Replace switch to unreachable by assume statements

[cjgillot]

UnreachablePropagation currently keeps some switch terminators alive in order to ensure codegen can infer the inequalities on the discriminants.

This PR proposes to encode those inequalities as Assume statements.

This allows to simplify MIR further by removing some useless terminators.

[rustbot]

r? @wesleywiser

(rustbot has picked a reviewer for you, use r? to override)

[rustbot]

Some changes occurred to MIR optimizations

cc @rust-lang/wg-mir-opt

[cjgillot]

@bors try @rust-timer queue

[bors]

⌛ Trying commit 0657bc785d7ffb2c86cf1fce7f7cc0744d5e52ae with merge ad0888358a489103ed6806cffede10c65252400d...

[bors]

☀️ Try build successful - checks-actions
Build commit: ad0888358a489103ed6806cffede10c65252400d (ad0888358a489103ed6806cffede10c65252400d)

[rust-timer]

Finished benchmarking commit (ad0888358a489103ed6806cffede10c65252400d): 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)	0.4%	[0.4%, 0.4%]	1
Regressions ❌ (secondary)	0.3%	[0.3%, 0.3%]	1
Improvements ✅ (primary)	-0.4%	[-0.5%, -0.4%]	2
Improvements ✅ (secondary)	-0.4%	[-0.4%, -0.4%]	2
All ❌✅ (primary)	-0.2%	[-0.5%, 0.4%]	3

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)	4.2%	[0.6%, 10.2%]	6
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-2.6%	[-2.7%, -2.5%]	2
All ❌✅ (primary)	4.2%	[0.6%, 10.2%]	6

Cycles

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

Binary size

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)	0.0%	[0.0%, 0.1%]	5
Regressions ❌ (secondary)	0.1%	[0.1%, 0.1%]	3
Improvements ✅ (primary)	-0.1%	[-1.0%, -0.0%]	44
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-0.1%	[-1.0%, 0.1%]	49

Bootstrap: 651.047s -> 650.252s (-0.12%)

[apiraino]

@cjgillot a comment on the last perf run? Apart from that this seems ready for review, thanks!

@rustbot ready

[cjgillot]

Perf : small improvements and regressions balance out.

[apiraino]

r? compiler

[apiraino]

r? compiler

[petrochenkov]

r? compiler

[bors]

☔ The latest upstream changes (presumably #116569) made this pull request unmergeable. Please resolve the merge conflicts.

[apiraino]

This PR has received 2 r+ (here and here). Can it be merged or is there more work to do (or comments to be addressed)?

[cjgillot]

The tests failed repeatedly. At this point, I have not found a cause, but I cannot rule out this PR causes them.

[cjgillot]

Rebased. Let's see if the failure is gone.
@bors r=nikic

[bors]

📌 Commit ae2e211 has been approved by nikic

It is now in the queue for this repository.

[bors]

⌛ Testing commit ae2e211 with merge 98f5ebb...

[bors]

☀️ Test successful - checks-actions
Approved by: nikic
Pushing 98f5ebb to master...

[rust-timer]

Finished benchmarking commit (98f5ebb): comparison URL.

Overall result: no relevant changes - no action needed

@rustbot label: -perf-regression

Instruction count

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

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)	4.0%	[2.5%, 5.6%]	4
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-1.7%	[-2.8%, -0.1%]	5
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	0.8%	[-2.8%, 5.6%]	9

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)	-	-	0
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-6.8%	[-6.8%, -6.8%]	1
All ❌✅ (primary)	-	-	0

Binary size

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)	0.0%	[0.0%, 0.1%]	8
Regressions ❌ (secondary)	0.1%	[0.1%, 0.1%]	3
Improvements ✅ (primary)	-0.1%	[-0.6%, -0.0%]	39
Improvements ✅ (secondary)	-0.0%	[-0.0%, -0.0%]	1
All ❌✅ (primary)	-0.1%	[-0.6%, 0.1%]	47

Bootstrap: 638.855s -> 636.96s (-0.30%)
Artifact size: 304.47 MiB -> 304.45 MiB (-0.01%)