.NET 9.0.200 broke ICSharpCode.Decompiler due to changed IL generation for yield return

[foriequal0]

Input code

public sealed class Target
{
    private IEnumerable<int> GetEnumerable()
    {
        yield return 1;
    }
}

Erroneous output

9.0.103

public sealed class Target
{
        private IEnumerable<int> GetEnumerable ()
        {
                yield return 1;
        }
}

9.0.200

using System;
using System.Collections;
using System.Collections.Generic;
using System.Diagnostics;
using System.Runtime.CompilerServices;

public sealed class Target
{
        [CompilerGenerated]
        private sealed class <GetEnumerable>d__0 : IEnumerable<int>, IEnumerable, IEnumerator<int>, IEnumerator, IDisposable
        {
                private int <>1__state;

                private int <>2__current;

                private int <>l__initialThreadId;

                public Target <>4__this;

                int IEnumerator<int>.Current {
                        [DebuggerHidden]
                        get {
                                return <>2__current;
                        }
                }

                object IEnumerator.Current {
                        [DebuggerHidden]
                        get {
                                return <>2__current;
                        }
                }

                [DebuggerHidden]
                public <GetEnumerable>d__0 (int <>1__state)
                {
                        this.<>1__state = <>1__state;
                        <>l__initialThreadId = Environment.CurrentManagedThreadId;
                }

                [DebuggerHidden]
                void IDisposable.Dispose ()
                {
                        <>1__state = -2;
                }

                private bool MoveNext ()
                {
                        switch (<>1__state) {
                        default:
                                return false;
                        case 0:
                                <>1__state = -1;
                                <>2__current = 1;
                                <>1__state = 1;
                                return true;
                        case 1:
                                <>1__state = -1;
                                return false;
                        }
                }

                bool IEnumerator.MoveNext ()
                {
                        //ILSpy generated this explicit interface implementation from .override directive in MoveNext
                        return this.MoveNext ();
                }

                [DebuggerHidden]
                void IEnumerator.Reset ()
                {
                        throw new NotSupportedException ();
                }

                [DebuggerHidden]
                IEnumerator<int> IEnumerable<int>.GetEnumerator ()
                {
                        <GetEnumerable>d__0 result;
                        if (<>1__state == -2 && <>l__initialThreadId == Environment.CurrentManagedThreadId) {
                                <>1__state = 0;
                                result = this;
                        } else {
                                result = new <GetEnumerable>d__0 (0) {
                                        <>4__this = <>4__this
                                };
                        }
                        return result;
                }

                [DebuggerHidden]
                IEnumerator IEnumerable.GetEnumerator ()
                {
                        return ((IEnumerable<int>)this).GetEnumerator ();
                }
        }

        [IteratorStateMachine (typeof(<GetEnumerable>d__0))]
        private IEnumerable<int> GetEnumerable ()
        {
                //yield-return decompiler failed: Unexpected instruction in Iterator.Dispose()
                return new <GetEnumerable>d__0 (-2) {
                        <>4__this = this
                };
        }
}

Details

• Product in use: ICSharpCode.Decompiler nuget package
• Version in use: 9.0.0.7889
• Any other relevant information to the issue, or your interest in contributing a fix.

Generated IL is slightly changed after 9.0.200

9.0.103

.class public sealed auto ansi beforefieldinit
  Target
    extends [System.Runtime]System.Object
{

  .class nested private sealed auto ansi beforefieldinit
    '<GetEnumerable>d__0'
      extends [System.Runtime]System.Object
      implements
        class [System.Runtime]System.Collections.Generic.IEnumerable`1<int32>,
        [System.Runtime]System.Collections.IEnumerable,
        class [System.Runtime]System.Collections.Generic.IEnumerator`1<int32>,
        [System.Runtime]System.Collections.IEnumerator,
        [System.Runtime]System.IDisposable
  {
    .custom instance void [System.Runtime]System.Runtime.CompilerServices.CompilerGeneratedAttribute::.ctor()
      = (01 00 00 00 )

    .field private int32 '<>1__state'

    .field private int32 '<>2__current'

    .field private int32 '<>l__initialThreadId'

    .field public class Target '<>4__this'

    .method public hidebysig specialname rtspecialname instance void
      .ctor(
        int32 '<>1__state'
      ) cil managed
    {
      .custom instance void [System.Runtime]System.Diagnostics.DebuggerHiddenAttribute::.ctor()
        = (01 00 00 00 )
      .maxstack 8

      IL_0000: ldarg.0      // this
      IL_0001: call         instance void [System.Runtime]System.Object::.ctor()
      IL_0006: nop
      IL_0007: ldarg.0      // this
      IL_0008: ldarg.1      // '<>1__state'
      IL_0009: stfld        int32 Target/'<GetEnumerable>d__0'::'<>1__state'
      IL_000e: ldarg.0      // this
      IL_000f: call         int32 [System.Runtime]System.Environment::get_CurrentManagedThreadId()
      IL_0014: stfld        int32 Target/'<GetEnumerable>d__0'::'<>l__initialThreadId'
      IL_0019: ret

    } // end of method '<GetEnumerable>d__0'::.ctor

    .method private final hidebysig virtual newslot instance void
      System.IDisposable.Dispose() cil managed
    {
      .custom instance void [System.Runtime]System.Diagnostics.DebuggerHiddenAttribute::.ctor()
        = (01 00 00 00 )
      .override method instance void [System.Runtime]System.IDisposable::Dispose()
      .maxstack 8

      IL_0000: ret

    } // end of method '<GetEnumerable>d__0'::System.IDisposable.Dispose

    .method private final hidebysig virtual newslot instance bool
      MoveNext() cil managed
    {
      .override method instance bool [System.Runtime]System.Collections.IEnumerator::MoveNext()
      .maxstack 2
      .locals init (
        [0] int32 V_0
      )

      IL_0000: ldarg.0      // this
      IL_0001: ldfld        int32 Target/'<GetEnumerable>d__0'::'<>1__state'
      IL_0006: stloc.0      // V_0
      IL_0007: ldloc.0      // V_0
      IL_0008: brfalse.s    IL_0012
      IL_000a: br.s         IL_000c
      IL_000c: ldloc.0      // V_0
      IL_000d: ldc.i4.1
      IL_000e: beq.s        IL_0014
      IL_0010: br.s         IL_0016
      IL_0012: br.s         IL_0018
      IL_0014: br.s         IL_0030
      IL_0016: ldc.i4.0
      IL_0017: ret
      IL_0018: ldarg.0      // this
      IL_0019: ldc.i4.m1
      IL_001a: stfld        int32 Target/'<GetEnumerable>d__0'::'<>1__state'

      // [27 5 - 27 6]
      IL_001f: nop

      // [28 9 - 28 24]
      IL_0020: ldarg.0      // this
      IL_0021: ldc.i4.1
      IL_0022: stfld        int32 Target/'<GetEnumerable>d__0'::'<>2__current'
      IL_0027: ldarg.0      // this
      IL_0028: ldc.i4.1
      IL_0029: stfld        int32 Target/'<GetEnumerable>d__0'::'<>1__state'
      IL_002e: ldc.i4.1
      IL_002f: ret

      IL_0030: ldarg.0      // this
      IL_0031: ldc.i4.m1
      IL_0032: stfld        int32 Target/'<GetEnumerable>d__0'::'<>1__state'

      // [29 5 - 29 6]
      IL_0037: ldc.i4.0
      IL_0038: ret

    } // end of method '<GetEnumerable>d__0'::MoveNext

    .method private final hidebysig virtual newslot specialname instance int32
      'System.Collections.Generic.IEnumerator<System.Int32>.get_Current'() cil managed
    {
      .custom instance void [System.Runtime]System.Diagnostics.DebuggerHiddenAttribute::.ctor()
        = (01 00 00 00 )
      .override method instance !0/*T*/ class [System.Runtime]System.Collections.Generic.IEnumerator`1<int32>::get_Current()
      .maxstack 8

      IL_0000: ldarg.0      // this
      IL_0001: ldfld        int32 Target/'<GetEnumerable>d__0'::'<>2__current'
      IL_0006: ret

    } // end of method '<GetEnumerable>d__0'::'System.Collections.Generic.IEnumerator<System.Int32>.get_Current'

    .method private final hidebysig virtual newslot instance void
      System.Collections.IEnumerator.Reset() cil managed
    {
      .custom instance void [System.Runtime]System.Diagnostics.DebuggerHiddenAttribute::.ctor()
        = (01 00 00 00 )
      .override method instance void [System.Runtime]System.Collections.IEnumerator::Reset()
      .maxstack 8

      IL_0000: newobj       instance void [System.Runtime]System.NotSupportedException::.ctor()
      IL_0005: throw

    } // end of method '<GetEnumerable>d__0'::System.Collections.IEnumerator.Reset

    .method private final hidebysig virtual newslot specialname instance object
      System.Collections.IEnumerator.get_Current() cil managed
    {
      .custom instance void [System.Runtime]System.Diagnostics.DebuggerHiddenAttribute::.ctor()
        = (01 00 00 00 )
      .override method instance object [System.Runtime]System.Collections.IEnumerator::get_Current()
      .maxstack 8

      IL_0000: ldarg.0      // this
      IL_0001: ldfld        int32 Target/'<GetEnumerable>d__0'::'<>2__current'
      IL_0006: box          [System.Runtime]System.Int32
      IL_000b: ret

    } // end of method '<GetEnumerable>d__0'::System.Collections.IEnumerator.get_Current

    .method private final hidebysig virtual newslot instance class [System.Runtime]System.Collections.Generic.IEnumerator`1<int32>
      'System.Collections.Generic.IEnumerable<System.Int32>.GetEnumerator'() cil managed
    {
      .custom instance void [System.Runtime]System.Diagnostics.DebuggerHiddenAttribute::.ctor()
        = (01 00 00 00 )
      .param [0]
        .custom instance void [System.Runtime]System.Runtime.CompilerServices.NullableAttribute::.ctor(unsigned int8)
          = (01 00 01 00 00 ) // .....
          // unsigned int8(1) // 0x01
      .override method instance class [System.Runtime]System.Collections.Generic.IEnumerator`1<!0/*T*/> class [System.Runtime]System.Collections.Generic.IEnumerable`1<int32>::GetEnumerator()
      .maxstack 2
      .locals init (
        [0] class Target/'<GetEnumerable>d__0' V_0
      )

      IL_0000: ldarg.0      // this
      IL_0001: ldfld        int32 Target/'<GetEnumerable>d__0'::'<>1__state'
      IL_0006: ldc.i4.s     -2 // 0xfe
      IL_0008: bne.un.s     IL_0022
      IL_000a: ldarg.0      // this
      IL_000b: ldfld        int32 Target/'<GetEnumerable>d__0'::'<>l__initialThreadId'
      IL_0010: call         int32 [System.Runtime]System.Environment::get_CurrentManagedThreadId()
      IL_0015: bne.un.s     IL_0022
      IL_0017: ldarg.0      // this
      IL_0018: ldc.i4.0
      IL_0019: stfld        int32 Target/'<GetEnumerable>d__0'::'<>1__state'
      IL_001e: ldarg.0      // this
      IL_001f: stloc.0      // V_0
      IL_0020: br.s         IL_0035
      IL_0022: ldc.i4.0
      IL_0023: newobj       instance void Target/'<GetEnumerable>d__0'::.ctor(int32)
      IL_0028: stloc.0      // V_0
      IL_0029: ldloc.0      // V_0
      IL_002a: ldarg.0      // this
      IL_002b: ldfld        class Target Target/'<GetEnumerable>d__0'::'<>4__this'
      IL_0030: stfld        class Target Target/'<GetEnumerable>d__0'::'<>4__this'
      IL_0035: ldloc.0      // V_0
      IL_0036: ret

    } // end of method '<GetEnumerable>d__0'::'System.Collections.Generic.IEnumerable<System.Int32>.GetEnumerator'

    .method private final hidebysig virtual newslot instance class [System.Runtime]System.Collections.IEnumerator
      System.Collections.IEnumerable.GetEnumerator() cil managed
    {
      .custom instance void [System.Runtime]System.Diagnostics.DebuggerHiddenAttribute::.ctor()
        = (01 00 00 00 )
      .param [0]
        .custom instance void [System.Runtime]System.Runtime.CompilerServices.NullableAttribute::.ctor(unsigned int8)
          = (01 00 01 00 00 ) // .....
          // unsigned int8(1) // 0x01
      .override method instance class [System.Runtime]System.Collections.IEnumerator [System.Runtime]System.Collections.IEnumerable::GetEnumerator()
      .maxstack 8

      IL_0000: ldarg.0      // this
      IL_0001: call         instance class [System.Runtime]System.Collections.Generic.IEnumerator`1<int32> Target/'<GetEnumerable>d__0'::'System.Collections.Generic.IEnumerable<System.Int32>.GetEnumerator'()
      IL_0006: ret

    } // end of method '<GetEnumerable>d__0'::System.Collections.IEnumerable.GetEnumerator

    .property instance int32 'System.Collections.Generic.IEnumerator<System.Int32>.Current'()
    {
      .get instance int32 Target/'<GetEnumerable>d__0'::'System.Collections.Generic.IEnumerator<System.Int32>.get_Current'()
    } // end of property '<GetEnumerable>d__0'::'System.Collections.Generic.IEnumerator<System.Int32>.Current'

    .property instance object 'System.Collections.IEnumerator.Current'()
    {
      .get instance object Target/'<GetEnumerable>d__0'::System.Collections.IEnumerator.get_Current()
    } // end of property '<GetEnumerable>d__0'::System.Collections.IEnumerator.Current
  } // end of class '<GetEnumerable>d__0'

  .method private hidebysig instance class [System.Runtime]System.Collections.Generic.IEnumerable`1<int32>
    GetEnumerable() cil managed
  {
    .custom instance void [System.Runtime]System.Runtime.CompilerServices.NullableContextAttribute::.ctor(unsigned int8)
      = (01 00 01 00 00 ) // .....
      // unsigned int8(1) // 0x01
    .custom instance void [System.Runtime]System.Runtime.CompilerServices.IteratorStateMachineAttribute::.ctor(class [System.Runtime]System.Type)
      = (
        01 00 1a 54 61 72 67 65 74 2b 3c 47 65 74 45 6e // ...Target+<GetEn
        75 6d 65 72 61 62 6c 65 3e 64 5f 5f 30 00 00    // umerable>d__0..
      )
      // type(class Target/'<GetEnumerable>d__0')
    .maxstack 8

    IL_0000: ldc.i4.s     -2 // 0xfe
    IL_0002: newobj       instance void Target/'<GetEnumerable>d__0'::.ctor(int32)
    IL_0007: dup
    IL_0008: ldarg.0      // this
    IL_0009: stfld        class Target Target/'<GetEnumerable>d__0'::'<>4__this'
    IL_000e: ret

  } // end of method Target::GetEnumerable

  .method public hidebysig specialname rtspecialname instance void
    .ctor() cil managed
  {
    .maxstack 8

    IL_0000: ldarg.0      // this
    IL_0001: call         instance void [System.Runtime]System.Object::.ctor()
    IL_0006: nop
    IL_0007: ret

  } // end of method Target::.ctor
} // end of class Target

9.0.200

// Type: Target 
// Assembly: ConsoleApp1, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null
// MVID: 03D82503-62C1-4247-8ED3-D013EB2E59BB
// Location: E:\workspace\CSharpDecompilerRepro\Solution1\ConsoleApp1\bin\Debug\net9.0\ConsoleApp1.dll
// Sequence point data and variable names from e:\workspace\csharpdecompilerrepro\solution1\consoleapp1\bin\debug\net9.0\consoleapp1.pdb

.class public sealed auto ansi beforefieldinit
  Target
    extends [System.Runtime]System.Object
{

  .class nested private sealed auto ansi beforefieldinit
    '<GetEnumerable>d__0'
      extends [System.Runtime]System.Object
      implements
        class [System.Runtime]System.Collections.Generic.IEnumerable`1<int32>,
        [System.Runtime]System.Collections.IEnumerable,
        class [System.Runtime]System.Collections.Generic.IEnumerator`1<int32>,
        [System.Runtime]System.Collections.IEnumerator,
        [System.Runtime]System.IDisposable
  {
    .custom instance void [System.Runtime]System.Runtime.CompilerServices.CompilerGeneratedAttribute::.ctor()
      = (01 00 00 00 )

    .field private int32 '<>1__state'

    .field private int32 '<>2__current'

    .field private int32 '<>l__initialThreadId'

    .field public class Target '<>4__this'

    .method public hidebysig specialname rtspecialname instance void
      .ctor(
        int32 '<>1__state'
      ) cil managed
    {
      .custom instance void [System.Runtime]System.Diagnostics.DebuggerHiddenAttribute::.ctor()
        = (01 00 00 00 )
      .maxstack 8

      IL_0000: ldarg.0      // this
      IL_0001: call         instance void [System.Runtime]System.Object::.ctor()
      IL_0006: nop
      IL_0007: ldarg.0      // this
      IL_0008: ldarg.1      // '<>1__state'
      IL_0009: stfld        int32 Target/'<GetEnumerable>d__0'::'<>1__state'
      IL_000e: ldarg.0      // this
      IL_000f: call         int32 [System.Runtime]System.Environment::get_CurrentManagedThreadId()
      IL_0014: stfld        int32 Target/'<GetEnumerable>d__0'::'<>l__initialThreadId'
      IL_0019: ret

    } // end of method '<GetEnumerable>d__0'::.ctor

    .method private final hidebysig virtual newslot instance void
      System.IDisposable.Dispose() cil managed
    {
      .custom instance void [System.Runtime]System.Diagnostics.DebuggerHiddenAttribute::.ctor()
        = (01 00 00 00 )
      .override method instance void [System.Runtime]System.IDisposable::Dispose()
      .maxstack 8

      IL_0000: ldarg.0      // this
      IL_0001: ldc.i4.s     -2 // 0xfe
      IL_0003: stfld        int32 Target/'<GetEnumerable>d__0'::'<>1__state'
      IL_0008: ret

    } // end of method '<GetEnumerable>d__0'::System.IDisposable.Dispose

    .method private final hidebysig virtual newslot instance bool
      MoveNext() cil managed
    {
      .override method instance bool [System.Runtime]System.Collections.IEnumerator::MoveNext()
      .maxstack 2
      .locals init (
        [0] int32 V_0
      )

      IL_0000: ldarg.0      // this
      IL_0001: ldfld        int32 Target/'<GetEnumerable>d__0'::'<>1__state'
      IL_0006: stloc.0      // V_0
      IL_0007: ldloc.0      // V_0
      IL_0008: brfalse.s    IL_0012
      IL_000a: br.s         IL_000c
      IL_000c: ldloc.0      // V_0
      IL_000d: ldc.i4.1
      IL_000e: beq.s        IL_0014
      IL_0010: br.s         IL_0016
      IL_0012: br.s         IL_0018
      IL_0014: br.s         IL_0030
      IL_0016: ldc.i4.0
      IL_0017: ret
      IL_0018: ldarg.0      // this
      IL_0019: ldc.i4.m1
      IL_001a: stfld        int32 Target/'<GetEnumerable>d__0'::'<>1__state'

      // [27 5 - 27 6]
      IL_001f: nop

      // [28 9 - 28 24]
      IL_0020: ldarg.0      // this
      IL_0021: ldc.i4.1
      IL_0022: stfld        int32 Target/'<GetEnumerable>d__0'::'<>2__current'
      IL_0027: ldarg.0      // this
      IL_0028: ldc.i4.1
      IL_0029: stfld        int32 Target/'<GetEnumerable>d__0'::'<>1__state'
      IL_002e: ldc.i4.1
      IL_002f: ret

      IL_0030: ldarg.0      // this
      IL_0031: ldc.i4.m1
      IL_0032: stfld        int32 Target/'<GetEnumerable>d__0'::'<>1__state'

      // [29 5 - 29 6]
      IL_0037: ldc.i4.0
      IL_0038: ret

    } // end of method '<GetEnumerable>d__0'::MoveNext

    .method private final hidebysig virtual newslot specialname instance int32
      'System.Collections.Generic.IEnumerator<System.Int32>.get_Current'() cil managed
    {
      .custom instance void [System.Runtime]System.Diagnostics.DebuggerHiddenAttribute::.ctor()
        = (01 00 00 00 )
      .override method instance !0/*T*/ class [System.Runtime]System.Collections.Generic.IEnumerator`1<int32>::get_Current()
      .maxstack 8

      IL_0000: ldarg.0      // this
      IL_0001: ldfld        int32 Target/'<GetEnumerable>d__0'::'<>2__current'
      IL_0006: ret

    } // end of method '<GetEnumerable>d__0'::'System.Collections.Generic.IEnumerator<System.Int32>.get_Current'

    .method private final hidebysig virtual newslot instance void
      System.Collections.IEnumerator.Reset() cil managed
    {
      .custom instance void [System.Runtime]System.Diagnostics.DebuggerHiddenAttribute::.ctor()
        = (01 00 00 00 )
      .override method instance void [System.Runtime]System.Collections.IEnumerator::Reset()
      .maxstack 8

      IL_0000: newobj       instance void [System.Runtime]System.NotSupportedException::.ctor()
      IL_0005: throw

    } // end of method '<GetEnumerable>d__0'::System.Collections.IEnumerator.Reset

    .method private final hidebysig virtual newslot specialname instance object
      System.Collections.IEnumerator.get_Current() cil managed
    {
      .custom instance void [System.Runtime]System.Diagnostics.DebuggerHiddenAttribute::.ctor()
        = (01 00 00 00 )
      .override method instance object [System.Runtime]System.Collections.IEnumerator::get_Current()
      .maxstack 8

      IL_0000: ldarg.0      // this
      IL_0001: ldfld        int32 Target/'<GetEnumerable>d__0'::'<>2__current'
      IL_0006: box          [System.Runtime]System.Int32
      IL_000b: ret

    } // end of method '<GetEnumerable>d__0'::System.Collections.IEnumerator.get_Current

    .method private final hidebysig virtual newslot instance class [System.Runtime]System.Collections.Generic.IEnumerator`1<int32>
      'System.Collections.Generic.IEnumerable<System.Int32>.GetEnumerator'() cil managed
    {
      .custom instance void [System.Runtime]System.Diagnostics.DebuggerHiddenAttribute::.ctor()
        = (01 00 00 00 )
      .param [0]
        .custom instance void [System.Runtime]System.Runtime.CompilerServices.NullableAttribute::.ctor(unsigned int8)
          = (01 00 01 00 00 ) // .....
          // unsigned int8(1) // 0x01
      .override method instance class [System.Runtime]System.Collections.Generic.IEnumerator`1<!0/*T*/> class [System.Runtime]System.Collections.Generic.IEnumerable`1<int32>::GetEnumerator()
      .maxstack 2
      .locals init (
        [0] class Target/'<GetEnumerable>d__0' V_0
      )

      IL_0000: ldarg.0      // this
      IL_0001: ldfld        int32 Target/'<GetEnumerable>d__0'::'<>1__state'
      IL_0006: ldc.i4.s     -2 // 0xfe
      IL_0008: bne.un.s     IL_0022
      IL_000a: ldarg.0      // this
      IL_000b: ldfld        int32 Target/'<GetEnumerable>d__0'::'<>l__initialThreadId'
      IL_0010: call         int32 [System.Runtime]System.Environment::get_CurrentManagedThreadId()
      IL_0015: bne.un.s     IL_0022
      IL_0017: ldarg.0      // this
      IL_0018: ldc.i4.0
      IL_0019: stfld        int32 Target/'<GetEnumerable>d__0'::'<>1__state'
      IL_001e: ldarg.0      // this
      IL_001f: stloc.0      // V_0
      IL_0020: br.s         IL_0035
      IL_0022: ldc.i4.0
      IL_0023: newobj       instance void Target/'<GetEnumerable>d__0'::.ctor(int32)
      IL_0028: stloc.0      // V_0
      IL_0029: ldloc.0      // V_0
      IL_002a: ldarg.0      // this
      IL_002b: ldfld        class Target Target/'<GetEnumerable>d__0'::'<>4__this'
      IL_0030: stfld        class Target Target/'<GetEnumerable>d__0'::'<>4__this'
      IL_0035: ldloc.0      // V_0
      IL_0036: ret

    } // end of method '<GetEnumerable>d__0'::'System.Collections.Generic.IEnumerable<System.Int32>.GetEnumerator'

    .method private final hidebysig virtual newslot instance class [System.Runtime]System.Collections.IEnumerator
      System.Collections.IEnumerable.GetEnumerator() cil managed
    {
      .custom instance void [System.Runtime]System.Diagnostics.DebuggerHiddenAttribute::.ctor()
        = (01 00 00 00 )
      .param [0]
        .custom instance void [System.Runtime]System.Runtime.CompilerServices.NullableAttribute::.ctor(unsigned int8)
          = (01 00 01 00 00 ) // .....
          // unsigned int8(1) // 0x01
      .override method instance class [System.Runtime]System.Collections.IEnumerator [System.Runtime]System.Collections.IEnumerable::GetEnumerator()
      .maxstack 8

      IL_0000: ldarg.0      // this
      IL_0001: call         instance class [System.Runtime]System.Collections.Generic.IEnumerator`1<int32> Target/'<GetEnumerable>d__0'::'System.Collections.Generic.IEnumerable<System.Int32>.GetEnumerator'()
      IL_0006: ret

    } // end of method '<GetEnumerable>d__0'::System.Collections.IEnumerable.GetEnumerator

    .property instance int32 'System.Collections.Generic.IEnumerator<System.Int32>.Current'()
    {
      .get instance int32 Target/'<GetEnumerable>d__0'::'System.Collections.Generic.IEnumerator<System.Int32>.get_Current'()
    } // end of property '<GetEnumerable>d__0'::'System.Collections.Generic.IEnumerator<System.Int32>.Current'

    .property instance object 'System.Collections.IEnumerator.Current'()
    {
      .get instance object Target/'<GetEnumerable>d__0'::System.Collections.IEnumerator.get_Current()
    } // end of property '<GetEnumerable>d__0'::System.Collections.IEnumerator.Current
  } // end of class '<GetEnumerable>d__0'

  .method private hidebysig instance class [System.Runtime]System.Collections.Generic.IEnumerable`1<int32>
    GetEnumerable() cil managed
  {
    .custom instance void [System.Runtime]System.Runtime.CompilerServices.NullableContextAttribute::.ctor(unsigned int8)
      = (01 00 01 00 00 ) // .....
      // unsigned int8(1) // 0x01
    .custom instance void [System.Runtime]System.Runtime.CompilerServices.IteratorStateMachineAttribute::.ctor(class [System.Runtime]System.Type)
      = (
        01 00 1a 54 61 72 67 65 74 2b 3c 47 65 74 45 6e // ...Target+<GetEn
        75 6d 65 72 61 62 6c 65 3e 64 5f 5f 30 00 00    // umerable>d__0..
      )
      // type(class Target/'<GetEnumerable>d__0')
    .maxstack 8

    IL_0000: ldc.i4.s     -2 // 0xfe
    IL_0002: newobj       instance void Target/'<GetEnumerable>d__0'::.ctor(int32)
    IL_0007: dup
    IL_0008: ldarg.0      // this
    IL_0009: stfld        class Target Target/'<GetEnumerable>d__0'::'<>4__this'
    IL_000e: ret

  } // end of method Target::GetEnumerable

  .method public hidebysig specialname rtspecialname instance void
    .ctor() cil managed
  {
    .maxstack 8

    IL_0000: ldarg.0      // this
    IL_0001: call         instance void [System.Runtime]System.Object::.ctor()
    IL_0006: nop
    IL_0007: ret

  } // end of method Target::.ctor
} // end of class Target

diff for you

--- 9.0.103
+++ 9.0.200
@@ -60,7 +60,10 @@
       .override method instance void [System.Runtime]System.IDisposable::Dispose()
       .maxstack 8
 
-      IL_0000: ret
+      IL_0000: ldarg.0      // this
+      IL_0001: ldc.i4.s     -2 // 0xfe
+      IL_0003: stfld        int32 Target/'<GetEnumerable>d__0'::'<>1__state'
+      IL_0008: ret
 
     } // end of method '<GetEnumerable>d__0'::System.IDisposable.Dispose

I think it would be equivalent to this

--- 9.0.103
+++ 9.0.200
@@ -41,6 +41,7 @@
                 [DebuggerHidden]
                 void IDisposable.Dispose ()
                 {
+                        <>1__state = -2;
                 }
 
                 private bool MoveNext ()

If there are captured enumerators, then they set default them.

public sealed class Target
{
    private IEnumerable<int> GetEnumerable(List<int> a, List<int> b)
    {
        foreach (var x in a)
        {
            yield return x;
        }

        foreach (var x in b)
        {
            yield return x;
        }
    }
}

--- 9.0.103
+++ 9.0.200
@@ -111,7 +111,16 @@
         IL_0043: endfinally
       } // end of finally
       IL_0044: br.s         IL_0046
-      IL_0046: ret
+      IL_0046: ldarg.0      // this
+      IL_0047: ldflda       valuetype [System.Collections]System.Collections.Generic.List`1/Enumerator<int32> Target/'<GetEnumerable>d__0'::'<>s__1'
+      IL_004c: initobj      valuetype [System.Collections]System.Collections.Generic.List`1/Enumerator<int32>
+      IL_0052: ldarg.0      // this
+      IL_0053: ldflda       valuetype [System.Collections]System.Collections.Generic.List`1/Enumerator<int32> Target/'<GetEnumerable>d__0'::'<>s__3'
+      IL_0058: initobj      valuetype [System.Collections]System.Collections.Generic.List`1/Enumerator<int32>
+      IL_005e: ldarg.0      // this
+      IL_005f: ldc.i4.s     -2 // 0xfe
+      IL_0061: stfld        int32 Target/'<GetEnumerable>d__0'::'<>1__state'
+      IL_0066: ret
 
     } // end of method '<GetEnumerable>d__0'::System.IDisposable.Dispose
 

equivalent to

--- 9.0.103
+++ 9.0.200
@@ -73,6 +73,9 @@
                                 }
                                 break;
                         }
+                        <>s__1 = default(List<int>.Enumerator);
+                        <>s__3 = default(List<int>.Enumerator);
+                        <>1__state = -2;
                 }
 
                 private bool MoveNext ()

[foriequal0]

<>1__state = -2 is introduced with this dotnet/roslyn#76090

[foriequal0]

<>s__1 = default(List<int>.Enumerator);

is introduced with this dotnet/roslyn#75908

[siegfriedpammer]

Thank you for reporting! However, we will have to postpone fixing this issue until there is a newer NuGet release of Roslyn, so that we can add it to our unit tests and fix all the various changes in the C# compiler code-gen. This way we can make sure that we don't break older compiler versions and have a larger set of test cases available with no additional work to do.

[foriequal0]

Thanks.

I could pass ILPretty test by inserting the following case statement after this case statement:

ILSpy/ICSharpCode.Decompiler/IL/ControlFlow/StateRangeAnalysis.cs

Lines 214 to 227 in 7d715a4

	case StObj stobj when mode == StateRangeAnalysisMode.IteratorMoveNext:
	{
	if (stobj.MatchStFld(out var target, out var field, out var value)
	&& target.MatchLdThis() && field.MemberDefinition == stateField && value.MatchLdcI4(-1))
	{
	// Mono resets the state field during MoveNext();
	// don't consider this user code.
	return stateRange;
	}
	else
	{
	goto default;
	}
	}

				case StObj stobj when mode == StateRangeAnalysisMode.IteratorDispose:
				{
					if (stobj.MatchStFld(out var target, out var field, out var value) && target.MatchLdThis())
					{
						if (field.IsCompilerGeneratedOrIsInCompilerGeneratedClass() && (value.MatchDefaultValue(out _) || value.MatchLdNull()))
						{
							// >= .net 9.0.200 clears hoisted locals
							// don't consider this user code.
							return stateRange;
						}

						if (field.MemberDefinition == stateField && value.MatchLdcI4(-2))
						{
							// >= .net 9.0.200 sets the state field during Dispose();
							// don't consider this user code.
							return stateRange;
						}
					}

					goto default;
				}

But I'm unsure about the field.IsCompilerGeneratedOrIsInCompilerGeneratedClass() (I don't know how to determine whether the field is hoisted locals or not), and (value.MatchDefaultValue(out _) || value.MatchLdNull()) (it doesn't clear int to 0, but I'm not sure why), so I'll just leave this as a note.

[siegfriedpammer]

I had a look at this problem and arrived at the same solution you posted. The only difference is that I use MatchDefaultOrNullOrZero, which works for all types and we already use it in a similar case: detecting the clean-up logic of async/await.

But I'm unsure about the field.IsCompilerGeneratedOrIsInCompilerGeneratedClass() (I don't know how to determine whether the field is hoisted locals or not)

I think it's not necessary to check whether the field belongs to a compiler-generated class, just checking for this is sufficient. When the analysis is executed, the IL is still part of the compiler-generated class so IsCompilerGeneratedOrIsInCompilerGeneratedClass() would always return true.

I will be pushing my changes to #3417... thank you for looking into this!