[mir-opt] simplify Repeats that don't actually repeat the operand

[scottmcm]

Created because when I was writing this case in GVN

https://github.com/rust-lang/rust/pull/133324/files#diff-292b215fdc6b59e3f3c4173c2270b14591c5673832fbfb05cd69a05c2ef0c30eR977-R979

I happened to notice that it worked for [x] but not for [x; 1], so figured it would be good to simplify that Repeat to the simpler Aggregate.

[rustbot]

r? @Nadrieril

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[rustbot]

Some changes occurred to MIR optimizations

cc @rust-lang/wg-mir-opt

[lcnr]

exhaustively match here. This branch must not have false positives given that it means "definitely not"

[scottmcm]

Good point. Spurious false is benign in how it's actually used, but that's not what the comments say, so I should re-work it. Maybe just have the wildcard be _ => None, since that's more obviously fine, and add the known-false cases explicitly.

[bors]

☔ The latest upstream changes (presumably #135274) made this pull request unmergeable. Please resolve the merge conflicts.

[scottmcm]

@rustbot ready

[oli-obk]

@bors r+

[bors]

📌 Commit 7396ec3 has been approved by oli-obk

It is now in the queue for this repository.

[bors]

⌛ Testing commit 7396ec3 with merge 13f3924...

[bors]

☀️ Test successful - checks-actions
Approved by: oli-obk
Pushing 13f3924 to master...

[rust-timer]

Finished benchmarking commit (13f3924): 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 (primary 3.3%, secondary 7.8%)

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)	3.3%	[3.3%, 3.3%]	1
Regressions ❌ (secondary)	7.8%	[7.8%, 7.8%]	1
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	3.3%	[3.3%, 3.3%]	1

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: 761.42s -> 762.038s (0.08%)
Artifact size: 326.13 MiB -> 326.01 MiB (-0.04%)