Tell LLVM that partition_point returns a valid fencepost

[scottmcm]

This was already done for a successful binary_search, but this way partition_point can get similar optimizations.

Demonstration that nightly can't do this optimization today, and leaves in the panicking path: https://play.rust-lang.org/?version=nightly&mode=release&edition=2021&gist=e1074cd2faf5f68e49cffd728ded243a

r? @thomcc

[Kobzol]

Recently using partition_point helped the performance of rustc itself, let's see if this has any additional effect.

@bors try @rust-timer queue

[rust-timer]

Awaiting bors try build completion.

@rustbot label: +S-waiting-on-perf

[bors]

⌛ Trying commit c7af338 with merge 7c6425f66f7ebc2482f0812dfe07a02a67b36030...

[scottmcm]

I'd be extremely surprised if this showed up in perf, since the branch is probably perfectly predicted since LLVM knows the panic is cold, and this doesn't help the line lookup case.

The following use is the kind of thing that this PR should improve, but it's probably not hot enough to show up:

rust/compiler/rustc_data_structures/src/sorted_map/index_map.rs

Lines 98 to 99 in 5a7e4c6

	let lower_bound = self.idx_sorted_by_item_key.partition_point(|&i| self.items[i].0 < key);
	self.idx_sorted_by_item_key[lower_bound..].iter().map_while(move |&i| {

[bors]

☀️ Try build successful - checks-actions
Build commit: 7c6425f66f7ebc2482f0812dfe07a02a67b36030 (7c6425f66f7ebc2482f0812dfe07a02a67b36030)

[rust-timer]

Queued 7c6425f66f7ebc2482f0812dfe07a02a67b36030 with parent de341fe, future comparison URL.

[rust-timer]

Finished benchmarking commit (7c6425f66f7ebc2482f0812dfe07a02a67b36030): 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-review -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.

	mean1	range	count2
Regressions ❌ (primary)	-	-	0
Regressions ❌ (secondary)	1.4%	[1.2%, 1.6%]	6
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.

	mean1	range	count2
Regressions ❌ (primary)	-	-	0
Regressions ❌ (secondary)	4.7%	[3.6%, 6.4%]	3
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-	-	0

Cycles

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

Footnotes

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

2. number of relevant changes ↩ ↩²

[Kobzol]

Ok, basically no changes.

[thomcc]

This is great, thanks!

@bors r+

[bors]

📌 Commit c7af338 has been approved by thomcc

It is now in the queue for this repository.

[bors]

⌛ Testing commit c7af338 with merge c2590e6...

[bors]

☀️ Test successful - checks-actions
Approved by: thomcc
Pushing c2590e6 to master...

[rust-timer]

Finished benchmarking commit (c2590e6): 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

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	range	count2
Regressions ❌ (primary)	-	-	0
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-3.2%	[-3.2%, -3.2%]	1
Improvements ✅ (secondary)	-4.3%	[-4.3%, -4.3%]	1
All ❌✅ (primary)	-3.2%	[-3.2%, -3.2%]	1

Cycles

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

Footnotes

1. the arithmetic mean of the percent change ↩

2. number of relevant changes ↩