JIT: Devirtualize non-shared generic virtual methods #122023

hez2010 · 2025-11-27T17:12:36Z

Enable devirtualization support for generic virtual methods.

When we see a base method having a method instantiation, we use FindOrCreateAssociatedMethodDesc to obtain the devirted method.

Also introduced a jit knob so that it can be turned off at any time.

AOT support is not included in this PR, which needs additional work in managed type system.

Also, if we end up with an instantiating stub (i.e. a shared generic method that requires runtime lookup), we don't have the correct generic context so we need to bail out for now.

Codegen example:

public class IntProcessor : VirtualGenericClass, IVritualGenericInterface
{
    public override void Process<T>(T item)
    {
        Console.WriteLine(item.ToString());
    }
}

public interface IVritualGenericInterface
{
    void Process<T>(T item) where T : notnull;
}

public static void Test<T>(IVritualGenericInterface ifce, T item) where T : notnull
{
    ifce.Process(item);
}

public static void Test<T>(VirtualGenericClass baseClass, T item) where T : notnull
{
    baseClass.Process(item);
}

static void Test()
{
    IVritualGenericInterface i = new IntProcessor();
    Test(i, 42);

    VirtualGenericClass c = new IntProcessor();
    Test(c, 42);
}

Codegen diff:

 G_M27646_IG01:  ;; offset=0x0000
-       push     rsi
        push     rbx
-       sub      rsp, 40
+       sub      rsp, 32
-                                                ;; size=6 bbWeight=1 PerfScore 2.25
+                                                ;; size=5 bbWeight=1 PerfScore 1.25
-G_M27646_IG02:  ;; offset=0x0006
+G_M27646_IG02:  ;; offset=0x0005
-       mov      rbx, 0x7FFE0803F318      ; Program+IntProcessor
+       mov      rbx, 0x221CA429C38      ; 'System.Int32'
        mov      rcx, rbx
-       call     CORINFO_HELP_NEWSFAST
+       call     [System.Console:WriteLine(System.Object)]
-       mov      rsi, rax
+       mov      ecx, 42
-       mov      rcx, rsi
+       call     [System.Number:Int32ToDecStr(int):System.String]
-       mov      rdx, 0x7FFE0803F100      ; Program+IVritualGenericInterface
+       mov      rcx, rax
-       mov      r8, 0x7FFE0803F6A8      ; token handle
+       call     [System.Console:WriteLine(System.String)]
-       call     CORINFO_HELP_VIRTUAL_FUNC_PTR
-       mov      rcx, rsi
-       mov      edx, 42
-       call     rax
        mov      rcx, rbx
-       call     CORINFO_HELP_NEWSFAST
+       call     [System.Console:WriteLine(System.Object)]
-       mov      rbx, rax
+       mov      ecx, 42
-       mov      rcx, rbx
+       call     [System.Number:Int32ToDecStr(int):System.String]
-       mov      rdx, 0x7FFE0803EF30      ; Program+VirtualGenericClass
+       mov      rcx, rax
-       mov      r8, 0x7FFE0803F8A8      ; token handle
+       call     [System.Console:WriteLine(System.String)]
-       call     CORINFO_HELP_VIRTUAL_FUNC_PTR
-       mov      rcx, rbx
-       mov      edx, 42
-       call     rax
        nop
-                                                ;; size=109 bbWeight=1 PerfScore 14.00
+                                                ;; size=69 bbWeight=1 PerfScore 20.00
-G_M27646_IG03:  ;; offset=0x0073
+G_M27646_IG03:  ;; offset=0x004A
-       add      rsp, 40
+       add      rsp, 32
        pop      rbx
-       pop      rsi
        ret
-                                                ;; size=7 bbWeight=1 PerfScore 2.25
+                                                ;; size=6 bbWeight=1 PerfScore 1.75

Contributes to #112596

cc: @dotnet/jit-contrib

Copilot

Pull request overview

This PR enables devirtualization support for generic virtual methods in the JIT compiler, allowing calls to generic virtual methods to be devirtualized when the exact type is known at JIT time. This optimization eliminates virtual dispatch overhead and enables further optimizations like inlining.

Key changes:

Removes the assertion that previously blocked generic method devirtualization
Generalizes array interface devirtualization to support generic virtual methods by renaming wasArrayInterfaceDevirt to needsMethodContext
Adds runtime lookup support for generic method instantiation parameters

Reviewed changes

Copilot reviewed 13 out of 13 changed files in this pull request and generated 4 comments.

Show a summary per file

File	Description
src/coreclr/vm/jitinterface.cpp	Removes assertion blocking generic method devirtualization and adds logic to handle generic virtual methods using `FindOrCreateAssociatedMethodDesc`
src/coreclr/inc/corinfo.h	Renames `wasArrayInterfaceDevirt` to `needsMethodContext` to generalize the field meaning
src/coreclr/jit/jitconfigvalues.h	Adds `JitEnableGenericVirtualDevirtualization` configuration flag to control the feature
src/coreclr/jit/gentree.h	Adds `IsGenericVirtual()` helper method to identify generic virtual method calls
src/coreclr/jit/gentree.cpp	Updates `IsDevirtualizationCandidate()` to include generic virtual methods (non-AOT only)
src/coreclr/jit/importercalls.cpp	Implements devirtualization logic for generic virtual methods including runtime lookup handling, updates comments and variable names, and introduces DEVIRT label for control flow
src/coreclr/jit/inline.h	Renames `arrayInterface` field to `needsMethodContext` in `InlineCandidateInfo` struct
src/coreclr/jit/indirectcalltransformer.cpp	Updates to use renamed `needsMethodContext` field
src/coreclr/tools/Common/JitInterface/CorInfoTypes.cs	Updates managed struct definition to match renamed field
src/coreclr/tools/Common/JitInterface/CorInfoImpl.cs	Updates to use renamed field in managed implementation
src/coreclr/tools/superpmi/superpmi-shared/agnostic.h	Updates SuperPMI data structure with renamed field
src/coreclr/tools/superpmi/superpmi-shared/methodcontext.cpp	Updates SuperPMI recording/replay to use renamed field

src/coreclr/jit/importercalls.cpp

hez2010 · 2025-11-28T00:52:25Z

@MihuBot

src/coreclr/jit/importercalls.cpp

src/coreclr/vm/jitinterface.cpp

jakobbotsch

LGTM apart from that. Thanks!
@davidwrighton can you take a look too?

davidwrighton · 2026-01-05T18:33:10Z

@hez2010 sorry about the delay, I got stuck in a bunch of work just before the holidays and wasn't able to do the review before vacation began.

jakobbotsch · 2026-01-06T18:55:02Z

I'm guessing the crossgen issues are related, I don't see them on other PRs. Can you see if you can reproduce them?

hez2010 · 2026-01-08T16:53:07Z

I'm guessing the crossgen issues are related, I don't see them on other PRs. Can you see if you can reproduce them?

I managed to reproduce the freebsd one on my local cross-build environment. Will investigate it soon to see whether it's related or not.

hez2010 · 2026-01-09T13:06:42Z

We hit the assertion here:

/home/i/runtime/src/coreclr/jit/importercalls.cpp:8666
Assertion failed 'call->IsVirtualStub()' in 'System.Threading.StackHelper:CallOnEmptyStack[System.__Canon,System.__Canon,System.__Canon,System.__Canon](System.Func`4[System.__Canon,System.__Canon,System.__Canon,System.__Canon],System.__Canon,System.__Canon,System.__Canon):System.__Canon' during 'Importation' (IL size 116; hash 0x7bf56612; FullOpts)

/home/i/runtime/src/coreclr/jit/importercalls.cpp:8666
Assertion failed 'call->IsVirtualStub()' in 'System.Threading.StackHelper:CallOnEmptyStack[System.__Canon,System.__Canon](System.Func`2[System.__Canon,System.__Canon],System.__Canon):System.__Canon' during 'Importation' (IL size 102; hash 0x657768d4; FullOpts)

https://github.com/hez2010/runtime/blob/40d7569852bd8cecef706532d374ab0e8f7e53f2/src/coreclr/jit/importercalls.cpp#L8664-L8670

I think GVM applies the same with virtual stub, where in R2R mode, we might see GVM calls to non-virtuals. I think we should change the assertion to call->IsVirtualStub() || call->IsGenericVirtual(). What do you think? @jakobbotsch

jakobbotsch · 2026-01-09T13:30:04Z

I think GVM applies the same with virtual stub, where in R2R mode, we might see GVM calls to non-virtuals. I think we should change the assertion to call->IsVirtualStub() || call->IsGenericVirtual(). What do you think? @jakobbotsch

Seems reasonable to me.

src/coreclr/jit/importercalls.cpp

hez2010 · 2026-01-11T12:35:46Z

CI is green now.
By the way, do you know why the assertion message didn't show up in the CI log before? It makes it hard to spot the cause of bug without a local repro. (I guess it's because MSBuild somehow omitted all the logs from crossgen2?)

jakobbotsch · 2026-01-12T12:45:13Z

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

azure-pipelines · 2026-01-12T12:45:34Z

Azure Pipelines successfully started running 2 pipeline(s).

jakobbotsch · 2026-01-12T12:46:49Z

CI is green now. By the way, do you know why the assertion message didn't show up in the CI log before? It makes it hard to spot the cause of bug without a local repro. (I guess it's because MSBuild somehow omitted all the logs from crossgen2?)

I am not sure, perhaps that is something specific to how the crossgen2 testing is done for the community targets.

I kicked off some more testing. There are some known test failures in jitstress (for async), so might take some filtering once it's done to validate things.

hez2010 · 2026-01-12T17:37:36Z

I kicked off some more testing. There are some known test failures in jitstress (for async), so might take some filtering once it's done to validate things.

All failures seem to be preexisting and unrelated.

jakobbotsch · 2026-01-13T13:10:09Z

/ba-g Failure is #122345 that is not being matched automatically

jakobbotsch · 2026-01-13T13:11:49Z

Thanks!

hez2010 added 3 commits November 27, 2025 23:34

Rename wasArrayInterfaceDevirt to needsMethodContext

fbff8d6

Devirtualize generic virtual methods

729b269

Disable GVM devirt for AOT

5c15b23

Copilot AI review requested due to automatic review settings November 27, 2025 17:12

hez2010 requested a review from MichalStrehovsky as a code owner November 27, 2025 17:12

dotnet-policy-service bot added the community-contribution Indicates that the PR has been added by a community member label Nov 27, 2025

github-actions bot added the area-CodeGen-coreclr CLR JIT compiler in src/coreclr/src/jit and related components such as SuperPMI label Nov 27, 2025

Copilot started reviewing on behalf of hez2010 November 27, 2025 17:13 View session

Copilot finished reviewing on behalf of hez2010 November 27, 2025 17:16

Copilot AI reviewed Nov 27, 2025

View reviewed changes

src/coreclr/jit/importercalls.cpp Outdated Show resolved Hide resolved

src/coreclr/jit/importercalls.cpp Outdated Show resolved Hide resolved

src/coreclr/jit/importercalls.cpp Outdated Show resolved Hide resolved

src/coreclr/jit/importercalls.cpp Outdated Show resolved Hide resolved

Unblock late devirt as well

6e678a5

hez2010 force-pushed the gvm-devirt-2 branch from 530e75d to 6e678a5 Compare November 27, 2025 17:26

hez2010 added 6 commits November 28, 2025 02:42

Set single-def

c488b84

Address feedbacks

0ca8b93

Merge branch 'main' into gvm-devirt-2

b396d26

Meh

0ac9d6d

JIT format

8976d4a

JIT format again

8d0845e

This was referenced Nov 27, 2025

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

Open

[8.0] GC Large array test failure #114222

Open

Check methHndArg

1d389f1

MihuBot mentioned this pull request Nov 28, 2025

[JitDiff X64] [hez2010] JIT: Devirtualize generic virtual methods MihuBot/runtime-utils#1649

Open

hez2010 marked this pull request as draft November 28, 2025 02:33

This was referenced Nov 28, 2025

CryptographicException in NonPowerOfTwoKeySizeOaepRoundtrip test #120606

Open

SIGSEGV in System.Net.Quic.Functional.Tests #121575

Closed

jakobbotsch reviewed Nov 28, 2025

View reviewed changes

src/coreclr/jit/importercalls.cpp Outdated Show resolved Hide resolved

hez2010 added 3 commits November 29, 2025 23:54

Rework how inst param being embedded

217c9f2

Bail out GVM devirt in managed type system instead

4b64c2e

Remove the out-dated comments

e8668a1

Copilot AI mentioned this pull request Dec 12, 2025

Disable UniqueMarshalling COM tests causing "Over release of MOW - COM" assertion #122473

Closed

jakobbotsch reviewed Dec 12, 2025

View reviewed changes

src/coreclr/vm/jitinterface.cpp Outdated Show resolved Hide resolved

jakobbotsch approved these changes Dec 12, 2025

View reviewed changes

jakobbotsch requested a review from davidwrighton December 12, 2025 10:31

hez2010 added 2 commits December 12, 2025 19:56

Always set needsMethodContext and isInstantiatingStub to false

e22692c

Merge branch 'main' into gvm-devirt-2

d2af9f4

davidwrighton approved these changes Jan 5, 2026

View reviewed changes

jakobbotsch closed this Jan 6, 2026

jakobbotsch reopened this Jan 6, 2026

build-analysis bot mentioned this pull request Jan 6, 2026

iOS.Device test WorkItemExecutions #122874

Open

Merge branch 'main' into gvm-devirt-2

40d7569

jakobbotsch reviewed Jan 9, 2026

View reviewed changes

src/coreclr/jit/importercalls.cpp Outdated Show resolved Hide resolved

Address the crossgen2 assertion

7b4c2c8

jakobbotsch approved these changes Jan 9, 2026

View reviewed changes

jakobbotsch merged commit 87b470c into dotnet:main Jan 13, 2026
184 of 189 checks passed

dotnet-maestro bot mentioned this pull request Jan 14, 2026

[main] Source code updates from dotnet/runtime dotnet/dotnet#4196

Merged

This was referenced Jan 14, 2026

JIT: Devirtualize non-shared GVMs in R2R #123183

Open

JIT: Devirtualize shared GVM that doesn't need a runtime lookup #123323

Open

JIT: Devirtualize non-shared generic virtual methods #122023

JIT: Devirtualize non-shared generic virtual methods #122023

Uh oh!

Conversation

hez2010 commented Nov 27, 2025 • edited Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Uh oh!

Copilot AI left a comment

Choose a reason for hiding this comment

Pull request overview

Reviewed changes

Uh oh!

Uh oh!

Uh oh!

Uh oh!

Uh oh!

hez2010 commented Nov 28, 2025

Uh oh!

Uh oh!

Uh oh!

jakobbotsch left a comment

Choose a reason for hiding this comment

Uh oh!

davidwrighton commented Jan 5, 2026

Uh oh!

jakobbotsch commented Jan 6, 2026

Uh oh!

hez2010 commented Jan 8, 2026

Uh oh!

hez2010 commented Jan 9, 2026 • edited Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Uh oh!

jakobbotsch commented Jan 9, 2026

Uh oh!

Uh oh!

hez2010 commented Jan 11, 2026 • edited Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Uh oh!

jakobbotsch commented Jan 12, 2026

Uh oh!

azure-pipelines bot commented Jan 12, 2026

Uh oh!

jakobbotsch commented Jan 12, 2026

Uh oh!

hez2010 commented Jan 12, 2026 • edited Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Uh oh!

jakobbotsch commented Jan 13, 2026

Uh oh!

Uh oh!

jakobbotsch commented Jan 13, 2026

Uh oh!

Reviewers

Assignees

Labels

Projects

Milestone

Development

Uh oh!

5 participants

hez2010 commented Nov 27, 2025 •

edited

Loading

hez2010 commented Jan 9, 2026 •

edited

Loading

hez2010 commented Jan 11, 2026 •

edited

Loading

hez2010 commented Jan 12, 2026 •

edited

Loading