gvn: Invalid dereferences for all non-local mutations

[dianqk]

Fixes #132353.

This PR removes the computation value by traversing SSA locals through for_each_assignment_mut.

Because the for_each_assignment_mut traversal skips statements which have side effects, such as dereference assignments, the computation may be unsound. Instead of for_each_assignment_mut, we compute values by traversing in reverse postorder.

Because we compute and use the symbolic representation of values on the fly, I invalidate all old values when encountering a dereference assignment. The current approach does not prevent the optimization of a clone to a copy.

In the future, we may add an alias model, or dominance information for dereference assignments, or SSA form to help GVN.

r? cjgillot

cc @jieyouxu #132356
cc @RalfJung #133474

[dianqk]

@bors try @rust-timer queue

[bors]

⌛ Trying commit 64d0f48 with merge 0011660...

[bors]

☀️ Try build successful - checks-actions
Build commit: 0011660 (0011660807de999202661fd942d6b7f77fdc9c8e)

[rust-timer]

Finished benchmarking commit (0011660): 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)	0.5%	[0.3%, 0.7%]	3
Regressions ❌ (secondary)	0.5%	[0.2%, 0.7%]	10
Improvements ✅ (primary)	-1.2%	[-6.4%, -0.2%]	14
Improvements ✅ (secondary)	-0.5%	[-0.6%, -0.5%]	10
All ❌✅ (primary)	-0.9%	[-6.4%, 0.7%]	17

Max RSS (memory usage)

Results (primary -0.1%)

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)	3.3%	[2.1%, 5.8%]	4
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-6.9%	[-10.5%, -3.3%]	2
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-0.1%	[-10.5%, 5.8%]	6

Cycles

Results (primary -1.6%)

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)	0.8%	[0.8%, 0.8%]	1
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-2.1%	[-5.8%, -0.8%]	5
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-1.6%	[-5.8%, 0.8%]	6

Binary size

Results (primary -0.1%, secondary -0.3%)

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)	0.1%	[0.0%, 0.4%]	33
Regressions ❌ (secondary)	0.0%	[0.0%, 0.1%]	14
Improvements ✅ (primary)	-0.3%	[-2.4%, -0.0%]	23
Improvements ✅ (secondary)	-0.7%	[-1.2%, -0.0%]	10
All ❌✅ (primary)	-0.1%	[-2.4%, 0.4%]	56

Bootstrap: 780.173s -> 782.091s (0.25%)
Artifact size: 335.37 MiB -> 335.25 MiB (-0.03%)

[dianqk]

I will update this after #132461.

[dianqk]

@bors try @rust-timer queue

[bors]

🔒 Merge conflict

This pull request and the master branch diverged in a way that cannot be automatically merged. Please rebase on top of the latest master branch, and let the reviewer approve again.

How do I rebase?

Assuming self is your fork and upstream is this repository, you can resolve the conflict following these steps:

1. git checkout gvn-stmt-iter (switch to your branch)
2. git fetch upstream master (retrieve the latest master)
3. git rebase upstream/master -p (rebase on top of it)
4. Follow the on-screen instruction to resolve conflicts (check git status if you got lost).
5. git push self gvn-stmt-iter --force-with-lease (update this PR)

You may also read Git Rebasing to Resolve Conflicts by Drew Blessing for a short tutorial.

Please avoid the "Resolve conflicts" button on GitHub. It uses git merge instead of git rebase which makes the PR commit history more difficult to read.

Sometimes step 4 will complete without asking for resolution. This is usually due to difference between how Cargo.lock conflict is handled during merge and rebase. This is normal, and you should still perform step 5 to update this PR.

Error message

Auto-merging tests/mir-opt/pre-codegen/vec_deref.vec_deref_to_slice.PreCodegen.after.panic-unwind.mir
CONFLICT (content): Merge conflict in tests/mir-opt/pre-codegen/vec_deref.vec_deref_to_slice.PreCodegen.after.panic-unwind.mir
Auto-merging tests/mir-opt/pre-codegen/vec_deref.vec_deref_to_slice.PreCodegen.after.panic-abort.mir
CONFLICT (content): Merge conflict in tests/mir-opt/pre-codegen/vec_deref.vec_deref_to_slice.PreCodegen.after.panic-abort.mir
Automatic merge failed; fix conflicts and then commit the result.

[bors]

☔ The latest upstream changes (presumably #133841) made this pull request unmergeable. Please resolve the merge conflicts.

[dianqk]

@bors try @rust-timer queue

[dianqk]

Thanks! 🟩
@bors r=oli-obk

[dianqk]

Hmm...
@bors r=oli-obk

[bors]

📌 Commit d9fbe5d has been approved by oli-obk

It is now in the queue for this repository.

[bors]

⌛ Testing commit d9fbe5d with merge 7f4f652...

[bors]

💔 Test failed - checks-actions

[dianqk]

diff

@bors r=oli-obk

[bors]

📌 Commit 7d44887 has been approved by oli-obk

It is now in the queue for this repository.

[bors]

⌛ Testing commit 7d44887 with merge 00095b3...

[bors]

☀️ Test successful - checks-actions
Approved by: oli-obk
Pushing 00095b3 to master...

[github-actions]

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 82eb03e (parent) -> 00095b3 (this PR)

Test differences

Show 10 test diffs

Additionally, 10 doctest diffs were found. These are ignored, as they are noisy.

Job group index

Job duration changes

1. x86_64-apple-1: 8032.6s -> 9790.8s (21.9%)
2. dist-apple-various: 7790.2s -> 9248.6s (18.7%)
3. x86_64-msvc-2: 6619.9s -> 7417.9s (12.1%)
4. x86_64-msvc-1: 8420.5s -> 8868.0s (5.3%)
5. x86_64-msvc-ext1: 7167.9s -> 7498.9s (4.6%)
6. dist-x86_64-linux: 5250.2s -> 5470.6s (4.2%)
7. i686-mingw-1: 7448.3s -> 7689.9s (3.2%)
8. x86_64-mingw-1: 8846.9s -> 9106.3s (2.9%)
9. i686-mingw-2: 6559.0s -> 6742.6s (2.8%)
10. dist-riscv64-linux: 5019.5s -> 5155.0s (2.7%)

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]

Finished benchmarking commit (00095b3): comparison URL.

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

Our benchmarks found a performance regression caused by this PR.
This might be an actual regression, but it can also be just noise.

Next Steps:

• If the regression was expected or you think it can be justified,
  please write a comment with sufficient written justification, and add
  @rustbot label: +perf-regression-triaged to it, to mark the regression as triaged.
• If you think that you know of a way to resolve the regression, try to create
  a new PR with a fix for the regression.
• If you do not understand the regression or you think that it is just noise,
  you can ask the @rust-lang/wg-compiler-performance working group for help (members of this group
  were already notified of this PR).

@rustbot label: +perf-regression
cc @rust-lang/wg-compiler-performance

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)	0.3%	[0.1%, 0.9%]	37
Regressions ❌ (secondary)	0.5%	[0.1%, 1.3%]	29
Improvements ✅ (primary)	-0.9%	[-1.7%, -0.6%]	6
Improvements ✅ (secondary)	-1.7%	[-1.8%, -1.5%]	6
All ❌✅ (primary)	0.2%	[-1.7%, 0.9%]	43

Max RSS (memory usage)

Results (primary 2.3%, secondary -3.8%)

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)	3.1%	[1.3%, 7.4%]	6
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-2.7%	[-2.7%, -2.7%]	1
Improvements ✅ (secondary)	-3.8%	[-4.4%, -3.1%]	5
All ❌✅ (primary)	2.3%	[-2.7%, 7.4%]	7

Cycles

Results (primary -0.2%, secondary 3.4%)

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)	0.7%	[0.7%, 0.7%]	1
Regressions ❌ (secondary)	3.4%	[2.7%, 4.0%]	12
Improvements ✅ (primary)	-1.2%	[-1.2%, -1.2%]	1
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-0.2%	[-1.2%, 0.7%]	2

Binary size

Results (primary -0.0%, secondary -0.5%)

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%, 1.1%]	39
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-0.3%	[-3.4%, -0.0%]	27
Improvements ✅ (secondary)	-0.5%	[-1.1%, -0.0%]	19
All ❌✅ (primary)	-0.0%	[-3.4%, 1.1%]	66

Bootstrap: 776.514s -> 774.699s (-0.23%)
Artifact size: 366.01 MiB -> 365.85 MiB (-0.04%)