bootstrap: use git merge-base for LLVM CI download logic

[RalfJung]

This re-lands #113588, now that the perf issues are hopefully fixed by rust-lang/rustc-perf#1684.
r? @lqd @Mark-Simulacrum

Fixes #101907

[rustbot]

This PR changes how LLVM is built. Consider updating src/bootstrap/download-ci-llvm-stamp.

[lqd]

Let's see if things are indeed fixed on the server: @bors try @rust-timer queue

[bors]

⌛ Trying commit 270f777 with merge f1c9020500cdc9220a341bcda5e514d21c30913c...

[bors]

☀️ Try build successful - checks-actions
Build commit: f1c9020500cdc9220a341bcda5e514d21c30913c (f1c9020500cdc9220a341bcda5e514d21c30913c)

[rust-timer]

Finished benchmarking commit (f1c9020500cdc9220a341bcda5e514d21c30913c): 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)	0.4%	[0.4%, 0.4%]	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)	0.9%	[0.5%, 1.3%]	2
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	0.9%	[0.5%, 1.3%]	2

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: 631.374s -> 630.267s (-0.18%)
Artifact size: 316.55 MiB -> 316.49 MiB (-0.02%)

[lqd]

Looks like there's no issue on bootstrap anymore 🎉

@bors r+ rollup=never

[bors]

📌 Commit 270f777 has been approved by lqd

It is now in the queue for this repository.

[bors]

⌛ Testing commit 270f777 with merge 585bb5e...

[bors]

☀️ Test successful - checks-actions
Approved by: lqd
Pushing 585bb5e to master...

[RalfJung]

Thanks, let's hope it all works out this time. :)

[rust-timer]

Finished benchmarking commit (585bb5e): 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)	1.0%	[0.6%, 1.5%]	7
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-0.4%	[-0.4%, -0.4%]	1
Improvements ✅ (secondary)	-0.4%	[-0.5%, -0.3%]	2
All ❌✅ (primary)	0.8%	[-0.4%, 1.5%]	8

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)	1.6%	[0.6%, 3.1%]	4
Regressions ❌ (secondary)	3.3%	[3.3%, 3.3%]	1
Improvements ✅ (primary)	-1.1%	[-1.1%, -1.1%]	1
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	1.1%	[-1.1%, 3.1%]	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)	3.1%	[2.0%, 5.8%]	7
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	3.1%	[2.0%, 5.8%]	7

Binary size

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

Bootstrap: 628.825s -> 630.176s (0.21%)
Artifact size: 316.55 MiB -> 316.58 MiB (0.01%)

[pnkfelix]

• this is a collection of spurious regressions to bitmaps-3.1.0
  • see e.g. this graph and note the blip.
• marked as triaged

@rustbot label: +perf-regression-triaged