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/* ****************************************************************************
*
* Copyright (c) Microsoft Corporation.
*
* This source code is subject to terms and conditions of the Apache License, Version 2.0. A
* copy of the license can be found in the License.html file at the root of this distribution. If
* you cannot locate the Apache License, Version 2.0, please send an email to
* dlr@microsoft.com. By using this source code in any fashion, you are agreeing to be bound
* by the terms of the Apache License, Version 2.0.
*
* You must not remove this notice, or any other, from this software.
*
*
* ***************************************************************************/
using System;
using System.Diagnostics;
using System.Dynamic.Utils;
#if CLR2
namespace Microsoft.Scripting.Ast {
#else
namespace System.Linq.Expressions {
#endif
internal enum AnalyzeTypeIsResult {
KnownFalse,
KnownTrue,
KnownAssignable, // need null check only
Unknown, // need full runtime check
}
internal static class ConstantCheck {
internal static bool IsNull(Expression e) {
if (e.NodeType == ExpressionType.Constant) {
return ((ConstantExpression)e).Value == null;
}
return false;
}
/// <summary>
/// If the result of a TypeBinaryExpression is known statically, this
/// returns the result, otherwise it returns null, meaning we'll need
/// to perform the IsInst instruction at runtime.
///
/// The result of this function must be equivalent to IsInst, or
/// null.
/// </summary>
internal static AnalyzeTypeIsResult AnalyzeTypeIs(TypeBinaryExpression typeIs) {
return AnalyzeTypeIs(typeIs.Expression, typeIs.TypeOperand);
}
/// <summary>
/// If the result of an isinst opcode is known statically, this
/// returns the result, otherwise it returns null, meaning we'll need
/// to perform the IsInst instruction at runtime.
///
/// The result of this function must be equivalent to IsInst, or
/// null.
/// </summary>
private static AnalyzeTypeIsResult AnalyzeTypeIs(Expression operand, Type testType) {
Type operandType = operand.Type;
// Oddly, we allow void operands
// This is LinqV1 behavior of TypeIs
if (operandType == typeof(void)) {
return AnalyzeTypeIsResult.KnownFalse;
}
//
// Type comparisons treat nullable types as if they were the
// underlying type. The reason is when you box a nullable it
// becomes a boxed value of the underlying type, or null.
//
Type nnOperandType = operandType.GetNonNullableType();
Type nnTestType = testType.GetNonNullableType();
//
// See if we can determine the answer based on the static types
//
// Extensive testing showed that Type.IsAssignableFrom,
// Type.IsInstanceOfType, and the isinst instruction were all
// equivalent when used against a live object
//
if (nnTestType.IsAssignableFrom(nnOperandType)) {
// If the operand is a value type (other than nullable), we
// know the result is always true.
if (operandType.IsValueType && !operandType.IsNullableType()) {
return AnalyzeTypeIsResult.KnownTrue;
}
// For reference/nullable types, we need to compare to null at runtime
return AnalyzeTypeIsResult.KnownAssignable;
}
// We used to have an if IsSealed, return KnownFalse check here.
// but that doesn't handle generic types & co/contravariance correctly.
// So just use IsInst, which we know always gives us the right answer.
// Otherwise we need a full runtime check
return AnalyzeTypeIsResult.Unknown;
}
}
}
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