Don't generate unecessary &&self.field in deriving Debug

[clubby789]

Since unsized fields may only be the last one in a struct, we only need to generate a double reference (&&self.field) for the final one.

cc @nnethercote

[rustbot]

r? @lcnr

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

[Noratrieb]

@bors try @rust-timer queue

[bors]

⌛ Trying commit a61ba621df635d2b44336422189d813a698461b0 with merge 0c567e3f492ab5edc9a8b5b787574aa6a2e37c7b...

[bors]

☀️ Try build successful - checks-actions
Build commit: 0c567e3f492ab5edc9a8b5b787574aa6a2e37c7b (0c567e3f492ab5edc9a8b5b787574aa6a2e37c7b)

[nnethercote]

r? @nnethercote

[nnethercote]

Looks reasonable, just some nitpicks. Thanks.

[rust-timer]

Finished benchmarking commit (0c567e3f492ab5edc9a8b5b787574aa6a2e37c7b): comparison URL.

Overall result: ❌✅ regressions and improvements - 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.

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 a highly reliable metric that was used to determine the overall result at the top of this comment.

	mean	range	count
Regressions ❌ (primary)	0.4%	[0.3%, 0.4%]	3
Regressions ❌ (secondary)	0.7%	[0.2%, 1.3%]	10
Improvements ✅ (primary)	-1.0%	[-2.9%, -0.4%]	9
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-0.7%	[-2.9%, 0.4%]	12

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)	2.0%	[1.1%, 2.9%]	2
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-3.5%	[-7.8%, -0.1%]	3
Improvements ✅ (secondary)	-1.5%	[-2.6%, -0.6%]	4
All ❌✅ (primary)	-1.3%	[-7.8%, 2.9%]	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)	1.1%	[1.1%, 1.1%]	1
Improvements ✅ (primary)	-2.2%	[-3.4%, -1.3%]	4
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-2.2%	[-3.4%, -1.3%]	4

[nnethercote]

I strongly suspect those perf results are noise, this change really shouldn't impact perf on those benchmarks in any significant way.

@bors r+

[bors]

📌 Commit d8651aa has been approved by nnethercote

It is now in the queue for this repository.

[bors]

⌛ Testing commit d8651aa with merge 9545094...

[bors]

☀️ Test successful - checks-actions
Approved by: nnethercote
Pushing 9545094 to master...

[rust-timer]

Finished benchmarking commit (9545094): comparison URL.

Overall result: ❌✅ regressions and improvements - ACTION NEEDED

Next Steps: If you can justify the regressions found in this perf run, please indicate this with @rustbot label: +perf-regression-triaged along with sufficient written justification. If you cannot justify the regressions please open an issue or create a new PR that fixes the regressions, add a comment linking to the newly created issue or PR, and then add the perf-regression-triaged label to this PR.

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

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)	0.4%	[0.3%, 0.4%]	2
Regressions ❌ (secondary)	1.0%	[0.2%, 4.9%]	7
Improvements ✅ (primary)	-1.0%	[-2.9%, -0.4%]	9
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-0.8%	[-2.9%, 0.4%]	11

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)	-	-	0
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-2.7%	[-8.2%, -0.1%]	8
Improvements ✅ (secondary)	-2.6%	[-4.6%, -0.8%]	44
All ❌✅ (primary)	-2.7%	[-8.2%, -0.1%]	8

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)	2.6%	[2.6%, 2.6%]	1
Improvements ✅ (primary)	-2.4%	[-3.2%, -1.4%]	3
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-2.4%	[-3.2%, -1.4%]	3

[nnethercote]

I think this is noisy. The pre-merge perf run also had quite some variance, though it looked a bit different. Also, there's no good reason why this change should make much difference.

@rustbot label: +perf-regression-triaged