Simplify the canonical enum clone branches to a copy statement

[dianqk]

I have overhauled MatchBranchSimplification in this PR. This pass is tested merge cases one by one, which is more readable and extensible.

This PR also merges 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)

[rust-timer]

Finished benchmarking commit (da8af3c): 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)	0.1%	[0.1%, 0.1%]	1
Improvements ✅ (primary)	-0.9%	[-2.5%, -0.1%]	6
Improvements ✅ (secondary)	-0.2%	[-0.2%, -0.1%]	6
All ❌✅ (primary)	-0.7%	[-2.5%, 0.7%]	7

Max RSS (memory usage)

Results (primary 3.0%)

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

	mean	range	count
Regressions ❌ (primary)	3.0%	[2.1%, 4.0%]	2
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	3.0%	[2.1%, 4.0%]	2

Cycles

Results (secondary -2.1%)

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)	-	-	0
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-2.1%	[-2.1%, -2.1%]	1
All ❌✅ (primary)	-	-	0

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%	[0.1%, 0.2%]	2
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-0.1%	[-0.5%, -0.0%]	17
Improvements ✅ (secondary)	-0.1%	[-0.1%, -0.0%]	43
All ❌✅ (primary)	-0.1%	[-0.5%, 0.2%]	19

Bootstrap: 475.08s -> 474.068s (-0.21%)
Artifact size: 390.51 MiB -> 390.49 MiB (-0.00%)

[rustbot]

Some changes occurred to MIR optimizations

cc @rust-lang/wg-mir-opt

[rustbot]

r? @madsmtm

rustbot has assigned @madsmtm.
They will have a look at your PR within the next two weeks and either review your PR or reassign to another reviewer.

Use r? to explicitly pick a reviewer

[dianqk]

r? cjgillot

[madsmtm]

r? cjgillot

Yeah, that's probably a better choice, I'm not that familiar with MIR.