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Deconstruction-assignment: nested scenario #11715

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Jun 7, 2016
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Deconstruction-assignment: nested scenario #11715

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c71be15
Deconstruction-assignment: nested scenario
jcouv Jun 1, 2016
86ca7d3
Flattening variables in bound node
jcouv Jun 2, 2016
dd3b674
Fixing warning with OneOrMany
jcouv Jun 2, 2016
199c6ad
PR feedback (1)
jcouv Jun 2, 2016
461b419
Adding error for tuple cardinality mismatch
jcouv Jun 3, 2016
6e68b8d
PR feedback (2)
jcouv Jun 3, 2016
3b6d012
Removing nested variables from data flow analysis, since now flattened
jcouv Jun 3, 2016
6f354a1
PR feedback (3)
jcouv Jun 4, 2016
f205d5f
Don't use a bound node for nested deconstruction variables
jcouv Jun 4, 2016
ba975f7
Capture as many deconstruction and assignment steps as possible when …
jcouv Jun 4, 2016
1748df1
Adding PROTOTYPE markers
jcouv Jun 4, 2016
4e531c6
PR feedback (4)
jcouv Jun 6, 2016
87ee4f4
PR feedback (5)
jcouv Jun 6, 2016
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294 changes: 245 additions & 49 deletions src/Compilers/CSharp/Portable/Binder/Binder_Statements.cs
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13 changes: 10 additions & 3 deletions src/Compilers/CSharp/Portable/BoundTree/BoundExpression.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -280,11 +280,18 @@ public override Symbol ExpressionSymbol

internal sealed partial class BoundDeconstructionAssignmentOperator : BoundExpression
{
internal class AssignmentInfo
internal class AssignmentStep
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I think AssignmentStep and DeconstructStep should be regular bound nodes

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Done.

{
public BoundAssignmentOperator Assignment;
public BoundLValuePlaceholder LValuePlaceholder;
public BoundRValuePlaceholder RValuePlaceholder;
public BoundDeconstructValuePlaceholder OutputPlaceholder;
public BoundDeconstructValuePlaceholder TargetPlaceholder;
}

internal class DeconstructStep
{
public MethodSymbol DeconstructMemberOpt; // the deconstruct member, or null if tuple deconstruction
public BoundDeconstructValuePlaceholder TargetPlaceholder;
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I would make this BoundExpression and put Right directly as the target for the first deconstruct, removing it from the parent node.

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put Right directly as the target for the first deconstruct, removing it from the parent node.

I didn't get that part.

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Never mind, since we might not create the deconstruct step in case of an error, the suggestion is not an option.

In reply to: 65796074 [](ancestors = 65796074)

public ImmutableArray<BoundDeconstructValuePlaceholder> OutputPlaceholders; // placeholders for the outputs produced by this deconstruction
}
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Consider making these two types immutable.

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Can these types be structs?

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Yes, I thought about struct too. I have a note on that #11299. I think I'll just make the change.

Also, from our discussion, I will move back from OneOrMany to simply use ImmutableArray.

}

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16 changes: 11 additions & 5 deletions src/Compilers/CSharp/Portable/BoundTree/BoundNodes.xml
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Expand Up @@ -84,9 +84,7 @@
This node is used to represent an expression returning value of a certain type.
It is used to perform intermediate binding, and will not survive the local rewriting.
-->
<Node Name="BoundLValuePlaceholder" Base="BoundValuePlaceholderBase" HasValidate="true">
</Node>
<Node Name="BoundRValuePlaceholder" Base="BoundValuePlaceholderBase" HasValidate="true">
<Node Name="BoundDeconstructValuePlaceholder" Base="BoundValuePlaceholderBase" HasValidate="true">
</Node>

<!-- only used by codegen -->
Expand Down Expand Up @@ -394,13 +392,21 @@
<!-- Non-null type is required for this node kind -->
<Field Name="Type" Type="TypeSymbol" Override="true" Null="disallow"/>

<!-- Various assignable expressions, including some BoundDeconstructionVariables for nested variables -->
<Field Name="LeftVariables" Type="ImmutableArray&lt;BoundExpression&gt;"/>
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Why do we need BoundDeconstructionVariables in this list?

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Presence of these node can potentially confuse SemanticModel, etc.

In reply to: 65776149 [](ancestors = 65776149)

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Ok, given the current implementation, it looks like LeftVariable is always a flat list of targets, BoundDeconstructionVariables is never among them. Please adjust the comment accordingly.

In reply to: 65778993 [](ancestors = 65778993,65776149)

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@jcouv jcouv Jun 4, 2016 •
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@AlekseyTs, from discussion with Chuck I will remove the BoundDeconstructionVariables node and store the tree of variables some other way (without creating new kind of bound node).


<Field Name="Right" Type="BoundExpression"/>
<Field Name="DeconstructMemberOpt" Type="MethodSymbol" Null="allow"/>

<Field Name="DeconstructSteps" Type="OneOrMany&lt;BoundDeconstructionAssignmentOperator.DeconstructStep&gt;" Null="NotApplicable" SkipInVisitor="true" />

<!-- The assignments have placeholders for the left and right part of the assignment -->
<Field Name="Assignments" Type="ImmutableArray&lt;BoundDeconstructionAssignmentOperator.AssignmentInfo&gt;" Null="NotApplicable" SkipInVisitor="true"/>
<Field Name="AssignmentSteps" Type="ImmutableArray&lt;BoundDeconstructionAssignmentOperator.AssignmentStep&gt;" Null="NotApplicable" SkipInVisitor="true"/>
</Node>

<Node Name="BoundDeconstructionVariables" Base="BoundExpression">
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Why a BoundExpression rather than BoundNode?

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So, this bound node is never output from binding at all. But during binding, I have bound expressions for the LHS, which need to be organized in a tree.
Because all simple variables are BoundExpression, it is convenient that this is also BoundExpression (rather than BoundNode). But I'm open to suggestions.
I agree that having a bound node that never escapes binding is strange.

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Where do we use checkedVariables as (array of) BoundExpression rather than BoundNode? Or is it more than just checkedVariables that is the concern?

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Given the current implementation, it looks like BoundDeconstructionVariables never escapes the binder. This is just a helper node, used in the process of binding, never gets stored in the tree produced by the Binder. Please provide a comment reflecting that.

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Removed BoundDeconstructionVariables in favor of a simple tree structure (which is not a bound node):

        private class DeconstructionVariable
        {
            public BoundExpression Single;
            public ImmutableArray<DeconstructionVariable>? Nested;
            ...
        }

<Field Name="Type" Type="TypeSymbol" Override="true" Null="always"/>

<Field Name="Variables" Type="ImmutableArray&lt;BoundExpression&gt;"/>
</Node>

<Node Name="BoundVoid" Base="BoundExpression">
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32 changes: 16 additions & 16 deletions src/Compilers/CSharp/Portable/BoundTree/Expression.cs
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Expand Up @@ -33,22 +33,7 @@ Optional<object> IOperation.ConstantValue
public abstract TResult Accept<TArgument, TResult>(OperationVisitor<TArgument, TResult> visitor, TArgument argument);
}

internal sealed partial class BoundLValuePlaceholder : BoundValuePlaceholderBase, IPlaceholderExpression
{
protected override OperationKind ExpressionKind => OperationKind.PlaceholderExpression;

public override void Accept(OperationVisitor visitor)
{
visitor.VisitPlaceholderExpression(this);
}

public override TResult Accept<TArgument, TResult>(OperationVisitor<TArgument, TResult> visitor, TArgument argument)
{
return visitor.VisitPlaceholderExpression(this, argument);
}
}

internal sealed partial class BoundRValuePlaceholder : BoundValuePlaceholderBase, IPlaceholderExpression
internal sealed partial class BoundDeconstructValuePlaceholder : BoundValuePlaceholderBase, IPlaceholderExpression
{
protected override OperationKind ExpressionKind => OperationKind.PlaceholderExpression;

Expand Down Expand Up @@ -1049,6 +1034,21 @@ public override void Accept(OperationVisitor visitor)
}
}

internal sealed partial class BoundDeconstructionVariables : BoundExpression
{
protected override OperationKind ExpressionKind => OperationKind.None;

public override void Accept(OperationVisitor visitor)
{
visitor.VisitNoneOperation(this);
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Why not visit Variables?

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This is a dummy implementation, like BoundTupleExpression.
My understanding is that this implement IOperation, which John Hamby would take care of.

}

public override TResult Accept<TArgument, TResult>(OperationVisitor<TArgument, TResult> visitor, TArgument argument)
{
return visitor.VisitNoneOperation(this, argument);
}
}

internal sealed partial class BoundVoid : BoundExpression
{
protected override OperationKind ExpressionKind => OperationKind.None;
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34 changes: 30 additions & 4 deletions src/Compilers/CSharp/Portable/FlowAnalysis/DataFlowPass.cs
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Expand Up @@ -1485,7 +1485,7 @@ public override BoundNode VisitFixedStatement(BoundFixedStatement node)
{
foreach (LocalSymbol local in node.Locals)
{
switch(local.DeclarationKind)
switch (local.DeclarationKind)
{
case LocalDeclarationKind.RegularVariable:
case LocalDeclarationKind.PatternVariable:
Expand Down Expand Up @@ -1721,14 +1721,40 @@ public override BoundNode VisitAssignmentOperator(BoundAssignmentOperator node)
Assign(node.Left, node.Right, refKind: node.RefKind);
return null;
}

public override BoundNode VisitDeconstructionAssignmentOperator(BoundDeconstructionAssignmentOperator node)
{
base.VisitDeconstructionAssignmentOperator(node);

foreach(BoundExpression variable in node.LeftVariables)
foreach (BoundExpression variable in node.LeftVariables)
{
if (variable.Kind == BoundKind.DeconstructionVariables)
{
VisitDeconstructionVariables((BoundDeconstructionVariables)variable);
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Doesn't base.VisitDeconstructionAssignment do this? Same comment for VisitDeconstructionVariables below.

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If the Assign call is the only difference from the base call, consider adding a virtual VisitDeconstructionAssignmentLeftVariable method to PreciseAbstractFlowPass and override that method here instead. Similarly for VisitDeconstructionVariables.

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So, I removed BoundDeconstructionVariables, which simplifies and removes a bunch of data flow code. I'm leaving the rest as-is with PROTOTYPE(tuples).
The Assign call is a stub, not the full implementation that I intend.

}
else
{
Assign(variable, null, refKind: RefKind.None);
}
}

return null;
}

public override BoundNode VisitDeconstructionVariables(BoundDeconstructionVariables node)
{
base.VisitDeconstructionVariables(node);

foreach (BoundExpression variable in node.Variables)
{
Assign(variable, null, refKind: RefKind.None);
if (variable.Kind == BoundKind.DeconstructionVariables)
{
VisitDeconstructionVariables((BoundDeconstructionVariables)variable);
}
else
{
Assign(variable, null, refKind: RefKind.None);
}
}

return null;
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26 changes: 25 additions & 1 deletion src/Compilers/CSharp/Portable/FlowAnalysis/PreciseAbstractFlowPass.cs
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Expand Up @@ -1518,14 +1518,38 @@ public override BoundNode VisitDeconstructionAssignmentOperator(BoundDeconstruct
{
foreach (BoundExpression variable in node.LeftVariables)
{
VisitLvalue(variable);
if (variable.Kind == BoundKind.DeconstructionVariables)
{
VisitDeconstructionVariables((BoundDeconstructionVariables)variable);
}
else
{
VisitLvalue(variable);
}
}

VisitRvalue(node.Right);

return null;
}

public override BoundNode VisitDeconstructionVariables(BoundDeconstructionVariables node)
{
foreach (BoundExpression variable in node.Variables)
{
if (variable.Kind == BoundKind.DeconstructionVariables)
{
VisitDeconstructionVariables((BoundDeconstructionVariables)variable);
}
else
{
VisitLvalue(variable);
}
}

return null;
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I think it is more appropriate to throw Unreachable here.

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And seal the method.

In reply to: 65786461 [](ancestors = 65786461)

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Removed BoundDeconstructionVariables.

}

public override BoundNode VisitCompoundAssignmentOperator(BoundCompoundAssignmentOperator node)
{
// TODO: should events be handled specially too?
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18 changes: 12 additions & 6 deletions src/Compilers/CSharp/Portable/Lowering/LocalRewriter/LocalRewriter.cs
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Expand Up @@ -230,12 +230,7 @@ public override BoundNode VisitLocalFunctionStatement(BoundLocalFunctionStatemen
}
}

public override BoundNode VisitLValuePlaceholder(BoundLValuePlaceholder node)
{
return PlaceholderReplacement(node);
}

public override BoundNode VisitRValuePlaceholder(BoundRValuePlaceholder node)
public override BoundNode VisitDeconstructValuePlaceholder(BoundDeconstructValuePlaceholder node)
{
return PlaceholderReplacement(node);
}
Expand Down Expand Up @@ -287,6 +282,17 @@ private void RemovePlaceholderReplacement(BoundValuePlaceholderBase placeholder)
Debug.Assert(removed);
}

/// <summary>
/// Remove all the listed placeholders.
/// </summary>
private void RemovePlaceholderReplacements(IEnumerable<BoundValuePlaceholderBase> placeholders)
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Could we use more specific type rather than IEnumerable? ArrayBuilder/ImmutableArray

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Perhaps inline the method since it is only used in one place.

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I suspect in the future it will be handy again to be able to remove multiple placeholders. I'm not sure what is the downside of using IEnumerable to keep options open.

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@AlekseyTs Why not IEnumerable?

{
foreach (var placeholder in placeholders)
{
RemovePlaceholderReplacement(placeholder);
}
}

public override BoundNode VisitBadExpression(BoundBadExpression node)
{
// Cannot recurse into BadExpression children since the BadExpression
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