Perform unused assignment and unused variables lints on MIR.

[cjgillot]

Rebase of #101500

Fixes #51003.

The first commit moves detection of uninhabited types from the current liveness pass to MIR building.

In order to keep the same level of diagnostics, I had to instrument MIR a little more:

• keep for which original local a guard local is created;
• store in the VarBindingForm the list of introducer places and whether this was a shorthand pattern.

I am not very proud of the handling of self-assignments. The proposed scheme is in two parts: first detect probable self-assignments, by pattern matching on MIR, and second treat them specially during dataflow analysis. I welcome ideas.

Please review carefully the changes in tests. There are many small changes to behaviour, and I'm not sure all of them are desirable.

[rustbot]

r? @wesleywiser

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[rustbot]

Some changes occurred in src/tools/clippy

cc @rust-lang/clippy

rust-analyzer is developed in its own repository. If possible, consider making this change to rust-lang/rust-analyzer instead.

cc @rust-lang/rust-analyzer

Some changes occurred in match lowering

cc @Nadrieril

Some changes occurred in match checking

cc @Nadrieril

Some changes occurred to MIR optimizations

cc @rust-lang/wg-mir-opt

[cjgillot]

@bors2 try @rust-timer queue

[rust-bors]

⌛ Trying commit 1d8df21 with merge 50ba7f2…

To cancel the try build, run the command @bors2 try cancel.

[bors]

⌛ Trying commit 1d8df21 with merge b0d7157...

[rust-bors]

☀️ Try build successful (CI)
Build commit: 50ba7f2 (50ba7f2d41092ac03e7b2d705a93e2e3e56bbf24, parent: 573a01569000d395498a5f98f916d6e5305ac81a)

[bors]

☀️ Try build successful - checks-actions
Build commit: b0d7157 (b0d7157996aa3b283f7f26ec09fc81c1612b5fce)

[rust-timer]

Finished benchmarking commit (50ba7f2): 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)	0.6%	[0.2%, 1.4%]	65
Regressions ❌ (secondary)	0.7%	[0.2%, 2.8%]	103
Improvements ✅ (primary)	-0.5%	[-0.6%, -0.5%]	2
Improvements ✅ (secondary)	-0.4%	[-0.7%, -0.3%]	22
All ❌✅ (primary)	0.6%	[-0.6%, 1.4%]	67

Max RSS (memory usage)

Results (primary 0.8%, secondary 0.2%)

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

	mean	range	count
Regressions ❌ (primary)	1.6%	[1.0%, 2.9%]	12
Regressions ❌ (secondary)	2.5%	[0.7%, 9.0%]	14
Improvements ✅ (primary)	-4.2%	[-7.0%, -1.4%]	2
Improvements ✅ (secondary)	-6.2%	[-10.9%, -2.3%]	5
All ❌✅ (primary)	0.8%	[-7.0%, 2.9%]	14

Cycles

Results (primary 1.3%, secondary 3.2%)

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

	mean	range	count
Regressions ❌ (primary)	1.3%	[0.9%, 1.7%]	14
Regressions ❌ (secondary)	3.2%	[2.4%, 4.4%]	11
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	1.3%	[0.9%, 1.7%]	14

Binary size

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

Bootstrap: 754.801s -> 755.907s (0.15%)
Artifact size: 372.21 MiB -> 372.18 MiB (-0.01%)

[davidtwco]

@bors r+

[bors]

📌 Commit 864a46e has been approved by davidtwco

It is now in the queue for this repository.

[bors]

⌛ Testing commit 864a46e with merge 13e4f0a...

[rust-log-analyzer]

The job dist-powerpc64-linux failed! Check out the build log: (web) (plain enhanced) (plain)

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

[RUSTC-TIMING] hashbrown test:false 1.244
   Compiling miniz_oxide v0.8.9
[RUSTC-TIMING] alloc test:false 5.853
[RUSTC-TIMING] miniz_oxide test:false 0.566
##[error]The runner has received a shutdown signal. This can happen when the runner service is stopped, or a manually started runner is canceled.

[bors]

💔 Test failed - checks-actions

[cjgillot]

@bors retry

[bors]

⌛ Testing commit 864a46e with merge b87a3a6...

[bors]

💔 Test failed - checks-actions

[rust-log-analyzer]

A job failed! Check out the build log: (web) (plain enhanced) (plain)

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

#1 ERROR: Error response from daemon: Head "https://ghcr.io/v2/rust-lang/buildkit/manifests/buildx-stable-1": dial tcp 140.82.116.34:443: i/o timeout
------
 > [internal] booting buildkit:
------
ERROR: failed to build: Error response from daemon: Head "https://ghcr.io/v2/rust-lang/buildkit/manifests/buildx-stable-1": dial tcp 140.82.116.34:443: i/o timeout
Command failed. Attempt 2/5:
#0 building with "suspicious_carver" instance using docker-container driver

#1 [internal] booting buildkit
#1 pulling image ghcr.io/rust-lang/buildkit:buildx-stable-1
---
2f3814262e1c: Retrying in 2 seconds
2f3814262e1c: Retrying in 1 second
2f3814262e1c: Pushed
6070b70f5a16: Pushed
Put "https://ghcr.io/v2/rust-lang/rust-ci/manifests/65183c42cb45e920ab6f91284f9355a68331cbeba1aff36362f7c95a68664982b850b35b8fc297397bcd636efc8c21319be5141bd08476e044eab5817132ff89": dial tcp 140.82.116.34:443: i/o timeout
##[error]Process completed with exit code 1.
Post job cleanup.

[Kobzol]

@bors retry

[bors]

⌛ Testing commit 864a46e with merge f964245...

[rust-log-analyzer]

The job x86_64-gnu-llvm-19-3 failed! Check out the build log: (web) (plain enhanced) (plain)

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

To only update this specific test, also pass `--test-args asm/x86_64/goto.rs`

error: 1 errors occurred comparing output.
status: exit status: 0
command: env -u RUSTC_LOG_COLOR RUSTC_ICE="0" RUST_BACKTRACE="short" "/checkout/obj/build/x86_64-unknown-linux-gnu/stage1/bin/rustc" "/checkout/tests/ui/asm/x86_64/goto.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=/cargo" "-Z" "ignore-directory-in-diagnostics-source-blocks=/checkout/vendor" "--sysroot" "/checkout/obj/build/x86_64-unknown-linux-gnu/stage1" "--target=x86_64-unknown-linux-gnu" "--check-cfg" "cfg(test,FALSE)" "-O" "--error-format" "json" "--json" "future-incompat" "-Ccodegen-units=1" "-Zui-testing" "-Zdeduplicate-diagnostics=no" "-Zwrite-long-types-to-disk=no" "-Cstrip=debuginfo" "-C" "prefer-dynamic" "-o" "/checkout/obj/build/x86_64-unknown-linux-gnu/test/ui/asm/x86_64/goto/a" "-A" "internal_features" "-A" "unused_parens" "-A" "unused_braces" "-Crpath" "-Cdebuginfo=0" "-Lnative=/checkout/obj/build/x86_64-unknown-linux-gnu/native/rust-test-helpers"
stdout: none
--- stderr -------------------------------
warning: unreachable statement
##[warning]  --> /checkout/tests/ui/asm/x86_64/goto.rs:144:9
   |
LL | /         asm!(
LL | |             "jmp {}",
LL | |             label {
LL | |                 return;
LL | |             },
LL | |             options(noreturn)
LL | |         );
   | |_________- any code following this expression is unreachable

[bors]

💔 Test failed - checks-actions