Always permit ConstProp to exploit arithmetic identities

[saethlin]

Fixes #72751

Initially, I thought I would need to enable operand propagation then do something else, but actually #74491 already has the fix for the issue in question! It looks like this optimization was put under MIR opt level 3 due to possible soundness/stability implications, then demoted further to MIR opt level 4 when MIR opt level 2 became associated with --release.

Perhaps in the past we were doing CTFE on optimized MIR? We aren't anymore, so this optimization has no stability implications.

r? @oli-obk

[saethlin]

@bors try @rust-timer queue

[bors]

⌛ Trying commit 9d69572fb3d2e01a3416eda9c100ee8214f2bb7d with merge c4c846ffd62c360cb758c2a53e7be1d294fe4aea...

[bors]

☀️ Try build successful - checks-actions
Build commit: c4c846ffd62c360cb758c2a53e7be1d294fe4aea (c4c846ffd62c360cb758c2a53e7be1d294fe4aea)

[rust-timer]

Finished benchmarking commit (c4c846ffd62c360cb758c2a53e7be1d294fe4aea): 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%	[0.2%, 0.9%]	19
Regressions ❌ (secondary)	0.4%	[0.3%, 0.6%]	9
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-1.3%	[-1.3%, -1.3%]	2
All ❌✅ (primary)	0.5%	[0.2%, 0.9%]	19

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)	5.9%	[3.0%, 9.8%]	5
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-2.2%	[-2.2%, -2.2%]	1
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	4.6%	[-2.2%, 9.8%]	6

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)	1.9%	[1.9%, 1.9%]	1
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-1.6%	[-1.8%, -1.3%]	3
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-0.7%	[-1.8%, 1.9%]	4

[saethlin]

@bors try @rust-timer queue

[bors]

⌛ Trying commit e25d9701adb52d554c73beae6c9d9efc06b006f8 with merge 8ba671ff5e120f17892e0c8125ad1e347076093a...

[bors]

☀️ Try build successful - checks-actions
Build commit: 8ba671ff5e120f17892e0c8125ad1e347076093a (8ba671ff5e120f17892e0c8125ad1e347076093a)

[rust-timer]

Finished benchmarking commit (8ba671ff5e120f17892e0c8125ad1e347076093a): comparison URL.

Overall result: ❌ regressions - 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 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%	[0.5%, 0.5%]	1
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	0.5%	[0.5%, 0.5%]	1

Max RSS (memory usage)

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

Cycles

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

[rustbot]

Some changes occurred to MIR optimizations

cc @rust-lang/wg-mir-opt

[oli-obk]

@bors r+

[bors]

📌 Commit 82f0973 has been approved by oli-obk

It is now in the queue for this repository.

[bors]

⌛ Testing commit 82f0973 with merge 89e0576...

[bors]

☀️ Test successful - checks-actions
Approved by: oli-obk
Pushing 89e0576 to master...

[rust-timer]

Finished benchmarking commit (89e0576): comparison URL.

Overall result: ❌✅ regressions and improvements - no action needed

@rustbot label: -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
Regressions ❌ (secondary)	0.8%	[0.7%, 0.8%]	6
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-0.7%	[-0.7%, -0.7%]	1
All ❌✅ (primary)	-	-	0

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)	2.9%	[2.9%, 2.9%]	1
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	2.9%	[2.9%, 2.9%]	1

Cycles

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