Ignore intrinsic calls in cross-crate-inlining cost model #145910

saethlin · 2025-08-27T01:08:42Z

I noticed in a side project that a function which just compares to [u64; 2] for equality is not cross-crate-inlinable. That was surprising to me because I didn't think that code contained a function call, but of course our array comparisons are lowered to an intrinsic. Intrinsic calls don't make a function no longer a leaf, so it makes sense to add this as an exception to the "only leaves" cross-crate-inline heuristic.

This is the useful compare link: https://perf.rust-lang.org/compare.html?start=7cb1a81145a739c4fd858abe3c624ce8e6e5f9cd&end=c3f0a64dbf9fba4722dacf8e39d2fe00069c995e&stat=instructions%3Au because it disables CGU merging in both commits, so effects that cause changes in the sysroot to perturb partitioning downstream are excluded. Perturbations to what is and isn't cross-crate-inlinable in the sysroot has chaotic effects on what items are in which CGUs after merging. It looks like before this PR by sheer luck some of the CGUs dirtied by the patch in eza incr-unchanged happened to be merged together, and with this PR they are not.

The perf runs on this PR point to a nice runtime performance improvement.

saethlin · 2025-08-27T01:08:51Z

@bors try @rust-timer queue

Ignore intrinsic calls in cross-crate-inlining cost model

joshtriplett · 2025-08-27T02:18:32Z

compiler/rustc_mir_transform/src/cross_crate_inline.rs

+                if let Some((fn_def_id, _)) = func.const_fn_def() {
+                    if self.tcx.intrinsic(fn_def_id).is_some() {


Nit: this would benefit from combining into one if using either let-chaining or is_some_and.

rust-bors · 2025-08-27T03:29:12Z

☀️ Try build successful (CI)
Build commit: e8d1f9d (e8d1f9d5716f4389b8330b02fb30ec690c68624a, parent: 160e7623e8cbbf1feab2b6e2a24733a98c7bde9c)

rust-timer · 2025-08-27T04:40:23Z

Finished benchmarking commit (e8d1f9d): comparison URL.

Overall result: ❌✅ regressions and improvements - please read the text below

Benchmarking this pull request means it may be perf-sensitive – we'll automatically label it not fit for rolling up. You can override this, but we strongly advise not to, due to possible changes in compiler perf.

Next Steps: If you can justify the regressions found in this try perf run, please do so in sufficient writing along with @rustbot label: +perf-regression-triaged. If not, please fix the regressions and do another perf run. If its results are neutral or positive, the label will be automatically removed.

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

Instruction count

Our most reliable metric. Used to determine the overall result above. However, even this metric can be noisy.

	mean	range	count
Regressions ❌ (primary)	1.1%	[0.4%, 2.6%]	8
Regressions ❌ (secondary)	0.3%	[0.1%, 0.5%]	4
Improvements ✅ (primary)	-0.5%	[-0.7%, -0.3%]	4
Improvements ✅ (secondary)	-0.3%	[-0.6%, -0.0%]	15
All ❌✅ (primary)	0.6%	[-0.7%, 2.6%]	12

Max RSS (memory usage)

Results (primary -1.1%, secondary -3.0%)

A less reliable metric. May be of interest, but not used to determine the overall result above.

	mean	range	count
Regressions ❌ (primary)	1.0%	[1.0%, 1.0%]	1
Regressions ❌ (secondary)	3.0%	[0.8%, 5.1%]	2
Improvements ✅ (primary)	-2.2%	[-3.6%, -0.8%]	2
Improvements ✅ (secondary)	-4.0%	[-5.9%, -1.8%]	13
All ❌✅ (primary)	-1.1%	[-3.6%, 1.0%]	3

Cycles

Results (primary 0.8%, secondary 0.6%)

A less reliable metric. May be of interest, but not used to determine the overall result above.

	mean	range	count
Regressions ❌ (primary)	2.7%	[2.1%, 3.2%]	2
Regressions ❌ (secondary)	3.0%	[2.1%, 4.0%]	4
Improvements ✅ (primary)	-2.9%	[-2.9%, -2.9%]	1
Improvements ✅ (secondary)	-4.2%	[-6.0%, -2.5%]	2
All ❌✅ (primary)	0.8%	[-2.9%, 3.2%]	3

Binary size

Results (primary 0.1%, secondary -0.1%)

A less reliable metric. May be of interest, but not used to determine the overall result above.

	mean	range	count
Regressions ❌ (primary)	0.2%	[0.0%, 1.0%]	32
Regressions ❌ (secondary)	0.1%	[0.1%, 0.3%]	10
Improvements ✅ (primary)	-0.1%	[-0.2%, -0.0%]	14
Improvements ✅ (secondary)	-0.2%	[-0.2%, -0.1%]	37
All ❌✅ (primary)	0.1%	[-0.2%, 1.0%]	46

Bootstrap: 466.645s -> 466.461s (-0.04%)
Artifact size: 391.15 MiB -> 391.41 MiB (0.07%)

saethlin · 2025-08-27T18:36:24Z

@bors try @rust-timer queue

Ignore intrinsic calls in cross-crate-inlining cost model

saethlin · 2025-08-27T18:45:42Z

@bors try cancel

rust-bors · 2025-08-27T18:45:45Z

Try build cancelled. Cancelled workflows:

https://github.com/rust-lang/rust/actions/runs/17275566119

saethlin · 2025-08-27T18:45:50Z

@bors try @rust-timer queue

Ignore intrinsic calls in cross-crate-inlining cost model

rust-bors · 2025-08-27T21:11:42Z

☀️ Try build successful (CI)
Build commit: 0f272e5 (0f272e5b0ae53eac2844ed412fcedfbe9ecf3a9d, parent: 3c91be712d3d84f6345cd22eae34c47b3a22a3d3)

rust-timer · 2025-08-27T22:31:37Z

Finished benchmarking commit (0f272e5): comparison URL.

Overall result: ❌✅ regressions and improvements - please read the text below

Benchmarking this pull request means it may be perf-sensitive – we'll automatically label it not fit for rolling up. You can override this, but we strongly advise not to, due to possible changes in compiler perf.

Next Steps: If you can justify the regressions found in this try perf run, please do so in sufficient writing along with @rustbot label: +perf-regression-triaged. If not, please fix the regressions and do another perf run. If its results are neutral or positive, the label will be automatically removed.

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

Instruction count

Our most reliable metric. Used to determine the overall result above. However, even this metric can be noisy.

	mean	range	count
Regressions ❌ (primary)	1.1%	[0.1%, 2.8%]	9
Regressions ❌ (secondary)	1.8%	[0.1%, 3.0%]	10
Improvements ✅ (primary)	-0.5%	[-0.6%, -0.3%]	4
Improvements ✅ (secondary)	-0.3%	[-0.6%, -0.1%]	14
All ❌✅ (primary)	0.6%	[-0.6%, 2.8%]	13

Max RSS (memory usage)

Results (primary -0.0%, secondary -2.6%)

A less reliable metric. May be of interest, but not used to determine the overall result above.

	mean	range	count
Regressions ❌ (primary)	3.9%	[1.6%, 6.2%]	2
Regressions ❌ (secondary)	4.2%	[3.3%, 5.1%]	3
Improvements ✅ (primary)	-3.9%	[-4.7%, -3.1%]	2
Improvements ✅ (secondary)	-4.1%	[-6.7%, -1.7%]	13
All ❌✅ (primary)	-0.0%	[-4.7%, 6.2%]	4

Cycles

Results (primary 2.5%, secondary 0.4%)

A less reliable metric. May be of interest, but not used to determine the overall result above.

	mean	range	count
Regressions ❌ (primary)	2.5%	[2.3%, 2.7%]	2
Regressions ❌ (secondary)	3.1%	[2.1%, 4.3%]	6
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-3.6%	[-5.5%, -2.0%]	4
All ❌✅ (primary)	2.5%	[2.3%, 2.7%]	2

Binary size

Results (primary 0.1%, secondary -0.1%)

A less reliable metric. May be of interest, but not used to determine the overall result above.

	mean	range	count
Regressions ❌ (primary)	0.2%	[0.0%, 1.1%]	32
Regressions ❌ (secondary)	0.2%	[0.1%, 0.3%]	10
Improvements ✅ (primary)	-0.1%	[-0.2%, -0.0%]	15
Improvements ✅ (secondary)	-0.2%	[-0.2%, -0.1%]	37
All ❌✅ (primary)	0.1%	[-0.2%, 1.1%]	47

Bootstrap: 468.329s -> 467.725s (-0.13%)
Artifact size: 391.15 MiB -> 391.41 MiB (0.07%)

saethlin · 2025-09-02T05:13:21Z

The perf impact that's concerning to me is the regression in eza incr-patched, where it looks like we are dirtying 5 additional CGUs. @Kobzol this is the kind of perf issue I saying in Delft that I really want tooling to diagnose.

I have locally hacked a compiler to see what functions are affected by this change and I can't find how they are related to the diffs in eza. I could brush off the regressions but I think there is a legitimate undesirable regression that I can't figure out how to understand.

Kobzol · 2025-09-02T11:00:23Z

Adding it to my TODO list. Sadly I'm still stuck on fixing bootstrap after the stage0 redesign, and didn't have time yet to go back to incremental profiling.

saethlin · 2025-09-03T06:21:35Z

@bors try @rust-timer queue

Ignore intrinsic calls in cross-crate-inlining cost model

rust-bors · 2025-09-03T08:36:31Z

☀️ Try build successful (CI)
Build commit: c3f0a64 (c3f0a64dbf9fba4722dacf8e39d2fe00069c995e, parent: 51ff895062ba60a7cba53f57af928c3fb7b0f2f4)

rust-timer · 2025-09-03T09:46:07Z

Finished benchmarking commit (c3f0a64): comparison URL.

Overall result: ❌✅ regressions and improvements - please read the text below

Benchmarking this pull request means it may be perf-sensitive – we'll automatically label it not fit for rolling up. You can override this, but we strongly advise not to, due to possible changes in compiler perf.

Next Steps: If you can justify the regressions found in this try perf run, please do so in sufficient writing along with @rustbot label: +perf-regression-triaged. If not, please fix the regressions and do another perf run. If its results are neutral or positive, the label will be automatically removed.

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

Instruction count

Our most reliable metric. Used to determine the overall result above. However, even this metric can be noisy.

	mean	range	count
Regressions ❌ (primary)	1.1%	[0.1%, 4.0%]	25
Regressions ❌ (secondary)	12.8%	[0.1%, 59.7%]	12
Improvements ✅ (primary)	-5.7%	[-84.8%, -0.1%]	19
Improvements ✅ (secondary)	-0.3%	[-0.7%, -0.0%]	31
All ❌✅ (primary)	-1.8%	[-84.8%, 4.0%]	44

Max RSS (memory usage)

Results (primary -2.0%, secondary -0.6%)

A less reliable metric. May be of interest, but not used to determine the overall result above.

	mean	range	count
Regressions ❌ (primary)	4.3%	[1.5%, 7.2%]	2
Regressions ❌ (secondary)	2.0%	[2.0%, 2.0%]	2
Improvements ✅ (primary)	-8.3%	[-12.7%, -3.9%]	2
Improvements ✅ (secondary)	-3.2%	[-5.1%, -1.3%]	2
All ❌✅ (primary)	-2.0%	[-12.7%, 7.2%]	4

Cycles

Results (primary -6.7%, secondary 12.9%)

A less reliable metric. May be of interest, but not used to determine the overall result above.

	mean	range	count
Regressions ❌ (primary)	2.7%	[1.6%, 3.8%]	6
Regressions ❌ (secondary)	20.1%	[4.4%, 48.0%]	7
Improvements ✅ (primary)	-16.1%	[-84.4%, -1.5%]	6
Improvements ✅ (secondary)	-3.8%	[-5.0%, -2.0%]	3
All ❌✅ (primary)	-6.7%	[-84.4%, 3.8%]	12

Binary size

Results (primary 1.3%, secondary 0.4%)

A less reliable metric. May be of interest, but not used to determine the overall result above.

	mean	range	count
Regressions ❌ (primary)	1.6%	[0.0%, 15.8%]	60
Regressions ❌ (secondary)	1.5%	[0.1%, 3.8%]	16
Improvements ✅ (primary)	-0.1%	[-0.2%, -0.0%]	17
Improvements ✅ (secondary)	-0.1%	[-0.2%, -0.1%]	37
All ❌✅ (primary)	1.3%	[-0.2%, 15.8%]	77

Bootstrap: 465.874s -> 466.593s (0.15%)
Artifact size: 388.34 MiB -> 388.32 MiB (-0.00%)

saethlin · 2025-09-03T15:57:39Z

This is the useful compare link: https://perf.rust-lang.org/compare.html?start=7cb1a81145a739c4fd858abe3c624ce8e6e5f9cd&end=c3f0a64dbf9fba4722dacf8e39d2fe00069c995e&stat=instructions%3Au

Because it disables CGU merging in both commits, so effects that cause changes in the sysroot to perturb partitioning downstream are excluded.

saethlin · 2025-09-06T00:45:20Z

@Kobzol I figured out this case, see the updated PR description

rustbot · 2025-09-06T00:45:26Z

r? @jieyouxu

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rustbot · 2025-09-06T00:45:28Z

Some changes occurred to MIR optimizations

cc @rust-lang/wg-mir-opt

rustbot added S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. T-compiler Relevant to the compiler team, which will review and decide on the PR/issue. labels Aug 27, 2025