Remove `box_free` lang item #100036

beepster4096 · 2022-08-01T21:59:49Z

This PR removes the box_free lang item, replacing it with Box's Drop impl. Box dropping is still slightly magic because the contained value is still dropped by the compiler.

rust-highfive · 2022-08-01T21:59:52Z

r? @wesleywiser

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rustbot · 2022-08-01T21:59:52Z

Hey! It looks like you've submitted a new PR for the library teams!

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.

Examples of T-libs-api changes:

Stabilizing library features
Introducing insta-stable changes such as new implementations of existing stable traits on existing stable types
Introducing new or changing existing unstable library APIs (excluding permanently unstable features / features without a tracking issue)
Changing public documentation in ways that create new stability guarantees
Changing observable runtime behavior of library APIs

Some changes occurred in compiler/rustc_codegen_gcc

cc @antoyo

Some changes occurred in compiler/rustc_codegen_cranelift

cc @bjorn3

src/doc/unstable-book/src/language-features/lang-items.md

compiler/rustc_codegen_cranelift/example/mini_core.rs

tmiasko · 2022-08-06T17:06:14Z

Failing test case enables -Zstack-protector=strong, which according to rustc --print stack-protector-strategies:

    strong
        Generate stack canaries in a function if it either:
        - has a local variable of `[T; N]` type, regardless of `T` and `N`
        - takes the address of a local variable.

          (Note that a local variable being borrowed is not equivalent to its
          address being taken: e.g. some borrows may be removed by optimization,
          while by-value argument passing may be implemented with reference to a
          local stack variable in the ABI.)

Freeing a box calls the drop implementation which accepts &mut Box<T> as a parameter. Now that the address of a box temporary is taken the stack canary seems expected. I think, it should be fine to update this part of the test case.

@bors try @rust-timer queue

rust-timer · 2022-08-06T17:06:16Z

Awaiting bors try build completion.

@rustbot label: +S-waiting-on-perf

bors · 2022-08-06T17:06:23Z

⌛ Trying commit 3247cc8bcd7ba9bcf0a5debf2d73f2b6b5e9ad2f with merge 3cd4647996dc90f68700aa3bbc775e1a318ab11f...

bors · 2022-08-06T18:56:46Z

☀️ Try build successful - checks-actions
Build commit: 3cd4647996dc90f68700aa3bbc775e1a318ab11f (3cd4647996dc90f68700aa3bbc775e1a318ab11f)

rust-timer · 2022-08-06T18:56:48Z

Queued 3cd4647996dc90f68700aa3bbc775e1a318ab11f with parent 76b0484, future comparison URL.

rust-timer · 2022-08-06T20:24:38Z

Finished benchmarking commit (3cd4647996dc90f68700aa3bbc775e1a318ab11f): comparison url.

Instruction count

Primary benchmarks: mixed results
Secondary benchmarks: mixed results

	mean¹	max	count²
Regressions 😿 (primary)	1.3%	2.6%	8
Regressions 😿 (secondary)	1.4%	4.6%	12
Improvements 🎉 (primary)	-1.5%	-2.4%	2
Improvements 🎉 (secondary)	-0.8%	-1.7%	9
All 😿🎉 (primary)	0.7%	2.6%	10

Max RSS (memory usage)

Results

Primary benchmarks: 😿 relevant regressions found
Secondary benchmarks: mixed results

	mean¹	max	count²
Regressions 😿 (primary)	6.7%	9.7%	6
Regressions 😿 (secondary)	4.5%	7.0%	3
Improvements 🎉 (primary)	N/A	N/A	0
Improvements 🎉 (secondary)	-2.2%	-2.7%	4
All 😿🎉 (primary)	6.7%	9.7%	6

Cycles

Results

Primary benchmarks: mixed results
Secondary benchmarks: no relevant changes found

	mean¹	max	count²
Regressions 😿 (primary)	2.4%	2.4%	1
Regressions 😿 (secondary)	N/A	N/A	0
Improvements 🎉 (primary)	-2.8%	-2.8%	1
Improvements 🎉 (secondary)	N/A	N/A	0
All 😿🎉 (primary)	-0.2%	-2.8%	2

If you disagree with this performance assessment, please file an issue in rust-lang/rustc-perf.

Benchmarking this pull request likely means that it is perf-sensitive, so we're automatically marking it as not fit for rolling up. While you can manually mark this PR as fit for rollup, we strongly recommend not doing so since this PR may lead to changes in compiler perf.

Next Steps: If you can justify the regressions found in this try perf run, please indicate this with @rustbot label: +perf-regression-triaged along with sufficient written justification. If you cannot justify the regressions please fix the regressions and do another perf run. If the next run shows neutral or positive results, the label will be automatically removed.

@bors rollup=never
@rustbot label: +S-waiting-on-review -S-waiting-on-perf +perf-regression

the arithmetic mean of the percent change ↩ ↩² ↩³
number of relevant changes ↩ ↩² ↩³

wesleywiser · 2022-08-24T13:48:43Z

@drmeepster does this need another perf run?

beepster4096 · 2022-10-03T03:25:55Z

Sorry for disappearing for a while!

Another perf run would be great, thanks.

tmiasko · 2022-10-03T19:43:37Z

@bors try @rust-timer queue

rust-timer · 2022-10-03T19:43:38Z

Awaiting bors try build completion.

@rustbot label: +S-waiting-on-perf

bors · 2022-10-03T19:43:46Z

⌛ Trying commit e1bb0f0ebcf38e3c22bf387c68b445a28cefc983 with merge 5b44952011bb7348f9ce89c5b0099b43c87531ba...

bors · 2023-06-07T21:35:49Z

⌛ Testing commit 12af10afed5a84cebd005dae90cb78be5c34ed7b with merge 26612d19e3967dd80d4c9b5f8717155b4f066bf4...

bors · 2023-06-07T22:02:18Z

💔 Test failed - checks-actions

bors · 2023-06-15T13:11:48Z

☔ The latest upstream changes (presumably #106343) made this pull request unmergeable. Please resolve the merge conflicts.

oli-obk · 2023-06-17T11:52:35Z

@bors r+

bors · 2023-06-17T11:52:38Z

📌 Commit a5c6cb8 has been approved by oli-obk

It is now in the queue for this repository.

bors · 2023-06-17T16:11:00Z

⌛ Testing commit a5c6cb8 with merge a8a2907...

bors · 2023-06-17T19:16:05Z

☀️ Test successful - checks-actions
Approved by: oli-obk
Pushing a8a2907 to master...

rust-timer · 2023-06-17T20:31:50Z

Finished benchmarking commit (a8a2907): 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)	1.2%	[1.0%, 1.7%]	4
Regressions ❌ (secondary)	1.7%	[1.1%, 3.4%]	5
Improvements ✅ (primary)	-0.6%	[-0.6%, -0.6%]	2
Improvements ✅ (secondary)	-2.5%	[-4.4%, -1.4%]	4
All ❌✅ (primary)	0.6%	[-0.6%, 1.7%]	6

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)	3.3%	[3.3%, 3.3%]	1
Regressions ❌ (secondary)	2.6%	[2.1%, 3.0%]	2
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-2.9%	[-2.9%, -2.9%]	1
All ❌✅ (primary)	3.3%	[3.3%, 3.3%]	1

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)	1.5%	[1.5%, 1.6%]	2
Regressions ❌ (secondary)	2.2%	[0.7%, 3.7%]	2
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-2.4%	[-3.4%, -1.4%]	3
All ❌✅ (primary)	1.5%	[1.5%, 1.6%]	2

Binary size

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)	0.7%	[0.0%, 1.6%]	39
Regressions ❌ (secondary)	1.6%	[0.4%, 3.7%]	82
Improvements ✅ (primary)	-0.3%	[-0.8%, -0.0%]	51
Improvements ✅ (secondary)	-1.6%	[-2.6%, -1.3%]	5
All ❌✅ (primary)	0.1%	[-0.8%, 1.6%]	90

Bootstrap: 656.011s -> 655.353s (-0.10%)

nnethercote · 2023-06-18T06:38:20Z

Lots of binary size regressions here. Is that expected?

klensy · 2023-06-18T20:36:29Z

library/alloc/src/boxed.rs

@@ -1211,8 +1211,16 @@ impl<T: ?Sized, A: Allocator> Box<T, A> {

 #[stable(feature = "rust1", since = "1.0.0")]
 unsafe impl<#[may_dangle] T: ?Sized, A: Allocator> Drop for Box<T, A> {
+    #[inline]


Idk, maybe that inline increased binary size?

box_free was also marked as inline, so I don't think that is the cause.

rylev · 2023-06-21T07:48:49Z

@oli-obk @drmeepster any thoughts on the binary size regressions?

beepster4096 · 2023-06-21T07:56:45Z

The only real difference is that box_free took fields by value but drop takes a mutable reference. I bet that affects how LLVM inlines.

Remove `box_free` lang item This PR removes the `box_free` lang item, replacing it with `Box`'s `Drop` impl. Box dropping is still slightly magic because the contained value is still dropped by the compiler.

rust-highfive assigned wesleywiser Aug 1, 2022

rustbot added 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 Aug 1, 2022

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rustbot added the S-waiting-on-perf Status: Waiting on a perf run to be completed. label Aug 6, 2022

rustbot added perf-regression Performance regression. and removed S-waiting-on-perf Status: Waiting on a perf run to be completed. labels Aug 6, 2022

beepster4096 force-pushed the box_free_free_box branch from d8303fa to e1bb0f0 Compare October 3, 2022 02:48

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bors added S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. and removed S-waiting-on-bors Status: Waiting on bors to run and complete tests. Bors will change the label on completion. labels Jun 7, 2023

remove box_free and replace with drop impl

a5c6cb8

beepster4096 force-pushed the box_free_free_box branch from 12af10a to a5c6cb8 Compare June 16, 2023 21:23

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 Jun 17, 2023

bors added the merged-by-bors This PR was explicitly merged by bors. label Jun 17, 2023

bors merged commit a8a2907 into rust-lang:master Jun 17, 2023

rustbot added this to the 1.72.0 milestone Jun 17, 2023

bors mentioned this pull request Jun 17, 2023

Better error for non const PartialEq call generated by match #112232

Merged

klensy reviewed Jun 18, 2023

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bjorn3 mentioned this pull request Jan 26, 2024

Sync rustc_codegen_cranelift #113960

Merged

This was referenced Aug 28, 2024

Rename "assumed" to "builtin" AeneasVerif/charon#338

Merged

Check that box_free is still used AeneasVerif/charon#230

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This was referenced Oct 1, 2024

Box sometimes forgets to drop its allocator when the Box is conditionally initialized. #131082

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Stop clearing box's drop flags early #131146

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Remove `box_free` lang item #100036

Remove `box_free` lang item #100036

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Remove box_free lang item #100036

Remove box_free lang item #100036

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Footnotes

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Overall result: ❌✅ regressions and improvements - ACTION NEEDED

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rylev commented Jun 21, 2023

beepster4096 commented Jun 21, 2023

Remove `box_free` lang item #100036

Remove `box_free` lang item #100036