JIT: Restore arm64, LA64 and RISCV64 OSR callee saves from tier0 frame by jakobbotsch · Pull Request #126880 · dotnet/runtime

jakobbotsch · 2026-04-14T14:36:59Z

Change OSR functions for arm64, loongarch64 and riscv64 to start their prolog out by restoring the values of all callee saves that were saved by the tier0 function. This should make it possible to transition from tier0 to OSR without requiring any unwinding – instead it can be done with a simple jump. The end goal is to fix #120865 which is showing up in ASP.NET benchmarks.

Also support saving patchpoint info produced by an altjit in the VM.

Copilot

Pull request overview

This PR updates CoreCLR JIT OSR support on ARM64 so OSR methods can correctly “inherit” callee-saved registers from the Tier0 frame and restore them on exit, instead of saving/restoring the already-mutated register state from Tier0.

Changes:

Record and consume Tier0 callee-save information for ARM64 OSR, and update ARM64 prolog/epilog code to avoid re-saving inherited callee-saves and to restore them from the Tier0 frame at return.
Extend patchpoint/callee-save bookkeeping (including SuperPMI replay handling for older collections).
Update genPushCalleeSavedRegisters signature across targets and wire OSR prolog handling for AMD64/ARM64.

Reviewed changes

Copilot reviewed 10 out of 10 changed files in this pull request and generated 4 comments.

Show a summary per file

File	Description
src/coreclr/vm/jitinterface.cpp	Adds debug-only AltJit patchpoint info tracking so AltJit OSR compilations can retrieve the right patchpoint info.
src/coreclr/tools/superpmi/superpmi-shared/methodcontext.cpp	Adjusts replayed OSR patchpoint info on ARM64 to include FP/LR in older collections.
src/coreclr/jit/lclvars.cpp	Ensures ARM64 Tier0 patchpoint methods save FP/LR with all callee-saves (needed for OSR interactions).
src/coreclr/jit/compiler.cpp	Updates patchpoint info generation for callee-save recording (incl. ARM64 LR) and updates debug dumping.
src/coreclr/jit/codegenxarch.cpp	Updates `genPushCalleeSavedRegisters` signature to match common prolog flow.
src/coreclr/jit/codegenwasm.cpp	Updates `genPushCalleeSavedRegisters` signature (no-op target).
src/coreclr/jit/codegencommon.cpp	Adds ARM64 OSR handling to the “inherit tier0” prolog path and avoids double-saving inherited callee-saves.
src/coreclr/jit/codegenarmarch.cpp	ARM64 prolog logic now skips saving FP/LR (and other inherited callee-saves) when OSR inherits them from Tier0.
src/coreclr/jit/codegenarm64.cpp	ARM64 epilog now restores inherited callee-saves from the Tier0 frame and then pops the Tier0 frame.
src/coreclr/jit/codegen.h	Updates CodeGen APIs to support unwind-only prolog save helpers and unified `genPushCalleeSavedRegisters` signature.

Copilot

Pull request overview

Copilot reviewed 10 out of 10 changed files in this pull request and generated 2 comments.

Copilot

Pull request overview

Copilot reviewed 10 out of 10 changed files in this pull request and generated 1 comment.

jakobbotsch · 2026-04-14T19:54:00Z

/azp run runtime-jit-experimental

azure-pipelines · 2026-04-14T19:54:18Z

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azure-pipelines · 2026-04-15T20:07:34Z

Azure Pipelines successfully started running 1 pipeline(s).

Copilot

Pull request overview

Copilot reviewed 14 out of 14 changed files in this pull request and generated 2 comments.

Copilot

Pull request overview

Copilot reviewed 13 out of 13 changed files in this pull request and generated 3 comments.

Copilot

Pull request overview

Copilot reviewed 13 out of 13 changed files in this pull request and generated 1 comment.

jakobbotsch · 2026-04-17T09:40:26Z

/azp run runtime-jit-experimental

azure-pipelines · 2026-04-17T09:40:37Z

Azure Pipelines successfully started running 1 pipeline(s).

jakobbotsch · 2026-04-17T18:08:38Z

+        newInfo->Next = s_altJitPatchpointInfoList;
+        newInfo->Method = m_pMethodBeingCompiled;
+        newInfo->Info = newPpi;
+        s_altJitPatchpointInfoList = newInfo;


@jkotas do we have something similar to the method table auxiliary data for MethodDesc where I could store this in debug builds? Or perhaps I should just use a hash table with a mutex.

We have MethodDescCodeData that should work for what you trying to do here.

Copilot

Pull request overview

Copilot reviewed 13 out of 13 changed files in this pull request and generated 1 comment.

Copilot · 2026-04-17T18:10:15Z

+        for (AltJitPatchpointInfo* altJitPpi = s_altJitPatchpointInfoList; altJitPpi != NULL; altJitPpi = altJitPpi->Next)
+        {
+            if (altJitPpi->Method == m_pMethodBeingCompiled)
+            {
+                result = altJitPpi->Info;
+                break;
+            }


This ALT_JIT debug-only cache grows monotonically and is never cleaned up. Beyond the memory leak, keeping MethodDesc* keys for collectible methods past unload can lead to false matches if addresses get reused, returning the wrong PatchpointInfo. Consider scoping the cache to a reclaimable lifetime (e.g., tied to a LoaderAllocator cleanup) or using a non-colliding key.

Suggested change

for (AltJitPatchpointInfo* altJitPpi = s_altJitPatchpointInfoList; altJitPpi != NULL; altJitPpi = altJitPpi->Next)

{

if (altJitPpi->Method == m_pMethodBeingCompiled)

{

result = altJitPpi->Info;

break;

}

AltJitPatchpointInfo* previousAltJitPpi = NULL;

for (AltJitPatchpointInfo* altJitPpi = s_altJitPatchpointInfoList; altJitPpi != NULL; altJitPpi = altJitPpi->Next)

{

if (altJitPpi->Method == m_pMethodBeingCompiled)

{

uint32_t ppiSize = altJitPpi->Info->PatchpointInfoSize();

PatchpointInfo* copiedPpi = new (new uint8_t[ppiSize]) PatchpointInfo;

copiedPpi->Initialize(altJitPpi->Info->NumberOfLocals(), altJitPpi->Info->TotalFrameSize());

copiedPpi->Copy(altJitPpi->Info);

if (previousAltJitPpi == NULL)

{

s_altJitPatchpointInfoList = altJitPpi->Next;

}

else

{

previousAltJitPpi->Next = altJitPpi->Next;

}

delete[] reinterpret_cast<uint8_t*>(altJitPpi->Info);

delete altJitPpi;

result = copiedPpi;

break;

}

previousAltJitPpi = altJitPpi;

jakobbotsch · 2026-04-17T18:17:47Z

cc @dotnet/jit-contrib PTAL @AndyAyersMS. Left a few comments above that I should address, but I think this is ready for review.

Diffs. Larger OSR method prologs. It will be understated a little bit since the collections do not have any callee saves in the patchpoint information, but using callee saves in tier0 functions is rare, so probably it isn't understated by that much.

After some thinking I was able to remove the tier0 frame type regression – we now put FP/LR into the callee save registers in the patchpoint info only if it was saved with the rest of the callee saves, and then we use that in OSR to determine the kind of frame. In the end we don't need to care about all 5 types of frames, only where fp/lr ends up being saved which turns out not to be too bad.

AndyAyersMS

Once we're done with this cycle of OSR changes we should reconcile the various bits of documentation like OSR Details and Debuggging: OSR Prolog and OSR x64 Epilog Redesign.

And make a pass through #33658

jakobbotsch added 5 commits April 14, 2026 13:29

WIP

8d48da0

WIP

f1d98d1

WIP

e3d29e7

WIP

2179ae7

Run jit-format

448d7cd

Copilot AI review requested due to automatic review settings April 14, 2026 14:37

github-actions bot added the area-CodeGen-coreclr CLR JIT compiler in src/coreclr/src/jit and related components such as SuperPMI label Apr 14, 2026

Copilot started reviewing on behalf of jakobbotsch April 14, 2026 14:38 View session

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Comment thread src/coreclr/jit/codegenarm64.cpp Outdated

Comment thread src/coreclr/jit/compiler.cpp Outdated

Comment thread src/coreclr/vm/jitinterface.cpp

Comment thread src/coreclr/tools/superpmi/superpmi-shared/methodcontext.cpp Outdated

jakobbotsch added 2 commits April 14, 2026 18:46

Fix

10cff17

Fix again

27db1a7

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Comment thread src/coreclr/jit/codegenarm64.cpp Outdated

Comment thread src/coreclr/jit/codegenarm64.cpp Outdated

jakobbotsch added 2 commits April 14, 2026 19:54

More hacking

05131c3

Build break

480d01e

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Comment thread src/coreclr/vm/jitinterface.cpp

jakobbotsch added 3 commits April 15, 2026 13:05

Switch to restoring callee saves instead

771df5f

Clean up

3474bd1

Run jit-format

60aa1f8

Copilot AI review requested due to automatic review settings April 15, 2026 11:13

jakobbotsch added 2 commits April 16, 2026 17:25

Remove unnecessary phantom unwind

06e9e7f

Partial compilation patchpoints

05ffa2d

Copilot AI review requested due to automatic review settings April 16, 2026 15:26

Copilot started reviewing on behalf of jakobbotsch April 16, 2026 15:27 View session

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Comment thread src/coreclr/jit/codegenxarch.cpp

Comment thread src/coreclr/jit/codegenwasm.cpp

jakobbotsch and others added 2 commits April 16, 2026 20:05

Merge branch 'main' into osr-arm64-restore-from-tier0

bbde19c

Support frames without fp/lr saved with callee saves

82ad389

Copilot AI review requested due to automatic review settings April 17, 2026 08:08

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Comment thread src/coreclr/jit/codegenarm64.cpp Outdated

Comment thread src/coreclr/jit/codegenwasm.cpp

Comment thread src/coreclr/jit/codegenarm.cpp

jakobbotsch added 2 commits April 17, 2026 10:19

Fixes

6d784e9

Remove SPMI hack

bd302fb

Copilot AI review requested due to automatic review settings April 17, 2026 08:21

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Comment thread src/coreclr/jit/codegenxarch.cpp

Feedback

87e6ce5

jakobbotsch mentioned this pull request Apr 17, 2026

JIT: Optimize async OSR resumptions #127074

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jakobbotsch marked this pull request as ready for review April 17, 2026 18:01

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Comment thread src/coreclr/jit/codegenarm64.cpp

jakobbotsch commented Apr 17, 2026

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jakobbotsch requested a review from AndyAyersMS April 17, 2026 18:18

A few fixes

e1f8e92

AndyAyersMS approved these changes Apr 17, 2026

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-        for (AltJitPatchpointInfo* altJitPpi = s_altJitPatchpointInfoList; altJitPpi != NULL; altJitPpi = altJitPpi->Next)
-        {
-            if (altJitPpi->Method == m_pMethodBeingCompiled)
-            {
-                result = altJitPpi->Info;
-                break;
-            }
+        AltJitPatchpointInfo* previousAltJitPpi = NULL;
+        for (AltJitPatchpointInfo* altJitPpi = s_altJitPatchpointInfoList; altJitPpi != NULL; altJitPpi = altJitPpi->Next)
+        {
+            if (altJitPpi->Method == m_pMethodBeingCompiled)
+            {
+                uint32_t ppiSize = altJitPpi->Info->PatchpointInfoSize();
+                PatchpointInfo* copiedPpi = new (new uint8_t[ppiSize]) PatchpointInfo;
+                copiedPpi->Initialize(altJitPpi->Info->NumberOfLocals(), altJitPpi->Info->TotalFrameSize());
+                copiedPpi->Copy(altJitPpi->Info);
+                if (previousAltJitPpi == NULL)
+                {
+                    s_altJitPatchpointInfoList = altJitPpi->Next;
+                }
+                else
+                {
+                    previousAltJitPpi->Next = altJitPpi->Next;
+                }
+                delete[] reinterpret_cast<uint8_t*>(altJitPpi->Info);
+                delete altJitPpi;
+                result = copiedPpi;
+                break;
+            }
+            previousAltJitPpi = altJitPpi;

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