[andrew-kulikov]

Fixes #135942

Problem

• MethodInternKey hashes code bytes, GC info, frame infos and EH bytes, but not relocations, so bodies that differ only in their relocation targets always share a hash code.
• With optimized code this is very common: each async method has its own struct state machine, so every async method gets its own byte-identical copy of AsyncStateMachineBox<TResult, TSM>.MoveNext, AsyncMethodBuilderCore.Start<TSM>, etc.
• All of those land in one HashSet bucket, and each insertion runs AreSame against every earlier copy, so deduplication is O(n²) per method family, per pass.

Change

Relocations are mixed into the hash, consistently with MethodInternComparer.AreSame:

• Reloc type and offset: compared exactly by AreSame.
• MethodReadOnlyDataNode targets: their data bytes. AreSame compares them by content, and the hash covers a subset of what is compared.
• Other targets: the identity of the target after mapping it through the previous pass's remapping.
  • AreSame treats t1 and t2 as equal when remapping[t1] == t2 (or vice versa).
  • Remapping values are never keys: a body only becomes a key when it matched a body already in the set, and bodies in the set are never keys. So both sides hash id(t2).

Why the output does not change:

• The set of pairs Equals accepts is unchanged; only the bucket distribution changes.
• The iteration order is still the sorted GetCompiledMethodBodies().
• ISymbolNodes already hash by identity.

Results

Measured with the same change on v10.0.13 (osx-arm64 host, M1 Pro):

	before	after
iOS app, ~12,000 async methods, ILC wall time	~1200 s	247-252 s
same, --methodbodyfolding:none	252 s
sample with 8000 async Task<int> methods, dotnet publish	271 s	16 s
sample, 4000 methods	47 s	9 s

• The object files are byte-identical to the unpatched compiler in all cases: the iOS app's 1.19 GB .o (two runs) and the sample's .o.
• __managedcode keeps the folding savings (69.3 MB vs 80.0 MB without folding).

Repro: https://github.com/andrew-kulikov/runtime-samples/tree/master/nativeaot-async-folding

[azure-pipelines]

Azure Pipelines:
Successfully started running 3 pipeline(s).
13 pipeline(s) were filtered out due to trigger conditions.
There may be pipelines that require an authorized user to comment /azp run to run.

[dotnet-policy-service]

Tagging subscribers to this area: @dotnet/crossgen-contrib
See info in area-owners.md if you want to be subscribed.

[andrew-kulikov]

@andrew-kulikov please read the following Contributor License Agreement(CLA). If you agree with the CLA, please reply with the following information.

@dotnet-policy-service agree [company="{your company}"]

Options:

• (default - no company specified) I have sole ownership of intellectual property rights to my Submissions and I am not making Submissions in the course of work for my employer.

@dotnet-policy-service agree

• (when company given) I am making Submissions in the course of work for my employer (or my employer has intellectual property rights in my Submissions by contract or applicable law). I have permission from my employer to make Submissions and enter into this Agreement on behalf of my employer. By signing below, the defined term “You” includes me and my employer.

@dotnet-policy-service agree company="Microsoft"

Contributor License Agreement

@dotnet-policy-service agree

[dotnet-policy-service]

Tagging subscribers to this area: @agocke, @dotnet/ilc-contrib
See info in area-owners.md if you want to be subscribed.

[agocke]

LGTM, thanks!

I also noticed that in large apps we repeatedly run passes even though most of the benefit is in the first pass, but after your change this doesn't seem to matter too much.

[agocke]

/ba-g all failures known

[agocke]

/backport to release/11.0

[github-actions]

Started backporting to release/11.0 (link to workflow run)