Simplify the canonical enum clone branches to a copy statement

[dianqk]

I have overhauled MatchBranchSimplification in this PR. This pass tries to unify statements one by one, which is more readable and extensible.

This PR also unifies the following pattern that is mostly generated by GVN into one basic block that contains the copy statement:

match a {
    Foo::A(_) => *a,
    Foo::B => Foo::B
}

Fixes #128081.

[dianqk]

@bors try @rust-timer queue

[rust-bors]

💔 Test for b4269e3 failed: CI. Failed jobs:

• try - dist-x86_64-linux (web logs, extended logs)

[dianqk]

@bors try @rust-timer queue

[rust-bors]

☀️ Try build successful (CI)
Build commit: 673e3f6 (673e3f61f8b218d304147e821d485edf0ebf3b09, parent: 6501e64fcb02d22b49d6e59d10a7692ec8095619)

[rust-timer]

Finished benchmarking commit (673e3f6): 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)	0.7%	[0.7%, 0.7%]	1
Regressions ❌ (secondary)	0.3%	[0.3%, 0.4%]	6
Improvements ✅ (primary)	-1.0%	[-2.4%, -0.1%]	6
Improvements ✅ (secondary)	-0.2%	[-1.3%, -0.1%]	17
All ❌✅ (primary)	-0.8%	[-2.4%, 0.7%]	7

Max RSS (memory usage)

Results (primary 2.8%)

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

	mean	range	count
Regressions ❌ (primary)	2.8%	[1.9%, 4.3%]	3
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	2.8%	[1.9%, 4.3%]	3

Cycles

Results (primary -3.4%, secondary -2.0%)

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)	2.5%	[2.5%, 2.5%]	1
Improvements ✅ (primary)	-3.4%	[-3.4%, -3.4%]	1
Improvements ✅ (secondary)	-2.7%	[-4.5%, -2.1%]	6
All ❌✅ (primary)	-3.4%	[-3.4%, -3.4%]	1

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)	0.1%	[0.0%, 0.2%]	3
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-0.1%	[-0.4%, -0.0%]	20
Improvements ✅ (secondary)	-0.1%	[-0.1%, -0.0%]	41
All ❌✅ (primary)	-0.1%	[-0.4%, 0.2%]	23

Bootstrap: 476.496s -> 474.095s (-0.50%)
Artifact size: 390.49 MiB -> 390.42 MiB (-0.02%)

[dianqk]

@bors try @rust-timer queue

[rust-bors]

☀️ Try build successful (CI)
Build commit: da8af3c (da8af3c91a895fd9646d0e6ef1477767ea0b6076, parent: e5177985a5493c783d6ba20960d2723d9d2e9214)

[rustbot]

This PR was rebased onto a different main commit. Here's a range-diff highlighting what actually changed.

Rebasing is a normal part of keeping PRs up to date, so no action is needed—this note is just to help reviewers.

[dianqk]

@rustbot author

[dianqk]

@bors try @rust-timer queue

[rust-bors]

☀️ Try build successful (CI)
Build commit: 8e941f2 (8e941f231426d82f25aa9c9df9407de6e7e936e0, parent: d29e4783dff30f9526eeba3929ebfe86c00c9dad)

[rust-timer]

Finished benchmarking commit (8e941f2): comparison URL.

Overall result: ✅ improvements - no action needed

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.

@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)	0.7%	[0.7%, 0.7%]	1
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-1.0%	[-2.5%, -0.2%]	6
Improvements ✅ (secondary)	-0.2%	[-0.4%, -0.1%]	6
All ❌✅ (primary)	-0.8%	[-2.5%, 0.7%]	7

Max RSS (memory usage)

Results (primary 4.3%, secondary 1.0%)

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

	mean	range	count
Regressions ❌ (primary)	5.5%	[3.2%, 8.2%]	5
Regressions ❌ (secondary)	4.8%	[4.8%, 4.8%]	1
Improvements ✅ (primary)	-1.7%	[-1.7%, -1.7%]	1
Improvements ✅ (secondary)	-2.9%	[-2.9%, -2.9%]	1
All ❌✅ (primary)	4.3%	[-1.7%, 8.2%]	6

Cycles

Results (primary 2.0%, secondary 5.7%)

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

	mean	range	count
Regressions ❌ (primary)	2.0%	[2.0%, 2.0%]	1
Regressions ❌ (secondary)	5.7%	[5.7%, 5.7%]	1
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	2.0%	[2.0%, 2.0%]	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)	0.2%	[0.0%, 0.3%]	10
Regressions ❌ (secondary)	0.1%	[0.1%, 0.1%]	1
Improvements ✅ (primary)	-0.2%	[-1.1%, -0.0%]	14
Improvements ✅ (secondary)	-0.1%	[-0.2%, -0.0%]	9
All ❌✅ (primary)	-0.0%	[-1.1%, 0.3%]	24

Bootstrap: 472.528s -> 473.524s (0.21%)
Artifact size: 383.22 MiB -> 383.24 MiB (0.00%)

[dianqk]

@bors try parent=d29e4783dff30f9526eeba3929ebfe86c00c9dad @rust-timer queue

[rust-log-analyzer]

The job x86_64-gnu-tools failed! Check out the build log: (web) (plain enhanced) (plain)

Click to see the possible cause of the failure (guessed by this bot)

##[group]Runner Image Provisioner
Hosted Compute Agent
Version: 20260115.477
Commit: 4b342d620503cbe250a3154040964899ea7c9b00
Build Date: 2026-01-15T22:32:41Z
Worker ID: {fe0fca4a-3f86-4bd5-82a8-09f5f66721d5}
Azure Region: westcentralus
##[endgroup]
##[group]Operating System
Ubuntu
24.04.3
LTS
---
REPOSITORY                                   TAG       IMAGE ID       CREATED      SIZE
ghcr.io/dependabot/dependabot-updater-core   latest    354d02aa29ac   3 days ago   783MB
=> Removing docker images...
Deleted Images:
untagged: ghcr.io/dependabot/dependabot-updater-core:latest
untagged: ghcr.io/dependabot/dependabot-updater-core@sha256:596da3f22bcbdff2c96fd7126001278022c834c1621c5efa2ad1a7794590636c
deleted: sha256:354d02aa29acf525570c732b6e006ecf138de6d63ca525d552eb4b24880ddc6c
deleted: sha256:8b7af0e426bc2cbeeacfd96b8354d3b80016991520977197e62090e47abaede8
deleted: sha256:cadf11ef1de7fdd5eab563757942353684047f09b212dc99d6ed48e8acf34d62
deleted: sha256:569b0caf9d5285db44ccd2629a3470139eea755be423a33a54d8a24cb3926bfa
deleted: sha256:f9dc5feb048d8f9fd43137e3998f59e9acfbd76c47a4e14984d109654119e282
---
..............................................     (146/146)

======== tests/rustdoc-gui/globals.goml ========

[ERROR] line 14: The following errors happened: [Property named `"searchIndex"` doesn't exist]: for command `assert-window-property-false: {"searchIndex": null}`
    at <file:///checkout/obj/build/x86_64-unknown-linux-gnu/test/rustdoc-gui/doc/test_docs/index.html?search=Foo>

======== tests/rustdoc-gui/search-result-display.goml ========

[WARNING] line 39: Delta is 0 for "x", maybe try to use `compare-elements-position` instead?

[rust-bors]

☀️ Try build successful (CI)
Build commit: 4e6c6dc (4e6c6dc83bfbd42901372bdf346032a61b25c2f8, parent: d29e4783dff30f9526eeba3929ebfe86c00c9dad)

[rust-timer]

Finished benchmarking commit (4e6c6dc): 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)	0.7%	[0.7%, 0.7%]	1
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-1.1%	[-2.4%, -0.2%]	4
Improvements ✅ (secondary)	-0.2%	[-0.2%, -0.1%]	5
All ❌✅ (primary)	-0.7%	[-2.4%, 0.7%]	5

Max RSS (memory usage)

Results (primary 1.7%, secondary 0.0%)

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

	mean	range	count
Regressions ❌ (primary)	6.5%	[2.7%, 13.9%]	3
Regressions ❌ (secondary)	4.3%	[4.3%, 4.3%]	1
Improvements ✅ (primary)	-3.1%	[-3.8%, -2.0%]	3
Improvements ✅ (secondary)	-2.2%	[-2.9%, -1.4%]	2
All ❌✅ (primary)	1.7%	[-3.8%, 13.9%]	6

Cycles

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

Binary size

Results (primary -0.1%, secondary 0.0%)

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%, 0.2%]	3
Regressions ❌ (secondary)	0.1%	[0.0%, 0.1%]	5
Improvements ✅ (primary)	-0.1%	[-0.5%, -0.0%]	15
Improvements ✅ (secondary)	-0.0%	[-0.0%, -0.0%]	6
All ❌✅ (primary)	-0.1%	[-0.5%, 0.2%]	18

Bootstrap: 472.528s -> 472.063s (-0.10%)
Artifact size: 383.22 MiB -> 383.22 MiB (-0.00%)