Skip unused variables warning for unreachable code#149096

chenyukang · 2025-11-19T14:57:21Z

These warnings are not reported on stable branch, but are now reported on the beta.

I tried another solution to record whether a local is reachable in find_dead_assignments, but the code in this PR seems simpler.

r? @cjgillot

rustbot · 2025-11-19T14:57:24Z

Some changes occurred to MIR optimizations

cc @rust-lang/wg-mir-opt

compiler/rustc_mir_transform/src/liveness.rs

oli-obk · 2025-11-21T09:34:32Z

@bors try @rust-timer queue

…try> Skip unused variables warning for unreachable code

rust-bors · 2025-11-21T15:36:20Z

💥 Test timed out after 21600s

chenyukang · 2025-11-21T22:20:15Z

try again
@bors try @rust-timer queue

…try> Skip unused variables warning for unreachable code

rust-bors · 2025-11-22T00:36:49Z

☀️ Try build successful (CI)
Build commit: 3374816 (3374816c1a1db65919dbab38878ce39388385450, parent: e22dab387f6b4f6a87dfc54ac2f6013dddb41e68)

rust-timer · 2025-11-22T02:58:16Z

Finished benchmarking commit (3374816): 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
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-0.3%	[-0.5%, -0.2%]	3
All ❌✅ (primary)	-	-	0

Max RSS (memory usage)

Results (secondary 0.9%)

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)	0.9%	[0.9%, 0.9%]	1
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-	-	0

Cycles

Results (primary -2.3%)

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)	-2.3%	[-2.3%, -2.3%]	1
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-2.3%	[-2.3%, -2.3%]	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
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-0.1%	[-0.1%, -0.0%]	55
Improvements ✅ (secondary)	-0.1%	[-0.1%, -0.0%]	23
All ❌✅ (primary)	-0.1%	[-0.1%, -0.0%]	55

Bootstrap: 473.456s -> 471.878s (-0.33%)
Artifact size: 388.90 MiB -> 388.84 MiB (-0.01%)

oli-obk · 2025-11-22T11:04:02Z

r? @oli-obk

@bors r+

bors · 2025-11-22T11:04:05Z

📌 Commit 2c6b1d3 has been approved by oli-obk

It is now in the queue for this repository.

…li-obk Skip unused variables warning for unreachable code Fixes #148373 These warnings are not reported on stable branch, but are now reported on the beta. I tried another solution to record whether a `local` is reachable in `find_dead_assignments`, but the code in this PR seems simpler. r? `@cjgillot`

bors · 2025-11-22T12:56:35Z

⌛ Testing commit 2c6b1d3 with merge 64beea6...

rust-log-analyzer · 2025-11-22T14:52:11Z

The job x86_64-mingw-1 failed! Check out the build log: (web) (plain enhanced) (plain)

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


---- [codegen] tests\codegen-llvm\abi-main-signature-32bit-c-int.rs stdout ----
------rustc.exe stdout------------------------------

------rustc.exe stderr------------------------------

thread 'main' (7188) has overflowed its stack

------------------------------------------

error: compilation failed!
status: exit code: 0xc00000fd
command: PATH="D:\a\rust\rust\build\x86_64-pc-windows-gnu\stage2\bin;D:\a\rust\rust\build\x86_64-pc-windows-gnu\bootstrap-tools\x86_64-pc-windows-gnu\release\deps;D:\a\rust\rust\ninja;D:\a\rust\rust\mingw64\bin;C:\msys64\usr\bin;D:\a\rust\rust\sccache;C:\Program Files\MongoDB\Server\7.0\bin;C:\vcpkg;C:\tools\zstd;C:\hostedtoolcache\windows\stack\3.7.1\x64;C:\cabal\bin;C:\ghcup\bin;C:\mingw64\bin;C:\Program Files\dotnet;C:\Program Files\MySQL\MySQL Server 8.0\bin;C:\Program Files\R\R-4.5.2\bin\x64;C:\SeleniumWebDrivers\GeckoDriver;C:\SeleniumWebDrivers\EdgeDriver;C:\SeleniumWebDrivers\ChromeDriver;C:\Program Files (x86)\sbt\bin;C:\Program Files (x86)\GitHub CLI;C:\Program Files\Git\bin;C:\Program Files (x86)\pipx_bin;C:\npm\prefix;C:\hostedtoolcache\windows\go\1.24.9\x64\bin;C:\hostedtoolcache\windows\Python\3.9.13\x64\Scripts;C:\hostedtoolcache\windows\Python\3.9.13\x64;C:\hostedtoolcache\windows\Ruby\3.3.10\x64\bin;C:\Program Files\OpenSSL\bin;C:\tools\kotlinc\bin;C:\hostedtoolcache\windows\Java_Temurin-Hotspot_jdk\17.0.17-10\x64\bin;C:\Program Files\ImageMagick-7.1.2-Q16-HDRI;C:\Program Files\Microsoft SDKs\Azure\CLI2\wbin;C:\ProgramData\kind;C:\ProgramData\Chocolatey\bin;C:\Windows\system32;C:\Windows;C:\Windows\System32\Wbem;C:\Windows\System32\WindowsPowerShell\v1.0;C:\Windows\System32\OpenSSH;C:\Program Files\PowerShell\7;C:\Program Files\Microsoft\Web Platform Installer;C:\Program Files\Microsoft SQL Server\Client SDK\ODBC\170\Tools\Binn;C:\Program Files\Microsoft SQL Server\150\Tools\Binn;C:\Program Files\dotnet;C:\Program Files (x86)\Windows Kits\10\Windows Performance Toolkit;C:\Program Files (x86)\WiX Toolset v3.14\bin;C:\Program Files\Microsoft SQL Server\130\DTS\Binn;C:\Program Files\Microsoft SQL Server\140\DTS\Binn;C:\Program Files\Microsoft SQL Server\150\DTS\Binn;C:\Program Files\Microsoft SQL Server\160\DTS\Binn;C:\Program Files\Microsoft SQL Server\170\DTS\Binn;C:\ProgramData\chocolatey\lib\pulumi\tools\Pulumi\bin;C:\Program Files\CMake\bin;C:\Strawberry\c\bin;C:\Strawberry\perl\site\bin;C:\Strawberry\perl\bin;C:\ProgramData\chocolatey\lib\maven\apache-maven-3.9.11\bin;C:\Program Files\Microsoft Service Fabric\bin\Fabric\Fabric.Code;C:\Program Files\Microsoft SDKs\Service Fabric\Tools\ServiceFabricLocalClusterManager;C:\Program Files\nodejs;C:\Program Files\Git\cmd;C:\Program Files\Git\mingw64\bin;C:\Program Files\Git\usr\bin;C:\Program Files\GitHub CLI;C:\tools\php;C:\Program Files (x86)\sbt\bin;C:\Program Files\Amazon\AWSCLIV2;C:\Program Files\Amazon\SessionManagerPlugin\bin;C:\Program Files\Amazon\AWSSAMCLI\bin;C:\Program Files\Microsoft SQL Server\130\Tools\Binn;C:\Program Files\mongosh;C:\Program Files\LLVM\bin;C:\Program Files (x86)\LLVM\bin;C:\Users\runneradmin\.dotnet\tools;C:\Users\runneradmin\.cargo\bin;C:\Users\runneradmin\AppData\Local\Microsoft\WindowsApps" "D:\\a\\rust\\rust\\build\\x86_64-pc-windows-gnu\\stage2\\bin\\rustc.exe" "D:\\a\\rust\\rust\\tests\\codegen-llvm\\abi-main-signature-32bit-c-int.rs" "-Zthreads=1" "-Zsimulate-remapped-rust-src-base=/rustc/FAKE_PREFIX" "-Ztranslate-remapped-path-to-local-path=no" "-Z" "ignore-directory-in-diagnostics-source-blocks=C:\\Users\\runneradmin\\.cargo" "-Z" "ignore-directory-in-diagnostics-source-blocks=D:\\a\\rust\\rust\\vendor" "--sysroot" "D:\\a\\rust\\rust\\build\\x86_64-pc-windows-gnu\\stage2" "--target=x86_64-pc-windows-gnu" "--check-cfg" "cfg(test,FALSE)" "-O" "-Cdebug-assertions=no" "-Zcodegen-source-order" "--emit" "llvm-ir" "-C" "prefer-dynamic" "-o" "D:\\a\\rust\\rust\\build\\x86_64-pc-windows-gnu\\test\\codegen-llvm\\abi-main-signature-32bit-c-int\\abi-main-signature-32bit-c-int.ll" "-A" "internal_features" "-A" "unused_parens" "-A" "unused_braces" "-Crpath" "-Cdebuginfo=0"
stdout: none
--- stderr -------------------------------

thread 'main' (7188) has overflowed its stack
------------------------------------------
---

Some tests failed in compiletest suite=codegen-llvm mode=codegen host=x86_64-pc-windows-gnu target=x86_64-pc-windows-gnu
Bootstrap failed while executing `test --stage 2 --skip=compiler --skip=src`
Build completed unsuccessfully in 1:47:57
make: *** [Makefile:123: ci-mingw-x] Error 1
  local time: Sat Nov 22 14:51:55 CUT 2025
  network time: Sat, 22 Nov 2025 14:51:56 GMT
##[error]Process completed with exit code 2.
##[group]Run echo "disk usage:"
echo "disk usage:"

bors · 2025-11-22T14:52:56Z

💔 Test failed - checks-actions

chenyukang · 2025-11-23T00:49:35Z

not sure whether it is related to the change,
try again:

@bors retry jobs=x86_64-mingw-1

chenyukang · 2025-11-23T00:51:44Z

@bors try jobs=x86_64-mingw-1

…try> Skip unused variables warning for unreachable code try-job: x86_64-mingw-1

bors · 2025-11-23T04:14:42Z

⌛ Testing commit 2c6b1d3 with merge e0e204f...

rust-bors · 2025-11-23T04:15:39Z

💔 Test for d762293 failed: CI. Failed jobs:

try - x86_64-mingw-1 (web logs, extended logs)

bors · 2025-11-23T07:25:46Z

☀️ Test successful - checks-actions
Approved by: oli-obk
Pushing e0e204f to main...

github-actions · 2025-11-23T07:28:42Z

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 94b49fd (parent) -> e0e204f (this PR)

Test differences

Show 6 test diffs

Stage 1

[ui] tests/ui/lint/unused/unused-var-in-unreachable-code.rs: [missing] -> pass (J1)

Stage 2

[ui] tests/ui/lint/unused/unused-var-in-unreachable-code.rs: [missing] -> pass (J0)

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

Job group index

Test dashboard

Run

cargo run --manifest-path src/ci/citool/Cargo.toml -- \
    test-dashboard e0e204f3e97ad5f79524b9c259dc38df606ed82c --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

dist-various-1: 3730.9s -> 4675.0s (+25.3%)
i686-gnu-nopt-1: 8053.6s -> 6733.2s (-16.4%)
x86_64-gnu-tools: 3734.2s -> 3130.2s (-16.2%)
aarch64-gnu-debug: 4471.8s -> 3832.2s (-14.3%)
pr-check-1: 1969.9s -> 1695.7s (-13.9%)
x86_64-gnu-llvm-20: 2825.1s -> 2437.7s (-13.7%)
x86_64-rust-for-linux: 2978.3s -> 2619.3s (-12.1%)
x86_64-gnu-llvm-20-1: 3588.0s -> 3163.5s (-11.8%)
x86_64-gnu: 7174.0s -> 6361.5s (-11.3%)
dist-i586-gnu-i586-i686-musl: 5229.1s -> 4675.7s (-10.6%)

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 · 2025-11-23T08:46:19Z

Finished benchmarking commit (e0e204f): comparison URL.

Overall result: ❌✅ regressions and improvements - no action needed

@rustbot label: -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
Regressions ❌ (secondary)	0.6%	[0.6%, 0.6%]	1
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-0.3%	[-0.5%, -0.2%]	3
All ❌✅ (primary)	-	-	0

Max RSS (memory usage)

Results (primary 0.7%)

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

	mean	range	count
Regressions ❌ (primary)	0.7%	[0.7%, 0.7%]	1
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	0.7%	[0.7%, 0.7%]	1

Cycles

Results (secondary 1.9%)

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)	3.2%	[2.8%, 3.5%]	4
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-3.3%	[-3.3%, -3.3%]	1
All ❌✅ (primary)	-	-	0

Binary size

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

Bootstrap: 470.267s -> 468.131s (-0.45%)
Artifact size: 386.23 MiB -> 386.25 MiB (0.00%)

apiraino · 2025-11-27T15:14:53Z

Beta backport accepted as per compiler team on Zulip. A backport PR will be authored by the release team at the end of the current development cycle. Backport labels handled by them.

@rustbot label +beta-accepted

[beta] backports - rustdoc: Use configured target modifiers when collecting doctests #148068 - fix(rustdoc): Color doctest errors #148834 - Fix the issue of unused assignment from MIR liveness checking #149072 - Skip unused variables warning for unreachable code #149096 - In `BTreeMap::eq`, do not compare the elements if the sizes are different. #149125 - Handle cycles when checking impl candidates for `doc(hidden)` #149185 - Generalize branch references #148395 - only the commit updating CI scripts - Change default branch references #148564 r? cuviper

…8373, r=oli-obk Skip unused variables warning for unreachable code Fixes rust-lang#148373 These warnings are not reported on stable branch, but are now reported on the beta. I tried another solution to record whether a `local` is reachable in `find_dead_assignments`, but the code in this PR seems simpler. r? `@cjgillot`

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 Nov 19, 2025

rustbot assigned cjgillot Nov 19, 2025

Kivooeo reviewed Nov 19, 2025

View reviewed changes

compiler/rustc_mir_transform/src/liveness.rs Outdated Show resolved Hide resolved

Skip unused variables warning for unreachable code

2c6b1d3

chenyukang force-pushed the yukang-fix-unused-vars-148373 branch from 1f2c448 to 2c6b1d3 Compare November 21, 2025 00:49