[WIP] MIR move elimination pass by Amanieu · Pull Request #156046 · rust-lang/rust

Benchmarking means the PR may be perf-sensitive. It's automatically marked not fit for rolling up. Overriding is possible but disadvised: it risks changing compiler perf.

Next, please: If you can, justify the regressions found in this try perf run in writing along with @rustbot label: +perf-regression-triaged. If not, fix the regressions and do another perf run. Neutral or positive results will clear the label automatically.

@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)	1.7%	[0.2%, 13.7%]	27
Regressions ❌ (secondary)	16.1%	[0.0%, 772.0%]	54
Improvements ✅ (primary)	-1.0%	[-6.0%, -0.1%]	215
Improvements ✅ (secondary)	-1.2%	[-11.0%, -0.0%]	179
All ❌✅ (primary)	-0.7%	[-6.0%, 13.7%]	242

Max RSS (memory usage)

Results (primary 1.4%, secondary 0.3%)

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

	mean	range	count
Regressions ❌ (primary)	2.6%	[1.6%, 4.6%]	7
Regressions ❌ (secondary)	2.4%	[0.4%, 8.3%]	5
Improvements ✅ (primary)	-1.3%	[-1.5%, -1.1%]	3
Improvements ✅ (secondary)	-1.4%	[-2.3%, -0.6%]	6
All ❌✅ (primary)	1.4%	[-1.5%, 4.6%]	10

Cycles

Results (primary -2.5%, secondary 0.2%)

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

	mean	range	count
Regressions ❌ (primary)	5.5%	[2.3%, 11.5%]	4
Regressions ❌ (secondary)	35.2%	[2.0%, 287.2%]	10
Improvements ✅ (primary)	-3.1%	[-5.7%, -1.8%]	51
Improvements ✅ (secondary)	-6.4%	[-24.8%, -1.9%]	53
All ❌✅ (primary)	-2.5%	[-5.7%, 11.5%]	55

Binary size

Results (primary 0.5%, secondary 1.4%)

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

	mean	range	count
Regressions ❌ (primary)	1.6%	[0.1%, 6.7%]	77
Regressions ❌ (secondary)	2.2%	[0.1%, 6.7%]	93
Improvements ✅ (primary)	-1.0%	[-2.7%, -0.2%]	57
Improvements ✅ (secondary)	-1.1%	[-5.6%, -0.2%]	28
All ❌✅ (primary)	0.5%	[-2.7%, 6.7%]	134

Bootstrap: 512.33s -> 496.036s (-3.18%)
Artifact size: 400.60 MiB -> 397.34 MiB (-0.81%)

Amanieu · 2026-06-09T19:53:26Z

@bors try @rust-timer queue

[WIP] MIR move elimination pass

rust-bors · 2026-06-09T22:11:28Z

☀️ Try build successful (CI)
Build commit: 03cc207 (03cc207f628cd7ad629337650a84004a9fbeb00c, parent: beae781308e9ddef13074a03faf57ca2fac59a5b)

rust-timer · 2026-06-09T22:51:54Z

Finished benchmarking commit (03cc207): comparison URL.

Overall result: ❌✅ regressions and improvements - please read:

Benchmarking means the PR may be perf-sensitive. It's automatically marked not fit for rolling up. Overriding is possible but disadvised: it risks changing compiler perf.

Next, please: If you can, justify the regressions found in this try perf run in writing along with @rustbot label: +perf-regression-triaged. If not, fix the regressions and do another perf run. Neutral or positive results will clear the label automatically.

@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)	1.6%	[0.1%, 16.4%]	58
Regressions ❌ (secondary)	11.3%	[0.2%, 748.2%]	79
Improvements ✅ (primary)	-1.2%	[-5.4%, -0.2%]	123
Improvements ✅ (secondary)	-1.3%	[-10.6%, -0.2%]	141
All ❌✅ (primary)	-0.3%	[-5.4%, 16.4%]	181

Max RSS (memory usage)

Results (primary -0.7%, secondary -1.9%)

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

	mean	range	count
Regressions ❌ (primary)	2.3%	[0.7%, 3.8%]	5
Regressions ❌ (secondary)	3.6%	[0.5%, 7.0%]	3
Improvements ✅ (primary)	-2.0%	[-3.9%, -0.7%]	11
Improvements ✅ (secondary)	-2.8%	[-10.2%, -0.3%]	20
All ❌✅ (primary)	-0.7%	[-3.9%, 3.8%]	16

Cycles

Results (primary -1.6%, secondary 0.8%)

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

	mean	range	count
Regressions ❌ (primary)	6.1%	[2.0%, 13.0%]	7
Regressions ❌ (secondary)	55.0%	[6.8%, 279.2%]	6
Improvements ✅ (primary)	-2.9%	[-4.8%, -2.0%]	44
Improvements ✅ (secondary)	-5.4%	[-19.0%, -2.1%]	52
All ❌✅ (primary)	-1.6%	[-4.8%, 13.0%]	51

Binary size

Results (primary 0.9%, secondary 1.3%)

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

	mean	range	count
Regressions ❌ (primary)	1.7%	[0.0%, 17.5%]	94
Regressions ❌ (secondary)	2.5%	[0.0%, 17.5%]	98
Improvements ✅ (primary)	-0.8%	[-2.1%, -0.1%]	48
Improvements ✅ (secondary)	-0.6%	[-1.7%, -0.1%]	61
All ❌✅ (primary)	0.9%	[-2.1%, 17.5%]	142

Bootstrap: 523.273s -> 506.943s (-3.12%)
Artifact size: 400.81 MiB -> 397.89 MiB (-0.73%)

This is no longer true as of rust-lang#107267.

- Changed `iter_intervals` to return `RangeInclusive` instead of `Range` - Added `clear_row`, `disjoint_rows` and `intersects_range` methods

This flag also has the effect of disabling DestinationPropagation, which is already covered by move elimination.

Amanieu · 2026-06-15T22:43:30Z

Closed in favor of #157943 so reviewers don't need to wade through 100+ CI/bors/perf messages.

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 May 1, 2026