Optimize dataflow-const-prop place-tracking infra

[cjgillot]

Optimization opportunities found while investigating #110719

Computing places breadth-first ensures that we create short projections before deep projections, since the former are more likely to be propagated.

The most relevant is the pre-computation of flooded places. Callgrind showed flood_* methods and especially preorder_preinvoke were especially hot. This PR attempts to pre-compute the set of ValueIndex that preorder_invoke would visit.

Using this information, we make some PlaceIndex inaccessible when they contain no ValueIndex, allowing to skip computations for those places.

cc @jachris as original author

[rustbot]

r? @TaKO8Ki

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[rustbot]

Some changes occurred to MIR optimizations

cc @rust-lang/wg-mir-opt

[oli-obk]

@bors try @rust-timer queue

[bors]

⌛ Trying commit 3cfa1b1fa6c493ebbf8b4282eb92a161eb8563c7 with merge 8fffd5b5f897bb58af07618610dd7b1cef63d4e2...

[bors]

☀️ Try build successful - checks-actions
Build commit: 8fffd5b5f897bb58af07618610dd7b1cef63d4e2 (8fffd5b5f897bb58af07618610dd7b1cef63d4e2)

[rust-timer]

Finished benchmarking commit (8fffd5b5f897bb58af07618610dd7b1cef63d4e2): comparison URL.

Overall result: no relevant changes - 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 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.

	mean	range	count
Regressions ❌ (primary)	-	-	0
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-2.9%	[-2.9%, -2.9%]	1
All ❌✅ (primary)	-	-	0

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: 654.411s -> 654.14s (-0.04%)

[cjgillot]

The perf results are expected: those code paths are not enabled by default.

[oli-obk]

r=me with question answered as a comment or addressed otherwise

[oli-obk]

how deep can this recursion get? We can have some very long projections from user code. A recursion limit could either cause a miscompilation or a hard error where there shouldn't be one, so maybe use ensure_sufficient_stack?

[cjgillot]

This recursion is required for correctness, so I added the ensure_sufficient_stack.
I don't think this is much of an issue in practice: we have a limit on the number of created values in register_with_filter.

[oli-obk]

@bors r+

[bors]

📌 Commit e858997ad21c730972d6f3f254ad6821f64f50f6 has been approved by oli-obk

It is now in the queue for this repository.

[bors]

⌛ Testing commit e858997ad21c730972d6f3f254ad6821f64f50f6 with merge 390e41af383ca43944ee332c68e3f3cb1e84b122...

[bors]

💔 Test failed - checks-actions

[cjgillot]

@bors r=oli-obk

[bors]

📌 Commit ccc1da2 has been approved by oli-obk

It is now in the queue for this repository.

[bors]

⌛ Testing commit ccc1da2 with merge b73d98147a1d4b1f392b6e38c052d8151e1a2dfa...

[bors]

💔 Test failed - checks-actions

[rust-log-analyzer]

A job failed! Check out the build log: (web) (plain)

Click to see the possible cause of the failure (guessed by this bot)

[cjgillot]

@bors retry

[Noratrieb]

@bors p=50
PR CI seems to be normal recently, let's see whether it passes here

[bors]

⌛ Testing commit ccc1da2 with merge 9a767b6...

[bors]

☀️ Test successful - checks-actions
Approved by: oli-obk
Pushing 9a767b6 to master...

[rust-timer]

Finished benchmarking commit (9a767b6): 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.

	mean	range	count
Regressions ❌ (primary)	-	-	0
Regressions ❌ (secondary)	2.6%	[2.6%, 2.6%]	1
Improvements ✅ (primary)	-5.6%	[-5.6%, -5.6%]	1
Improvements ✅ (secondary)	-4.8%	[-4.8%, -4.8%]	1
All ❌✅ (primary)	-5.6%	[-5.6%, -5.6%]	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)	-	-	0
Improvements ✅ (secondary)	-2.7%	[-3.2%, -2.3%]	3
All ❌✅ (primary)	-	-	0

Binary size

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

Bootstrap: 658.519s -> 659.961s (0.22%)