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Prefer equality in boolean comparisons #34166

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Prefer equality in boolean comparisons #34166

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3b90d81
Prefer equality in boolean comparisons
ranma42 Jul 5, 2024
b79642e
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ranma42 Jul 5, 2024
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89 changes: 49 additions & 40 deletions src/EFCore.Relational/Query/SqlNullabilityProcessor.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -1289,6 +1289,7 @@ protected virtual SqlExpression VisitSqlBinary(
right,
leftNullable,
rightNullable,
optimize,
out nullable);

if (optimized is SqlUnaryExpression { Operand: ColumnExpression optimizedUnaryColumnOperand } optimizedUnary)
Expand Down Expand Up @@ -1623,6 +1624,7 @@ private SqlExpression ProcessJoinPredicate(SqlExpression predicate)
right,
leftNullable,
rightNullable,
optimize: true,
out _);

return result;
Expand All @@ -1649,6 +1651,7 @@ private SqlExpression OptimizeComparison(
SqlExpression right,
bool leftNullable,
bool rightNullable,
bool optimize,
out bool nullable)
{
var leftNullValue = leftNullable && left is SqlConstantExpression or SqlParameterExpression;
Expand Down Expand Up @@ -1729,47 +1732,20 @@ private SqlExpression OptimizeComparison(
&& !rightNullable
&& sqlBinaryExpression.OperatorType is ExpressionType.Equal or ExpressionType.NotEqual)
{
var leftUnary = left as SqlUnaryExpression;
var rightUnary = right as SqlUnaryExpression;

var leftNegated = IsLogicalNot(leftUnary);
var rightNegated = IsLogicalNot(rightUnary);

if (leftNegated)
{
left = leftUnary!.Operand;
}

if (rightNegated)
{
right = rightUnary!.Operand;
}

// a == b <=> !a == !b -> a == b
// !a == b <=> a == !b -> a != b
// a != b <=> !a != !b -> a != b
// !a != b <=> a != !b -> a == b

nullable = false;

return sqlBinaryExpression.OperatorType == ExpressionType.Equal ^ leftNegated == rightNegated
? _sqlExpressionFactory.NotEqual(left, right)
: _sqlExpressionFactory.Equal(left, right);
return OptimizeBooleanComparison(sqlBinaryExpression, left, right, optimize);
}

nullable = false;

return sqlBinaryExpression.Update(left, right);
}

private SqlExpression RewriteNullSemantics(
private SqlExpression OptimizeBooleanComparison(
SqlBinaryExpression sqlBinaryExpression,
SqlExpression left,
SqlExpression right,
bool leftNullable,
bool rightNullable,
bool optimize,
out bool nullable)
bool optimize)
{
var leftUnary = left as SqlUnaryExpression;
var rightUnary = right as SqlUnaryExpression;
Expand All @@ -1787,22 +1763,49 @@ private SqlExpression RewriteNullSemantics(
right = rightUnary!.Operand;
}

var notEqual = sqlBinaryExpression.OperatorType == ExpressionType.Equal ^ leftNegated == rightNegated;

// prefer equality in predicates
if (optimize && notEqual && left.Type == typeof(bool))
{
if (right is ColumnExpression && (left is not ColumnExpression || leftNegated))
{
left = _sqlExpressionFactory.Not(left);
}
else
{
right = _sqlExpressionFactory.Not(right);
}

return _sqlExpressionFactory.Equal(left, right);
}

// a == b <=> !a == !b -> a == b
// !a == b <=> a == !b -> a != b
// a != b <=> !a != !b -> a != b
// !a != b <=> a != !b -> a == b

return notEqual
? _sqlExpressionFactory.NotEqual(left, right)
: _sqlExpressionFactory.Equal(left, right);
}

private SqlExpression RewriteNullSemantics(
SqlBinaryExpression sqlBinaryExpression,
SqlExpression left,
SqlExpression right,
bool leftNullable,
bool rightNullable,
bool optimize,
out bool nullable)
{
var leftIsNull = ProcessNullNotNull(_sqlExpressionFactory.IsNull(left), leftNullable);
var leftIsNotNull = _sqlExpressionFactory.Not(leftIsNull);

var rightIsNull = ProcessNullNotNull(_sqlExpressionFactory.IsNull(right), rightNullable);
var rightIsNotNull = _sqlExpressionFactory.Not(rightIsNull);

SqlExpression body;
if (leftNegated == rightNegated)
{
body = _sqlExpressionFactory.Equal(left, right);
}
else
{
// a == !b and !a == b in SQL evaluate the same as a != b
body = _sqlExpressionFactory.NotEqual(left, right);
}
var body = OptimizeBooleanComparison(sqlBinaryExpression, left, right, optimize);

// optimized expansion which doesn't distinguish between null and false
if (optimize && sqlBinaryExpression.OperatorType == ExpressionType.Equal)
Expand All @@ -1815,6 +1818,12 @@ private SqlExpression RewriteNullSemantics(
// doing a full null semantics rewrite - removing all nulls from truth table
nullable = false;

if (sqlBinaryExpression.OperatorType == ExpressionType.NotEqual)
{
// the factory takes care of simplifying equal <-> not-equal
body = _sqlExpressionFactory.Not(body);
}

// (a == b && (a != null && b != null)) || (a == null && b == null)
body = _sqlExpressionFactory.OrElse(
_sqlExpressionFactory.AndAlso(body, _sqlExpressionFactory.AndAlso(leftIsNotNull, rightIsNotNull)),
Expand Down
4 changes: 2 additions & 2 deletions test/EFCore.SqlServer.FunctionalTests/Query/FunkyDataQuerySqlServerTest.cs
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Expand Up @@ -562,9 +562,9 @@ public override async Task String_ends_with_not_equals_nullable_column(bool asyn
FROM [FunkyCustomers] AS [f]
CROSS JOIN [FunkyCustomers] AS [f0]
WHERE CASE
WHEN [f].[FirstName] IS NOT NULL AND [f0].[LastName] IS NOT NULL AND RIGHT([f].[FirstName], LEN([f0].[LastName])) = [f0].[LastName] THEN CAST(1 AS bit)
WHEN [f].[FirstName] IS NULL OR [f0].[LastName] IS NULL OR RIGHT([f].[FirstName], LEN([f0].[LastName])) <> [f0].[LastName] THEN CAST(1 AS bit)
ELSE CAST(0 AS bit)
END <> [f].[NullableBool] OR [f].[NullableBool] IS NULL
END = [f].[NullableBool] OR [f].[NullableBool] IS NULL
""");
}

Expand Down
6 changes: 3 additions & 3 deletions test/EFCore.SqlServer.FunctionalTests/Query/GearsOfWarQuerySqlServerTest.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -6831,7 +6831,7 @@ FROM [Gears] AS [g]
LEFT JOIN (
SELECT [w].[Id], [w].[OwnerFullName]
FROM [Weapons] AS [w]
WHERE [w].[IsAutomatic] <> @__isAutomatic_0
WHERE [w].[IsAutomatic] = ~@__isAutomatic_0
) AS [w0] ON [g].[FullName] = [w0].[OwnerFullName]
""");
}
Expand Down Expand Up @@ -7555,15 +7555,15 @@ public override async Task Logical_operation_with_non_null_parameter_optimizes_n

SELECT [g].[Nickname], [g].[SquadId], [g].[AssignedCityName], [g].[CityOfBirthName], [g].[Discriminator], [g].[FullName], [g].[HasSoulPatch], [g].[LeaderNickname], [g].[LeaderSquadId], [g].[Rank]
FROM [Gears] AS [g]
WHERE [g].[HasSoulPatch] <> @__prm_0
WHERE [g].[HasSoulPatch] = ~@__prm_0
""",
//
"""
@__prm_0='False'

SELECT [g].[Nickname], [g].[SquadId], [g].[AssignedCityName], [g].[CityOfBirthName], [g].[Discriminator], [g].[FullName], [g].[HasSoulPatch], [g].[LeaderNickname], [g].[LeaderSquadId], [g].[Rank]
FROM [Gears] AS [g]
WHERE [g].[HasSoulPatch] <> @__prm_0
WHERE [g].[HasSoulPatch] = ~@__prm_0
""");
}

Expand Down
4 changes: 2 additions & 2 deletions test/EFCore.SqlServer.FunctionalTests/Query/NorthwindWhereQuerySqlServerTest.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -1347,7 +1347,7 @@ public override async Task Where_not_bool_member_compared_to_binary_expression(b
"""
SELECT [p].[ProductID], [p].[Discontinued], [p].[ProductName], [p].[SupplierID], [p].[UnitPrice], [p].[UnitsInStock]
FROM [Products] AS [p]
WHERE [p].[Discontinued] <> CASE
WHERE [p].[Discontinued] = ~CASE
WHEN [p].[ProductID] > 50 THEN CAST(1 AS bit)
ELSE CAST(0 AS bit)
END
Expand Down Expand Up @@ -1381,7 +1381,7 @@ FROM [Products] AS [p]
WHERE CASE
WHEN [p].[ProductID] > 50 THEN CAST(1 AS bit)
ELSE CAST(0 AS bit)
END <> @__prm_0
END = ~@__prm_0
""");
}

Expand Down
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