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In simplify_repeated_aggregate, don't test first element against itself #139411

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merged 1 commit into from
Apr 6, 2025
Merged

In simplify_repeated_aggregate, don't test first element against itself #139411

merged 1 commit into from
Apr 6, 2025
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yotamofek
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r? @saethlin
Noticed that in InstSimplifyContext::simplify_repeated_aggregate, we're accidentally evaluating the first element's value twice, and then comparing it with itself, instead of just checking whether the rest of the elements are equal to the first one.
This will probably save very few cycles, but since InstSimplify is always enabled, this might improve perf by a bit.

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rustbot commented Apr 5, 2025

Could not assign reviewer from: saethlin.
User(s) saethlin are either the PR author, already assigned, or on vacation. Please use r? to specify someone else to assign.

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rustbot commented Apr 5, 2025

r? @petrochenkov

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@rustbot 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 5, 2025
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rustbot commented Apr 5, 2025

Some changes occurred to MIR optimizations

cc @rust-lang/wg-mir-opt

yotamofek
yotamofek commented Apr 5, 2025
View reviewed changes
compiler/rustc_mir_transform/src/instsimplify.rs
@@ -78,20 +78,20 @@ impl<'tcx> InstSimplifyContext<'_, 'tcx> {
/// GVN can also do this optimization, but GVN is only run at mir-opt-level 2 so having this in
/// InstSimplify helps unoptimized builds.
fn simplify_repeated_aggregate(&self, rvalue: &mut Rvalue<'tcx>) {
let Rvalue::Aggregate(box AggregateKind::Array(_), fields) = rvalue else {
let Rvalue::Aggregate(box AggregateKind::Array(_), fields) = &*rvalue else {
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This is just so fields is immutable, which makes it a bit easier to reason about, IMHO.

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Kobzol commented Apr 5, 2025

@bors try @rust-timer queue

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@rustbot rustbot added the S-waiting-on-perf Status: Waiting on a perf run to be completed. label Apr 5, 2025
bors added a commit to rust-lang-ci/rust that referenced this pull request Apr 5, 2025
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Auto merge of rust-lang#139411 - yotamofek:pr/mir_transform/instsimpl…
fa2c9b1 
…ify, r=<try>

In `simplify_repeated_aggregate`, don't test first element against itself

r? `@saethlin`
Noticed that in `InstSimplifyContext::simplify_repeated_aggregate`, we're accidentally evaluating the first element's value twice, and then comparing it with itself, instead of just checking whether the rest of the elements are equal to the first one.
This will probably save very few cycles, but since `InstSimplify` is always enabled, this might improve perf by a bit.
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bors commented Apr 5, 2025

⌛ Trying commit 5b596cd with merge fa2c9b15eafb4a4051228168e5cdfbe2161a2248...

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r=me (i.e. I will approve) when perf comes back.

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bors commented Apr 5, 2025

☀️ Try build successful - checks-actions
Build commit: fa2c9b1 (fa2c9b15eafb4a4051228168e5cdfbe2161a2248)

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Finished benchmarking commit (fa2c9b1): comparison URL.

Overall result: no relevant changes - no 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.

@bors rollup=never
@rustbot label: -S-waiting-on-perf -perf-regression

Instruction count

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

Max RSS (memory usage)

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

Cycles

Results (secondary 2.3%)

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

Binary size

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

Bootstrap: 776.909s -> 777.668s (0.10%)
Artifact size: 365.93 MiB -> 365.98 MiB (0.01%)

@rustbot rustbot removed the S-waiting-on-perf Status: Waiting on a perf run to be completed. label Apr 5, 2025
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@bors r+ rollup-

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bors commented Apr 5, 2025

📌 Commit 5b596cd has been approved by compiler-errors

It is now in the queue for this repository.

@bors bors added S-waiting-on-bors Status: Waiting on bors to run and complete tests. Bors will change the label on completion. and removed S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. labels Apr 5, 2025
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bors commented Apr 6, 2025

⌛ Testing commit 5b596cd with merge 1de931283df18f3af4922fe9a96adcc8936ac42e...

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bors commented Apr 6, 2025

☀️ Test successful - checks-actions
Approved by: compiler-errors
Pushing 1de9312 to master...

@bors bors added the merged-by-bors This PR was explicitly merged by bors. label Apr 6, 2025
@bors bors merged commit 1de9312 into rust-lang:master Apr 6, 2025
7 checks passed
@rustbot rustbot added this to the 1.88.0 milestone Apr 6, 2025
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github-actions bot commented Apr 6, 2025

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 c211076 (parent) -> 1de9312 (this PR)

Test differences

No test diffs found

Job duration changes

  1. x86_64-apple-1: 5974.0s -> 6881.4s (15.2%)
  2. x86_64-msvc-2: 7053.7s -> 7486.8s (6.1%)
  3. dist-aarch64-msvc: 8350.4s -> 8731.8s (4.6%)
  4. x86_64-gnu: 6398.4s -> 6683.8s (4.5%)
  5. dist-x86_64-musl: 7196.6s -> 7431.1s (3.3%)
  6. dist-x86_64-illumos: 5529.0s -> 5702.1s (3.1%)
  7. x86_64-msvc-ext3: 7414.2s -> 7604.9s (2.6%)
  8. x86_64-mingw-2: 7021.1s -> 7194.1s (2.5%)
  9. x86_64-gnu-distcheck: 4698.4s -> 4810.9s (2.4%)
  10. dist-powerpc64-linux: 5293.7s -> 5419.8s (2.4%)
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.

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Finished benchmarking commit (1de9312): 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 (secondary -3.3%)

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
Regressions ❌
(secondary)		 - - 0
Improvements ✅
(primary)		 - - 0
Improvements ✅
(secondary)		 -3.3% [-3.3%, -3.3%] 1
All ❌✅ (primary) - - 0

Cycles

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

Binary size

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

Bootstrap: 775.586s -> 775.764s (0.02%)
Artifact size: 365.94 MiB -> 365.91 MiB (-0.01%)

@yotamofek yotamofek deleted the pr/mir_transform/instsimplify branch April 6, 2025 08:19
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