Stop spilling ldvirtftn

[hez2010]

We first need to stop spilling ldvirtftn before we can take the next step on GVM devirt.
Let's stop spilling them and see what we need to take to handle potential regressions.

Contributes to #112596

[Copilot]

Pull Request Overview

This PR refactors devirtualization handling by renaming a field and removing function pointer spilling for ldvirtftn operations. The change aims to improve performance by avoiding unnecessary temporary storage while preparing for further Generic Virtual Method (GVM) devirtualization improvements.

Key changes:

• Renamed wasArrayInterfaceDevirt to needsMethodContext to better reflect its broader purpose
• Removed spilling of ldvirtftn function pointers to temporary locals
• Added better handling for cloned "this" pointers in virtual function calls

Reviewed Changes

Copilot reviewed 6 out of 6 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
src/coreclr/vm/jitinterface.cpp	Updated field assignments from wasArrayInterfaceDevirt to needsMethodContext
src/coreclr/tools/superpmi/superpmi-shared/methodcontext.cpp	Updated SuperPMI recording/replay to use the renamed field
src/coreclr/tools/superpmi/superpmi-shared/agnostic.h	Renamed struct field from wasArrayInterfaceDevirt to needsMethodContext
src/coreclr/jit/importercalls.cpp	Removed function pointer spilling, improved "this" pointer handling, updated field references
src/coreclr/jit/compiler.hpp	Fixed comment for helper function
src/coreclr/inc/corinfo.h	Updated struct definition and comments to use the new field name

[hez2010]

This is just a rename without any meaningful change.

[dotnet-policy-service]

Tagging subscribers to this area: @JulieLeeMSFT, @jakobbotsch
See info in area-owners.md if you want to be subscribed.

[hez2010]

This is the only actual change.

[hez2010]

trigger mihubot since spmi jobs are broken @MihuBot

[EgorBo]

It looks like what you're trying to achieve is the devirtualization of indirect calls (GVM specifically), but you seems to be focused on a very specific case where the actual type is created right before the call (judging by your example in #112596 and the fact that you try to avoid spills).

I think we should focus on implementing #44610 for PGO first, e.g.

using System.Runtime.CompilerServices;

for (int i = 0; i < 200; i++)
{
    Test(new MyValueProcessor());
    Thread.Sleep(16);
}


[MethodImpl(MethodImplOptions.NoInlining)]
static void Test(IProcessor p)
{
    p.Process(42); // should devirtualize, but doesn't today.
}

public interface IProcessor
{
    void Process<T>(T item);
}

public class MyValueProcessor : IProcessor
{
    public void Process<T>(T item)
    {
        Console.WriteLine(item?.ToString());
    }
}

today we give up on instrumenting indirect calls.

And then, if you also want to have it divirtualized without the PGO (e.g. NAOT) you can just create fake (speculative) GDVs (which then will be folded once we hit a phase that can see through locals). Instead of just un-spilling the target that might be changed by the args?

cc @AndyAyersMS @dotnet/jit-contrib

[EgorBo]

what is the motivation behind this change?

[hez2010]

It's trying to suppress an assertion before addressing the lowering issue that is specific to windows-x86:

15:32:19.222 Running test: JIT/Directed/tailcall/more_tailcalls/more_tailcalls.cmd

Assert failure(PID 204 [0x000000cc], Thread: 2564 [0x0a04]): Assertion failed 'node->GetRegNum() != REG_NA' in 'GenInstance`2[System.__Canon,int]:VirtForward[System.__Canon,System.__Canon](System.__Canon,int,System.__Canon,System.__Canon):System.String:this' during 'Lowering nodeinfo' (IL size 23; hash 0xb3dc36bf; FullOpts)

    File: D:\a\_work\1\s\src\coreclr\jit\lower.cpp:9445
    Image: C:\h\w\ABFD09AF\p\corerun.exe

15:36:59.890 Running test: JIT/Regression/JitBlue/Runtime_87393/Runtime_87393/Runtime_87393.cmd

Assert failure(PID 9576 [0x00002568], Thread: 9588 [0x2574]): Assertion failed 'node->GetRegNum() != REG_NA' in 'Runtime_87393.Bar:M2[int](int,int,int,int,int,int,int,int,int,int,int,int,int,int,int,int):int' during 'Lowering nodeinfo' (IL size 41; hash 0x12b37abb; FullOpts)

    File: D:\a\_work\1\s\src\coreclr\jit\lower.cpp:9445
    Image: C:\h\w\ABFD09AF\p\corerun.exe