Support devirtualization for virtual methods that require an instantiating stub by hez2010 · Pull Request #128702 · dotnet/runtime

hez2010 · 2026-05-28T14:13:51Z

Enable devirtualization of virtual methods that require an instantiating stub.
We have landed the refactor in the JIT so that now we are able to handle instantiating stub naturally without a JIT change.

This covers both shared generic virtual methods that don't require a runtime lookup, and generic interface methods that have a default implementation.

GVM devirt for NativeAOT requires more changes which is out of scope of this PR.

IGenericA<string>a=newAImpl();a.B("GVM");a.C("Generic DIM");interfaceIA{voidA(objecto);voidB<T>(To);}interfaceIGenericA<T>:IA{voidC(To)=>B(o);}classAImpl:IGenericA<string>{publicvoidA(objecto){Console.WriteLine(o);}publicvoidB<T>(To){Console.WriteLine(o);}}

Before:

G_M000_IG01: ;; offset=0x0000pushrbxsubrsp,32G_M000_IG02: ;; offset=0x0005movrcx,0x7FFB383AF518call CORINFO_HELP_NEWSFASTmovrbx,raxmovrcx,rbxmovrdx,0x7FFB383AF348movr8,0x7FFB383AF828call CORINFO_HELP_VIRTUAL_FUNC_PTRmovrcx,rbxmovrdx,0xA025C36200callraxmovrcx,rbxmovr11,0x7FFB380E0070movrdx,0xA025C36220call[r11]IGenericA`1[System.__Canon]:C(System.__Canon):thisnopG_M000_IG03: ;; offset=0x005Daddrsp,32poprbxret; Total bytes of code 99

After:

G_M56640_IG01: ;; offset=0x0000subrsp,40G_M56640_IG02: ;; offset=0x0004movrcx,0xA0261EE6F0 ; 'GVM'call[System.Console:WriteLine(System.Object)]movrcx,0xA0261EE710 ; 'Generic DIM'call[System.Console:WriteLine(System.Object)]nopG_M56640_IG03: ;; offset=0x0025addrsp,40ret; Total bytes of code 42

Similar for R2R:

G_M56640_IG01: ;; offset=0x0000pushrbxsubrsp,32G_M56640_IG02: ;; offset=0x0005call[CORINFO_HELP_READYTORUN_NEW]movrbx,raxmovrcx, qword ptr [(reloc 0x4000000000420148)] ; const ptrmovrcx, gword ptr [rcx]call[System.Console:WriteLine(System.Object)]movrdx, qword ptr [(reloc 0x4000000000420150)] ; const ptrmovrdx, gword ptr [rdx]movrcx,rbxlear11,[(reloc 0x40000000004200f8)] ; function addresscall[r11]IGenericA`1[System.String]:C(System.String):thisnopG_M56640_IG03: ;; offset=0x0036addrsp,32poprbxret

For NativeAOT:

Before:

 G_M000_IG01: ;; offset=0x0000pushrbxsubrsp,32 G_M000_IG02: ;; offset=0x0005learcx,[(reloc 0x420c38)]call CORINFO_HELP_NEWSFASTmovrbx,raxmovrcx,rbxleardx,[(reloc 0x420c48)]call CORINFO_HELP_GVMLOOKUP_FOR_SLOTtestal,2je SHORT G_M000_IG04 G_M000_IG03: ;; offset=0x0027movrdx, qword ptr [rax+0x06]movrcx,rbxlear8, gword ptr [(reloc 0x420c68)]call[rax-0x02]jmp SHORT G_M000_IG05 G_M000_IG04: ;; offset=0x003Amovrcx,rbxleardx, gword ptr [(reloc 0x420c68)]callrax G_M000_IG05: ;; offset=0x0046movrcx,rbxlear11,[(reloc 0x420c58)]leardx, gword ptr [(reloc 0x420c70)]call[r11]IGenericA`1[System.String]:C(System.String):thisnop G_M000_IG06: ;; offset=0x005Baddrsp,32poprbxret ; Total bytes of code 97

After:

G_M56640_IG01: ;; offset=0x0000pushrdipushrsipushrbxsubrsp,32 ;; size=7 bbWeight=1 PerfScore 3.25G_M56640_IG02: ;; offset=0x0007learcx,[(reloc 0x4000000000420c30)] ; AImplcall CORINFO_HELP_NEWSFASTmovrbx,raxmovrcx,rbxleardx,[(reloc 0x4000000000420c40)] ; IA:B[System.String](System.String):thiscall CORINFO_HELP_GVMLOOKUP_FOR_SLOTmovrsi,raxmovedi,eaxandedi,2je SHORT G_M56640_IG04G_M56640_IG03: ;; offset=0x002Fmovrdx, qword ptr [rax+0x06]movrcx,rbxlear8, gword ptr [(reloc 0x4000000000420c90)] ; '"GVM"'call[rax-0x02]jmp SHORT G_M56640_IG05G_M56640_IG04: ;; offset=0x0042movrcx,rbxleardx, gword ptr [(reloc 0x4000000000420c90)] ; '"GVM"'callraxG_M56640_IG05: ;; offset=0x004Etestedi,edije SHORT G_M56640_IG07G_M56640_IG06: ;; offset=0x0052movrdx, qword ptr [rsi+0x06]movrcx,rbxlear8, gword ptr [(reloc 0x4000000000420c98)] ; '"Generic DIM"'call[rsi-0x02]jmp SHORT G_M56640_IG08G_M56640_IG07: ;; offset=0x0065movrcx,rbxleardx, gword ptr [(reloc 0x4000000000420c98)] ; '"Generic DIM"'callrsiG_M56640_IG08: ;; offset=0x0071nopG_M56640_IG09: ;; offset=0x0072addrsp,32poprbxpoprsipoprdiret; Total bytes of code 122

Also added a couple of tests from #43668.

Closes#9588
Contributes to #112596

/cc: @jakobbotsch @davidwrighton @MichalStrehovsky

Copilot

Pull request overview

Note

Copilot was unable to run its full agentic suite in this review.

Enables devirtualization of generic virtual methods and default interface methods (DIMs) on generic interfaces, by computing and passing the instantiation argument needed at runtime, instead of failing devirtualization in those cases.

Changes:

In the VM JIT interface, remove the early bail-out for generic DIMs and shared generic virtual methods, and instead compute instParamLookup / re-resolve via the exact (non-shared) MethodDesc when possible; defer the instantiating-stub unwrap until after tokenLookupContext is set.
In the managed JIT interface (CorInfoImpl), add parallel logic to populate instParamLookup for generic DIM / generic virtual / array-interface devirtualization (R2R uses TypeDictionary / MethodHandle helpers; NativeAOT path returns FAILED_CANON for now), and switch tokenLookupContext to a method context where appropriate.
In DevirtualizationManager, drop the unconditional generic-virtual canon bail-out and, for R2R, only fail DIM resolution on variant dispatch (allowing generic DIMs); keep the stricter pre-existing behavior for NativeAOT.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 7 comments.

File	Description
src/coreclr/vm/jitinterface.cpp	Allow devirt to generic DIM / shared GVM by computing exact MD and `instParamLookup`; move instantiating-stub unwrap after context setup.
src/coreclr/tools/Common/JitInterface/CorInfoImpl.cs	Add `instParamLookup` population for generic DIM / GVM / array-interface cases; adjust `tokenLookupContext`; gate AOT vs R2R behavior.
src/coreclr/tools/Common/Compiler/DevirtualizationManager.cs	For R2R, only fail DIM resolution on variant dispatch; remove unconditional shared-GVM canon bail-out.
src/coreclr/tools/aot/ILCompiler.ReadyToRun/Compiler/DependencyAnalysis/ReadyToRun/DevirtualizationManager.cs	Update stale comment numbering after removing the DIM-restriction note.

Copilot

Pull request overview

Copilot reviewed 4 out of 4 changed files in this pull request and generated 6 comments.

Copilot

Pull request overview

Copilot reviewed 4 out of 4 changed files in this pull request and generated 5 comments.

Copilot

Pull request overview

Copilot reviewed 5 out of 5 changed files in this pull request and generated 4 comments.

hez2010 · 2026-05-28T16:07:25Z

@MihuBot

hez2010 · 2026-05-28T16:37:46Z

@MihuBot -nuget

MichalStrehovsky · 2026-06-26T05:29:22Z

@MichalStrehovsky I disabled the generic recursion test for NativeAOT in 87b4e0c due to #129855. Can you take a look?

These are not scenarios we're concerned about for native AOT, correct? Otherwise it would be nice to write it in a way that it doesn't trigger a recursion.

hez2010 · 2026-06-26T05:58:11Z

These are not scenarios we're concerned about for native AOT, correct?

Right. I think this test can be disabled for NativeAOT fine. The type is a struct here is just for testing the interaction between runtime lookups and unboxing stubs, we have other cases that don't need a recursion which works fine under NativeAOT.

Otherwise it would be nice to write it in a way that it doesn't trigger a recursion.

The test here performs a runtime lookup through delegates to resolve to itself with a different instantiation to exercise whether we use the right generic context before / after devirtualization against the same method, and that's why a generic recursion is here.

Copilot

Copilot was unable to review this pull request because the user who requested the review has reached their quota limit.

hez2010 · 2026-06-26T06:51:48Z

I added several tests to cover NativeAOT's behavior of unboxing stubs + runtime lookups in a non-recursive way.

MichalStrehovsky

Thank you!

MichalStrehovsky · 2026-06-26T08:23:44Z

/azp run runtime-coreclr outerloop, runtime-coreclr pgo, runtime-coreclr pgostress, runtime-nativeaot-outerloop

azure-pipelines · 2026-06-26T08:23:50Z

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.

Copilot

Copilot was unable to review this pull request because the user who requested the review has reached their quota limit.

hez2010 · 2026-06-26T08:25:29Z

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.

I updated the branch to resolve this. Also fixed a copy-paste error which dismissed the approval.

@MichalStrehovsky Can you trigger the run again?

MichalStrehovsky · 2026-06-27T01:23:06Z

/azp run runtime-coreclr outerloop, runtime-coreclr pgo, runtime-coreclr pgostress, runtime-nativeaot-outerloop

azure-pipelines · 2026-06-27T01:23:34Z

Azure Pipelines successfully started running 4 pipeline(s).

hez2010 · 2026-06-27T07:51:52Z

Test failures seem unrelated?

hez2010 · 2026-06-28T12:26:20Z

Test failures seem unrelated?

Pri1 failures:

Error loading shared library libatomic.so.1: No such file or directory (needed by /root/helix/work/correlation/SuperFileCheck/runtimes/linux-musl-x64/native/libc++.so.1)

which are #129876.

NativeAOT outerloop failures are #129755 (comment) and #129832.

MichalStrehovsky · 2026-06-29T07:20:47Z

/ba-g the native AOT failures are known, the owner is now known not to care about it. I have a fix in a PR.

…9730) We missed a spot. Fixes#129697 Test is in #128702.

#129729) Fixes#129696. When a single type load needs both an unboxing and non-unboxing entrypoint at the same time, we'd build the same generic dictionary twice and fail during registration. The surgical fix is to allow type loader to do the work twice, but stop at the point where we would try to allocate it. Runtime type loader having unboxing MethodDescs was a mistake. This is not a problem if we don't need both at the same time since the all the lookups for existing dictionary already ignore the unboxing bit. (Which is why we fail during registration in the bug - unboxing bit is not part of the key.) No regression test because the test is in #128702.

@jakobbotsch

…ating stub (#128702) Enable devirtualization of virtual methods that require an instantiating stub. We have landed the refactor in the JIT so that now we are able to handle instantiating stub naturally without a JIT change. This covers both shared generic virtual methods that don't require a runtime lookup, and generic interface methods that have a default implementation. GVM devirt for NativeAOT requires more changes which is out of scope of this PR. ```cs IGenericA<string> a = new AImpl(); a.B("GVM"); a.C("Generic DIM"); interface IA { void A(object o); void B<T>(T o); } interface IGenericA<T> : IA { void C(T o) => B(o); } class AImpl : IGenericA<string> { public void A(object o) { Console.WriteLine(o); } public void B<T>(T o) { Console.WriteLine(o); } } ``` Before: ```nasm G_M000_IG01: ;; offset=0x0000 push rbx sub rsp, 32 G_M000_IG02: ;; offset=0x0005 mov rcx, 0x7FFB383AF518 call CORINFO_HELP_NEWSFAST mov rbx, rax mov rcx, rbx mov rdx, 0x7FFB383AF348 mov r8, 0x7FFB383AF828 call CORINFO_HELP_VIRTUAL_FUNC_PTR mov rcx, rbx mov rdx, 0xA025C36200 call rax mov rcx, rbx mov r11, 0x7FFB380E0070 mov rdx, 0xA025C36220 call [r11]IGenericA`1[System.__Canon]:C(System.__Canon):this nop G_M000_IG03: ;; offset=0x005D add rsp, 32 pop rbx ret ; Total bytes of code 99 ``` After: ```nasm G_M56640_IG01: ;; offset=0x0000 sub rsp, 40 G_M56640_IG02: ;; offset=0x0004 mov rcx, 0xA0261EE6F0 ; 'GVM' call [System.Console:WriteLine(System.Object)] mov rcx, 0xA0261EE710 ; 'Generic DIM' call [System.Console:WriteLine(System.Object)] nop G_M56640_IG03: ;; offset=0x0025 add rsp, 40 ret ; Total bytes of code 42 ``` Similar for R2R: ```nasm G_M56640_IG01: ;; offset=0x0000 push rbx sub rsp, 32 G_M56640_IG02: ;; offset=0x0005 call [CORINFO_HELP_READYTORUN_NEW] mov rbx, rax mov rcx, qword ptr [(reloc 0x4000000000420148)] ; const ptr mov rcx, gword ptr [rcx] call [System.Console:WriteLine(System.Object)] mov rdx, qword ptr [(reloc 0x4000000000420150)] ; const ptr mov rdx, gword ptr [rdx] mov rcx, rbx lea r11, [(reloc 0x40000000004200f8)] ; function address call [r11]IGenericA`1[System.String]:C(System.String):this nop G_M56640_IG03: ;; offset=0x0036 add rsp, 32 pop rbx ret ``` For NativeAOT: Before: ```nasm G_M000_IG01: ;; offset=0x0000 push rbx sub rsp, 32 G_M000_IG02: ;; offset=0x0005 lea rcx, [(reloc 0x420c38)] call CORINFO_HELP_NEWSFAST mov rbx, rax mov rcx, rbx lea rdx, [(reloc 0x420c48)] call CORINFO_HELP_GVMLOOKUP_FOR_SLOT test al, 2 je SHORT G_M000_IG04 G_M000_IG03: ;; offset=0x0027 mov rdx, qword ptr [rax+0x06] mov rcx, rbx lea r8, gword ptr [(reloc 0x420c68)] call [rax-0x02] jmp SHORT G_M000_IG05 G_M000_IG04: ;; offset=0x003A mov rcx, rbx lea rdx, gword ptr [(reloc 0x420c68)] call rax G_M000_IG05: ;; offset=0x0046 mov rcx, rbx lea r11, [(reloc 0x420c58)] lea rdx, gword ptr [(reloc 0x420c70)] call [r11]IGenericA`1[System.String]:C(System.String):this nop G_M000_IG06: ;; offset=0x005B add rsp, 32 pop rbx ret ; Total bytes of code 97 ``` After: ```nasm G_M56640_IG01: ;; offset=0x0000 push rdi push rsi push rbx sub rsp, 32 ;; size=7 bbWeight=1 PerfScore 3.25 G_M56640_IG02: ;; offset=0x0007 lea rcx, [(reloc 0x4000000000420c30)] ; AImpl call CORINFO_HELP_NEWSFAST mov rbx, rax mov rcx, rbx lea rdx, [(reloc 0x4000000000420c40)] ; IA:B[System.String](System.String):this call CORINFO_HELP_GVMLOOKUP_FOR_SLOT mov rsi, rax mov edi, eax and edi, 2 je SHORT G_M56640_IG04 G_M56640_IG03: ;; offset=0x002F mov rdx, qword ptr [rax+0x06] mov rcx, rbx lea r8, gword ptr [(reloc 0x4000000000420c90)] ; '"GVM"' call [rax-0x02] jmp SHORT G_M56640_IG05 G_M56640_IG04: ;; offset=0x0042 mov rcx, rbx lea rdx, gword ptr [(reloc 0x4000000000420c90)] ; '"GVM"' call rax G_M56640_IG05: ;; offset=0x004E test edi, edi je SHORT G_M56640_IG07 G_M56640_IG06: ;; offset=0x0052 mov rdx, qword ptr [rsi+0x06] mov rcx, rbx lea r8, gword ptr [(reloc 0x4000000000420c98)] ; '"Generic DIM"' call [rsi-0x02] jmp SHORT G_M56640_IG08 G_M56640_IG07: ;; offset=0x0065 mov rcx, rbx lea rdx, gword ptr [(reloc 0x4000000000420c98)] ; '"Generic DIM"' call rsi G_M56640_IG08: ;; offset=0x0071 nop G_M56640_IG09: ;; offset=0x0072 add rsp, 32 pop rbx pop rsi pop rdi ret ; Total bytes of code 122 ``` Also added a couple of tests from #43668. Closes#9588 Contributes to #112596 /cc: @jakobbotsch @davidwrighton @MichalStrehovsky

hez2010 added 4 commits May 28, 2026 21:43

Devirtualize virtual methods that require an instantiating stub
61a278f

R2R support
f01f4f4

Bail shared MT for generic DIM as well
b42c291

Stop returning an instantiating stub
b96fc2e

CopilotAI review requested due to automatic review settings May 28, 2026 14:13

hez2010 requested a review from MichalStrehovsky as a code owner May 28, 2026 14:13

github-actionsBot added the area-CodeGen-coreclr CLR JIT compiler in src/coreclr/src/jit and related components such as SuperPMI label May 28, 2026

dotnet-policy-serviceBot added the community-contribution Indicates that the PR has been added by a community member label May 28, 2026

Nit
de840c2

CopilotAI reviewed May 28, 2026
View reviewed changes

hez2010 added 2 commits May 28, 2026 23:17

Nit 2
181e88e

Remove redundant empty line
9331cc1

CopilotAI review requested due to automatic review settings May 28, 2026 14:18

CopilotAI reviewed May 28, 2026
View reviewed changes

hez2010 added 2 commits May 28, 2026 23:28

Generic DIM devirt for NativeAOT
f635686

Meh
5da42c5

CopilotAI review requested due to automatic review settings May 28, 2026 14:29

CopilotAI reviewed May 28, 2026
View reviewed changes

hez2010 added 2 commits May 28, 2026 23:39

More NativeAOT support
66c8d6a

Address an assertion
152c44a

CopilotAI review requested due to automatic review settings May 28, 2026 14:50

Use IsSharedByGenericMethodInstantiations
466ba2c

CopilotAI reviewed May 28, 2026
View reviewed changes

hez2010 mentioned this pull request May 28, 2026
JIT: Devirtualization for generic virtual methods #112596
Open
14 tasks

Add a couple of tests
dca1834

MihuBot mentioned this pull request May 28, 2026
[JitDiff X64] [hez2010] Support devirtualization for virtual methods that re ... MihuBot/runtime-utils#1947
Open

MihuBot mentioned this pull request May 28, 2026
[JitDiff X64] [hez2010] Support devirtualization for virtual methods that re ... MihuBot/runtime-utils#1948
Open

build-analysisBot mentioned this pull request May 29, 2026
XHarness package install failure on iOS due to devicectl NSPOSIXErrorDomain error 49 #123796
Open

Don't capture generic arity mismatch
79a2bdf

Meh
42dc0d2

CopilotAI review requested due to automatic review settings June 26, 2026 06:23

CopilotAI reviewed Jun 26, 2026

Add non-recursive derived struct tests
0f840d7

MichalStrehovsky approved these changes Jun 26, 2026
View reviewed changes

Merge branch 'main' into devirt-instantiating-stub-coreclr
b4d9776

CopilotAI review requested due to automatic review settings June 26, 2026 08:25

CopilotAI reviewed Jun 26, 2026

Oops
b527c60

MichalStrehovsky approved these changes Jun 29, 2026
View reviewed changes

MichalStrehovsky merged commit 664063f into dotnet:mainJun 29, 2026
206 of 227 checks passed

dotnet-maestroBot mentioned this pull request Jun 30, 2026
[main] Source code updates from dotnet/runtime dotnet/dotnet#7477
Merged

dotnet-milestone-botBot added this to the 11.0-preview7 milestone Jun 30, 2026

eiriktsarpalis pushed a commit that referenced this pull request Jul 15, 2026
Better generic cycle detection in MethodEntryGenericLookupResult (#12…
f707d16
…9730) We missed a spot. Fixes#129697 Test is in #128702.

hez2010 mentioned this pull request Jul 16, 2026
Default implementations on IXmlReadHandler are a footgun xoofx/TurboXml#3
Open

github-actionsBot locked and limited conversation to collaborators Jul 30, 2026

Uh oh!

Conversation

hez2010 commented May 28, 2026• edited Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Uh oh!

CopilotAI 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!

Uh oh!

Uh oh!

Uh oh!

CopilotAI left a comment

Choose a reason for hiding this comment

Pull request overview

Uh oh!

Uh oh!

Uh oh!

Uh oh!

Uh oh!

Uh oh!

Uh oh!

CopilotAI left a comment

Choose a reason for hiding this comment

Pull request overview

Uh oh!

Uh oh!

Uh oh!

Uh oh!

Uh oh!

Uh oh!

CopilotAI left a comment

Choose a reason for hiding this comment

Pull request overview

Uh oh!

Uh oh!

Uh oh!

Uh oh!

Uh oh!

hez2010 commented May 28, 2026

Uh oh!

hez2010 commented May 28, 2026

Uh oh!

MichalStrehovsky commented Jun 26, 2026

Uh oh!

hez2010 commented Jun 26, 2026• edited Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Uh oh!

CopilotAI left a comment

Choose a reason for hiding this comment

Uh oh!

hez2010 commented Jun 26, 2026

Uh oh!

MichalStrehovsky left a comment

Choose a reason for hiding this comment

Uh oh!

MichalStrehovsky commented Jun 26, 2026

Uh oh!

azure-pipelinesBot commented Jun 26, 2026

Uh oh!

CopilotAI left a comment

Choose a reason for hiding this comment

Uh oh!

hez2010 commented Jun 26, 2026• edited Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Uh oh!

MichalStrehovsky commented Jun 27, 2026

Uh oh!

azure-pipelinesBot commented Jun 27, 2026

Uh oh!

hez2010 commented Jun 27, 2026• edited Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Uh oh!

hez2010 commented Jun 28, 2026• edited Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

hez2010 commented May 28, 2026•
edited
Loading

hez2010 commented Jun 26, 2026•
edited
Loading

hez2010 commented Jun 26, 2026•
edited
Loading

hez2010 commented Jun 27, 2026•
edited
Loading

hez2010 commented Jun 28, 2026•
edited
Loading