[wasm] `mono-aot-cross` asserts with `function:mono_method_to_ir, VAR 1 (TValue_REF) cannot be expanded in this context with 1 instantiations `

[martinothamar]

Description

Migrated a Blazor application from .NET 5 to latest 6 preview and wanted to test AOT which led me to this error.
Managed to narrow it down to a dictionary implementation which had a strange equality operator overload using EqualityComparer<>.Default.Equals(left, right);. Changing it to just Equals(left, right); fixed it (IEquatable<> is implemented). I have a full repro in the zip-file below.

> dotnet publish -c Release
Microsoft (R) Build Engine version 17.0.0-preview-21378-03+d592862ed for .NET
Copyright (C) Microsoft Corporation. All rights reserved.

  Determining projects to restore...
  All projects are up-to-date for restore.
  You are using a preview version of .NET. See: https://aka.ms/dotnet-core-preview
  SomeTestLib -> C:\code\private\wasmtest\SomeTestLib\bin\Release\net6.0\SomeTestLib.dll
  wasmtest -> C:\code\private\wasmtest\wasmtest\bin\Release\net6.0\wasmtest.dll
  wasmtest (Blazor output) -> C:\code\private\wasmtest\wasmtest\bin\Release\net6.0\wwwroot
  Optimizing assemblies for size, which may change the behavior of the app. Be sure to test after publishing. See: https://aka.ms/dotnet-illink
  AOT'ing 30 assemblies
C:\Program Files\dotnet\packs\Microsoft.NET.Runtime.WebAssembly.Sdk\6.0.0-preview.7.21377.19\Sdk\WasmApp.Native.targets(443,5): error : Precompiling failed for C:\code\private\wasmtest\wasmtest\obj\Release\net6.0\linked\SomeTestLib.dll: Mono Ahead of Time compiler - compiling assembly C:\code\private\wasmtest\wasmtest\obj\Release\net6.0\linked\SomeTestLib.dll [C:\code\private\wasmtest\wasmtest\wasmtest.csproj]
C:\Program Files\dotnet\packs\Microsoft.NET.Runtime.WebAssembly.Sdk\6.0.0-preview.7.21377.19\Sdk\WasmApp.Native.targets(443,5): error : * Assertion at D:\workspace\_work\1\s\src\mono\mono\mini\method-to-ir.c:7318, condition `is_ok (error)' not met, function:mono_method_to_ir, VAR 1 (TValue_REF) cannot be expanded in this context with 1 instantiations [C:\code\private\wasmtest\wasmtest\wasmtest.csproj]

Repro solution:
wasmtest.zip

In Classes.cs, make the following modification to let the build complete successfully with AOT.

    public static bool operator ==(ValueDictionary<TKey, TValue>? left, ValueDictionary<TKey, TValue>? right) =>
-        EqualityComparer<ValueDictionary<TKey, TValue>>.Default.Equals(left, right);
+        Equals(left, right);

dotnet publish -c Release

Configuration

• Windows 10, x64

PS > dotnet --info
.NET SDK (reflecting any global.json):
 Version:   6.0.100-preview.7.21379.14
 Commit:    22d70b47bc

Runtime Environment:
 OS Name:     Windows
 OS Version:  10.0.19043
 OS Platform: Windows
 RID:         win10-x64
 Base Path:   C:\Program Files\dotnet\sdk\6.0.100-preview.7.21379.14\

Host (useful for support):
  Version: 6.0.0-preview.7.21377.19
  Commit:  91ba01788d

Regression?

I haven't tried to reproduce in older previews.

I couldn't figure out the best area label to add to this issue. If you have write-permissions please help me learn by adding exactly one area label.

Tagging subscribers to 'arch-wasm': @lewing
See info in area-owners.md if you want to be subscribed.

Issue Details

---

Description

Migrated a Blazor application from .NET 5 to latest 6 preview and wanted to test AOT which led me to this error.
Managed to narrow it down to a dictionary implementation which had a strange equality operator overload using EqualityComparer<>.Default.Equals(left, right);. Changing it to just Equals(left, right); fixed it (IEquatable<> is implemented). I have a full repro in the zip-file below.

> dotnet publish -c Release
Microsoft (R) Build Engine version 17.0.0-preview-21378-03+d592862ed for .NET
Copyright (C) Microsoft Corporation. All rights reserved.

  Determining projects to restore...
  All projects are up-to-date for restore.
  You are using a preview version of .NET. See: https://aka.ms/dotnet-core-preview
  SomeTestLib -> C:\code\private\wasmtest\SomeTestLib\bin\Release\net6.0\SomeTestLib.dll
  wasmtest -> C:\code\private\wasmtest\wasmtest\bin\Release\net6.0\wasmtest.dll
  wasmtest (Blazor output) -> C:\code\private\wasmtest\wasmtest\bin\Release\net6.0\wwwroot
  Optimizing assemblies for size, which may change the behavior of the app. Be sure to test after publishing. See: https://aka.ms/dotnet-illink
  AOT'ing 30 assemblies
C:\Program Files\dotnet\packs\Microsoft.NET.Runtime.WebAssembly.Sdk\6.0.0-preview.7.21377.19\Sdk\WasmApp.Native.targets(443,5): error : Precompiling failed for C:\code\private\wasmtest\wasmtest\obj\Release\net6.0\linked\SomeTestLib.dll: Mono Ahead of Time compiler - compiling assembly C:\code\private\wasmtest\wasmtest\obj\Release\net6.0\linked\SomeTestLib.dll [C:\code\private\wasmtest\wasmtest\wasmtest.csproj]
C:\Program Files\dotnet\packs\Microsoft.NET.Runtime.WebAssembly.Sdk\6.0.0-preview.7.21377.19\Sdk\WasmApp.Native.targets(443,5): error : * Assertion at D:\workspace\_work\1\s\src\mono\mono\mini\method-to-ir.c:7318, condition `is_ok (error)' not met, function:mono_method_to_ir, VAR 1 (TValue_REF) cannot be expanded in this context with 1 instantiations [C:\code\private\wasmtest\wasmtest\wasmtest.csproj]

Repro solution:
wasmtest.zip

In Classes.cs, make the following modification to let the build complete successfully with AOT.

    public static bool operator ==(ValueDictionary<TKey, TValue>? left, ValueDictionary<TKey, TValue>? right) =>
-        EqualityComparer<ValueDictionary<TKey, TValue>>.Default.Equals(left, right);
+        Equals(left, right);

dotnet publish -c Release

Configuration

• Windows 10, x64

PS > dotnet --info
.NET SDK (reflecting any global.json):
 Version:   6.0.100-preview.7.21379.14
 Commit:    22d70b47bc

Runtime Environment:
 OS Name:     Windows
 OS Version:  10.0.19043
 OS Platform: Windows
 RID:         win10-x64
 Base Path:   C:\Program Files\dotnet\sdk\6.0.100-preview.7.21379.14\

Host (useful for support):
  Version: 6.0.0-preview.7.21377.19
  Commit:  91ba01788d

Regression?

I haven't tried to reproduce in older previews.

Author:	martinothamar
Assignees:	-
Labels:	arch-wasm, untriaged, area-Codegen-AOT-mono
Milestone:	-

[radical]

This can be reproduced with the wasm/console sample in src/mono/sample/wasm/console:

1. Add ValueDictionary.cs with:

using System;
using System.Collections.Generic;

#nullable enable

public sealed class ValueDictionary<TKey, TValue>
        : Dictionary<TKey, TValue>, IEquatable<Dictionary<TKey, TValue>>, IEquatable<ValueDictionary<TKey, TValue>>
        where TKey : notnull
{
    public ValueDictionary()
        : base()
    {
    }

    public ValueDictionary(IDictionary<TKey, TValue> other)
        : base(other)
    {
    }

    public override bool Equals(object? obj) => obj is Dictionary<TKey, TValue> other && Equals(other);

    public bool Equals(Dictionary<TKey, TValue>? other)
    {
        if (other is null)
            return false;

        if (ReferenceEquals(this, other))
            return true;

        if (Count != other.Count)
            return false;

        var valueComparer = EqualityComparer<TValue>.Default;

        foreach (var kvp in this)
        {
            if (!other.TryGetValue(kvp.Key, out var otherValue))
                return false;

            if (!valueComparer.Equals(kvp.Value, otherValue))
                return false;
        }

        return true;
    }

    public bool Equals(ValueDictionary<TKey, TValue>? other) => Equals(other as Dictionary<TKey, TValue>);

    public override int GetHashCode() => base.GetHashCode();

    public static bool operator ==(ValueDictionary<TKey, TValue>? left, ValueDictionary<TKey, TValue>? right) =>
        EqualityComparer<ValueDictionary<TKey, TValue>>.Default.Equals(left, right);

    public static bool operator !=(ValueDictionary<TKey, TValue>? left, ValueDictionary<TKey, TValue>? right) =>
        !(left == right);
}

2. And add ValueDictionary<string, string> vd = new(); to Program.cs

src/mono/sample/wasm/console$ make all V=1 AOT=1

  Mono Ahead of Time compiler - compiling assembly /Users/radical/dev/r2/src/mono/sample/wasm/console/bin/browser-wasm/publish/Wasm.Console.Sample.dll
  * Assertion at /Users/radical/dev/r2/src/mono/mono/mini/method-to-ir.c:7319, condition `is_ok (error)' not met, function:mono_method_to_ir, VAR 1 (TValue_REF) cannot be expanded in this context with 1 instantiations

cc @vargaz @BrzVlad

[lewing]

cc @SamMonoRT

[vargaz]

If this is release critical, the assert can simple by removed, i.e. change it to:

if (is_ok (error)) { <rest> }

Since this is just an optimization, disabling it in this case is not going to matter much.