Remove metadata decoding DefPathHash cache

[Mark-Simulacrum]

My expectation is that this cache is largely useless. Decoding a DefPathHash from metadata is essentially a pair of memory loads - there's no heavyweight processing involved. Caching it behind a HashMap just adds extra cost and incurs hashing overheads for the indices.

Based on #119238.

[Mark-Simulacrum]

@bors try @rust-timer queue

[rustbot]

r? @TaKO8Ki

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

[bors]

⌛ Trying commit f098f34 with merge bd2706d...

[bors]

☀️ Try build successful - checks-actions
Build commit: bd2706d (bd2706db8872d068a8943e19851e1a1428ea1f5b)

[rust-timer]

Finished benchmarking commit (bd2706d): 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)	0.8%	[0.8%, 0.8%]	1
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-0.5%	[-1.4%, -0.2%]	96
Improvements ✅ (secondary)	-1.1%	[-3.0%, -0.2%]	52
All ❌✅ (primary)	-0.5%	[-1.4%, 0.8%]	97

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)	3.5%	[2.0%, 6.0%]	4
Improvements ✅ (primary)	-1.8%	[-3.4%, -0.8%]	34
Improvements ✅ (secondary)	-2.2%	[-2.9%, -1.4%]	13
All ❌✅ (primary)	-1.8%	[-3.4%, -0.8%]	34

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%	[-1.7%, -0.9%]	13
Improvements ✅ (secondary)	-2.3%	[-2.9%, -1.0%]	15
All ❌✅ (primary)	-1.3%	[-1.7%, -0.9%]	13

Binary size

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)	-1.0%	[-2.8%, -0.1%]	114
Improvements ✅ (secondary)	-1.7%	[-4.8%, -0.0%]	72
All ❌✅ (primary)	-1.0%	[-2.8%, -0.1%]	114

Bootstrap: 669.829s -> 670.678s (0.13%)
Artifact size: 312.74 MiB -> 312.59 MiB (-0.05%)

[Mark-Simulacrum]

Regression looks like possible noise to me, either way outweighed by improvements. My takeaway is that this is a good change to make, seems like a slight win and also simplifies code.

[cjgillot]

r=me once the other PR lands.

[cjgillot]

@bors r+

[bors]

📌 Commit f098f34 has been approved by cjgillot

It is now in the queue for this repository.

[bors]

⌛ Testing commit f098f34 with merge ebb821f...

[bors]

☀️ Test successful - checks-actions
Approved by: cjgillot
Pushing ebb821f to master...

[rust-timer]

Finished benchmarking commit (ebb821f): 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)	0.9%	[0.9%, 0.9%]	1
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-0.6%	[-2.1%, -0.2%]	101
Improvements ✅ (secondary)	-1.2%	[-3.2%, -0.2%]	65
All ❌✅ (primary)	-0.6%	[-2.1%, 0.9%]	102

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)	3.3%	[2.1%, 6.0%]	5
Improvements ✅ (primary)	-1.3%	[-1.3%, -1.3%]	1
Improvements ✅ (secondary)	-1.8%	[-3.0%, -1.2%]	4
All ❌✅ (primary)	-1.3%	[-1.3%, -1.3%]	1

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%	[-1.6%, -0.9%]	9
Improvements ✅ (secondary)	-2.3%	[-3.1%, -1.0%]	10
All ❌✅ (primary)	-1.3%	[-1.6%, -0.9%]	9

Binary size

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

Bootstrap: 669.722s -> 671.86s (0.32%)
Artifact size: 312.65 MiB -> 312.67 MiB (0.01%)

[Kobzol]

The single small regression is probably just noise for that benchmark returning back to steady state. In any case, it would be definitely offset by the wide range of improvements across the board.

@rustbot label: +perf-regression-triaged