JumpThreading: compute place and value indices on-demand

[cjgillot]

Profiling JumpThreading reveals that a large part of the runtime happens constructing the place and value Map. This is unfortunate, as jump-threading may end up not even doing anything.

The cause for this large up-front cost is following: Map attempts to create a PlaceIndex for each place that may hold a relevant value. This means all places that appear in MIR, but also all places whose value is accessed by a projection of a copy of a larger place.

This PR refactors the creation of Map to happen on-demand: place and value indices are created when threading computation happens.

The up-front mode is still relevant for DataflowConstProp, so is not touched.

[cjgillot]

@bors try @rust-timer queue

[bors]

⌛ Trying commit ba3a8c5 with merge 1587bef...

[bors]

☀️ Try build successful - checks-actions
Build commit: 1587bef (1587bef3b2c2aea88de9b552efbf7febe7cd5fc4)

[rust-timer]

Finished benchmarking commit (1587bef): comparison URL.

Overall result: ❌✅ regressions and improvements - please read the text below

Benchmarking this pull request means it may be perf-sensitive – we'll automatically label it not fit for rolling up. You can override this, but we strongly advise not to, due to possible changes in compiler perf.

Next Steps: If you can justify the regressions found in this try perf run, please do so in sufficient writing along with @rustbot label: +perf-regression-triaged. If not, please fix the regressions and do another perf run. If its results are neutral or positive, the label will be automatically removed.

@bors rollup=never
@rustbot label: -S-waiting-on-perf +perf-regression

Instruction count

Our most reliable metric. Used to determine the overall result above. However, even this metric can be noisy.

	mean	range	count
Regressions ❌ (primary)	1.0%	[0.7%, 1.3%]	2
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-0.3%	[-1.4%, -0.1%]	142
Improvements ✅ (secondary)	-0.4%	[-1.7%, -0.1%]	93
All ❌✅ (primary)	-0.3%	[-1.4%, 1.3%]	144

Max RSS (memory usage)

Results (primary 3.6%, secondary 2.0%)

A less reliable metric. May be of interest, but not used to determine the overall result above.

	mean	range	count
Regressions ❌ (primary)	3.6%	[3.4%, 3.8%]	2
Regressions ❌ (secondary)	2.0%	[2.0%, 2.0%]	1
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	3.6%	[3.4%, 3.8%]	2

Cycles

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

Binary size

Results (primary -0.1%, secondary 0.1%)

A less reliable metric. May be of interest, but not used to determine the overall result above.

	mean	range	count
Regressions ❌ (primary)	0.2%	[0.0%, 0.4%]	12
Regressions ❌ (secondary)	0.2%	[0.0%, 0.4%]	42
Improvements ✅ (primary)	-0.3%	[-1.4%, -0.0%]	20
Improvements ✅ (secondary)	-0.3%	[-0.9%, -0.0%]	5
All ❌✅ (primary)	-0.1%	[-1.4%, 0.4%]	32

Bootstrap: 689.082s -> 684.233s (-0.70%)
Artifact size: 371.89 MiB -> 372.00 MiB (0.03%)

[rustbot]

r? @eholk

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[rustbot]

Some changes occurred to MIR optimizations

cc @rust-lang/wg-mir-opt

[rustbot]

Some changes occurred in coverage tests.

cc @Zalathar