Use dispatch cells for generic virtual method dispatch by MichalStrehovsky · Pull Request #129609 · dotnet/runtime

MichalStrehovsky · 2026-06-19T06:19:52Z

This puts generic virtual method dispatch on the same plan as interface method dispatch.

Benefits:

The cost of generic virtual methods went down (still not quite same as interface calls due to fat pointers, but closer)
- Monomorpic GVM callsite: Before: ~2.45 ns/call. After: 1.74 ns/call
- Polymorphic GVM callsite: Before: ~2.45 ns/call. After: 2.10 ns/call.
GVM methods no longer implicitly considered targets of reflection due to LDTOKEN used as implementation detail.
The weird RuntimeMethodHandle for async method variants that reflection should never see is gone

This is three commits:

First just deletes some dead code I noticed.
Second moves some of the dispatch resolution to CoreLib. We've been breaking the "interface dispatch lives in Runtime.Base" boundary for a while. This puts us closer to it living in CoreLib. We can move rest of the interface resolution later, didn't want to perturb this too much. The cache itself stays in Runtime.Base because the assembly helper can only handle one. (We can decide the assembly helper is also owned by CoreLib I guess, but we don't currently have such layer.) I think copilot could easily undo this if this is not the split we want.
Third commit switches the GVM calls to use the dispatch cell. We need a resolve helper variant because GVM dispatch is a resolver due to fat calls, not a dispatcher.

dotnet-policy-service · 2026-06-19T06:21:29Z

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Copilot

Pull request overview

This PR reworks NativeAOT generic virtual method (GVM) dispatch to use dispatch cells (aligning it more closely with interface dispatch), adds new ReadyToRun sections/nodes to emit GVM dispatch-cell metadata, and updates the JIT/AOT toolchain to consume the new helper + lookup shapes.

Changes:

Introduces GVM dispatch-cell sections/metadata in the compiler output and routes GVM lookups through a dispatch-cell-based helper.
Refactors “interface dispatch cell” infrastructure into a generalized “dispatch cell” concept used for both interface dispatch and GVM dispatch.
Moves parts of dispatch resolution into CoreLib (classlib function table) and adds new per-architecture “resolve” helper entrypoints.

Reviewed changes

Copilot reviewed 70 out of 70 changed files in this pull request and generated 7 comments.

Show a summary per file

File	Description
src/coreclr/tools/Common/Internal/Runtime/RuntimeConstants.cs	Introduces `GvmDispatchCellFlags` for encoding async-variant bit in GVM dispatch-cell metadata.
src/coreclr/tools/Common/Internal/Runtime/ModuleHeaders.cs	Adds new ReadyToRun section types for GVM dispatch-cell regions.
src/coreclr/tools/Common/Internal/Runtime/InterfaceDispatchCellCachePointerFlags.cs	Removes unused interface-dispatch cache-pointer flags enum.
src/coreclr/tools/Common/Internal/Runtime/DispatchCell.cs	Adds shared dispatch-cell structs (including dynamic dispatch-cell layouts).
src/coreclr/tools/Common/Internal/NativeFormat/NativeFormat.cs	Allocates `FixupSignatureKind.GvmDispatchCell`.
src/coreclr/tools/Common/Compiler/DependencyAnalysis/SortableDependencyNode.cs	Adds ordered node kinds for GVM dispatch-cell sections.
src/coreclr/tools/Common/Compiler/DependencyAnalysis/GVMDependenciesNode.cs	Marks compilation with an analysis characteristic when GVMs are present.
src/coreclr/tools/aot/ILCompiler.RyuJit/JitInterface/CorInfoImpl.RyuJit.cs	Switches call-info emission to use dispatch-cell helpers/const lookups for interface+GVM cases.
src/coreclr/tools/aot/ILCompiler.ReadyToRun/JitInterface/CorInfoImpl.ReadyToRun.cs	Uses dispatch-cell symbol node instead of interface-only dispatch cell.
src/coreclr/tools/aot/ILCompiler.ReadyToRun/Compiler/DependencyAnalysis/ReadyToRunSymbolNodeFactory.cs	Consolidates cell cache from interface-only to general dispatch cells.
src/coreclr/tools/aot/ILCompiler.Compiler/ILCompiler.Compiler.csproj	Adds new dispatch-cell nodes/sections; removes old interface-dispatch-cell node source.
src/coreclr/tools/aot/ILCompiler.Compiler/IL/ILImporter.Scanner.cs	Updates dependency scanning for dispatch-cell-based GVM/interface lookups.
src/coreclr/tools/aot/ILCompiler.Compiler/Compiler/MetadataManager.cs	Tracks generalized dispatch cells; emits new GVM dispatch-cell sections into the R2R header.
src/coreclr/tools/aot/ILCompiler.Compiler/Compiler/JitHelper.cs	Maps `GVMLookupForSlot` to the new `RhpDispatchResolve` entrypoint.
src/coreclr/tools/aot/ILCompiler.Compiler/Compiler/DependencyAnalysis/Target_X86/X86ReadyToRunHelperNode.cs	Emits dispatch-cell references for interface dispatch helper.
src/coreclr/tools/aot/ILCompiler.Compiler/Compiler/DependencyAnalysis/Target_X86/X86ReadyToRunGenericHelperNode.cs	Routes generic helper ID from `VirtualDispatchCell` to `DispatchCell`.
src/coreclr/tools/aot/ILCompiler.Compiler/Compiler/DependencyAnalysis/Target_X64/X64ReadyToRunHelperNode.cs	Emits dispatch-cell references for interface dispatch helper.
src/coreclr/tools/aot/ILCompiler.Compiler/Compiler/DependencyAnalysis/Target_X64/X64ReadyToRunGenericHelperNode.cs	Routes generic helper ID from `VirtualDispatchCell` to `DispatchCell`.
src/coreclr/tools/aot/ILCompiler.Compiler/Compiler/DependencyAnalysis/Target_RiscV64/RiscV64ReadyToRunHelperNode.cs	Emits dispatch-cell references for interface dispatch helper.
src/coreclr/tools/aot/ILCompiler.Compiler/Compiler/DependencyAnalysis/Target_RiscV64/RiscV64ReadyToRunGenericHelperNode.cs	Routes generic helper ID from `VirtualDispatchCell` to `DispatchCell`.
src/coreclr/tools/aot/ILCompiler.Compiler/Compiler/DependencyAnalysis/Target_LoongArch64/LoongArch64ReadyToRunHelperNode.cs	Emits dispatch-cell references for interface dispatch helper.
src/coreclr/tools/aot/ILCompiler.Compiler/Compiler/DependencyAnalysis/Target_LoongArch64/LoongArch64ReadyToRunGenericHelperNode.cs	Routes generic helper ID from `VirtualDispatchCell` to `DispatchCell`.
src/coreclr/tools/aot/ILCompiler.Compiler/Compiler/DependencyAnalysis/Target_ARM64/ARM64ReadyToRunHelperNode.cs	Emits dispatch-cell references for interface dispatch helper.
src/coreclr/tools/aot/ILCompiler.Compiler/Compiler/DependencyAnalysis/Target_ARM64/ARM64ReadyToRunGenericHelperNode.cs	Routes generic helper ID from `VirtualDispatchCell` to `DispatchCell`.
src/coreclr/tools/aot/ILCompiler.Compiler/Compiler/DependencyAnalysis/Target_ARM/ARMReadyToRunHelperNode.cs	Emits dispatch-cell references for interface dispatch helper.
src/coreclr/tools/aot/ILCompiler.Compiler/Compiler/DependencyAnalysis/Target_ARM/ARMReadyToRunGenericHelperNode.cs	Routes generic helper ID from `VirtualDispatchCell` to `DispatchCell`.
src/coreclr/tools/aot/ILCompiler.Compiler/Compiler/DependencyAnalysis/RuntimeMethodHandleNode.cs	Removes async-variant encoding from runtime method handle node emission.
src/coreclr/tools/aot/ILCompiler.Compiler/Compiler/DependencyAnalysis/ReadyToRunHelperNode.cs	Renames helper ID `VirtualDispatchCell` to `DispatchCell`.
src/coreclr/tools/aot/ILCompiler.Compiler/Compiler/DependencyAnalysis/ReadyToRunGenericHelperNode.cs	Updates generic-lookup signatures/comparisons to use dispatch-cell lookup kind.
src/coreclr/tools/aot/ILCompiler.Compiler/Compiler/DependencyAnalysis/NodeFactory.NativeLayout.cs	Adds native-layout dictionary slot node for GVM dispatch-cell fixup signatures.
src/coreclr/tools/aot/ILCompiler.Compiler/Compiler/DependencyAnalysis/NodeFactory.GenericLookups.cs	Generalizes “virtual dispatch cell” generic lookup result into “dispatch cell”.
src/coreclr/tools/aot/ILCompiler.Compiler/Compiler/DependencyAnalysis/NodeFactory.cs	Generalizes dispatch-cell node cache/factory API.
src/coreclr/tools/aot/ILCompiler.Compiler/Compiler/DependencyAnalysis/NativeLayoutVertexNode.cs	Adds `NativeLayoutGvmDispatchGenericDictionarySlotNode` implementation.
src/coreclr/tools/aot/ILCompiler.Compiler/Compiler/DependencyAnalysis/InterfaceDispatchCellInfoSectionNode.cs	Updates section emission to operate on generalized dispatch cells (filters out GVM instantiations).
src/coreclr/tools/aot/ILCompiler.Compiler/Compiler/DependencyAnalysis/GvmDispatchCellInfoSectionNode.cs	Adds new section emitting GVM dispatch-cell info (token+flags+instantiation).
src/coreclr/tools/aot/ILCompiler.Compiler/Compiler/DependencyAnalysis/GenericLookupResult.cs	Renames/expands dispatch-cell lookup result to support interface and GVM.
src/coreclr/tools/aot/ILCompiler.Compiler/Compiler/DependencyAnalysis/DispatchCellSectionNode.cs	Splits dispatch-cell BSS into interface vs GVM sections via filtering.
src/coreclr/tools/aot/ILCompiler.Compiler/Compiler/DependencyAnalysis/DispatchCellNode.cs	Generalizes interface dispatch cell node into a dispatch cell node.
src/coreclr/tools/aot/ILCompiler.Compiler/Compiler/DelegateCreationInfo.cs	Switches delegate creation for GVM/interface targets to dispatch-cell-based lookup.
src/coreclr/tools/aot/ILCompiler.Compiler/Compiler/Compilation.cs	Updates runtime-lookup decision for the new dispatch-cell helper ID.
src/coreclr/nativeaot/Test.CoreLib/src/Test.CoreLib.csproj	Links in shared dispatch-cell type(s) and adds a `ResolveDispatch` export stub.
src/coreclr/nativeaot/Test.CoreLib/src/Internal/Runtime/Dispatch.cs	Adds Test.CoreLib `ResolveDispatch` export (currently stubbed).
src/coreclr/nativeaot/System.Private.TypeLoader/src/System.Private.TypeLoader.csproj	Adds `AnalysisCharacteristicAttribute` compilation input.
src/coreclr/nativeaot/System.Private.TypeLoader/src/Internal/Runtime/TypeLoader/TypeLoaderEnvironment.Metadata.cs	Updates GVM token handle construction call signature.
src/coreclr/nativeaot/System.Private.TypeLoader/src/Internal/Runtime/TypeLoader/TypeLoaderEnvironment.LdTokenResultLookup.cs	Removes async-variant handling from runtime-method-handle ldtoken cache machinery.
src/coreclr/nativeaot/System.Private.TypeLoader/src/Internal/Runtime/TypeLoader/TypeLoaderEnvironment.GVMResolution.cs	Reworks GVM resolution input shape (declaring type + handle + instantiation list + async flag).
src/coreclr/nativeaot/System.Private.TypeLoader/src/Internal/Runtime/TypeLoader/TypeLoaderEnvironment.cs	Adds `GenericVirtualMethodsPresent` analysis characteristic gate and new callback signature.
src/coreclr/nativeaot/System.Private.TypeLoader/src/Internal/Runtime/TypeLoader/GenericDictionaryCell.cs	Allocates dynamic dispatch-cell layouts for interface cells and new GVM dispatch cells.
src/coreclr/nativeaot/System.Private.CoreLib/src/System/RuntimeMethodHandle.cs	Removes async-variant flag from handle layout; adds helper to resolve GVM targets via callbacks.
src/coreclr/nativeaot/System.Private.CoreLib/src/System/Runtime/TypeLoaderExports.cs	Removes old `GVMLookupForSlot` cache-based implementation.
src/coreclr/nativeaot/System.Private.CoreLib/src/System/Delegate.cs	Updates GVM delegate initialization to go through dispatch-cell-based resolution.
src/coreclr/nativeaot/System.Private.CoreLib/src/System.Private.CoreLib.csproj	Links dispatch-cell types and adds CoreLib `ResolveDispatch` implementation source.
src/coreclr/nativeaot/System.Private.CoreLib/src/Internal/Runtime/Dispatch.cs	Implements `ResolveDispatch` and static/dynamic dispatch-cell resolution.
src/coreclr/nativeaot/System.Private.CoreLib/src/Internal/Runtime/CompilerServices/OpenMethodResolver.cs	Updates open-method resolver to resolve GVM targets via the new handle helper.
src/coreclr/nativeaot/System.Private.CoreLib/src/Internal/Runtime/Augments/TypeLoaderCallbacks.cs	Changes callback signature for resolving GVM targets (more explicit components).
src/coreclr/nativeaot/System.Private.CoreLib/src/CompatibilitySuppressions.xml	Adds compat suppressions for new public dispatch-cell types.
src/coreclr/nativeaot/Runtime/riscv64/DispatchResolve.S	Adds `RhpDispatchResolve` entrypoint (returns target rather than dispatching).
src/coreclr/nativeaot/Runtime/loongarch64/DispatchResolve.S	Adds `RhpDispatchResolve` entrypoint (returns target rather than dispatching).
src/coreclr/nativeaot/Runtime/i386/DispatchResolve.asm	Adds x86 `RhpDispatchResolve` (cache probe + fallback to worker).
src/coreclr/nativeaot/Runtime/EHHelpers.cpp	Teaches EH helper classification about `RhpDispatchResolve` AV locations/addresses.
src/coreclr/nativeaot/Runtime/arm64/DispatchResolve.S	Factors common macro + adds `RhpDispatchResolve` variant (returning target).
src/coreclr/nativeaot/Runtime/arm64/DispatchResolve.asm	Adds `RhpDispatchResolve` variant and calls `RhpCidResolve_Worker` for return-only slow path.
src/coreclr/nativeaot/Runtime/arm/DispatchResolve.S	Adds ARM32 `RhpDispatchResolve` with a barrier before reading cached code.
src/coreclr/nativeaot/Runtime/amd64/DispatchResolve.S	Adds `RhpDispatchResolve` macro variant (returning target).
src/coreclr/nativeaot/Runtime/amd64/DispatchResolve.asm	Adds `RhpDispatchResolve` macro variant and optimized slow path.
src/coreclr/nativeaot/Runtime.Base/src/System/Runtime/InternalCalls.cs	Adds `ClassLibFunctionId.ResolveDispatch` entry.
src/coreclr/nativeaot/Runtime.Base/src/System/Runtime/CachedInterfaceDispatch.cs	Routes cache misses to classlib `ResolveDispatch` and exports `RhpCidResolve_Worker`.
src/coreclr/nativeaot/Bootstrap/main.cpp	Exposes `ResolveDispatch` in the classlib function table.
src/coreclr/jit/importer.cpp	Switches NativeAOT GVM `ldvirtftn` import to pass dispatch cell instead of runtime method handle.
src/coreclr/inc/corinfo.h	Updates helper comment to document dispatch-cell argument for GVM lookup helper.

+    internal static class Dispatch
+    {
+        [RuntimeExport("ResolveDispatch")]
+        internal static unsafe MethodTable* ResolveDispatch(object pObject, DispatchCell* pCell)
+        {
+            // Assume this is a static dispatch cell first
+            foreach (TypeManagerHandle typeManager in StartupCodeHelpers.GetLoadedModules())
+            {


+                var pDispatchCellRegion = (DispatchCell*)RuntimeImports.RhGetModuleSection(typeManager, ReadyToRunSectionType.InterfaceDispatchCellRegion, out int length);
+                if (pCell >= pDispatchCellRegion && pCell < (byte*)pDispatchCellRegion + length)
+                {
+                    return ResolveStaticInterfaceDispatch(typeManager, pObject, (nint)(pCell - pDispatchCellRegion));
+                }
+
+                pDispatchCellRegion = (DispatchCell*)RuntimeImports.RhGetModuleSection(typeManager, ReadyToRunSectionType.GvmDispatchCellRegion, out length);
+                if (pCell >= pDispatchCellRegion && pCell < (byte*)pDispatchCellRegion + length)
+                {
+                    return ResolveGvmDispatch(typeManager, pObject, (nint)(pCell - pDispatchCellRegion));
+                }


+        ld      t0, 0(a0)
+
+        ld      t1, 0(a1)               // load cached MethodTable
+        bne     t0, t1, LOCAL_LABEL(ResolveInterfaceMethod)
+
+        ld      a0, 8(a1)               // return cached monomorphic resolved code address
+        ret


+        ld.d    $t0, $a0, 0
+
+        ld.d    $t1, $a1, 0             // load cached MethodTable
+        bne     $t0, $t1, LOCAL_LABEL(ResolveInterfaceMethod)
+
+        ld.d    $a0, $a1, 8             // return cached monomorphic resolved code address
+        jirl    $r0, $ra, 0


MichalStrehovsky · 2026-06-19T10:28:45Z

/azp run runtime-nativeaot-outerloop

azure-pipelines · 2026-06-19T10:29:00Z

Azure Pipelines successfully started running 1 pipeline(s).

Copilot

Pull request overview

Copilot reviewed 70 out of 70 changed files in this pull request and generated 4 comments.

+        private static nint GVMLookupForSlot(object o, RuntimeMethodHandle method)
+            => method.ResolveGenericVirtualMethodTarget(o);
+


MichalStrehovsky · 2026-06-24T04:41:03Z

/azp run runtime-nativeaot-outerloop

azure-pipelines · 2026-06-24T04:41:13Z

Azure Pipelines successfully started running 1 pipeline(s).

MichalStrehovsky added 3 commits June 19, 2026 12:14

Dead code

c919049

Refactor: route dispatch resolution to CoreLib

4cebf2e

Put GVM dispatch on the interface dispatch cell plan

0757b76

Copilot AI review requested due to automatic review settings June 19, 2026 06:19

github-actions Bot added the area-NativeAOT-coreclr label Jun 19, 2026

Copilot started reviewing on behalf of MichalStrehovsky June 19, 2026 06:20 View session

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Merge branch 'main' into gvmdispatch

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129609 MichalStrehovsky/rt-sz#232

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		private static nint GVMLookupForSlot(object o, RuntimeMethodHandle method)
		=> method.ResolveGenericVirtualMethodTarget(o);

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