JIT: Devirtualize shared generic virtual methods by hez2010 · Pull Request #123323 · dotnet/runtime

hez2010 · 2026-01-18T11:52:05Z

Previously in #122023, we hit an issue with GVM devirtualization when the devirtualized target is a shared generic method. GVM calls are imported with a runtime lookup that is specific to the base method. After devirtualization, the call requires the instantiation argument for the implementing method, and the existing lookup cannot be reused.

This PR unblocks devirtualization for shared generic targets by ensuring the call receives the correct instantiation parameter for the devirtualized method:

The multiple ad-hoc flags in dvInfo now have been unified into a single instParamLookup
When the target does not require a runtime lookup, we already know the exact generic context. We pass the instantiating stub as the inst param (shared with the existing array interface devirtualization path).
When the target requires a runtime lookup, we now introduced a new DictionaryEntryKind::DevirtualizedMethodDescSlot, and pass it to the instParamLookup so that later the VM knows that it needs to encode the class token from the devirtualized method instead of the original token.

Also due to the instParamLookup change I implement the support for R2R as well.

Example:

IVritualGenericInterface i = new Processor();
Test(i, "test");

VirtualGenericClass c = new Processor();
Test(c, "test");

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

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

public class Processor : VirtualGenericClass, IVritualGenericInterface
{
    [MethodImpl(MethodImplOptions.AggressiveInlining)]
    public override void Process<T>(T item)
    {
        Console.WriteLine(typeof(T));
        Console.WriteLine(item.ToString());
    }
}

Codegen diff:

  G_M27646_IG01:
-       push     rdi
        push     rsi
        push     rbx
-       sub      rsp, 32
+       sub      rsp, 40
-                                                ;; size=7 bbWeight=1 PerfScore 3.25
+                                                ;; size=6 bbWeight=1 PerfScore 2.25
 G_M27646_IG02:
-       mov      rbx, 0xD1FFAB1E      ; Program+Processor
+       mov      rbx, 0xD1FFAB1E      ; 'System.String'
        mov      rcx, rbx
-       call     CORINFO_HELP_NEWSFAST
+       call     [System.Console:WriteLine(System.Object)]
-       mov      rsi, rax
+       mov      rsi, 0xD1FFAB1E      ; 'test'
-       mov      rdi, 0xD1FFAB1E      ; 'test'
        mov      rcx, rsi
-       mov      rdx, 0xD1FFAB1E      ; Program+IVritualGenericInterface
+       call     [System.Console:WriteLine(System.String)]
-       mov      r8, 0xD1FFAB1E      ; token handle
-       call     CORINFO_HELP_VIRTUAL_FUNC_PTR
+       mov      rcx, rbx
+       call     [System.Console:WriteLine(System.Object)]
        mov      rcx, rsi
-       mov      rdx, rdi
+       call     [System.Console:WriteLine(System.String)]
-       call     rax
+       nop
-       mov      rcx, rbx
+                                                ;; size=57 bbWeight=1 PerfScore 13.75
-       call     CORINFO_HELP_NEWSFAST
+G_M27646_IG03:
-       mov      rbx, rax
+       add      rsp, 40
-       mov      rcx, rbx
+       pop      rbx
-       mov      rdx, 0xD1FFAB1E      ; Program+VirtualGenericClass
+       pop      rsi
-       mov      r8, 0xD1FFAB1E      ; token handle
+       ret
-       call     CORINFO_HELP_VIRTUAL_FUNC_PTR
+                                                ;; size=7 bbWeight=1 PerfScore 2.25
-       mov      rcx, rbx
-       mov      rdx, rdi
-       call     rax
-       nop
-                                                ;; size=115 bbWeight=1 PerfScore 14.25
-G_M27646_IG03:
-       add      rsp, 32
-       pop      rbx
-       pop      rsi
-       pop      rdi
-       ret
-                                                ;; size=8 bbWeight=1 PerfScore 2.75

Contributes to #112596

Copilot

Pull request overview

This PR enables JIT devirtualization for shared generic virtual methods (GVM) that don't require runtime lookups. Previously, all shared GVMs were blocked from devirtualization due to concerns about having the right generic context. This change unblocks devirtualization when the instantiating stub doesn't need a runtime lookup, by checking for the presence of a GT_RUNTIMELOOKUP node before proceeding.

Changes:

Introduced needsMethodContext flag to track when a method context is needed for devirtualization
For shared generic methods, obtain the instantiating stub and set needsMethodContext = true
Unified handling of array interface and generic virtual method devirtualization paths
Added runtime lookup check in the JIT to bail out when a lookup is needed but context is unavailable

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.

File	Description
src/coreclr/vm/jitinterface.cpp	Added logic to detect shared generic methods and obtain instantiating stubs, unified array and GVM devirtualization handling
src/coreclr/jit/importercalls.cpp	Updated assertions to allow GVM in AOT scenarios, added runtime lookup check to prevent devirtualization when context is unavailable

src/coreclr/vm/jitinterface.cpp

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

hez2010 · 2026-01-18T12:51:29Z

@MihuBot

src/coreclr/jit/importercalls.cpp

hez2010 · 2026-01-18T15:27:20Z

Failures seem to be caused by missing context during spmi replay. Otherwise all tests are passing.

src/coreclr/vm/jitinterface.cpp

Copilot

Pull request overview

Copilot reviewed 8 out of 8 changed files in this pull request and generated 3 comments.

src/coreclr/jit/importercalls.cpp

src/coreclr/vm/jitinterface.cpp

hez2010 · 2026-02-10T19:14:04Z

I realised that the existing runtime lookup tests are not actually doing runtime lookup, they are const lookup.
So I updated the runtime lookup tests to make them really perform a runtime lookup.

Copilot

Pull request overview

Copilot reviewed 18 out of 18 changed files in this pull request and generated 1 comment.

Copilot · 2026-02-10T19:23:10Z

src/coreclr/jit/importercalls.cpp

+            // If we don't know the array type exactly we may have the wrong interface type here.
+            // Bail out.
+            //
+            if (!isExact)


The needsCompileTimeLookup path unconditionally bails out when !isExact with an "Array interface devirt" message, but needsCompileTimeLookup can now also be true for shared generic virtual method devirtualization (not just array-interface devirt). This can prevent devirtualization in cases where objClassIsFinal/derivedMethodIsFinal would otherwise allow it. Consider gating the !isExact bailout (and the diagnostic text) to the array-interface scenario only, and allow the GVM path to proceed without requiring isExact.

Suggested change

// If we don't know the array type exactly we may have the wrong interface type here.

// Bail out.

//

if (!isExact)

// For array interface devirtualization, if we don't know the array type exactly

// we may have the wrong interface type here. Bail out.

//

if (!call->IsGenericVirtual(this) && !isExact)

Copilot

Pull request overview

Copilot reviewed 18 out of 18 changed files in this pull request and generated no new comments.

Copilot

Pull request overview

Copilot reviewed 18 out of 18 changed files in this pull request and generated 1 comment.

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

hez2010 · 2026-02-11T12:32:19Z

Test failures seem unrelated.
@jakobbotsch Can I have another pri1 test run?

jakobbotsch · 2026-02-11T13:01:55Z

/azp run runtime-coreclr outerloop

azure-pipelines · 2026-02-11T13:02:16Z

Azure Pipelines successfully started running 1 pipeline(s).

Copilot

Pull request overview

Copilot reviewed 18 out of 18 changed files in this pull request and generated 1 comment.

Copilot · 2026-02-12T13:42:37Z

src/coreclr/tools/aot/ILCompiler.ReadyToRun/JitInterface/CorInfoImpl.ReadyToRun.cs

-                            helperArg = new MethodWithToken(methodDesc, HandleToModuleToken(ref pResolvedToken), constrainedType, unboxing: false, context: sharedMethod);
+                            if (helperArgToken.tokenType == CorInfoTokenKind.CORINFO_TOKENKIND_DevirtualizedMethod)
+                            {
+                                helperArg = ComputeMethodWithToken(HandleToObject(pResolvedToken.hMethod), ref helperArgToken, constrainedType, false);


In getReadyToRunHelper, when handling a generic handle lookup for a devirtualized method token (CORINFO_TOKENKIND_DevirtualizedMethod), the code calls ComputeMethodWithToken using HandleToObject(pResolvedToken.hMethod). At this point pResolvedToken is the token passed to the helper request (often the original/base token), while helperArgToken is the devirtualized token. This can cause the ReadyToRun helper to be constructed for the wrong method. Use the devirtualized method handle (e.g., methodDesc / helperArgToken.hMethod) when calling ComputeMethodWithToken so the fixup encodes the devirtualized target correctly.

Suggested change

helperArg = ComputeMethodWithToken(HandleToObject(pResolvedToken.hMethod), ref helperArgToken, constrainedType, false);

helperArg = ComputeMethodWithToken(methodDesc, ref helperArgToken, constrainedType, false);

hez2010 · 2026-02-12T18:07:50Z

I think the pri1 failure should be addressed (it was crossgen2 related). @jakobbotsch I would like one more outerloop run.

jakobbotsch · 2026-02-12T18:11:16Z

/azp run runtime-coreclr outerloop

azure-pipelines · 2026-02-12T18:11:23Z

Azure Pipelines will not run the associated pipelines, because the pull request was updated after the run command was issued. Review the pull request again and issue a new run command.

jakobbotsch · 2026-02-12T18:34:13Z

/azp run runtime-coreclr outerloop

azure-pipelines · 2026-02-12T18:34:37Z

Azure Pipelines successfully started running 1 pipeline(s).

hez2010 · 2026-02-13T15:21:53Z

Confirmed the pri1 failure is unrelated. The failure is runtime async:

I think the PR is ready now. Please take a look.

Support for shared GVM devirt that doesn't require a runtime lookup

789055d

Copilot AI review requested due to automatic review settings January 18, 2026 11:52

github-actions bot added the area-CodeGen-coreclr CLR JIT compiler in src/coreclr/src/jit and related components such as SuperPMI label Jan 18, 2026

dotnet-policy-service bot added the community-contribution Indicates that the PR has been added by a community member label Jan 18, 2026

Copilot started reviewing on behalf of hez2010 January 18, 2026 11:52 View session

Copilot AI reviewed Jan 18, 2026

View reviewed changes

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

Update src/coreclr/vm/jitinterface.cpp

555ba83

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

MihuBot mentioned this pull request Jan 18, 2026

[JitDiff X64] [hez2010] JIT: Devirtualize shared GVM that doesn't need a run ... MihuBot/runtime-utils#1717

Open

hez2010 commented Jan 18, 2026

View reviewed changes

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

A better way to check runtime lookup

25c0967

hez2010 requested a review from MichalStrehovsky as a code owner January 18, 2026 13:15

Add a TODO

65a61bb

hez2010 mentioned this pull request Jan 18, 2026

JIT: Devirtualization for generic virtual methods #112596

Open

16 tasks

hez2010 commented Jan 20, 2026

View reviewed changes

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

Merge branch 'main' into gvm-devirt-shared

8d74fdb

This was referenced Jan 29, 2026

[android-arm64] The Operation will be canceled. The next steps may not contain expected logs. dotnet/dnceng#6408

Open

The Operation will be canceled. The next steps may not contain expected logs. dotnet/dnceng#3008

Open

Copilot AI review requested due to automatic review settings February 1, 2026 18:06

Copilot started reviewing on behalf of hez2010 February 1, 2026 18:07 View session

hez2010 changed the title ~~JIT: Devirtualize shared GVM that doesn't need a runtime lookup~~ JIT: Devirtualize shared generic virtual methods Feb 1, 2026

Add support for runtime lookup as well

c8b7f69

hez2010 force-pushed the gvm-devirt-shared branch from bf5b09a to c8b7f69 Compare February 1, 2026 18:12

Copilot AI reviewed Feb 1, 2026

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/vm/jitinterface.cpp Outdated Show resolved Hide resolved

hez2010 marked this pull request as draft February 1, 2026 18:23

hez2010 added 2 commits February 2, 2026 04:04

Try another approach

0aea180

Nit

5fbd527

Copilot AI review requested due to automatic review settings February 1, 2026 19:06

Copilot started reviewing on behalf of hez2010 February 1, 2026 19:07 View session

Copilot started reviewing on behalf of hez2010 February 10, 2026 19:13 View session

Copilot AI reviewed Feb 10, 2026

View reviewed changes

hez2010 added 2 commits February 11, 2026 04:47

Fix R2R const lookup

1aea555

Bail on runtime lookup for R2R

d5e3485

Copilot AI review requested due to automatic review settings February 10, 2026 20:25

Copilot started reviewing on behalf of hez2010 February 10, 2026 20:26 View session

Copilot AI reviewed Feb 10, 2026

View reviewed changes

hez2010 added 2 commits February 11, 2026 06:20

R2R runtime lookup support

267e187

Merge branch 'main' into gvm-devirt-shared

ca8f876

Copilot AI review requested due to automatic review settings February 11, 2026 09:26

Copilot started reviewing on behalf of hez2010 February 11, 2026 09:28 View session

Copilot AI reviewed Feb 11, 2026

View reviewed changes

src/coreclr/tools/Common/JitInterface/CorInfoImpl.cs Outdated Show resolved Hide resolved

build-analysis bot mentioned this pull request Feb 11, 2026

System.IO.Tests.Directory_Create_Tests.FileSystemWatcher_Directory_Create_InNestedDirectory fails with "Created event did not occur as expected" #103630

Open

hez2010 added 2 commits February 12, 2026 21:47

Use the correct impl method token

757043d

Remove the no longer necessary assertion

2906173

Copilot AI review requested due to automatic review settings February 12, 2026 13:32

Copilot started reviewing on behalf of hez2010 February 12, 2026 13:33 View session

Copilot AI reviewed Feb 12, 2026

View reviewed changes

	helperArg = ComputeMethodWithToken(HandleToObject(pResolvedToken.hMethod), ref helperArgToken, constrainedType, false);
	helperArg = ComputeMethodWithToken(methodDesc, ref helperArgToken, constrainedType, false);

Conversation

hez2010 commented Jan 18, 2026 • 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!

hez2010 commented Jan 18, 2026

Uh oh!

Uh oh!

hez2010 commented Jan 18, 2026 • edited Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Uh oh!

Uh oh!

Copilot AI left a comment

Choose a reason for hiding this comment

Pull request overview

Uh oh!

Uh oh!

Uh oh!

Uh oh!

hez2010 commented Feb 10, 2026

Uh oh!

Copilot AI left a comment

Choose a reason for hiding this comment

Pull request overview

Uh oh!

Copilot AI Feb 10, 2026

Choose a reason for hiding this comment

Uh oh!

Copilot AI left a comment

Choose a reason for hiding this comment

Pull request overview

Uh oh!

Copilot AI left a comment

Choose a reason for hiding this comment

Pull request overview

Uh oh!

Uh oh!

hez2010 commented Feb 11, 2026

Uh oh!

jakobbotsch commented Feb 11, 2026

Uh oh!

azure-pipelines bot commented Feb 11, 2026

Uh oh!

Copilot AI left a comment

Choose a reason for hiding this comment

Pull request overview

Uh oh!

Copilot AI Feb 12, 2026

Choose a reason for hiding this comment

Uh oh!

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

Uh oh!

Uh oh!

jakobbotsch commented Feb 12, 2026

Uh oh!

azure-pipelines bot commented Feb 12, 2026

Uh oh!

jakobbotsch commented Feb 12, 2026

Uh oh!

azure-pipelines bot commented Feb 12, 2026

Uh oh!

hez2010 commented Feb 13, 2026

Uh oh!

Reviewers

Assignees

Labels

Projects

Milestone

Development

Uh oh!

3 participants

hez2010 commented Jan 18, 2026 •

edited

Loading

hez2010 commented Jan 18, 2026 •

edited

Loading

hez2010 commented Feb 12, 2026 •

edited

Loading