Pre-compute MIR CFG caches for borrowck and other analyses #142540

cjgillot · 2025-06-15T14:35:45Z

I was puzzled that #142390 introduces additional computations of CFG traversals: borrowck computes them, right?

It turns out that borrowck clones the MIR body, so doesn't share its cache with other analyses.

This PR:

forces the computation of all caches in mir_promoted query;
modifies region renumbering to avoid dropping that cache.

rustbot · 2025-06-15T14:35:49Z

rustbot has assigned @fee1-dead.
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rustbot · 2025-06-15T14:35:51Z

Some changes occurred to MIR optimizations

cc @rust-lang/wg-mir-opt

cjgillot · 2025-06-15T14:41:37Z

@bors2 try @rust-timer queue

rust-bors · 2025-06-15T14:41:40Z

⌛ Trying commit e7e8f6d with merge 18218cc…

To cancel the try build, run the command @bors2 try cancel.

Pre-compute MIR CFG caches for borrowck and other analyses I was puzzled that #142390 introduces additional computations of CFG traversals: borrowck computes them, right? It turns out that borrowck clones the MIR body, so doesn't share its cache with other analyses. This PR: - forces the computation of all caches in `mir_promoted` query; - modifies region renumbering to avoid dropping that cache.

rust-bors · 2025-06-15T17:08:29Z

☀️ Try build successful (CI)
Build commit: 18218cc (18218cc5c664c3521f4769f46ef5e5e10128c92c, parent: 75e7cf5f85aad82331a38deff24845b63eaf30f3)

rust-timer · 2025-06-15T18:49:48Z

Finished benchmarking commit (18218cc): comparison URL.

Overall result: ❌ regressions - 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)	0.5%	[0.2%, 2.9%]	68
Regressions ❌ (secondary)	0.7%	[0.2%, 1.8%]	47
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	0.5%	[0.2%, 2.9%]	68

Max RSS (memory usage)

Results (primary 1.7%, 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%	[0.9%, 2.8%]	12
Regressions ❌ (secondary)	2.5%	[2.0%, 3.0%]	2
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-1.2%	[-1.2%, -1.2%]	1
All ❌✅ (primary)	1.7%	[0.9%, 2.8%]	12

Cycles

Results (primary 1.1%)

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

	mean	range	count
Regressions ❌ (primary)	1.1%	[0.7%, 1.4%]	2
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	1.1%	[0.7%, 1.4%]	2

Binary size

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

Bootstrap: 756.494s -> 756.086s (-0.05%)
Artifact size: 372.15 MiB -> 372.18 MiB (0.01%)

compiler/rustc_middle/src/mir/basic_blocks.rs

cjgillot · 2025-06-15T20:25:34Z

Perf deserves investigation. I really didn't expect mir_borrowck to get slower.

cjgillot · 2025-06-15T20:34:53Z

@bors2 try @rust-timer queue

rust-bors · 2025-06-15T20:34:56Z

⌛ Trying commit 3e77d40 with merge 98e2e6a…

To cancel the try build, run the command @bors2 try cancel.

Pre-compute MIR CFG caches for borrowck and other analyses I was puzzled that #142390 introduces additional computations of CFG traversals: borrowck computes them, right? It turns out that borrowck clones the MIR body, so doesn't share its cache with other analyses. This PR: - forces the computation of all caches in `mir_promoted` query; - modifies region renumbering to avoid dropping that cache.

rust-bors · 2025-06-15T23:01:48Z

☀️ Try build successful (CI)
Build commit: 98e2e6a (98e2e6aea9abc7e12f76e27d72aced95f45b5260, parent: 586ad391f5ee4519acc7cae340e34673bae762b1)

rust-timer · 2025-06-16T00:32:57Z

Finished benchmarking commit (98e2e6a): comparison URL.

Overall result: ❌ regressions - 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)	1.8%	[1.0%, 2.6%]	4
Regressions ❌ (secondary)	1.2%	[0.6%, 1.6%]	6
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	1.8%	[1.0%, 2.6%]	4

Max RSS (memory usage)

Results (primary 0.1%, secondary -2.5%)

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

	mean	range	count
Regressions ❌ (primary)	3.1%	[0.5%, 6.5%]	3
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-1.4%	[-1.8%, -0.8%]	6
Improvements ✅ (secondary)	-2.5%	[-2.7%, -2.2%]	2
All ❌✅ (primary)	0.1%	[-1.8%, 6.5%]	9

Cycles

Results (secondary 1.2%)

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

	mean	range	count
Regressions ❌ (primary)	-	-	0
Regressions ❌ (secondary)	1.2%	[1.2%, 1.2%]	1
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-	-	0

Binary size

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

Bootstrap: 755.712s -> 754.846s (-0.11%)
Artifact size: 372.06 MiB -> 372.09 MiB (0.01%)

cjgillot · 2025-06-16T12:33:37Z

Rebased onto #142542
@bors2 try @rust-timer queue

rust-bors · 2025-06-16T12:33:42Z

⌛ Trying commit ba39fdf with merge 0e5f13e…

To cancel the try build, run the command @bors2 try cancel.

Pre-compute MIR CFG caches for borrowck and other analyses I was puzzled that #142390 introduces additional computations of CFG traversals: borrowck computes them, right? It turns out that borrowck clones the MIR body, so doesn't share its cache with other analyses. This PR: - forces the computation of all caches in `mir_promoted` query; - modifies region renumbering to avoid dropping that cache.

rust-bors · 2025-06-16T15:07:38Z

☀️ Try build successful (CI)
Build commit: 0e5f13e (0e5f13e67fc7c60a66efdb5b082d6f76b02f2fec, parent: 68ac5abb067806a88464ddbfbd3c7eec877b488d)

rust-timer · 2025-06-16T17:17:58Z

Finished benchmarking commit (0e5f13e): 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)	1.3%	[0.7%, 2.0%]	4
Regressions ❌ (secondary)	0.9%	[0.8%, 1.2%]	5
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-0.4%	[-0.4%, -0.4%]	1
All ❌✅ (primary)	1.3%	[0.7%, 2.0%]	4

Max RSS (memory usage)

Results (primary -0.7%, secondary -2.5%)

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

	mean	range	count
Regressions ❌ (primary)	0.9%	[0.6%, 1.1%]	2
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-1.2%	[-1.7%, -0.5%]	7
Improvements ✅ (secondary)	-2.5%	[-2.9%, -2.1%]	6
All ❌✅ (primary)	-0.7%	[-1.7%, 1.1%]	9

Cycles

Results (secondary 8.2%)

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

	mean	range	count
Regressions ❌ (primary)	-	-	0
Regressions ❌ (secondary)	8.2%	[8.2%, 8.2%]	1
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-	-	0

Binary size

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

Bootstrap: 757.272s -> 757.834s (0.07%)
Artifact size: 372.17 MiB -> 372.09 MiB (-0.02%)

fee1-dead · 2025-06-17T08:26:27Z

mir_borrowck still seems to be doing more work somehow

JohnCSimon · 2025-07-12T01:07:32Z

@cjgillot
ping from triage - can you post your status on this PR? There hasn't been an update in a month. Thanks!

cjgillot · 2025-07-12T16:34:34Z

@bors try @rust-timer queue

bors · 2025-07-12T16:36:48Z

⌛ Trying commit 184e17c with merge 5fb1b8a...

Pre-compute MIR CFG caches for borrowck and other analyses I was puzzled that #142390 introduces additional computations of CFG traversals: borrowck computes them, right? It turns out that borrowck clones the MIR body, so doesn't share its cache with other analyses. This PR: - forces the computation of all caches in `mir_promoted` query; - modifies region renumbering to avoid dropping that cache.

bors · 2025-07-12T18:51:28Z

☀️ Try build successful - checks-actions
Build commit: 5fb1b8a (5fb1b8ad555998c495db6e47c6e0109579c409a1)

rust-timer · 2025-07-12T20:21:46Z

Finished benchmarking commit (5fb1b8a): 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)	1.0%	[0.4%, 2.0%]	6
Regressions ❌ (secondary)	0.7%	[0.5%, 0.9%]	4
Improvements ✅ (primary)	-0.1%	[-0.2%, -0.1%]	7
Improvements ✅ (secondary)	-0.2%	[-0.5%, -0.0%]	13
All ❌✅ (primary)	0.4%	[-0.2%, 2.0%]	13

Max RSS (memory usage)

Results (primary -1.1%, secondary -2.7%)

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

	mean	range	count
Regressions ❌ (primary)	0.5%	[0.5%, 0.5%]	1
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-1.4%	[-2.3%, -1.0%]	5
Improvements ✅ (secondary)	-2.7%	[-5.3%, -1.4%]	6
All ❌✅ (primary)	-1.1%	[-2.3%, 0.5%]	6

Cycles

Results (primary -4.4%, secondary 1.8%)

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

	mean	range	count
Regressions ❌ (primary)	-	-	0
Regressions ❌ (secondary)	3.6%	[2.2%, 5.0%]	5
Improvements ✅ (primary)	-4.4%	[-4.4%, -4.4%]	1
Improvements ✅ (secondary)	-2.6%	[-3.0%, -2.2%]	2
All ❌✅ (primary)	-4.4%	[-4.4%, -4.4%]	1

Binary size

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

Bootstrap: 466.126s -> 465.176s (-0.20%)
Artifact size: 374.63 MiB -> 374.80 MiB (0.04%)

rustbot · 2025-08-16T16:43:20Z

This PR was rebased onto a different master commit! Check out the changes with our range-diff.

rustbot assigned fee1-dead Jun 15, 2025

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 Jun 15, 2025