Add support for array interface devirtualization in R2R by hez2010 · Pull Request #131265 · dotnet/runtime

hez2010 · 2026-07-23T13:40:04Z

Support array interface devirtualization in R2R.

When we see an interface method on System.Array, we check if it's an implicitly implemented array interface. For implicitly implemented array interfaces we get the actual implementation from SZArrayHelper.

Example:

public class Program
{
    [MethodImpl(MethodImplOptions.AggressiveInlining)]
    static IList<string> Get() => new string[] { "a", "b", "c" };

    static void Main(string[] args)
    {
        var list = Get();
        Console.WriteLine(list.Count);
        foreach (var item in list)
        {
            Console.WriteLine(item);
        }
    }
}

Before:

G_M24006_IG01:  ;; offset=0x0000
       push     rbp
       push     rbx
       sub      rsp, 40
       lea      rbp, [rsp+0x30]
                                                ;; size=11 bbWeight=1 PerfScore 2.75
G_M24006_IG02:  ;; offset=0x000B
       mov      ecx, 3
       call     [CORINFO_HELP_READYTORUN_NEWARR_1]
       mov      rbx, rax
       lea      rcx, bword ptr [rbx+0x10]
       mov      rdx, qword ptr [(reloc 0x420050)]      ; const ptr
       mov      rdx, gword ptr [rdx]
       call     [CORINFO_HELP_ASSIGN_REF]
       lea      rcx, bword ptr [rbx+0x18]
       mov      rdx, qword ptr [(reloc 0x420058)]      ; const ptr
       mov      rdx, gword ptr [rdx]
       call     [CORINFO_HELP_ASSIGN_REF]
       lea      rcx, bword ptr [rbx+0x20]
       mov      rdx, qword ptr [(reloc 0x420060)]      ; const ptr
       mov      rdx, gword ptr [rdx]
       call     [CORINFO_HELP_ASSIGN_REF]
       mov      rcx, rbx
       lea      r11, [(reloc 0x420118)]      ; function address
       call     [r11]System.Collections.Generic.ICollection`1[System.String]:get_Count():int:this
       mov      ecx, eax
       call     [System.Console:WriteLine(int)]
       mov      rcx, rbx
       lea      r11, [(reloc 0x420138)]      ; function address
       call     [r11]System.Collections.Generic.IEnumerable`1[System.String]:GetEnumerator():System.Collections.Generic.IEnumerator`1[System.String]:this
       mov      rbx, rax
       mov      gword ptr [rbp-0x10], rbx
                                                ;; size=115 bbWeight=1 PerfScore 38.00
G_M24006_IG03:  ;; offset=0x007E
       mov      rcx, rbx
       lea      r11, [(reloc 0x420150)]      ; function address
       call     [r11]System.Collections.IEnumerator:MoveNext():bool:this
       test     eax, eax
       je       SHORT G_M24006_IG05
                                                ;; size=17 bbWeight=8 PerfScore 40.00
G_M24006_IG04:  ;; offset=0x008F
       mov      rcx, rbx
       lea      r11, [(reloc 0x420160)]      ; function address
       call     [r11]System.Collections.Generic.IEnumerator`1[System.String]:get_Current():System.String:this
       mov      rcx, rax
       call     [System.Console:WriteLine(System.String)]
       jmp      SHORT G_M24006_IG03
                                                ;; size=24 bbWeight=4 PerfScore 36.00
G_M24006_IG05:  ;; offset=0x00A7
       mov      rcx, rbx
       lea      r11, [(reloc 0x420180)]      ; function address
       call     [r11]System.IDisposable:Dispose():this
       nop
                                                ;; size=14 bbWeight=1 PerfScore 4.00
G_M24006_IG06:  ;; offset=0x00B5
       add      rsp, 40
       pop      rbx
       pop      rbp
       ret
                                                ;; size=7 bbWeight=1 PerfScore 2.25
G_M24006_IG07:  ;; offset=0x00BC
       sub      rsp, 40
                                                ;; size=4 bbWeight=0 PerfScore 0.00
G_M24006_IG08:  ;; offset=0x00C0
       cmp      gword ptr [rbp-0x10], 0
       je       SHORT G_M24006_IG09
       mov      rcx, gword ptr [rbp-0x10]
       lea      r11, [(reloc 0x420180)]      ; function address
       call     [r11]System.IDisposable:Dispose():this
                                                ;; size=21 bbWeight=0 PerfScore 0.00
G_M24006_IG09:  ;; offset=0x00D5
       nop
                                                ;; size=1 bbWeight=0 PerfScore 0.00
G_M24006_IG10:  ;; offset=0x00D6
       add      rsp, 40
       ret
                                                ;; size=5 bbWeight=0 PerfScore 0.00

After:

G_M24006_IG01:  ;; offset=0x0000
       push     rbp
       push     rsi
       push     rbx
       sub      rsp, 32
       lea      rbp, [rsp+0x30]
                                                ;; size=12 bbWeight=1 PerfScore 3.75
G_M24006_IG02:  ;; offset=0x000C
       mov      ecx, 3
       call     [CORINFO_HELP_READYTORUN_NEWARR_1]
       mov      rbx, rax
       lea      rcx, bword ptr [rbx+0x10]
       mov      rdx, qword ptr [(reloc 0x420050)]      ; const ptr
       mov      rdx, gword ptr [rdx]
       call     [CORINFO_HELP_ASSIGN_REF]
       lea      rcx, bword ptr [rbx+0x18]
       mov      rdx, qword ptr [(reloc 0x420058)]      ; const ptr
       mov      rdx, gword ptr [rdx]
       call     [CORINFO_HELP_ASSIGN_REF]
       lea      rcx, bword ptr [rbx+0x20]
       mov      rdx, qword ptr [(reloc 0x420060)]      ; const ptr
       mov      rdx, gword ptr [rdx]
       call     [CORINFO_HELP_ASSIGN_REF]
       mov      ecx, 3
       call     [System.Console:WriteLine(int)]
       xor      esi, esi
                                                ;; size=87 bbWeight=1 PerfScore 29.50
G_M24006_IG03:  ;; offset=0x0063
       mov      ecx, esi
       mov      rcx, gword ptr [rbx+8*rcx+0x10]
       call     [System.Console:WriteLine(System.String)]
       inc      esi
       cmp      esi, 3
       jb       SHORT G_M24006_IG03
                                                ;; size=20 bbWeight=4 PerfScore 27.00
G_M24006_IG04:  ;; offset=0x0077
       add      rsp, 32
       pop      rbx
       pop      rsi
       pop      rbp
       ret
                                                ;; size=8 bbWeight=1 PerfScore 2.75

cc: @MichalStrehovsky @davidwrighton

azure-pipelines · 2026-07-23T13:40:50Z

Azure Pipelines: Successfully started running 3 pipeline(s). 13 pipeline(s) were filtered out due to trigger conditions. There may be pipelines that require an authorized user to comment /azp run to run.

Copilot

Pull request overview

This PR updates the CoreCLR R2R compilation toolchain to allow devirtualization of interface calls on arrays by recognizing implicitly-implemented array interfaces and resolving the actual target methods on System.SZArrayHelper.

Changes:

Extend the well-known type system to include SZArrayHelper and key generic collection interfaces used by arrays.
Teach MetadataTypeSystemContext to resolve well-known types across multiple namespaces (e.g., System.Collections.Generic).
Enable R2R devirtualization for array interface calls by removing the previous R2R block and adding a SZArrayHelper-based resolution path in DevirtualizationManager.

Reviewed changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
src/coreclr/tools/Common/TypeSystem/Common/WellKnownType.cs	Adds well-known type enum entries for `SZArrayHelper` and array-relevant generic interfaces.
src/coreclr/tools/Common/TypeSystem/Common/TypeDesc.cs	Classifies the new well-known types as `Class`/`Interface` for cached type flag computation.
src/coreclr/tools/Common/TypeSystem/Common/MetadataTypeSystemContext.cs	Switches well-known type table to `(Namespace, TypeName)` to support non-`System` namespaces during system module initialization.
src/coreclr/tools/Common/JitInterface/CorInfoImpl.cs	Removes the R2R-time “array interface devirt not supported” early-fail, allowing devirtualization to proceed.
src/coreclr/tools/Common/Compiler/DevirtualizationManager.cs	Adds array-interface recognition and maps eligible interface methods on `System.Array` to instantiated `SZArrayHelper` methods.

Copilot

Pull request overview

Copilot reviewed 6 out of 6 changed files in this pull request and generated 1 comment.

Comments suppressed due to low confidence (2)

src/coreclr/tools/Common/Compiler/DevirtualizationManager.cs:93

GetActualImplementationForArrayGenericIListOrIReadOnlyListMethod assumes SZArrayHelper and the target method are always present, and will throw (TypeLoadException / NullReferenceException) if they aren't. Since well-known types are optionally present on some profiles, this should fail devirtualization gracefully instead of failing the compilation. This also fixes the typo "theT's" -> "T's" in the comment.

            MethodDesc genericImplementor = declMethod.Context.GetWellKnownType(WellKnownType.SZArrayHelper).GetMethod(declMethod.Name, null);
            Debug.Assert(genericImplementor != null);
            // OPTIMIZATION: For any method other than GetEnumerator(), we can safely substitute
            // "Object" for reference-type theT's. This causes fewer methods to be instantiated.
            if (genericImplementor.Name != "GetEnumerator"u8 && !typeParam.IsValueType)

src/coreclr/tools/Common/Compiler/DevirtualizationManager.cs:126

If GetActualImplementationForArrayGenericIListOrIReadOnlyListMethod can't locate SZArrayHelper (or the target method), the array-interface fast-path should set an explicit failure detail and return null, rather than returning a null MethodDesc and failing later.

                        return GetActualImplementationForArrayGenericIListOrIReadOnlyListMethod(declMethod, resultElemType);

Copilot

Pull request overview

Copilot reviewed 7 out of 7 changed files in this pull request and generated 1 comment.

Comments suppressed due to low confidence (1)

src/coreclr/tools/Common/TypeSystem/Common/MetadataTypeSystemContext.cs:55

MetadataTypeSystemContext.WellKnownTypeNames is a public API, and this PR changes its type from IEnumerable<string> to a tuple enumerable. That’s an API-breaking change for any out-of-repo consumers of the type system libraries.

To avoid breaking existing callers, keep WellKnownTypeNames with the original IEnumerable<string> shape and introduce a new property for (Namespace, TypeName) pairs (and update in-repo callers to use the new property).

        public static IEnumerable<(string Namespace, string TypeName)> WellKnownTypeNames => s_wellKnownTypeNames;

Copilot

Pull request overview

Copilot reviewed 7 out of 7 changed files in this pull request and generated 1 comment.

Copilot

Pull request overview

Copilot reviewed 7 out of 7 changed files in this pull request and generated 2 comments.

azure-pipelines · 2026-07-27T08:37:18Z

Azure Pipelines: Successfully started running 1 pipeline(s).

hez2010 · 2026-07-27T12:55:24Z

Switched away from using WellKnownTypes.
@MichalStrehovsky PTAL.

Copilot

Pull request overview

Copilot reviewed 5 out of 5 changed files in this pull request and generated 2 comments.

Copilot

Pull request overview

Copilot reviewed 5 out of 5 changed files in this pull request and generated 1 comment.

Comments suppressed due to low confidence (1)

src/coreclr/tools/aot/ILCompiler.ReadyToRun/Compiler/DependencyAnalysis/ReadyToRun/DevirtualizationManager.cs:170

This block assumes the interface type has an instantiation and unconditionally accesses declMethod.OwningType.Instantiation[0]. For non-generic array interface calls (e.g., IEnumerable, IList), Instantiation is empty and this will throw, preventing fallback to the base resolution logic.

                    // The instantiation we want is based on the interface element type, not the array element type.
                    TypeDesc resultElemType = declMethod.OwningType.Instantiation[0];
                    SimpleArrayOfTRuntimeInterfacesAlgorithm runtimeInterfacesAlgorithm =
                        (SimpleArrayOfTRuntimeInterfacesAlgorithm)context.GetRuntimeInterfacesAlgorithmForType(context.GetArrayType(resultElemType));

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hez2010 · 2026-07-30T06:17:34Z

I would still like to get this into .NET 11 as it's actually a trivial change (i.e. resolving I<T>.M calls on System.Array as SZArrayHelper.M<T>) but can address array interface call perf penalty when R2R is enabled.

@davidwrighton could you take a look?

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Support array interface devirtualization for R2R

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hez2010 requested a review from MichalStrehovsky as a code owner July 23, 2026 13:40

github-actions Bot added the area-CodeGen-coreclr CLR JIT compiler in src/coreclr/src/jit and related components such as SuperPMI label Jul 23, 2026

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Fix dotnet-pgo

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Comment thread src/coreclr/tools/Common/Compiler/DevirtualizationManager.cs Outdated

Nit

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Don't throw when not found

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Comment thread src/coreclr/nativeaot/System.Private.CoreLib/src/System/Array.NativeAot.cs

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Comment thread src/coreclr/tools/dotnet-pgo/TypeRefTypeSystem/TypeRefTypeSystemContext.cs Outdated

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Comment thread src/coreclr/tools/Common/Compiler/DevirtualizationManager.cs Outdated

Address feedbacks

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Comment thread src/coreclr/tools/Common/TypeSystem/Common/WellKnownType.cs Outdated

Comment thread src/coreclr/tools/Common/Compiler/DevirtualizationManager.cs Outdated

R2R only

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hez2010 added 2 commits July 27, 2026 21:33

Revert WellKnownTypes change

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Rework array interface devirt

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Nit

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Add an assertion

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Nit

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Comment thread src/coreclr/tools/aot/ILCompiler.ReadyToRun/Compiler/ReadyToRunCompilerContext.cs

Comment thread .../aot/ILCompiler.ReadyToRun/Compiler/DependencyAnalysis/ReadyToRun/DevirtualizationManager.cs Outdated

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Comment thread src/coreclr/tools/aot/ILCompiler.ReadyToRun/Compiler/ReadyToRunCompilerContext.cs

Meh

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Merge branch 'main' into r2r-array-devirt

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Merge branch 'main' into r2r-array-devirt

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build-analysis Bot mentioned this pull request Aug 15, 2026

System.Net.Tests.InvalidClientRequestTests.GetContext_InvalidRequest_DoesNotGetContext times out #132336

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hez2010 commented Jul 27, 2026 •

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