`dup` instruction interferes with collection initialization for value types

[ds5678]

Input code

.class public auto ansi abstract sealed beforefieldinit ICSharpCode.Decompiler.Tests.TestCases.ILPretty.Issue3552
    extends [System.Runtime]System.Object
{
    // Methods
    .method public hidebysig static 
        valuetype ICSharpCode.Decompiler.Tests.TestCases.ILPretty.Issue3552_IntegerPair MakePair1 (
            int32 x,
            int32 y
        ) cil managed 
    {
        // Method begins at RVA 0x2050
        // Header size: 12
        // Code size: 34 (0x22)
        .maxstack 2
        .locals init (
            [0] valuetype ICSharpCode.Decompiler.Tests.TestCases.ILPretty.Issue3552_IntegerPairBuilder
        )

        IL_0000: ldloca.s 0
        IL_0002: initobj ICSharpCode.Decompiler.Tests.TestCases.ILPretty.Issue3552_IntegerPairBuilder
        IL_0008: ldloca.s 0
        IL_000a: ldarg.0
        IL_000b: call instance void ICSharpCode.Decompiler.Tests.TestCases.ILPretty.Issue3552_IntegerPairBuilder::Add(int32)
        IL_0010: ldloca.s 0
        IL_0012: ldarg.1
        IL_0013: call instance void ICSharpCode.Decompiler.Tests.TestCases.ILPretty.Issue3552_IntegerPairBuilder::Add(int32)
        IL_0015: ldloca.s 0
        IL_001c: call instance valuetype ICSharpCode.Decompiler.Tests.TestCases.ILPretty.Issue3552_IntegerPair ICSharpCode.Decompiler.Tests.TestCases.ILPretty.Issue3552_IntegerPairBuilder::ToPair()
        IL_0021: ret
    } // end of method Issue3552::MakePair1

    .method public hidebysig static 
        valuetype ICSharpCode.Decompiler.Tests.TestCases.ILPretty.Issue3552_IntegerPair MakePair2 (
            int32 x,
            int32 y
        ) cil managed 
    {
        // Method begins at RVA 0x2050
        // Header size: 12
        // Code size: 34 (0x22)
        .maxstack 2
        .locals init (
            [0] valuetype ICSharpCode.Decompiler.Tests.TestCases.ILPretty.Issue3552_IntegerPairBuilder
        )

        IL_0000: ldloca.s 0
        IL_0001: dup
        IL_0002: initobj ICSharpCode.Decompiler.Tests.TestCases.ILPretty.Issue3552_IntegerPairBuilder
        IL_0008: dup
        IL_000a: ldarg.0
        IL_000b: call instance void ICSharpCode.Decompiler.Tests.TestCases.ILPretty.Issue3552_IntegerPairBuilder::Add(int32)
        IL_0012: ldarg.1
        IL_0013: call instance void ICSharpCode.Decompiler.Tests.TestCases.ILPretty.Issue3552_IntegerPairBuilder::Add(int32)
        IL_0015: ldloca.s 0
        IL_001c: call instance valuetype ICSharpCode.Decompiler.Tests.TestCases.ILPretty.Issue3552_IntegerPair ICSharpCode.Decompiler.Tests.TestCases.ILPretty.Issue3552_IntegerPairBuilder::ToPair()
        IL_0021: ret
    } // end of method Issue3552::MakePair2

    .method public hidebysig static 
        valuetype ICSharpCode.Decompiler.Tests.TestCases.ILPretty.Issue3552_IntegerPair MakePair3 (
            int32 x,
            int32 y
        ) cil managed 
    {
        // Method begins at RVA 0x2050
        // Header size: 12
        // Code size: 34 (0x22)
        .maxstack 2
        .locals init (
            [0] valuetype ICSharpCode.Decompiler.Tests.TestCases.ILPretty.Issue3552_IntegerPairBuilder
        )

        IL_0000: ldloca.s 0
        IL_0001: dup
        IL_0002: initobj ICSharpCode.Decompiler.Tests.TestCases.ILPretty.Issue3552_IntegerPairBuilder
        IL_0008: dup
        IL_000a: ldarg.0
        IL_000b: call instance void ICSharpCode.Decompiler.Tests.TestCases.ILPretty.Issue3552_IntegerPairBuilder::Add(int32)
        IL_0010: dup
        IL_0012: ldarg.1
        IL_0013: call instance void ICSharpCode.Decompiler.Tests.TestCases.ILPretty.Issue3552_IntegerPairBuilder::Add(int32)
        IL_001c: call instance valuetype ICSharpCode.Decompiler.Tests.TestCases.ILPretty.Issue3552_IntegerPair ICSharpCode.Decompiler.Tests.TestCases.ILPretty.Issue3552_IntegerPairBuilder::ToPair()
        IL_0021: ret
    } // end of method Issue3552::MakePair3

} // end of class ICSharpCode.Decompiler.Tests.TestCases.ILPretty.Issue3552

.class public sequential ansi sealed beforefieldinit ICSharpCode.Decompiler.Tests.TestCases.ILPretty.Issue3552_IntegerPair
    extends [System.Runtime]System.ValueType
{
    // Fields
    .field public int32 X
    .field public int32 Y

} // end of class ICSharpCode.Decompiler.Tests.TestCases.ILPretty.Issue3552_IntegerPair

.class public sequential ansi sealed beforefieldinit ICSharpCode.Decompiler.Tests.TestCases.ILPretty.Issue3552_IntegerPairBuilder
    extends [System.Runtime]System.ValueType
    implements class [System.Runtime]System.Collections.Generic.IEnumerable`1<int32>,
               [System.Runtime]System.Collections.IEnumerable
{
    // Fields
    .field private int32 index
    .field private valuetype ICSharpCode.Decompiler.Tests.TestCases.ILPretty.Issue3552_IntegerPair pair

    // Methods
    .method public hidebysig 
        instance valuetype ICSharpCode.Decompiler.Tests.TestCases.ILPretty.Issue3552_IntegerPair ToPair () cil managed 
    {
        .custom instance void [System.Runtime]System.Runtime.CompilerServices.IsReadOnlyAttribute::.ctor() = (
            01 00 00 00
        )
        // Method begins at RVA 0x207e
        // Header size: 1
        // Code size: 7 (0x7)
        .maxstack 8

        IL_0000: ldarg.0
        IL_0001: ldfld valuetype ICSharpCode.Decompiler.Tests.TestCases.ILPretty.Issue3552_IntegerPair ICSharpCode.Decompiler.Tests.TestCases.ILPretty.Issue3552_IntegerPairBuilder::pair
        IL_0006: ret
    } // end of method Issue3552_IntegerPairBuilder::ToPair

    .method public hidebysig 
        instance void Add (
            int32 'value'
        ) cil managed 
    {
        // Method begins at RVA 0x2088
        // Header size: 12
        // Code size: 65 (0x41)
        .maxstack 3
        .locals init (
            [0] int32
        )

        IL_0000: ldarg.0
        IL_0001: ldfld int32 ICSharpCode.Decompiler.Tests.TestCases.ILPretty.Issue3552_IntegerPairBuilder::index
        IL_0006: stloc.0
        IL_0007: ldloc.0
        IL_0008: brfalse.s IL_0010

        IL_000a: ldloc.0
        IL_000b: ldc.i4.1
        IL_000c: beq.s IL_001e

        IL_000e: br.s IL_002c

        IL_0010: ldarg.0
        IL_0011: ldflda valuetype ICSharpCode.Decompiler.Tests.TestCases.ILPretty.Issue3552_IntegerPair ICSharpCode.Decompiler.Tests.TestCases.ILPretty.Issue3552_IntegerPairBuilder::pair
        IL_0016: ldarg.1
        IL_0017: stfld int32 ICSharpCode.Decompiler.Tests.TestCases.ILPretty.Issue3552_IntegerPair::X
        IL_001c: br.s IL_0032

        IL_001e: ldarg.0
        IL_001f: ldflda valuetype ICSharpCode.Decompiler.Tests.TestCases.ILPretty.Issue3552_IntegerPair ICSharpCode.Decompiler.Tests.TestCases.ILPretty.Issue3552_IntegerPairBuilder::pair
        IL_0024: ldarg.1
        IL_0025: stfld int32 ICSharpCode.Decompiler.Tests.TestCases.ILPretty.Issue3552_IntegerPair::Y
        IL_002a: br.s IL_0032

        IL_002c: newobj instance void [System.Runtime]System.IndexOutOfRangeException::.ctor()
        IL_0031: throw

        IL_0032: ldarg.0
        IL_0033: ldarg.0
        IL_0034: ldfld int32 ICSharpCode.Decompiler.Tests.TestCases.ILPretty.Issue3552_IntegerPairBuilder::index
        IL_0039: ldc.i4.1
        IL_003a: add
        IL_003b: stfld int32 ICSharpCode.Decompiler.Tests.TestCases.ILPretty.Issue3552_IntegerPairBuilder::index
        IL_0040: ret
    } // end of method Issue3552_IntegerPairBuilder::Add

    .method public final hidebysig newslot virtual 
        instance class [System.Runtime]System.Collections.Generic.IEnumerator`1<int32> GetEnumerator () cil managed 
    {
        // Method begins at RVA 0x20d5
        // Header size: 1
        // Code size: 2 (0x2)
        .maxstack 8

        IL_0000: ldnull
        IL_0001: ret
    } // end of method Issue3552_IntegerPairBuilder::GetEnumerator

    .method private final hidebysig newslot virtual 
        instance class [System.Runtime]System.Collections.IEnumerator System.Collections.IEnumerable.GetEnumerator () cil managed 
    {
        .override method instance class [System.Runtime]System.Collections.IEnumerator [System.Runtime]System.Collections.IEnumerable::GetEnumerator()
        // Method begins at RVA 0x20d8
        // Header size: 1
        // Code size: 7 (0x7)
        .maxstack 8

        IL_0000: ldarg.0
        IL_0001: call instance class [System.Runtime]System.Collections.Generic.IEnumerator`1<int32> ICSharpCode.Decompiler.Tests.TestCases.ILPretty.Issue3552_IntegerPairBuilder::GetEnumerator()
        IL_0006: ret
    } // end of method Issue3552_IntegerPairBuilder::System.Collections.IEnumerable.GetEnumerator

} // end of class ICSharpCode.Decompiler.Tests.TestCases.ILPretty.Issue3552_IntegerPairBuilder

Based on:

https://lab.razor.fyi/#nVTNbhMxEBaIA7gXxBOM1EurolWQOGUJEoSqCgI1antoucDEO0msOvZqbCdZVXkK3gDxYlz7EiBvSDY_m6AyB3vX_uYbz8xnix8HQnTZDhhHiXQvvh8cNnO2ObEvoG1NXw0Co1fWtC5IEzoSwSkzgMvCeRqla39J22pNMqLd7p3kjAyxkqk4NEFr7GmCTLk4C4MjcjlKgk77coict21GyQeSdpQrTZxckfOuHNvoyCWdT10m7wtxJwAA8tDTSoLz6JUEqdE56DgX6HWj0SgRc9w2don62jGeBsRdVAyf8Zbix5EyHqYvIU7F8ZKiIotWS_E-KJ0Rg9q32QJDk_3-dzF8AbN0LSSTD2z2kidXtszguPKciWpcVoGD9PVHqK9bLMV1Wrd6kz6Mf5FiEzqnJoyIoxTeKOPfbkZmNUZPZRBlMpqmW1v1bcxRcSo2z8qEmTW62OG0qNuObv8t_Zy6quxmkLFVGbzLslJBY9SBdhG6ifJyCEdlZhVoGxhNoiNoNLfWy8ioOLmG1jzcumAW1mPC27Se9tUe2pv_os2oj0H7el4_ZDuZX4CY-Xnw5_0LNAM6nUrK45Oxql1YKmthZb1OTvY1YaErb7nUFZyRr5b-1eL4StWyr9CuSjd5EPsGePuWzsTHx0p_efb0_tfv-5_950--PfoD

I optimized MakePair in 3 ways.

Erroneous output

// Actual
public static Issue3552_IntegerPair MakePair1(int x, int y)
{
	Issue3552_IntegerPairBuilder issue3552_IntegerPairBuilder = new Issue3552_IntegerPairBuilder { x, y };
	return issue3552_IntegerPairBuilder.ToPair();
}
public static Issue3552_IntegerPair MakePair2(int x, int y)
{
	Issue3552_IntegerPairBuilder issue3552_IntegerPairBuilder = default(Issue3552_IntegerPairBuilder);
	issue3552_IntegerPairBuilder.Add(x);
	issue3552_IntegerPairBuilder.Add(y);
	return issue3552_IntegerPairBuilder.ToPair();
}
public static Issue3552_IntegerPair MakePair3(int x, int y)
{
	Issue3552_IntegerPairBuilder issue3552_IntegerPairBuilder = default(Issue3552_IntegerPairBuilder);
	issue3552_IntegerPairBuilder.Add(x);
	issue3552_IntegerPairBuilder.Add(y);
	return issue3552_IntegerPairBuilder.ToPair();
}

// Expected
public static Issue3552_IntegerPair MakePair1(int x, int y)
{
	Issue3552_IntegerPairBuilder issue3552_IntegerPairBuilder = new Issue3552_IntegerPairBuilder { x, y };
	return issue3552_IntegerPairBuilder.ToPair();
}
public static Issue3552_IntegerPair MakePair2(int x, int y)
{
	Issue3552_IntegerPairBuilder issue3552_IntegerPairBuilder = new Issue3552_IntegerPairBuilder { x, y };
	return issue3552_IntegerPairBuilder.ToPair();
}
public static Issue3552_IntegerPair MakePair3(int x, int y)
{
	Issue3552_IntegerPairBuilder issue3552_IntegerPairBuilder = new Issue3552_IntegerPairBuilder { x, y };
	return issue3552_IntegerPairBuilder.ToPair();
}

The actual and expected outputs are semantically equivalent, but it would be prettier if collection initializers were always used.

Details

• Product in use: ILSpy
• Version in use: 58bf5ef
• Any other relevant information to the issue, or your interest in contributing a fix.
  • I'm currently investigating why this is happening.

[ds5678]

From debugging TransformCollectionAndObjectInitializers, I see differences in the blocks:

// MakePair1
{Block IL_0000 (incoming: 1) {
	stloc V_0(default.value ICSharpCode.Decompiler.Tests.TestCases.ILPretty.Issue3552_IntegerPairBuilder)
	call Add(ldloca V_0, ldloc x)
	call Add(ldloca V_0, ldloc y)
	leave IL_0000 (call ToPair(ldloca V_0))
} at IL_0000}

// MakePair2
{Block IL_0000 (incoming: 1) {
	stloc V_0(default.value ICSharpCode.Decompiler.Tests.TestCases.ILPretty.Issue3552_IntegerPairBuilder)
	stloc S_0(ldloca V_0)
	call Add(ldloc S_0, ldloc x)
	call Add(ldloc S_0, ldloc y)
	leave IL_0000 (call ToPair(ldloca V_0))
} at IL_0000}

// MakePair3
{Block IL_0000 (incoming: 1) {
	stloc V_0(default.value ICSharpCode.Decompiler.Tests.TestCases.ILPretty.Issue3552_IntegerPairBuilder)
	stloc S_0(ldloca V_0)
	call Add(ldloc S_0, ldloc x)
	call Add(ldloc S_0, ldloc y)
	leave IL_0000 (call ToPair(ldloc S_0))
} at IL_0000}

I would appreciate some advice on how to approach this.

[siegfriedpammer]

hmm... I believe this can be solved by manually invoking CopyPropagation.Propagate on that assignment? May be worth a try :)

Example:

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

Lines 180 to 184 in 58bf5ef

	// Copy-propagate stack slots holding an 'ldloca':
	foreach (var stloc in function.Descendants.OfType<StLoc>().Where(s => s.Variable.Kind == VariableKind.StackSlot && s.Variable.IsSingleDefinition && s.Value is LdLoca).ToList())
	{
	CopyPropagation.Propagate(stloc, context);
	}