Clarify the overall result in the GitHub comment.

[nnethercote]

Specifics:

• Adds a big "Overall result" heading at the top of the comment, which
  includes "ACTION NEEDED" when there are regressions.
• Moves the next steps and "if you disagree..." text to the top of the
  comment, just below the overall result, before the tables of
  measurements. This means all the instructions that people need to read
  are in one place.
• Removes the short summaries in front of each table, because (a) they just
  duplicates what the table says, and (b) saying "regressions found" for
  cycles and max-rss is a bit misleading because it doesn't contribute
  to the overall conclusion. Replaces them with a sentence indicating if
  the measurements contributed to the overall result and why.
• Changes Direction::join to a non-static method, it's nicer that way.

[nnethercote]

Here is a before and after comparison of a real comment.

---

Finished benchmarking commit (b998821e4c51c44a9ebee395c91323c374236bbb): comparison url.

Instruction count

• Primary benchmarks: ❌ relevant regressions found
• Secondary benchmarks: ❌ relevant regression found

	mean1	max	count2
Regressions ❌ (primary)	0.3%	0.9%	6
Regressions ❌ (secondary)	0.2%	0.2%	1
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	0.3%	0.9%	6

Max RSS (memory usage)

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

Cycles

Results

• Primary benchmarks: ❌ relevant regression found
• Secondary benchmarks: mixed results

	mean1	max	count2
Regressions ❌ (primary)	4.3%	4.3%	1
Regressions ❌ (secondary)	7.3%	7.3%	1
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-3.7%	-4.2%	3
All ❌✅ (primary)	4.3%	4.3%	1

If you disagree with this performance assessment, please file an issue in rust-lang/rustc-perf.

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

---

Finished benchmarking commit (b998821e4c51c44a9ebee395c91323c374236bbb): 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

If you disagree with this performance assessment, please file an issue in rust-lang/rustc-perf.

Instruction count

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

	mean1	max	count2
Regressions ❌ (primary)	0.3%	0.9%	6
Regressions ❌ (secondary)	0.2%	0.2%	1
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	0.3%	0.9%	6

Max RSS (memory usage)

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

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.

	mean1	max	count2
Regressions ❌ (primary)	4.3%	4.3%	1
Regressions ❌ (secondary)	7.3%	7.3%	1
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-3.7%	-4.2%	3
All ❌✅ (primary)	4.3%	4.3%	1

Footnotes

1. the arithmetic mean of the percent change ↩ ↩² ↩³ ↩⁴

2. number of relevant changes ↩ ↩² ↩³ ↩⁴

[Kobzol]

Looks great! I like that the actions to do and especially the overall is are now clearly visible at the beginning.

[nnethercote]

I have addressed the review comments. I also added " - no action needed" to the heading in the case where no action is needed, for a clearer contrast to the " - ACTION NEEDED" case.