JIT: add NativeAOT support for non-shared GVM devirtualization by hez2010 · Pull Request #130202 · dotnet/runtime

hez2010 · 2026-07-04T15:25:48Z

Under NativeAOT, only mark the fat pointer calls but defer the transformation until we are going to perform indirect calls transform, so that the JIT can recognize the tree for GVM devirtualization.

Unfortunately, we are not able to support late devirtualization and guarded devirtualization because fat pointer call transformation happens too early.

Shared GVMs are also not supported due to IL scanner limitations.

Example:

interfaceIGvm{voidTest<T>(Tvalue);}classGvm:IGvm{publicvoidTest<T>(Tvalue){Console.WriteLine(value);}}classProgram{staticvoidMain(string[]args){IGvmgvm1=newGvm();gvm1.Test(42);}}

Before:

G_M24006_IG01:pushrbxsubrsp,32G_M24006_IG02:learcx,[(reloc 0x420b30)] ; Gvmcall CORINFO_HELP_NEWSFASTmovrbx,raxmovrcx,rbxleardx,[(reloc 0x420b40)] ; IGvm:Test[int](int):thiscall CORINFO_HELP_GVMLOOKUP_FOR_SLOTtestal,2je SHORT G_M24006_IG04G_M24006_IG03:movrdx, qword ptr [rax+0x06]movrcx,rbxmovr8d,42call[rax-0x02]jmp SHORT G_M24006_IG05G_M24006_IG04:movrcx,rbxmovedx,42callraxG_M24006_IG05:nopG_M24006_IG06:addrsp,32poprbxret

After:

G_M24006_IG01:subrsp,40G_M24006_IG02:learcx,[(reloc 0x420bc0)] ; System.Int32call CORINFO_HELP_NEWSFASTmov dword ptr [rax+0x08],42movrcx,raxcall System.Console:WriteLine(System.Object)nopG_M24006_IG03:addrsp,40ret

Contributes to #112596

dotnet-policy-service · 2026-07-04T15:26:54Z

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Pull request overview

Enables NativeAOT generic virtual method (GVM) devirtualization by preserving the helper-call-shaped indirection target long enough for the importer’s devirtualization logic to recognize it, while still supporting NativeAOT fat-pointer lowering later during indirect-call transformation.

Changes:

Stop spilling NativeAOT GVM ldvirtftn targets to a temp in the importer; instead only mark calls as fat-pointer candidates.
In indirect-call transformation, for generic-virtual fat-pointer candidates, split/spill as needed and then materialize the function pointer into a temp local before expanding the fat-pointer control-flow.
Ensure fat-pointer-candidate marking is cleared when a call is devirtualized to a direct call; additionally, skip guarded devirtualization for generic-virtual calls.

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

File	Description
src/coreclr/jit/indirectcalltransformer.cpp	Adds late temp materialization of GVM fat-pointer call targets (post-import) prior to fat-pointer expansion.
src/coreclr/jit/importercalls.cpp	Removes early temp spill for NativeAOT GVM `ldvirtftn` calls; blocks GDV for generic-virtual calls; clears fat-pointer candidate on devirtualization.

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Copilot reviewed 3 out of 3 changed files in this pull request and generated 2 comments.

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hez2010 · 2026-07-04T16:50:49Z

It's hitting IL scanner issues like

error : VTable of type 'DerivedFtnn`1<System.Object>' not computed by the IL scanner. You can work around by running the compilation with scanner disabled.

cc: @MichalStrehovsky does this ring a bell?

UPDATE: addressed in 2291537

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hez2010 · 2026-07-07T10:50:45Z

@MichalStrehovsky @jakobbotsch PTAL.

MichalStrehovsky · 2026-07-08T04:44:08Z

/azp run runtime-nativeaot-outerloop

azure-pipelines · 2026-07-08T04:44:24Z

Azure Pipelines successfully started running 1 pipeline(s).

MichalStrehovsky

The CorInfoImpl.cs change looks good to me!

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hez2010 · 2026-07-09T03:00:16Z

Test failures are unrelated.

@jakobbotsch PTAL.

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hez2010 · 2026-07-14T05:56:55Z

CI failures seem unrelated.

MichalStrehovsky · 2026-07-14T06:56:03Z

/azp run runtime-nativeaot-outerloop

azure-pipelines · 2026-07-14T06:56:19Z

Azure Pipelines successfully started running 1 pipeline(s).

hez2010 · 2026-07-14T12:31:07Z

naot outerloop failure seems to be #130647?

jakobbotsch · 2026-07-14T14:50:18Z

/ba-g Failure was #130647

@MichalStrehovsky

When resolving an instantiated interface GVM, we passed down the method generic instantiation. However, interface slot selection needs to be done on the GVM definition, otherwise it could resolve to whatever the first compatible interface slot we saw. This can produce the incorrect devirtualized target when a type implements an interface GVM with multiple variant-compatible instantiations. Fixed it by stripping the method instantiation before resolving the interface slot. The CoreCLR native type system already handles such cases well so we don't have any issue there. Found this issue while I was working on GVM devirt for NAOT in #130202. See added tests for repro: previously it failed for the `CallOnBase` cases. Tests are added to both the managed type system and the normal JIT tests to prevent future regressions in either side. cc: @MichalStrehovsky

Unblock GVM devirt for NativeAOT
3724cdb

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JIT: Devirtualization for generic virtual methods #112596
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Comment threadsrc/coreclr/jit/indirectcalltransformer.cpp Outdated

hez2010 added 2 commits July 5, 2026 00:43

Address feedbacks
da5b50c

Unblock unboxing stubs for NativeAOT
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Nit
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Comment threadsrc/coreclr/jit/indirectcalltransformer.cpp Outdated
Comment threadsrc/coreclr/jit/importercalls.cpp Outdated

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Comment threadsrc/coreclr/jit/importercalls.cpp Outdated

hez2010 added 2 commits July 5, 2026 12:53

Address more feedbacks
a013aaf

Fix IL scanner
2291537

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Merge branch 'main' into gvm-devirt-nativeaot
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Comment threadsrc/coreclr/jit/indirectcalltransformer.cpp Outdated
Comment threadsrc/coreclr/tools/aot/ILCompiler.Compiler/Compiler/ILScanner.cs Outdated

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Merge branch 'main' into gvm-devirt-nativeaot
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Refactor into a common SplitCall
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jakobbotsch merged commit a20e145 into dotnet:mainJul 14, 2026
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dotnet-maestroBot mentioned this pull request Jul 15, 2026
[main] Source code updates from dotnet/runtime dotnet/dotnet#7749
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hez2010 mentioned this pull request Jul 15, 2026
NativeAOT: GVM analysis only runs on canonical form for shared instantiations #130752
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[main] Source code updates from dotnet/runtime dotnet/dotnet#7752
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