Fix GetThreadStaticsBase to be included in R2R images #123812

Copilot · 2026-01-30T19:59:14Z

Description

GetThreadStaticsBase was bypassing ReadyToRun compilation to avoid recursive initialization dependency. This caused all thread static field access on iOS (composite-r2r with interpreter fallback) to execute through the interpreter, resulting in 35x performance degradation.

Changes

Added CORINFO_HELP_GETDIRECTONTHREADLOCALDATA_NONGCTHREADSTATIC_BASE helper as a normal JIT helper to enable R2R compilation of GetThreadStaticsBase:

New JIT helper: JIT_GetDirectOnThreadLocalDataNonGCThreadStaticBase returns &((ThreadLocalData*)&t_ThreadStatics)->pThread - the address of the pThread field within thread-local storage, which serves as the storage location for DirectOnThreadLocalData.pNativeThread
Helper type: JITHELPER (not DYNAMICJITHELPER or ReadyToRun helper)
prestub.cpp: Modified getHelperForStaticBase to detect DirectOnThreadLocalData MethodTable and use the new helper for READYTORUN_FIXUP_ThreadStaticBaseNonGC
Thread.CoreCLR.cs: Removed BypassReadyToRunAttribute from GetThreadStaticsBase
JIT interface: Updated version GUID in jiteeversionguid.h
ReadyToRun compiler: Added the helper to RequiresRuntimeJitException list - no ReadyToRun constants were changed

The new helper provides direct access to the pThread field in thread local storage without triggering recursive initialization, allowing GetThreadStaticsBase to be compiled into R2R images.

Testing

Built and verified CoreCLR with no errors
Confirmed all helper enums are consistent across runtime and compiler
Verified no ReadyToRun constants were modified

Microsoft Reviewers

Original prompt

This section details on the original issue you should resolve

<issue_title>GetThreadStaticsBase method is not included in R2R image</issue_title>
<issue_description>Thread static helpers were moved to managed code in https://github.com/dotnet/runtime/pull/108167/files. It seems GetThreadStaticsBase has a BypassReadyToRunAttribute as a workaround for some recursive dependency during initialization. On iOS this is relevant because every single thread static field access will now go through interpreter, which is much slower.

On the following microbenchmark, running in composite-r2r configuration with interpreter fallback (jit disabled) is 35x slower than default jit configuration.
using System;
using System.Runtime.CompilerServices;
using System.Threading;

public class Program {
    [ThreadStatic]
    private static int a;

    [MethodImpl(MethodImplOptions.NoInlining)]
    public static int GetA()
    {
        return a;
    }
    [MethodImpl(MethodImplOptions.NoInlining)]
    public static void SetA(int val)
    {
        a = val;
    }

    public static void Main(string[] args)
    {
        a = 1;

        for (int i = 0; i < 500000000; i++)
            SetA(GetA() + 1);
    }
}
```</issue_description>

<agent_instructions>This needs to be fixed by changing the behavior of getHelperForStaticBase when called with a MethodTable that is which is the same as the DIRECTONTHREADLOCALDATA methodtable, and a kind of READYTORUN_FIXUP_ThreadStaticBaseNonGC to return a helper which returns the address of the pThread field that is on the t_ThreadStatics thread local variable. To do this, the change will need to add a new helper to the helpers defined in jithelpers.h, and in the enumeration CorInfoHelpFunc in corinfo.h. That helper needs to be implemented in jithelpers.cpp. In addition, since it is modifying corinfo.h in a way that changes the jit interface it will need to update the guid in jiteeversionguid.h. In addition, the change should update Thread.CoreCLR.cs to remove the BypassReadyToRun attribute which is on GetThreadStaticsBase.</agent_instructions>

## Comments on the Issue (you are @copilot in this section)

<comments>
<comment_new><author>@BrzVlad</author><body>
@davidwrighton Could you please give this a thought ?</body></comment_new>
</comments>

Fixes GetThreadStaticsBase method is not included in R2R image #123616

💬 We'd love your input! Share your thoughts on Copilot coding agent in our 2 minute survey.

…LocalData This change adds a new JIT helper to handle thread static access for DirectOnThreadLocalData in ReadyToRun images. The new helper returns the address of the thread local data structure, which is used to access the pNativeThread field. This eliminates the need for the BypassReadyToRun attribute on GetThreadStaticsBase, allowing it to be included in R2R images and improving performance on platforms like iOS that rely on composite-r2r with interpreter fallback. Co-authored-by: davidwrighton <10779849+davidwrighton@users.noreply.github.com>

…ALBASE Update the CrossGen2 ReadyToRun compiler to handle the new CORINFO_HELP_READYTORUN_THREADLOCALBASE helper. This helper is used to get the address of the thread local data structure for DirectOnThreadLocalData. Co-authored-by: davidwrighton <10779849+davidwrighton@users.noreply.github.com>

Add the new GetThreadLocalBase helper to the ReadyToRunHelper enum and map it to the CORINFO_HELP_READYTORUN_THREADLOCALBASE helper in the ReadyToRun constants and helper mapping tables. Co-authored-by: davidwrighton <10779849+davidwrighton@users.noreply.github.com>

Corrected the comment to accurately state that the helper returns the address of the thread local data structure, not just the pThread field. Co-authored-by: davidwrighton <10779849+davidwrighton@users.noreply.github.com>

davidwrighton

@copilot, please adjust the change to respond to this feedback.

src/coreclr/inc/jithelpers.h

src/coreclr/inc/readytorun.h

src/coreclr/inc/readytorunhelpers.h

src/coreclr/tools/Common/Internal/Runtime/ReadyToRunConstants.cs

src/coreclr/vm/jithelpers.cpp

…helper - Changed CORINFO_HELP_READYTORUN_THREADLOCALBASE to CORINFO_HELP_GETDIRECTONTHREADLOCALDATA_NONGCTHREADSTATIC_BASE as a normal JIT helper - Renamed JIT_GetThreadLocalBase to JIT_GetDirectOnThreadLocalDataNonGCThreadStaticBase - Fixed implementation to return address of pThread field instead of entire ThreadLocalData structure - Reverted all ReadyToRun constant changes (readytorun.h, readytorunhelpers.h, ReadyToRunConstants.cs) - Removed ReadyToRun compiler awareness of this helper Co-authored-by: davidwrighton <10779849+davidwrighton@users.noreply.github.com>

Added the CORINFO_HELP_GETDIRECTONTHREADLOCALDATA_NONGCTHREADSTATIC_BASE helper definition that was missing from jithelpers.h, causing enum mismatch errors. Co-authored-by: davidwrighton <10779849+davidwrighton@users.noreply.github.com>

JIT_GetDirectOnThreadLocalDataNonGCThreadStaticBase should be a JITHELPER, not a DYNAMICJITHELPER. Co-authored-by: davidwrighton <10779849+davidwrighton@users.noreply.github.com>

The CORINFO_HELP_GETDIRECTONTHREADLOCALDATA_NONGCTHREADSTATIC_BASE helper should not be used during R2R compilation and should throw RequiresRuntimeJitException. Co-authored-by: davidwrighton <10779849+davidwrighton@users.noreply.github.com>

Copilot · 2026-01-30T21:09:42Z

@copilot, please adjust the change to respond to this feedback.

Addressed all feedback in commits 6388684, f699f05, 5964bd5, and c6772e4. Changes made:

Changed to normal JIT helper (not ReadyToRun) with name specific to DirectOnThreadLocalData
Reverted all ReadyToRun constants (readytorun.h, readytorunhelpers.h, ReadyToRunConstants.cs)
Fixed implementation to return address of pThread field: &((ThreadLocalData*)&t_ThreadStatics)->pThread
Changed from DYNAMICJITHELPER to JITHELPER
Added exception handling in ReadyToRun compiler

Added CORINFO_HELP_GETDIRECTONTHREADLOCALDATA_NONGCTHREADSTATIC_BASE to the CorInfoHelpFunc enum in the tools directory. Co-authored-by: davidwrighton <10779849+davidwrighton@users.noreply.github.com>

Made the comment more precise to clarify that this helper returns the address of the pThread field which serves as the storage location for DirectOnThreadLocalData.pNativeThread thread static field. Co-authored-by: davidwrighton <10779849+davidwrighton@users.noreply.github.com>

…cted

…://github.com/dotnet/runtime into copilot/fix-getthreadstaticsbase-in-r2r-image

Copilot

Pull request overview

This PR fixes a critical performance issue where GetThreadStaticsBase bypassed ReadyToRun compilation, causing 35x performance degradation on iOS with composite-r2r and interpreter fallback. The solution introduces a new JIT helper that provides direct access to thread-local storage for the DirectOnThreadLocalData type, enabling R2R compilation of GetThreadStaticsBase.

Changes:

Added CORINFO_HELP_GETDIRECTONTHREADLOCALDATA_NONGCTHREADSTATIC_BASE JIT helper with implementation JIT_GetDirectOnThreadLocalDataNonGCThreadStaticBase to return the address of the pThread field in thread-local storage
Modified getHelperForStaticBase in prestub.cpp to detect DirectOnThreadLocalData MethodTable and return the new helper for non-GC thread static base fixups
Removed BypassReadyToRunAttribute from GetThreadStaticsBase in Thread.CoreCLR.cs to enable R2R compilation
Updated JIT interface version GUID to reflect the interface change
Added the new helper to RequiresRuntimeJitException list in ReadyToRun compiler to ensure it's used at runtime, not during compilation

Reviewed changes

Copilot reviewed 8 out of 8 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
src/coreclr/vm/prestub.cpp	Added special case detection for DirectOnThreadLocalData to use the new helper during R2R fixup resolution
src/coreclr/vm/jithelpers.cpp	Implemented the new helper function that returns the address of pThread field in thread-local storage
src/coreclr/tools/aot/ILCompiler.ReadyToRun/JitInterface/CorInfoImpl.ReadyToRun.cs	Added new helper to RequiresRuntimeJitException list to prevent R2R compilation of the helper itself
src/coreclr/tools/Common/JitInterface/CorInfoHelpFunc.cs	Added new helper enum value to match corinfo.h
src/coreclr/inc/jithelpers.h	Defined the new helper as a JITHELPER mapped to the implementation function
src/coreclr/inc/jiteeversionguid.h	Updated JIT interface version GUID to reflect the interface change
src/coreclr/inc/corinfo.h	Added new CorInfoHelpFunc enum value for the DirectOnThreadLocalData helper
src/coreclr/System.Private.CoreLib/src/System/Threading/Thread.CoreCLR.cs	Removed BypassReadyToRunAttribute and associated comment to enable R2R compilation of GetThreadStaticsBase

src/coreclr/vm/jithelpers.cpp

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

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

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

Initial plan

2be6c60

Copilot AI assigned Copilot and davidwrighton Jan 30, 2026

Copilot started work on behalf of davidwrighton January 30, 2026 20:00 View session

Copilot AI and others added 4 commits January 30, 2026 20:05

Fix comment in JIT_GetThreadLocalBase helper

e5a6c50

Corrected the comment to accurately state that the helper returns the address of the thread local data structure, not just the pThread field. Co-authored-by: davidwrighton <10779849+davidwrighton@users.noreply.github.com>

Copilot AI changed the title ~~[WIP] Fix GetThreadStaticsBase method inclusion in R2R image~~ Fix GetThreadStaticsBase to be included in R2R images Jan 30, 2026

davidwrighton requested changes Jan 30, 2026

View reviewed changes

Copilot AI requested a review from davidwrighton January 30, 2026 20:49

Copilot finished work on behalf of davidwrighton January 30, 2026 20:49

Copilot started work on behalf of davidwrighton January 30, 2026 20:49 View session

Copilot AI and others added 4 commits January 30, 2026 20:55

Fix missing helper definition in jithelpers.h

f699f05

Added the CORINFO_HELP_GETDIRECTONTHREADLOCALDATA_NONGCTHREADSTATIC_BASE helper definition that was missing from jithelpers.h, causing enum mismatch errors. Co-authored-by: davidwrighton <10779849+davidwrighton@users.noreply.github.com>

Change helper from DYNAMICJITHELPER to JITHELPER

5964bd5

JIT_GetDirectOnThreadLocalDataNonGCThreadStaticBase should be a JITHELPER, not a DYNAMICJITHELPER. Co-authored-by: davidwrighton <10779849+davidwrighton@users.noreply.github.com>

Copilot AI and others added 2 commits January 30, 2026 21:11

Add helper to CorInfoHelpFunc.cs enum

e691c50

Added CORINFO_HELP_GETDIRECTONTHREADLOCALDATA_NONGCTHREADSTATIC_BASE to the CorInfoHelpFunc enum in the tools directory. Co-authored-by: davidwrighton <10779849+davidwrighton@users.noreply.github.com>

Copilot finished work on behalf of davidwrighton January 30, 2026 21:19

davidwrighton added 2 commits January 30, 2026 13:30

Adjust base address by CORINFO_Array__data to match the behavior expe…

af30be8

…cted

Merge branch 'copilot/fix-getthreadstaticsbase-in-r2r-image' of https…

320263b

…://github.com/dotnet/runtime into copilot/fix-getthreadstaticsbase-in-r2r-image

davidwrighton approved these changes Jan 30, 2026

View reviewed changes

jkotas approved these changes Jan 30, 2026

View reviewed changes

davidwrighton marked this pull request as ready for review January 30, 2026 23:08

davidwrighton requested a review from MichalStrehovsky as a code owner January 30, 2026 23:08

Copilot AI review requested due to automatic review settings January 30, 2026 23:08

Copilot started reviewing on behalf of davidwrighton January 30, 2026 23:09 View session

Copilot AI reviewed Jan 30, 2026

View reviewed changes

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

src/coreclr/tools/aot/ILCompiler.ReadyToRun/JitInterface/CorInfoImpl.ReadyToRun.cs Outdated Show resolved Hide resolved

This was referenced Jan 31, 2026

iOS.Device test WorkItemExecutions #122874

Open

XHarness package install failure on iOS due to devicectl NSPOSIXErrorDomain error 49 #123796

Open

davidwrighton and others added 2 commits January 31, 2026 02:40

Update src/coreclr/vm/jithelpers.cpp

dd91a8f

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

Update src/coreclr/tools/aot/ILCompiler.ReadyToRun/JitInterface/CorIn…

16cd619

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

davidwrighton enabled auto-merge (squash) January 31, 2026 02:40

davidwrighton merged commit 1c57781 into main Jan 31, 2026
99 of 101 checks passed

dotnet-maestro bot mentioned this pull request Feb 1, 2026

[main] Source code updates from dotnet/runtime dotnet/dotnet#4581

Merged

jkotas deleted the copilot/fix-getthreadstaticsbase-in-r2r-image branch February 2, 2026 23:13

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Fix GetThreadStaticsBase to be included in R2R images #123812

Fix GetThreadStaticsBase to be included in R2R images #123812

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Fix GetThreadStaticsBase to be included in R2R images #123812

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