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Avoid deep recursion while emitting deeply nested logical conditions #66993

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Feb 24, 2023
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Avoid deep recursion while emitting deeply nested logical conditions #66993

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3c35f65
Avoid deep recursion while emitting deeply nested logical conditions
AlekseyTs Feb 22, 2023
dc04955
Use more robust condition
AlekseyTs Feb 24, 2023
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88 changes: 65 additions & 23 deletions src/Compilers/CSharp/Portable/CodeGen/EmitStatement.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -10,6 +10,7 @@
using System.Diagnostics;
using System.Linq;
using System.Reflection.Metadata;
using System.Runtime.CompilerServices;
using Microsoft.CodeAnalysis.CodeGen;
using Microsoft.CodeAnalysis.CSharp.Symbols;
using Microsoft.CodeAnalysis.CSharp.Syntax;
Expand Down Expand Up @@ -415,43 +416,84 @@ private void EmitCondBranchCore(BoundExpression condition, ref object dest, bool
switch (condition.Kind)
{
case BoundKind.BinaryOperator:

var binOp = (BoundBinaryOperator)condition;
bool testBothArgs = sense;
Debug.Assert(binOp.ConstantValueOpt is null);

switch (binOp.OperatorKind.OperatorWithLogical())
#nullable enable
if (binOp.OperatorKind.OperatorWithLogical() is BinaryOperatorKind.LogicalOr or BinaryOperatorKind.LogicalAnd)
{
case BinaryOperatorKind.LogicalOr:
testBothArgs = !testBothArgs;
// Fall through
goto case BinaryOperatorKind.LogicalAnd;

case BinaryOperatorKind.LogicalAnd:
if (testBothArgs)
{
// gotoif(a != sense) fallThrough
// gotoif(b == sense) dest
// fallThrough:

object fallThrough = null;
var stack = ArrayBuilder<(BoundExpression? condition, StrongBox<object?> destBox, bool sense)>.GetInstance();
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@jjonescz jjonescz Feb 24, 2023 •
edited by AlekseyTs
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Why is dest wrapped in a StrongBox? Why not store just object? in the stack? #Resolved

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@AlekseyTs AlekseyTs Feb 24, 2023 •
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Why is dest wrapped in a StrongBox? Why not store just object? in the stack?

Its value is mutable and is supposed to be shared between different items on the stack (including mutations). If we simply store object?, we will store its current value (often null) and won't be able to observe the changes. We need an indirection in order to be able share the mutations as well. StrongBox gives us an indirection.

var destBox = new StrongBox<object?>(dest);
stack.Push((binOp, destBox, sense));

EmitCondBranch(binOp.Left, ref fallThrough, !sense);
EmitCondBranch(binOp.Right, ref dest, sense);
do
{
(BoundExpression? condition, StrongBox<object?> destBox, bool sense) top = stack.Pop();

if (top.condition is null)
{
// This is a special entry to indicate that it is time to append the block
object? fallThrough = top.destBox.Value;
if (fallThrough != null)
{
_builder.MarkLabel(fallThrough);
}
}
else
else if (top.condition.ConstantValueOpt is null &&
top.condition is BoundBinaryOperator binary &&
binary.OperatorKind.OperatorWithLogical() is BinaryOperatorKind.LogicalOr or BinaryOperatorKind.LogicalAnd)
{
// gotoif(a == sense) labDest
// gotoif(b == sense) labDest
if (binary.OperatorKind.OperatorWithLogical() is BinaryOperatorKind.LogicalOr ? !top.sense : top.sense)
{
// gotoif(a != sense) fallThrough
// gotoif(b == sense) dest
// fallThrough:

var fallThrough = new StrongBox<object?>();

// Note, operations are pushed to the stack in opposite order
stack.Push((null, fallThrough, true)); // This is a special entry to indicate that it is time to append the fallThrough block
stack.Push((binary.Right, top.destBox, top.sense));
stack.Push((binary.Left, fallThrough, !top.sense));
}
else
{
// gotoif(a == sense) labDest
// gotoif(b == sense) labDest

EmitCondBranch(binOp.Left, ref dest, sense);
condition = binOp.Right;
// Note, operations are pushed to the stack in opposite order
stack.Push((binary.Right, top.destBox, top.sense));
stack.Push((binary.Left, top.destBox, top.sense));
}
}
else if (stack.Count == 0 && ReferenceEquals(destBox, top.destBox))
{
// Instead of recursion we can restart from the top with new condition
condition = top.condition;
sense = top.sense;
dest = destBox.Value;
stack.Free();
goto oneMoreTime;
}
return;
else
{
EmitCondBranch(top.condition, ref top.destBox.Value, top.sense);
}
}
while (stack.Count != 0);

dest = destBox.Value;
stack.Free();
return;
}
#nullable disable

switch (binOp.OperatorKind.OperatorWithLogical())
{
case BinaryOperatorKind.LogicalOr:
case BinaryOperatorKind.LogicalAnd:
throw ExceptionUtilities.Unreachable();

case BinaryOperatorKind.Equal:
case BinaryOperatorKind.NotEqual:
Expand Down
38 changes: 30 additions & 8 deletions src/Compilers/CSharp/Test/Emit/CodeGen/CodeGenOperators.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -5286,9 +5286,9 @@ public static bool Calculate(bool[] a, bool[] f)
}

diagnostics.Verify(
// (10,16): error CS8078: An expression is too long or complex to compile
// return a[0] && f[0] || a[1] && f[1] || a[2] && f[2] || ...
Diagnostic(ErrorCode.ERR_InsufficientStack, "a").WithLocation(10, 16)
// (10,16): error CS8078: An expression is too long or complex to compile
// return a[0] & f[0] | a[1] & f[1] | a[2] & f[2] | ...
Diagnostic(ErrorCode.ERR_InsufficientStack, "a").WithLocation(10, 16)
);
}

Expand All @@ -5301,10 +5301,10 @@ private static string BuildSequenceOfBinaryExpressions_03(int count = 8192)
builder.Append("a[");
builder.Append(i);
builder.Append("]");
builder.Append(" && ");
builder.Append(" & ");
builder.Append("f[");
builder.Append(i);
builder.Append("] || ");
builder.Append("] | ");
}

builder.Append("a[");
Expand Down Expand Up @@ -5415,7 +5415,7 @@ static void Main()

public static bool Calculate(S1[] a, S1[] f)
{
" + $" return {BuildSequenceOfBinaryExpressions_03()};" + @"
" + $" return {BuildSequenceOfBinaryExpressions_06()};" + @"
}
}

Expand Down Expand Up @@ -5456,6 +5456,28 @@ public static implicit operator bool (S1 x)
);
}

private static string BuildSequenceOfBinaryExpressions_06(int count = 8192)
{
var builder = new System.Text.StringBuilder();
int i;
for (i = 0; i < count; i++)
{
builder.Append("a[");
builder.Append(i);
builder.Append("]");
builder.Append(" && ");
builder.Append("f[");
builder.Append(i);
builder.Append("] || ");
}

builder.Append("a[");
builder.Append(i);
builder.Append("]");

return builder.ToString();
}

[ConditionalFact(typeof(ClrOnly), typeof(NoIOperationValidation), Reason = "https://github.com/dotnet/roslyn/issues/29428")]
[WorkItem(63689, "https://github.com/dotnet/roslyn/issues/63689")]
public void EmitSequenceOfBinaryExpressions_07()
Expand All @@ -5478,7 +5500,7 @@ static void Main()

public static bool Calculate(S1[] a, S1[] f)
{
" + $" return {BuildSequenceOfBinaryExpressions_03(count)};" + @"
" + $" return {BuildSequenceOfBinaryExpressions_06(count)};" + @"
}
}

Expand Down Expand Up @@ -5544,7 +5566,7 @@ static void Main()

public static bool Calculate(bool[] a, bool[] f)
{
" + $" return {BuildSequenceOfBinaryExpressions_03(2048)};" + @"
" + $" return {BuildSequenceOfBinaryExpressions_06(2048)};" + @"
}
}
";
Expand Down
44 changes: 44 additions & 0 deletions src/Compilers/CSharp/Test/Semantic/Semantics/RecordTests.cs
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Expand Up @@ -30419,5 +30419,49 @@ class Attr : System.Attribute {}
Assert.DoesNotContain("System.Int32 y", model.LookupSymbols(attrApplication.ArgumentList!.OpenParenToken.SpanStart + 1).Select(s => s.ToTestDisplayString()));
Assert.DoesNotContain("System.Int32 y", model.LookupSymbols(mDefinition.SpanStart).Select(s => s.ToTestDisplayString()));
}

[Fact]
[WorkItem(66900, "https://github.com/dotnet/roslyn/issues/66900")]
public void Issue66900()
{
// public record ClassWithManyConstructorParameters(int P0, int P1, int P2, ...)
// {
// public static ClassWithManyConstructorParameters Create()
// {
// return new ClassWithManyConstructorParameters(P0: 0, P1: 1, P2: 2, ...);
// }
// }

var src = @"
public record ClassWithManyConstructorParameters(int P0";

const int count = 2000;

for (int i = 1; i < count; i++)
{
src += ", int P" + i;
}

src += @")
{
public static ClassWithManyConstructorParameters Create()
{
return new ClassWithManyConstructorParameters(P0: 0";

for (int i = 1; i < count; i++)
{
src += ", P" + i + ": " + i;
}

src += @");
}
}
";
var comp = CreateCompilation(new[] { src, IsExternalInitTypeDefinition }, targetFramework: TargetFramework.NetCoreApp);
CompileAndVerify(comp, verify: Verification.Skipped).VerifyDiagnostics();

comp = CreateCompilation(new[] { src, IsExternalInitTypeDefinition }, targetFramework: TargetFramework.DesktopLatestExtended);
CompileAndVerify(comp, verify: Verification.Skipped).VerifyDiagnostics();
}
}
}