Do not unify borrowed locals in CopyProp.

[cjgillot]

Instead of trying yet another scheme to unify borrowed locals in CopyProp, let's just stop trying. We had already enough miscompilations because of this.

I'm convinced it's possible to have both unification of some borrowed locals and soundness, but I don't have a simple and convincing formulation yet.

Fixes #143491

[rustbot]

r? @davidtwco

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[rustbot]

Some changes occurred to MIR optimizations

cc @rust-lang/wg-mir-opt

[compiler-errors]

Thanks

@bors r+ rollup=never p=1

[bors]

📌 Commit da431ec has been approved by compiler-errors

It is now in the queue for this repository.

[compiler-errors]

@bors r-

r=me after fixing test

[tmiasko]

@bors r+

[bors]

📌 Commit bab9c75 has been approved by tmiasko

It is now in the queue for this repository.

[bors]

⌛ Testing commit bab9c75 with merge 89486a4...

[bors]

💔 Test failed - checks-actions

[tmiasko]

@bors r+

[bors]

📌 Commit b1fdb4b has been approved by tmiasko

It is now in the queue for this repository.

[bors]

⌛ Testing commit b1fdb4b with merge a84ab0c...

[bors]

☀️ Test successful - checks-actions
Approved by: tmiasko
Pushing a84ab0c to master...

[github-actions]

What is this?

This is an experimental post-merge analysis report that shows differences in test outcomes between the merged PR and its parent PR.

Comparing de031bb (parent) -> a84ab0c (this PR)

Test differences

Show 4 test diffs

4 doctest diffs were found. These are ignored, as they are noisy.

Test dashboard

Run

cargo run --manifest-path src/ci/citool/Cargo.toml -- \
    test-dashboard a84ab0ce6c4557a2f01a3a6c3fdb0f92098db78d --output-dir test-dashboard

And then open test-dashboard/index.html in your browser to see an overview of all executed tests.

Job duration changes

1. x86_64-rust-for-linux: 3077.8s -> 2483.0s (-19.3%)
2. x86_64-gnu-tools: 3953.6s -> 3292.8s (-16.7%)
3. pr-check-1: 1869.9s -> 1584.9s (-15.2%)
4. dist-apple-various: 7478.4s -> 6340.5s (-15.2%)
5. aarch64-gnu-debug: 4226.4s -> 3663.6s (-13.3%)
6. x86_64-apple-2: 4378.7s -> 3891.8s (-11.1%)
7. x86_64-gnu-llvm-20-1: 3632.2s -> 3293.3s (-9.3%)
8. i686-gnu-nopt-1: 7948.8s -> 7233.7s (-9.0%)
9. i686-gnu-2: 6099.6s -> 5565.3s (-8.8%)
10. x86_64-gnu-llvm-19-1: 3654.7s -> 3338.0s (-8.7%)

How to interpret the job duration changes?

Job durations can vary a lot, based on the actual runner instance
that executed the job, system noise, invalidated caches, etc. The table above is provided
mostly for t-infra members, for simpler debugging of potential CI slow-downs.

[rust-timer]

Finished benchmarking commit (a84ab0c): comparison URL.

Overall result: ❌ regressions - please read the text below

Our benchmarks found a performance regression caused by this PR.
This might be an actual regression, but it can also be just noise.

Next Steps:

• If the regression was expected or you think it can be justified,
  please write a comment with sufficient written justification, and add
  @rustbot label: +perf-regression-triaged to it, to mark the regression as triaged.
• If you think that you know of a way to resolve the regression, try to create
  a new PR with a fix for the regression.
• If you do not understand the regression or you think that it is just noise,
  you can ask the @rust-lang/wg-compiler-performance working group for help (members of this group
  were already notified of this PR).

@rustbot label: +perf-regression
cc @rust-lang/wg-compiler-performance

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)	0.2%	[0.1%, 0.3%]	21
Regressions ❌ (secondary)	0.4%	[0.1%, 1.1%]	38
Improvements ✅ (primary)	-0.4%	[-0.4%, -0.4%]	2
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	0.1%	[-0.4%, 0.3%]	23

Max RSS (memory usage)

Results (primary -2.6%)

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

	mean	range	count
Regressions ❌ (primary)	2.1%	[2.1%, 2.1%]	1
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-3.8%	[-5.6%, -2.5%]	4
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-2.6%	[-5.6%, 2.1%]	5

Cycles

Results (primary 2.4%)

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

	mean	range	count
Regressions ❌ (primary)	2.4%	[2.4%, 2.4%]	1
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	2.4%	[2.4%, 2.4%]	1

Binary size

Results (primary 0.0%, 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)	0.1%	[0.0%, 0.3%]	30
Regressions ❌ (secondary)	0.1%	[0.0%, 0.6%]	26
Improvements ✅ (primary)	-0.3%	[-1.0%, -0.0%]	9
Improvements ✅ (secondary)	-0.1%	[-0.3%, -0.0%]	5
All ❌✅ (primary)	0.0%	[-1.0%, 0.3%]	39

Bootstrap: 460.528s -> 464.608s (0.89%)
Artifact size: 372.13 MiB -> 372.10 MiB (-0.01%)

[panstromek]

perf triage:

Are these regressions expected/warranted? IIUC this disables some parts of the optimization to fix soundness, so some regressions might be expected.