Re-enable removal of ZST writes to unions

[saethlin]

This was previously disabled because Miri was lazily allocating unsized locals. But we aren't doing that anymore since #98831, so we can have this optimization back.

[rustbot]

r? @oli-obk

(rustbot has picked a reviewer for you, use r? to override)

[saethlin]

@bors try @rust-timer queue

[bors]

⌛ Trying commit 74a270a with merge 53891f0fb5f6e157c950856141fa558eff4051d1...

[bors]

☀️ Try build successful - checks-actions
Build commit: 53891f0fb5f6e157c950856141fa558eff4051d1 (53891f0fb5f6e157c950856141fa558eff4051d1)

[rust-timer]

Finished benchmarking commit (53891f0fb5f6e157c950856141fa558eff4051d1): comparison URL.

Overall result: ❌ regressions - 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 is a highly reliable metric that was used to determine the overall result at the top of this comment.

	mean	range	count
Regressions ❌ (primary)	-	-	0
Regressions ❌ (secondary)	1.1%	[1.1%, 1.1%]	1
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-	-	0

Max RSS (memory usage)

Results

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)	2.9%	[2.1%, 3.7%]	3
Regressions ❌ (secondary)	2.4%	[1.9%, 2.8%]	2
Improvements ✅ (primary)	-1.2%	[-2.3%, -0.1%]	2
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	1.3%	[-2.3%, 3.7%]	5

Cycles

Results

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)	-1.3%	[-1.8%, -0.8%]	13
Improvements ✅ (secondary)	-2.8%	[-3.6%, -1.4%]	13
All ❌✅ (primary)	-1.3%	[-1.8%, -0.8%]	13

[saethlin]

@rust-timer build 53891f0fb5f6e157c950856141fa558eff4051d1 include=deep-vector

[saethlin]

🤷 I suppose the singular "significant" regression is probably noise? I can't imagine how this change would regress exactly that one benchmark.

[rustbot]

Some changes occurred to MIR optimizations

cc @rust-lang/wg-mir-opt

[oli-obk]

@bors r+ rollup=never

[bors]

📌 Commit 74a270a has been approved by oli-obk

It is now in the queue for this repository.

[bors]

⌛ Testing commit 74a270a with merge e60fbaf...

[bors]

☀️ Test successful - checks-actions
Approved by: oli-obk
Pushing e60fbaf to master...

[rust-timer]

Finished benchmarking commit (e60fbaf): comparison URL.

Overall result: ✅ improvements - no action needed

@rustbot label: -perf-regression

Instruction count

This is a highly reliable metric that was 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)	-0.4%	[-0.6%, -0.3%]	4
All ❌✅ (primary)	-	-	0

Max RSS (memory usage)

Results

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)	2.1%	[1.2%, 3.7%]	3
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-3.2%	[-3.2%, -3.2%]	1
Improvements ✅ (secondary)	-2.4%	[-2.4%, -2.4%]	1
All ❌✅ (primary)	0.8%	[-3.2%, 3.7%]	4

Cycles

Results

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)	-2.1%	[-2.1%, -2.1%]	1
All ❌✅ (primary)	-	-	0