Support devirtualization for virtual methods that require runtime lookups by hez2010 · Pull Request #129806 · dotnet/runtime

hez2010 · 2026-06-24T16:44:25Z

Add support for devirtualizing virtual methods that require a runtime lookup. In this case we can't avoid the expensive runtime lookup, but at least the callee now can be devirtualized and inlined, so that they can benefit from the downstream optimizations like escape analysis, struct promotion and etc.

When we see an inexact instantiating stub on an exact class, we compute a runtime lookup against the shared generic token of the virtual method.

public interface IProcessor
{
    object? Process<T>(T value);
}

public class PrintProcessor : IProcessor
{
    public object? Process<T>(T value)
    {
        return value;
    }
}

public static class Program
{
    public static void Main()
    {
        Console.WriteLine(Call("hello"));
    }

    [MethodImpl(MethodImplOptions.NoInlining)]
    static object? Call<T>(T value) where T : class
    {
        IProcessor processor = new PrintProcessor();
        return processor.Process(value);
    }
}

Codegen for Call:

Before:

G_M47477_IG01:  ;; offset=0x0000
       push     rdi
       push     rsi
       push     rbx
       sub      rsp, 48
       mov      qword ptr [rsp+0x28], rcx
       mov      rbx, rcx
       mov      rsi, rdx
                                                ;; size=18 bbWeight=1 PerfScore 4.75
G_M47477_IG02:  ;; offset=0x0012
       mov      rcx, 0x7FF9258BB130      ; PrintProcessor
       call     CORINFO_HELP_NEWSFAST
       mov      rdi, rax
       mov      rcx, qword ptr [rbx+0x48]
       mov      r8, qword ptr [rcx+0x10]
       test     r8, r8
       je       SHORT G_M47477_IG05
                                                ;; size=31 bbWeight=1 PerfScore 6.75
G_M47477_IG03:  ;; offset=0x0031
       mov      rcx, rdi
       mov      rdx, 0x7FF9258BAF08      ; IProcessor
       call     CORINFO_HELP_VIRTUAL_FUNC_PTR
       mov      rcx, rdi
       mov      rdx, rsi
       call     rax
       nop
                                                ;; size=27 bbWeight=1 PerfScore 5.25
G_M47477_IG04:  ;; offset=0x004C
       add      rsp, 48
       pop      rbx
       pop      rsi
       pop      rdi
       ret
                                                ;; size=8 bbWeight=1 PerfScore 2.75
G_M47477_IG05:  ;; offset=0x0054
       mov      rcx, rbx
       mov      rdx, 0x7FF9258E0DE8      ; global ptr
       call     CORINFO_HELP_RUNTIMEHANDLE_METHOD
       mov      r8, rax
       jmp      SHORT G_M47477_IG03
                                                ;; size=23 bbWeight=0.20 PerfScore 0.75

After:

G_M47477_IG01:  ;; offset=0x0000
       sub      rsp, 40
       mov      qword ptr [rsp+0x20], rcx
                                                ;; size=9 bbWeight=1 PerfScore 1.25
G_M47477_IG02:  ;; offset=0x0009
       mov      rax, qword ptr [rcx+0x48]
       cmp      qword ptr [rax+0x08], 24
       jle      SHORT G_M47477_IG03
                                                ;; size=11 bbWeight=1 PerfScore 5.00
G_M47477_IG03:  ;; offset=0x0014
       mov      rax, rdx
                                                ;; size=3 bbWeight=1 PerfScore 0.25
G_M47477_IG04:  ;; offset=0x0017
       add      rsp, 40
       ret
                                                ;; size=5 bbWeight=1 PerfScore 1.25

Contributes to #112596

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hez2010 · 2026-06-24T16:47:18Z

@MihuBot -nuget

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hez2010 · 2026-06-25T04:15:19Z

@MihuBot -nuget -dependsOn 128702

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hez2010 · 2026-07-01T11:46:22Z

This is now ready for review. It's the last piece of the whole story (at least for coreclr).

cc: @jakobbotsch @davidwrighton @MichalStrehovsky

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+            object helperArg;
+            if (entryKind == DictionaryEntryKind.DevirtualizedMethodDescSlot)
            {
-                var methodIL = HandleToObject(pResolvedToken.tokenScope);
-                MethodDesc sharedMethod = methodIL.OwningMethod.GetSharedRuntimeFormMethodTarget();
-                // We shouldn't be needing shared generics in resumption stubs - generics info should all be stored in the continuation
-                Debug.Assert(MethodBeingCompiled is not AsyncResumptionStub);
-                _compilation.NodeFactory.DetectGenericCycles(MethodBeingCompiled, sharedMethod);
-                helperArg = new MethodWithToken(methodDesc, HandleToModuleToken(ref pResolvedToken, out bool strippedInstantiation), constrainedType, unboxing: false, genericContextObject: sharedMethod, forceOwningTypeFromMethodDesc: strippedInstantiation);
+                Debug.Assert(templateMethod != null);
+                MethodDesc tokenMethod = (MethodDesc)GetRuntimeDeterminedObjectForToken(ref pResolvedToken);
+                if (tokenMethod.HasInstantiation)
+                {
+                    templateMethod = _compilation.TypeSystemContext.GetInstantiatedMethod(templateMethod.GetMethodDefinition(), tokenMethod.Instantiation);
+                }
+                _compilation.NodeFactory.DetectGenericCycles(MethodBeingCompiled, templateMethod);
+                ModuleToken templateMethodToken =
+                    _compilation.NodeFactory.Resolver.GetModuleTokenForMethod(templateMethod.GetTypicalMethodDefinition(), allowDynamicallyCreatedReference: false, throwIfNotFound: true);
+                helperArg = new MethodWithToken(templateMethod, templateMethodToken, constrainedType: null, unboxing: false, genericContextObject: null);
            }


hez2010 · 2026-07-01T13:05:11Z

@MihuBot -nuget

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jakobbotsch · 2026-07-01T15:16:46Z

/azp run runtime-coreclr outerloop, runtime-coreclr jitstress, runtime-coreclr libraries-jitstress

azure-pipelines · 2026-07-01T15:17:03Z

Azure Pipelines successfully started running 3 pipeline(s).

dotnet-policy-service · 2026-07-01T15:17:27Z

Tagging subscribers to this area: @JulieLeeMSFT, @jakobbotsch
See info in area-owners.md if you want to be subscribed.

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Copilot AI review requested due to automatic review settings June 24, 2026 16:44

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[JitDiff X64] [hez2010] Support devirtualization for virtual methods that re ... MihuBot/runtime-utils#2047

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hez2010 mentioned this pull request Jun 24, 2026

JIT: Devirtualization for generic virtual methods #112596

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[JitDiff X64] [hez2010] Support devirtualization for virtual methods that re ... MihuBot/runtime-utils#2050

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hez2010 added 5 commits June 29, 2026 22:05

CoreCLR support

2723cdd

R2R

9ce2f81

Various fixes

2f787b6

JIT format

071523a

Format

309d8fd

hez2010 force-pushed the devirt-runtime-lookups branch from 5497d14 to 309d8fd Compare June 29, 2026 13:07

hez2010 added 2 commits July 1, 2026 20:10

Merge branch 'main' into devirt-runtime-lookups

7721087

Remove unnecessary unboxing stub handling

0dc166e

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Support runtime lookup together with unboxing stub

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Comment thread src/coreclr/jit/importercalls.cpp

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Merge branch 'main' into devirt-runtime-lookups

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

Comment thread src/coreclr/vm/jitinterface.cpp

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[JitDiff X64] [hez2010] Support devirtualization for virtual methods that re ... MihuBot/runtime-utils#2057

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hez2010 added 3 commits July 1, 2026 22:43

Add a generic context shift test for runtime lookups

fd30d8d

Use the correct caller method

3704f25

Unboxed entry should not be an instantiating stub

ecb5475

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Comment thread src/coreclr/jit/importercalls.cpp

Comment thread src/coreclr/vm/jitinterface.cpp

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

jakobbotsch added area-CodeGen-coreclr CLR JIT compiler in src/coreclr/src/jit and related components such as SuperPMI and removed area-crossgen2-coreclr only use for closed issues labels Jul 1, 2026

hez2010 added 3 commits July 3, 2026 00:33

Find the lookup context from IR in late devirt

218669d

Add tests

e93af8c

Merge branch 'main' into devirt-runtime-lookups

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Comment thread src/coreclr/tools/superpmi/superpmi-shared/methodcontext.cpp

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hez2010 commented Jun 24, 2026 •

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