Directly call same-image managed R2R helpers by davidwrighton · Pull Request #134555 · dotnet/runtime

davidwrighton · 2026-09-23T21:23:03Z

Summary

Allow ReadyToRun code to call managed JIT-helper bodies directly when the helper can be compiled portably into the same binary.

Crossgen2 probe-compiles managed JIT helpers before compiling ordinary methods. Helpers that compile successfully without processor-feature fixups can call one another directly and are exposed to ordinary methods as local compiled bodies. Helpers that require runtime JIT or processor-specific dispatch continue to use the existing helper-cell path. The JIT treats an IAT_VALUE lookup as a direct call; on Wasm it passes zero for the portable-entrypoint argument rather than loading and calling through the PEP cell.

Direct calls bypass normal method-entrypoint resolution, so the compiler emits a METHOD_ENTRY_READYTORUN fixup in the ordinary Eager import section. CoreCLR processes eager imports at FILE_ACTIVE, immediately before Activate(), with method-entry fixups ordered after all other eager work. JIT-helper roots are also identified explicitly so throw-only managed helpers are emitted instead of being removed by FunctionJustThrows.

The new fixup updates the R2R format to version 31.0. This is a major version bump because runtimes implementing 30.x and earlier do not understand the new fixup.

Performance

Measured ArrayDeAbstraction.foreach_member_array_via_interface_property_in_loop on CoreCLR Wasm using a retail runtime and libraries built from this branch. Values are medians in ns/op; lower is better.

Scenario	Before	After	Change
Individual R2R	36,032	30,857.62	-14.4%
Composite R2R	34,143	28,088.91	-17.7%

Individual R2R benefits from direct helper calls within the CoreLib image. Composite R2R additionally permits the benchmark and CoreLib helpers to share one Wasm module, eliminating the helper-cell load and call_indirect for GetGCStaticBase and VirtualFunctionPointer.

A fresh five-second sampled profile was generated from an unmodified final composite image. It collected 18,491 attributed samples:

Symbol	Aggregated self-time
`VirtualFunctionPointer`	39.51%
`get_Current`	27.71%
`GetGCStaticBase`	9.49%
Benchmark method	8.86%
`MoveNext`	2.71%

An earlier description incorrectly said GetGCStaticBase fell from 10.49% to 3.10%. The 3.10% result came from a separate manual WAT experiment and is not attributable to the checked-in changes, so that comparison has been removed.

The interpreted path is not changed by this optimization. Five repeated interpreted runs had a median of medians of 88,718 ns/op and a 17.2% run-to-run spread; the previously observed +2.5% difference is therefore not evidence of a regression.

Wasm image size

Measured with a controlled same-worktree A/B against merged upstream/main (5b82fc4ae86): preserve the upstream image, apply only this PR's source diff, and rerun the same browser-Wasm Release build.

Layout	Upstream	PR	Difference
Standalone `System.Private.CoreLib.wasm`	28,498,561 bytes	27,355,419 bytes	-1,143,142 bytes (-4.01%)
Composite `composite.wasm`	25,676,102 bytes	24,421,328 bytes	-1,254,774 bytes (-4.89%)
Complete composite layout	31,587,642 bytes	30,332,868 bytes	-1,254,774 bytes (-3.97%)

The complete composite layout includes composite.wasm and the System.Private.CoreLib.wasm, System.Linq.wasm, and benchmark forwarding headers. wasm-objdump -h attributes nearly all of the reduction to the Wasm Code section.

Validation

./build.sh -os browser -c Release -subset clr+libs
./build.sh clr+libs+host -rc release -lc release
Interpreted, individual-R2R, and composite-R2R Wasm startup and focused benchmark runs
Fresh composite V8 sampled profile with no manual WAT edits
Native Linux build and testhost construction
R2RDump verification of R2R 31.0 and METHOD_ENTRY_READYTORUN helper entries ordered last in the ordinary eager section
Targeted CoreLib crossgen2 validation: Wasm compiled all 70 managed helpers directly; ARM compiled 69 directly and used the helper-cell fallback for SpanHelpers.Fill

Note

This pull request description was generated with GitHub Copilot.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

dotnet-policy-service · 2026-09-23T21:25:49Z

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

Copilot

Copilot review overview

🟡 Changes recommended

R2R version compatibility and non-local helper fallback issues remain unresolved, along with requested documentation and regression coverage.

Get a fresh assessment by requesting another Copilot review.

Review effort: Lite
Findings: 1 · 1

Open (2)

Reject incompatible ReadyToRun minor versions · New
Add tests for eager activation and helper fixups · New

What changed in this PR

This PR enables ReadyToRun code to directly call same-image managed JIT helpers, with eager activation fixups and WebAssembly support.

Changes:

Adds METHOD_ENTRY_READYTORUN and R2R format version 29.3.
Resolves and roots local managed helpers, including throw-only helpers.
Updates activation sequencing and Wasm direct-call lowering.

Outstanding issues include R2R version compatibility, a helper fallback bug, missing format documentation, and requested regression coverage.

File	Summary
`src/coreclr/vm/nativeimage.h`	Tracks activation fixups.
`src/coreclr/vm/nativeimage.cpp`	Initializes activation state.
`src/coreclr/vm/jitinterface.cpp`	Handles method-entry fixups; regression coverage is requested.
`src/coreclr/vm/ceeload.h`	Declares activation fixup APIs.
`src/coreclr/vm/ceeload.cpp`	Processes eager and activation fixups.
`src/coreclr/vm/assembly.hpp`	Declares activation-phase handling.
`src/coreclr/vm/assembly.cpp`	Runs activation fixups before activation.
`src/coreclr/tools/Common/JitInterface/CorInfoImpl.cs`	Caches helper methods.
`src/coreclr/tools/Common/Internal/Runtime/ReadyToRunConstants.cs`	Adds R2R flags and fixup kind.
`src/coreclr/tools/Common/Internal/Runtime/ModuleHeaders.cs`	Updates the R2R version.
`src/coreclr/tools/aot/ILCompiler.RyuJit/JitInterface/CorInfoImpl.RyuJit.cs`	Updates the helper lookup contract.
`src/coreclr/tools/aot/ILCompiler.Reflection.ReadyToRun/ReadyToRunSignature.cs`	Decodes the new fixup.
`src/coreclr/tools/aot/ILCompiler.ReadyToRun/JitInterface/CorInfoImpl.ReadyToRun.cs`	Resolves local helpers; fallback output handling requires correction.
`src/coreclr/tools/aot/ILCompiler.ReadyToRun/Compiler/ReadyToRunJitHelperRootProvider.cs`	Roots helper methods.
`src/coreclr/tools/aot/ILCompiler.ReadyToRun/Compiler/ReadyToRunCodegenCompilation.cs`	Tracks helper compilation.
`src/coreclr/tools/aot/ILCompiler.ReadyToRun/Compiler/IRootingServiceProvider.cs`	Extends root-provider metadata.
`src/coreclr/tools/aot/ILCompiler.ReadyToRun/Compiler/DependencyAnalysis/ReadyToRunSymbolNodeFactory.cs`	Creates activation imports.
`src/coreclr/tools/aot/ILCompiler.ReadyToRun/Compiler/DependencyAnalysis/ReadyToRunCodegenNodeFactory.cs`	Emits activation sections.
`src/coreclr/tools/aot/ILCompiler.ReadyToRun/Compiler/DependencyAnalysis/ReadyToRun/MethodWithGCInfo.cs`	Marks JIT helpers.
`src/coreclr/nativeaot/Runtime/inc/ModuleHeaders.h`	Updates the NativeAOT R2R version.
`src/coreclr/jit/lowerwasm.cpp`	Supports direct Wasm calls and PEP handling.
`src/coreclr/jit/lower.h`	Declares Wasm lowering helpers.
`src/coreclr/jit/lower.cpp`	Implements direct Wasm call lowering.
`src/coreclr/inc/readytorun.h`	Defines R2R 29.3 additions; compatibility and format documentation issues remain.

Preserve upstream's R2R 29.3 BulkWriteBarrierSmall update and use a major version bump for the incompatible EagerActivation import-section flag. Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Copilot

Copilot review overview

🟡 Changes recommended

Two critical runtime issues and missing R2R format documentation remain unresolved.

Get a fresh assessment by requesting another Copilot review.

Review effort: Lite
Findings: 2

Open (2)

Fix Wasm throw-helper handling for direct IAT_VALUE targets · New
Avoid duplicate code-range registration during eager activation · New

Resolved since last review (2)

Reject incompatible ReadyToRun minor versions
Add tests for eager activation and helper fixups

The relocation only arises with #134555, where a same-image managed helper is returned as IAT_VALUE but genEmitHelperCall still loads the PEP through an indirection cell. Encoding it as a function index would load from imageBase + funcIndex, so the fix belongs in the JIT. On main no code path emits it for composite images. Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>

Run all eager imports immediately before module activation and order managed helper method-entry fixups after ordinary eager imports. Keep direct managed helper selection restricted to Wasm so non-Wasm crossgen builds do not reference methods that require runtime JIT. Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Compile managed JIT helpers optimistically without publishing output, exclude helpers that fail or require processor feature fixups, and then compile the stable helper set before ordinary methods. This enables direct same-image helper calls across targets while retaining helper-cell fallback for unsupported methods. Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Copilot

Copilot review overview

🟡 Changes recommended

The helper-entry cache can retain stale direct-call eligibility; format documentation and end-to-end coverage are also requested.

Get a fresh assessment by requesting another Copilot review.

Review effort: Lite
Findings: 1

Open (1)

Invalidate cached helper entries when direct eligibility changes · New

Resolved since last review (2)

Avoid duplicate code-range registration during eager activation
Fix Wasm throw-helper handling for direct IAT_VALUE targets

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Copilot

Copilot review overview

🔵 Needs a closer look

Optional helper fallback and profiler behavior require resolution before approval.

Review effort: Lite
Findings: None

Resolved since last review (1)

Invalidate cached helper entries when direct eligibility changes

AndyAyersMS

JIT changes look good.

AndyAyersMS · 2026-09-25T23:38:55Z

-        LowerPEPCall(call);
+        if (call->gtDirectCallAddress != nullptr)
+        {
+            AddWasmPortableEntryPointArg(call, m_compiler->gtNewIconNode(0, TYP_I_IMPL));


This arg is just to fulfill the signature demand?

jkotas · 2026-09-26T03:33:26Z

+// R2R Version 31 adds READYTORUN_FIXUP_MethodEntry_ReadyToRun for initializing a
+// method's ReadyToRun entry point and fixups.
+//     R2R 31 is not backward compatible with 30.x or earlier.


Suggested change

// R2R Version 31 adds READYTORUN_FIXUP_MethodEntry_ReadyToRun for initializing a

// method's ReadyToRun entry point and fixups.

// R2R 31 is not backward compatible with 30.x or earlier.

// R2R Version 31 adds READYTORUN_FIXUP_MethodEntry_ReadyToRun

R2R 31 is not backward compatible with 30.x or earlier.

I am not sure what this is trying to say.

Also, the description can be shorter.

jkotas · 2026-09-26T03:36:18Z

-    Eager    = 0x0001, // Section at module load time.
-    PCode    = 0x0004, // Section contains pointers to code
+    None  = 0x0000,
+    Eager = 0x0001, // Section before module activation.


Suggested change

Eager = 0x0001, // Section before module activation.

Eager = 0x0001, // Fixups must be resolved at module load time before any code in the module runs.

Section before module activation.

Does not make sense

jkotas · 2026-09-26T03:44:07Z

        break;

    case FILE_ACTIVE:
+        EagerFixups();


I do not think it can be together with Activate (ie running module constructors). It would break if there are cycles between module constructors.

We should move the whole FILE_LOAD_EAGER_FIXUPS phase.

jkotas · 2026-09-26T03:47:51Z

+                        ReadyToRunFixupKind.MethodEntry_ReadyToRun,
+                        method,
+                        isInstantiatingStub: false),
+                    sortLast: true);


Why is sortLast: true needed here?

davidwrighton and others added 2 commits September 23, 2026 19:03

Enable direct managed helper calls on Wasm R2R

ba11517

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Activate direct managed R2R helpers before use

ac15457

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Copilot AI lite review requested due to automatic review settings September 23, 2026 21:23

davidwrighton requested a review from MichalStrehovsky as a code owner September 23, 2026 21:23

github-actions Bot added the area-ReadyToRun label Sep 23, 2026

Copilot started reviewing on behalf of davidwrighton September 23, 2026 21:23 View session

dotnet-policy-service Bot assigned davidwrighton Sep 23, 2026

Copilot AI reviewed Sep 23, 2026

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Comment thread src/coreclr/inc/readytorun.h Outdated

Comment thread src/coreclr/tools/aot/ILCompiler.ReadyToRun/JitInterface/CorInfoImpl.ReadyToRun.cs Outdated

AndyAyersMS mentioned this pull request Sep 23, 2026

JIT: Improve Wasm PEP calls #134490

Merged

Merge upstream/main and bump R2R format to 30.0

efc2b76

Preserve upstream's R2R 29.3 BulkWriteBarrierSmall update and use a major version bump for the incompatible EagerActivation import-section flag. Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Copilot AI review requested due to automatic review settings September 23, 2026 22:47

Copilot started reviewing on behalf of davidwrighton September 23, 2026 22:48 View session

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Comment thread src/coreclr/tools/aot/ILCompiler.ReadyToRun/JitInterface/CorInfoImpl.ReadyToRun.cs Outdated

Comment thread src/coreclr/vm/ceeload.cpp Outdated

jkotas reviewed Sep 24, 2026

View reviewed changes

Comment thread src/coreclr/tools/aot/ILCompiler.ReadyToRun/JitInterface/CorInfoImpl.ReadyToRun.cs Outdated

jkotas reviewed Sep 24, 2026

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Comment thread src/coreclr/tools/Common/Internal/Runtime/ReadyToRunConstants.cs Outdated

lewing mentioned this pull request Sep 24, 2026

[wasm][coreclr][R2R] Delegate construction skips alternate-constructor lowering and remains interpreted #134564

Open

build-analysis Bot mentioned this pull request Sep 24, 2026

LibraryImportGenerator.Unit.Tests crashing on linux-x64 mono interpreter #100800

Open

lewing mentioned this pull request Sep 24, 2026

[wasm] Lower CoreCLR R2R delegate constructors to R2R helpers #134611

Draft

davidwrighton and others added 2 commits September 25, 2026 18:17

davidwrighton enabled auto-merge (squash) September 25, 2026 18:56

davidwrighton disabled auto-merge September 25, 2026 18:57

davidwrighton and others added 2 commits September 25, 2026 19:13

Merge upstream main and bump R2R version

03a0bbb

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Unify managed ReadyToRun helper metadata

55a23c8

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

davidwrighton requested a lite review from Copilot September 25, 2026 22:07

Copilot started reviewing on behalf of davidwrighton September 25, 2026 22:07 View session

Copilot AI reviewed Sep 25, 2026

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Comment thread src/coreclr/tools/Common/JitInterface/CorInfoImpl.cs

Invalidate cached managed helper entries

665c35c

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davidwrighton requested a lite review from Copilot September 25, 2026 22:25

Copilot started reviewing on behalf of davidwrighton September 25, 2026 22:26 View session

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davidwrighton requested review from AndyAyersMS, adamperlin and lewing September 25, 2026 22:37

AndyAyersMS approved these changes Sep 25, 2026

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jkotas reviewed Sep 26, 2026

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build-analysis Bot mentioned this pull request Sep 26, 2026

"We stopped hearing from agent Azure Pipelines 32. Verify the agent machine is running and has a healthy network connection" dotnet/dnceng#1886

Open

3 tasks

	Eager = 0x0001, // Section before module activation.
	Eager = 0x0001, // Fixups must be resolved at module load time before any code in the module runs.

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Summary

Performance

Wasm image size

Validation

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