: invalid assignee

Note: Only org members, users with write permissions, or people who have commented on the PR may be assigned.

rustbot · 2023-02-25T02:36:18Z

Some changes occurred in compiler/rustc_codegen_cranelift

cc @bjorn3

Some changes occurred to MIR optimizations

cc @rust-lang/wg-mir-opt

This PR changes MIR

cc @oli-obk, @RalfJung, @JakobDegen, @davidtwco, @celinval, @vakaras

Some changes occurred to the CTFE / Miri engine

cc @rust-lang/miri

rustbot · 2023-02-25T02:47:11Z

Some changes occurred in src/tools/clippy

cc @rust-lang/clippy

src/tools/clippy/clippy_utils/src/qualify_min_const_fn.rs

compiler/rustc_borrowck/src/type_check/mod.rs

oli-obk · 2023-02-25T06:32:41Z

To test it you could make the intrinsic mir pass convert the transmute function calls into an assignment of the new rvalue. That should allow removing all the intrinsic logic for transmute from the various backends

tests/ui/consts/const-eval/validate_uninhabited_zsts.64bit.stderr

rustbot · 2023-02-25T23:32:45Z

The Miri subtree was changed

cc @rust-lang/miri

compiler/rustc_mir_transform/src/lower_intrinsics.rs

compiler/rustc_const_eval/src/transform/validate.rs

compiler/rustc_borrowck/src/type_check/mod.rs

scottmcm · 2023-02-27T18:13:56Z

@oli-obk I see you resolved some comment threads here. Anything else you need from me before this is good to go?

(If it's just that you need time to thoroughly review it that's totally ok!)

oli-obk · 2023-02-28T08:20:41Z

(If it's just that you need time to thoroughly review it that's totally ok!)

yea, just needed to get to a PC to be able to review the diff properly and look at code that isn't nearby your changes.

@bors r+

bors · 2023-02-28T08:20:43Z

📌 Commit 6f49f85 has been approved by oli-obk

It is now in the queue for this repository.

bors · 2023-03-23T18:43:07Z

⌛ Testing commit 64cce5f with merge e216300...

bors · 2023-03-23T21:16:48Z

☀️ Test successful - checks-actions
Approved by: oli-obk
Pushing e216300 to master...

rust-timer · 2023-03-23T23:14:52Z

Finished benchmarking commit (e216300): comparison URL.

Overall result: ❌✅ regressions and improvements - ACTION NEEDED

Next Steps: If you can justify the regressions found in this perf run, please indicate this with @rustbot label: +perf-regression-triaged along with sufficient written justification. If you cannot justify the regressions please open an issue or create a new PR that fixes the regressions, add a comment linking to the newly created issue or PR, and then add the perf-regression-triaged label to this PR.

@rustbot label: +perf-regression
cc @rust-lang/wg-compiler-performance

Instruction count

This is a highly reliable metric that was used to determine the overall result at the top of this comment.

	mean	range	count
Regressions ❌ (primary)	-	-	0
Regressions ❌ (secondary)	0.7%	[0.3%, 1.5%]	4
Improvements ✅ (primary)	-1.6%	[-1.6%, -1.6%]	1
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-1.6%	[-1.6%, -1.6%]	1

Max RSS (memory usage)

Results

This is a less reliable metric that may be of interest but was not used to determine the overall result at the top of this comment.

	mean	range	count
Regressions ❌ (primary)	3.0%	[2.9%, 3.1%]	2
Regressions ❌ (secondary)	1.2%	[0.9%, 1.5%]	2
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-0.9%	[-2.1%, -0.4%]	10
All ❌✅ (primary)	3.0%	[2.9%, 3.1%]	2

Cycles

Results

This is a less reliable metric that may be of interest but was not used to determine the overall result at the top of this comment.

	mean	range	count
Regressions ❌ (primary)	-	-	0
Regressions ❌ (secondary)	0.8%	[0.4%, 1.2%]	4
Improvements ✅ (primary)	-1.4%	[-1.4%, -1.4%]	1
Improvements ✅ (secondary)	-0.7%	[-1.3%, -0.5%]	5
All ❌✅ (primary)	-1.4%	[-1.4%, -1.4%]	1

Add `CastKind::Transmute` to MIR ~~Nothing actually produces it in this commit, so I don't know how to test it, but it also means it shouldn't be possible for it to break anything.~~ Includes lowering `transmute` calls to it, so it's used. Zulip Conversation: <https://rust-lang.zulipchat.com/#narrow/stream/189540-t-compiler.2Fwg-mir-opt/topic/Good.20first.20isssue/near/321849610>

rylev · 2023-03-28T14:33:43Z

The regressions are small enough that I don't think this is worth investigating.

@rustbot label: +perf-regression-triaged

Thanks to the combination of rust-lang#108246 and rust-lang#108442 it could already remove identity transmutes. With this PR, it can also simplify them to `IntToInt` casts, `Discriminant` reads, or `Field` projections.

…jgillot Simplify transmutes in MIR InstCombine Thanks to the combination of rust-lang#108246 and rust-lang#108442 it could already remove identity transmutes. With this PR, it can also simplify them to `IntToInt` casts, `Discriminant` reads, or `Field` projections.

…i-obk Add `intrinsics::transmute_unchecked` This takes a whole 3 lines in `compiler/` since it lowers to `CastKind::Transmute` in MIR *exactly* the same as the existing `intrinsics::transmute` does, it just doesn't have the fancy checking in `hir_typeck`. Added to enable experimenting with the request in <rust-lang#106281 (comment)> and because the portable-simd folks might be interested for dependently-sized array-vector conversions. It also simplifies a couple places in `core`. See also rust-lang#108442 (comment), where `CastKind::Transmute` was added having exactly these semantics before the lang meeting (which I wasn't in) independently expressed interest.

Add `CastKind::Transmute` to MIR ~~Nothing actually produces it in this commit, so I don't know how to test it, but it also means it shouldn't be possible for it to break anything.~~ Includes lowering `transmute` calls to it, so it's used. Zulip Conversation: <https://rust-lang.zulipchat.com/#narrow/stream/189540-t-compiler.2Fwg-mir-opt/topic/Good.20first.20isssue/near/321849610>

Add `intrinsics::transmute_unchecked` This takes a whole 3 lines in `compiler/` since it lowers to `CastKind::Transmute` in MIR *exactly* the same as the existing `intrinsics::transmute` does, it just doesn't have the fancy checking in `hir_typeck`. Added to enable experimenting with the request in <rust-lang/rust#106281 (comment)> and because the portable-simd folks might be interested for dependently-sized array-vector conversions. It also simplifies a couple places in `core`. See also rust-lang/rust#108442 (comment), where `CastKind::Transmute` was added having exactly these semantics before the lang meeting (which I wasn't in) independently expressed interest.

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. labels Feb 25, 2023

scottmcm force-pushed the mir-transmute branch from fd0978a to c6bce48 Compare February 25, 2023 02:47

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scottmcm force-pushed the mir-transmute branch from c6bce48 to 6025fc9 Compare February 25, 2023 22:38

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bors added S-waiting-on-bors Status: Waiting on bors to run and complete tests. Bors will change the label on completion. and removed S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. labels Feb 28, 2023

matthiaskrgr mentioned this pull request Mar 1, 2023

Rollup of 7 pull requests #108600

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bors added the merged-by-bors This PR was explicitly merged by bors. label Mar 23, 2023

bors merged commit e216300 into rust-lang:master Mar 23, 2023

rustbot added this to the 1.70.0 milestone Mar 23, 2023

scottmcm deleted the mir-transmute branch March 23, 2023 21:22

bors mentioned this pull request Mar 23, 2023

Rollup of 12 pull requests #109490

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rustbot added the perf-regression Performance regression. label Mar 23, 2023

scottmcm mentioned this pull request Mar 24, 2023

Avoid some allocas in codegen of CastKind::Transmute #109549

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scottmcm mentioned this pull request Mar 25, 2023

Simplify transmutes in MIR InstCombine #109612

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rustbot added the perf-regression-triaged The performance regression has been triaged. label Mar 28, 2023

scottmcm mentioned this pull request Apr 23, 2023

Add intrinsics::transmute_unchecked #110706

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Add `CastKind::Transmute` to MIR #108442

Add `CastKind::Transmute` to MIR #108442

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rylev commented Mar 28, 2023

Add CastKind::Transmute to MIR #108442

Add CastKind::Transmute to MIR #108442

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rust-timer commented Mar 23, 2023

Overall result: ❌✅ regressions and improvements - ACTION NEEDED

Instruction count

Max RSS (memory usage)

Cycles

rylev commented Mar 28, 2023

Add `CastKind::Transmute` to MIR #108442

Add `CastKind::Transmute` to MIR #108442

scottmcm commented Feb 25, 2023 •

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