Add assume into `NonZeroIntX::get` #119452

AngelicosPhosphoros · 2023-12-30T19:55:54Z

LLVM currently don't support range metadata for function arguments so it fails to optimize non zero integers using their invariant if they are provided using by-value function arguments.

Related to #119422
Related to llvm/llvm-project#76628
Related to #49572

rustbot · 2023-12-30T19:56:02Z

r? @joshtriplett

(rustbot has picked a reviewer for you, use r? to override)

AngelicosPhosphoros · 2023-12-30T19:59:01Z

I would also like to check if we can just add valid range attribute to the function call.

It seems to work.

There is also a problem that get function gets inlined by MIR optimizer.

saethlin · 2023-12-30T22:22:11Z

@bors try @rust-timer queue

bors · 2023-12-30T22:23:21Z

⌛ Trying commit b895a3e with merge 5a3a8b4...

…get_assume_nonzero, r=<try> Add assume into `NonZeroIntX::get` LLVM currently don't support range metadata for function arguments so it fails to optimize non zero integers using their invariant if they are provided using by-value function arguments. Related to rust-lang#119422 Related to llvm/llvm-project#76628 Related to rust-lang#49572

Noratrieb · 2023-12-30T22:46:33Z

library/core/src/num/nonzero.rs

+                    if self.0 == 0 {
+                        // SAFETY: It is an invariant of this type.
+                        unsafe {
+                            crate::hint::unreachable_unchecked()
+                        }
+                    }


Suggested change

if self.0 == 0 {

// SAFETY: It is an invariant of this type.

unsafe {

crate::hint::unreachable_unchecked()

}

}

unsafe { std::intrinsics::assume(self.0 != 0) };

@Nilstrieb assume is not const-stable, so it can’t be called here.

probably should be const stable then, I don't see any problems with that (cc @rust-lang/wg-const-eval)

Yeah seems fine to mark that intrinsic as callable from stable const fn

bors · 2023-12-30T23:51:46Z

☀️ Try build successful - checks-actions
Build commit: 5a3a8b4 (5a3a8b4ee378f283b1e4916e12f60874e412486b)

rust-timer · 2023-12-31T01:34:27Z

Finished benchmarking commit (5a3a8b4): comparison URL.

Overall result: no relevant changes - no action needed

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.

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

Instruction count

This benchmark run did not return any relevant results for this metric.

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)	10.1%	[10.1%, 10.1%]	1
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-3.3%	[-3.3%, -3.3%]	1
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	3.4%	[-3.3%, 10.1%]	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
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-2.4%	[-2.6%, -2.1%]	2
All ❌✅ (primary)	-	-	0

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)	0.1%	[0.0%, 0.3%]	5
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-0.8%	[-2.0%, -0.1%]	3
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-0.2%	[-2.0%, 0.3%]	8

Bootstrap: 669.431s -> 669.699s (0.04%)
Artifact size: 311.78 MiB -> 311.73 MiB (-0.02%)

Noratrieb · 2024-01-01T15:13:55Z

Doesn't make compilation or the compiler faster, but that of course doesn't mean it's not worth it. Seems reasonable to add this (with an assume) but looks like @scottmcm wants to do the final decision on that :)

EFanZh · 2024-01-01T15:21:24Z

@AngelicosPhosphoros: Could you also update the From<NonZero*> implementation to utilize this change?

AngelicosPhosphoros · 2024-01-02T16:27:41Z

@EFanZh Done.

scottmcm · 2024-01-03T01:59:07Z

I agree that this should be using assume -- it'll save space in MIR, among other things. As Ralf said, if unreachable_unchecked is const-stable, there's no concern about assume being const-stable too.

And feel free to review if you notice it first, @Nilstrieb -- I just wanted to make sure it didn't end up waiting on a libs-api person who could be doing ACP reviews instead :)

AngelicosPhosphoros · 2024-01-03T12:15:48Z

@Nilstrieb @RalfJung Do I need to run through whole stabilization process?
const_assume was started to be implemented in 2020 and seems to be inactive since: #76972

Noratrieb · 2024-01-03T12:19:26Z

It's an intrinsic, just mark it as stable, that's it.

RalfJung · 2024-01-03T17:46:23Z

Yeah, the intrinsic is still unstable, just const-stable. So it cannot be called directly, just internally in stable const fn inside core/std. You can just add the attribute with wg-const-eval approval.

scottmcm · 2024-01-03T18:10:35Z

@AngelicosPhosphoros For context, the reason for this gating is to be careful that we don't accidentally expose something that couldn't be done in const fn before. But assume doesn't make anything possible that wasn't already possible with unreachable_unchecked, so there's no concerns for this particular one.

(The conversation would be more complicated if it was an intrinsic for getting a random number or reading a file or something.)

Closes rust-lang#76972 Blocks rust-lang#119452 Approved in rust-lang#119452 (comment)

scottmcm · 2024-01-12T07:52:06Z

The last perf run here looks good, but since the biggest reason this wasn't done before was perf concerns, I want to do another one as the code has changed, just from an abundance of caution.

@bors try @rust-timer queue

But r=me assuming the perf results are still good! 🤞

bors · 2024-01-12T07:53:17Z

⌛ Trying commit 8f432d4 with merge 8a63333...

…get_assume_nonzero, r=<try> Add assume into `NonZeroIntX::get` LLVM currently don't support range metadata for function arguments so it fails to optimize non zero integers using their invariant if they are provided using by-value function arguments. Related to rust-lang#119422 Related to llvm/llvm-project#76628 Related to rust-lang#49572

bors · 2024-01-12T09:19:04Z

☀️ Try build successful - checks-actions
Build commit: 8a63333 (8a63333b5c8e305f85f6968d7b857cc6bc94b154)

rust-timer · 2024-01-12T10:36:32Z

Finished benchmarking commit (8a63333): comparison URL.

Overall result: ❌✅ regressions and improvements - ACTION NEEDED

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-perf +perf-regression

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)	0.5%	[0.4%, 0.6%]	3
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-0.7%	[-0.7%, -0.7%]	1
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	0.2%	[-0.7%, 0.6%]	4

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%	[1.1%, 7.5%]	5
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-3.9%	[-5.1%, -2.7%]	2
Improvements ✅ (secondary)	-0.9%	[-0.9%, -0.9%]	1
All ❌✅ (primary)	1.1%	[-5.1%, 7.5%]	7

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)	0.6%	[0.6%, 0.6%]	1
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-0.6%	[-0.6%, -0.6%]	1
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-0.0%	[-0.6%, 0.6%]	2

Binary size

This benchmark run did not return any relevant results for this metric.

Bootstrap: 666.39s -> 663.51s (-0.43%)
Artifact size: 308.38 MiB -> 308.40 MiB (0.00%)

AngelicosPhosphoros · 2024-01-12T17:21:48Z

Does that mean that using assume is different compared to unreachable_unchecked?

scottmcm · 2024-01-12T18:18:59Z

It's certainly different -- it changes the MIR, after all, such as fewer BBs by not having an if -- but to me these results are fine.

With more stuff in the methods, having the cycles being maybe slightly higher is, I think, ok. Looking at the overall wall time, including the non-significant ones, I think it's fair to call this roughly neutral. And 3 seconds saved on bootstrap is nothing to sneeze at!

@bors r+ rollup=never

bors · 2024-01-12T18:19:01Z

📌 Commit 8f432d4 has been approved by scottmcm

It is now in the queue for this repository.

bors · 2024-01-12T20:18:07Z

⌛ Testing commit 8f432d4 with merge 2319be8...

bors · 2024-01-12T22:14:47Z

☀️ Test successful - checks-actions
Approved by: scottmcm
Pushing 2319be8 to master...

rust-timer · 2024-01-12T23:30:50Z

Finished benchmarking commit (2319be8): 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)	0.5%	[0.4%, 0.9%]	4
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-0.7%	[-0.7%, -0.7%]	1
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	0.3%	[-0.7%, 0.9%]	5

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)	2.7%	[0.8%, 5.3%]	4
Regressions ❌ (secondary)	4.5%	[4.5%, 4.5%]	1
Improvements ✅ (primary)	-1.0%	[-1.3%, -0.5%]	3
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	1.1%	[-1.3%, 5.3%]	7

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
Improvements ✅ (primary)	-0.5%	[-0.7%, -0.4%]	3
Improvements ✅ (secondary)	-2.5%	[-4.1%, -0.9%]	3
All ❌✅ (primary)	-0.5%	[-0.7%, -0.4%]	3

Binary size

This benchmark run did not return any relevant results for this metric.

Bootstrap: 666.309s -> 665.459s (-0.13%)
Artifact size: 308.10 MiB -> 308.09 MiB (-0.00%)

scottmcm · 2024-01-13T00:39:37Z

Instructions have a couple red in instruction counts for opt, but that's entirely reasonable for something intended to enable optimizations. Notably, the cycles are green, with no regressions. So I think this is fine.

pnkfelix · 2024-01-16T18:08:13Z

scottmcm writes: "Instructions have a couple red in instruction counts for opt, but that's entirely reasonable for something intended to enable optimizations. Notably, the cycles are green, with no regressions. So I think this is fine."
marking as triaged

@rustbot label: +perf-regression-triaged

rustbot assigned joshtriplett Dec 30, 2023

rustbot added S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. T-libs Relevant to the library team, which will review and decide on the PR/issue. labels Dec 30, 2023

AngelicosPhosphoros mentioned this pull request Dec 30, 2023

Missed Optimization for NonZeroU32 to NonZeroUsize Conversions #119422

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AngelicosPhosphoros force-pushed the make_nonzeroint_get_assume_nonzero branch from 5acf68b to b895a3e Compare December 30, 2023 20:50

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Noratrieb mentioned this pull request Jan 1, 2024

Assert the value returned by NonZero*::get being non-zero #119490

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AngelicosPhosphoros force-pushed the make_nonzeroint_get_assume_nonzero branch from b895a3e to 97f74e7 Compare January 2, 2024 16:23

AngelicosPhosphoros mentioned this pull request Jan 3, 2024

Tracking Issue for const_assume feature #76972

Closed

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AngelicosPhosphoros added a commit to AngelicosPhosphoros/rust that referenced this pull request Jan 4, 2024

Make intrinsics::assume const stable

59c76fb

Closes rust-lang#76972 Blocks rust-lang#119452 Approved in rust-lang#119452 (comment)

AngelicosPhosphoros marked this pull request as ready for review January 6, 2024 13:57

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rustbot added perf-regression Performance regression. and removed S-waiting-on-perf Status: Waiting on a perf run to be completed. labels Jan 12, 2024

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 Jan 12, 2024

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Reduce inlining cost for statement #116708

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Consolidate all associated items on the NonZero integer types into a single impl block per type #118665

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AngelicosPhosphoros deleted the make_nonzeroint_get_assume_nonzero branch January 12, 2024 23:25

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dtolnay mentioned this pull request Feb 2, 2024

Make NonZero::get generic. #120563

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slanterns mentioned this pull request Aug 14, 2024

Cleanup NonZero<T>::get #129081

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Add assume into `NonZeroIntX::get` #119452

Add assume into `NonZeroIntX::get` #119452

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Add assume into NonZeroIntX::get #119452

Add assume into NonZeroIntX::get #119452

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Overall result: no relevant changes - no action needed

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Overall result: ❌✅ regressions and improvements - ACTION NEEDED

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Overall result: ❌✅ regressions and improvements - ACTION NEEDED

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pnkfelix commented Jan 16, 2024

Add assume into `NonZeroIntX::get` #119452

Add assume into `NonZeroIntX::get` #119452

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