MIR: Stop needing an explicit BB for `otherwise:unreachable` #124188

scottmcm · 2024-04-20T04:21:19Z

So many places to update :D

Zulip conversation: https://rust-lang.zulipchat.com/#narrow/stream/189540-t-compiler.2Fwg-mir-opt/topic/Pondering.20the.20SwitchInt.20.26.20unreachable/near/432988457

For this PR I tried to keep things doing essentially the same thing as before. No new passes to try to use it more, no change to MIR building for exhaustive matches, etc.

That said, UnreachableProp still picks it up, and thus there's still a bunch of otherwise arms removed and unreachable blocks that no longer show.

r? ghost
cc @JakobDegen @saethlin @cuviper @wesleywiser

scottmcm · 2024-04-20T04:25:40Z

compiler/rustc_mir_transform/src/unreachable_prop.rs

-
-    let terminator = match (num_targets, otherwise_unreachable) {
-        // If all targets are unreachable, we can be unreachable as well.
-        (1, true) => TerminatorKind::Unreachable,


This whole section I couldn't find a simple update, so please check the new logic carefully.

scottmcm · 2024-04-20T05:59:25Z

@bors try @rust-timer queue

…ble, r=<try> MIR: Stop needing an explicit BB for `otherwise:unreachable` So many places to update :D Zulip conversation: <https://rust-lang.zulipchat.com/#narrow/stream/189540-t-compiler.2Fwg-mir-opt/topic/Pondering.20the.20SwitchInt.20.26.20unreachable/near/432988457> For this PR I tried to keep things doing essentially the same thing as before. No new passes to try to use it more, no change to MIR building for exhaustive matches, etc. That said, `UnreachableProp` still picks it up, and thus there's still a bunch of `otherwise` arms removed and `unreachable` blocks that no longer show. r? ghost cc `@JakobDegen` `@saethlin` `@cuviper` `@wesleywiser`

bors · 2024-04-20T06:00:35Z

⌛ Trying commit acc7f0d with merge d8f8976...

bors · 2024-04-20T07:34:26Z

☀️ Try build successful - checks-actions
Build commit: d8f8976 (d8f8976ab3cbf35ab4e4d38ae51cee307c3a2f52)

rust-timer · 2024-04-20T09:33:35Z

Finished benchmarking commit (d8f8976): 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)	0.6%	[0.2%, 1.0%]	6
Regressions ❌ (secondary)	2.7%	[1.7%, 5.2%]	8
Improvements ✅ (primary)	-0.8%	[-0.8%, -0.8%]	1
Improvements ✅ (secondary)	-0.9%	[-1.3%, -0.7%]	3
All ❌✅ (primary)	0.4%	[-0.8%, 1.0%]	7

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)	3.0%	[0.1%, 6.0%]	2
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-2.2%	[-3.7%, -0.8%]	3
Improvements ✅ (secondary)	-2.7%	[-2.7%, -2.7%]	1
All ❌✅ (primary)	-0.1%	[-3.7%, 6.0%]	5

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)	2.4%	[1.0%, 3.1%]	11
Regressions ❌ (secondary)	3.9%	[0.9%, 7.0%]	5
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-2.0%	[-2.0%, -2.0%]	1
All ❌✅ (primary)	2.4%	[1.0%, 3.1%]	11

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)	0.4%	[0.1%, 1.9%]	57
Regressions ❌ (secondary)	1.6%	[0.1%, 5.3%]	15
Improvements ✅ (primary)	-0.2%	[-1.2%, -0.0%]	22
Improvements ✅ (secondary)	-0.2%	[-0.4%, -0.0%]	8
All ❌✅ (primary)	0.2%	[-1.2%, 1.9%]	79

Bootstrap: 670.134s -> 670.046s (-0.01%)
Artifact size: 315.30 MiB -> 315.35 MiB (0.02%)

bors · 2024-05-24T23:58:03Z

☔ The latest upstream changes (presumably #125521) made this pull request unmergeable. Please resolve the merge conflicts.

Dylan-DPC · 2024-10-23T07:48:27Z

@scottmcm any updates on this? thanks

So many places to update :D For this PR I tried to keep things doing essentially the same thing as before. No new passes to try to use it more, no change to MIR building for exhaustive matches, etc. That said, `UnreachableProp` still picks it up, and thus there's still a bunch of `otherwise` arms removed and `unreachable` blocks that no longer show.

scottmcm · 2025-01-07T02:06:54Z

@bors try @rust-timer queue

…ble, r=<try> MIR: Stop needing an explicit BB for `otherwise:unreachable` So many places to update :D Zulip conversation: <https://rust-lang.zulipchat.com/#narrow/stream/189540-t-compiler.2Fwg-mir-opt/topic/Pondering.20the.20SwitchInt.20.26.20unreachable/near/432988457> For this PR I tried to keep things doing essentially the same thing as before. No new passes to try to use it more, no change to MIR building for exhaustive matches, etc. That said, `UnreachableProp` still picks it up, and thus there's still a bunch of `otherwise` arms removed and `unreachable` blocks that no longer show. r? ghost cc `@JakobDegen` `@saethlin` `@cuviper` `@wesleywiser`

bors · 2025-01-07T02:08:06Z

⌛ Trying commit f6d0f73 with merge 5ed2b42...

bors · 2025-01-07T03:52:24Z

☀️ Try build successful - checks-actions
Build commit: 5ed2b42 (5ed2b4240c073e252a4ea1aed240628cbb282f5e)

rust-timer · 2025-01-07T06:12:21Z

Finished benchmarking commit (5ed2b42): comparison URL.

Overall result: ❌✅ regressions and improvements - please read the text below

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 the most reliable metric that we have; it was used to determine the overall result at the top of this comment. However, even this metric can sometimes exhibit noise.

	mean	range	count
Regressions ❌ (primary)	0.6%	[0.4%, 0.7%]	3
Regressions ❌ (secondary)	0.6%	[0.2%, 1.0%]	10
Improvements ✅ (primary)	-0.2%	[-0.2%, -0.2%]	1
Improvements ✅ (secondary)	-0.3%	[-0.3%, -0.2%]	5
All ❌✅ (primary)	0.4%	[-0.2%, 0.7%]	4

Max RSS (memory usage)

Results (primary 1.1%, secondary -0.2%)

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)	4.7%	[1.3%, 7.8%]	6
Regressions ❌ (secondary)	2.2%	[2.0%, 2.7%]	3
Improvements ✅ (primary)	-4.4%	[-5.8%, -2.6%]	4
Improvements ✅ (secondary)	-2.6%	[-2.8%, -2.3%]	3
All ❌✅ (primary)	1.1%	[-5.8%, 7.8%]	10

Cycles

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

Binary size

Results (primary -0.0%, secondary 0.4%)

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)	0.2%	[0.0%, 0.9%]	16
Regressions ❌ (secondary)	3.3%	[0.0%, 6.5%]	2
Improvements ✅ (primary)	-0.1%	[-0.5%, -0.0%]	33
Improvements ✅ (secondary)	-0.2%	[-0.5%, -0.0%]	11
All ❌✅ (primary)	-0.0%	[-0.5%, 0.9%]	49

Bootstrap: 763.24s -> 762.548s (-0.09%)
Artifact size: 325.59 MiB -> 324.97 MiB (-0.19%)

rustbot added S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. T-compiler Relevant to the compiler team, which will review and decide on the PR/issue. labels Apr 20, 2024

scottmcm commented Apr 20, 2024

View reviewed changes