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ILSpy/ICSharpCode.Decompiler/IL/Transforms/NullableLiftingTransform.cs

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// Copyright (c) 2017 Daniel Grunwald
//
// Permission is hereby granted, free of charge, to any person obtaining a copy of this
// software and associated documentation files (the "Software"), to deal in the Software
// without restriction, including without limitation the rights to use, copy, modify, merge,
// publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons
// to whom the Software is furnished to do so, subject to the following conditions:
//
// The above copyright notice and this permission notice shall be included in all copies or
// substantial portions of the Software.
//
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED,
// INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR
// PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE
// FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR
// OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
// DEALINGS IN THE SOFTWARE.
using System;
using System.Collections.Generic;
using System.Diagnostics;
using System.Linq;
using ICSharpCode.Decompiler.TypeSystem;
using ICSharpCode.Decompiler.Util;
namespace ICSharpCode.Decompiler.IL.Transforms
{
/// <summary>
/// Nullable lifting gets run in two places:
/// * the usual form looks at an if-else, and runs within the ExpressionTransforms.
/// * the NullableLiftingBlockTransform handles the cases where Roslyn generates
/// two 'ret' statements for the null/non-null cases of a lifted operator.
///
/// The transform handles the following languages constructs:
/// * lifted conversions
/// * lifted unary and binary operators
/// * lifted comparisons
/// * the ?? operator with type Nullable{T} on the left-hand-side
/// * the ?. operator (via NullPropagationTransform)
/// </summary>
struct NullableLiftingTransform
{
readonly ILTransformContext context;
List<ILVariable> nullableVars;
public NullableLiftingTransform(ILTransformContext context)
{
this.context = context;
this.nullableVars = null;
}
#region Run
/// <summary>
/// Main entry point into the normal code path of this transform.
/// Called by expression transform.
/// </summary>
public bool Run(IfInstruction ifInst)
{
var lifted = Lift(ifInst, ifInst.TrueInst, ifInst.FalseInst);
if (lifted != null) {
ifInst.ReplaceWith(lifted);
return true;
}
return false;
}
public bool RunStatements(Block block, int pos)
{
/// e.g.:
// if (!condition) Block {
// leave IL_0000 (default.value System.Nullable`1[[System.Int64]])
// }
// leave IL_0000 (newobj .ctor(exprToLift))
if (pos != block.Instructions.Count - 2)
return false;
if (!(block.Instructions[pos] is IfInstruction ifInst))
return false;
if (!(Block.Unwrap(ifInst.TrueInst) is Leave thenLeave))
return false;
if (!ifInst.FalseInst.MatchNop())
return false;
if (!(block.Instructions[pos + 1] is Leave elseLeave))
return false;
if (elseLeave.TargetContainer != thenLeave.TargetContainer)
return false;
var lifted = Lift(ifInst, thenLeave.Value, elseLeave.Value);
if (lifted != null) {
thenLeave.Value = lifted;
ifInst.ReplaceWith(thenLeave);
block.Instructions.Remove(elseLeave);
return true;
}
return false;
}
#endregion
#region AnalyzeCondition
bool AnalyzeCondition(ILInstruction condition)
{
if (MatchHasValueCall(condition, out ILVariable v)) {
if (nullableVars == null)
nullableVars = new List<ILVariable>();
nullableVars.Add(v);
return true;
} else if (condition is BinaryNumericInstruction bitand) {
if (!(bitand.Operator == BinaryNumericOperator.BitAnd && bitand.ResultType == StackType.I4))
return false;
return AnalyzeCondition(bitand.Left) && AnalyzeCondition(bitand.Right);
}
return false;
}
#endregion
#region Main lifting logic
/// <summary>
/// Main entry point for lifting; called by both the expression-transform
/// and the block transform.
/// </summary>
ILInstruction Lift(IfInstruction ifInst, ILInstruction trueInst, ILInstruction falseInst)
{
ILInstruction condition = ifInst.Condition;
while (condition.MatchLogicNot(out var arg)) {
condition = arg;
ExtensionMethods.Swap(ref trueInst, ref falseInst);
}
if (context.Settings.NullPropagation && !NullPropagationTransform.IsProtectedIfInst(ifInst)) {
var nullPropagated = new NullPropagationTransform(context)
.Run(condition, trueInst, falseInst, ifInst.ILRange);
if (nullPropagated != null)
return nullPropagated;
}
if (!context.Settings.LiftNullables)
return null;
if (AnalyzeCondition(condition)) {
// (v1 != null && ... && vn != null) ? trueInst : falseInst
// => normal lifting
return LiftNormal(trueInst, falseInst, ilrange: ifInst.ILRange);
}
if (MatchCompOrDecimal(condition, out var comp)) {
// This might be a C#-style lifted comparison
// (C# checks the underlying value before checking the HasValue bits)
if (comp.Kind.IsEqualityOrInequality()) {
// for equality/inequality, the HasValue bits must also compare equal/inequal
if (comp.Kind == ComparisonKind.Inequality) {
// handle inequality by swapping one last time
ExtensionMethods.Swap(ref trueInst, ref falseInst);
}
if (falseInst.MatchLdcI4(0)) {
// (a.GetValueOrDefault() == b.GetValueOrDefault()) ? (a.HasValue == b.HasValue) : false
// => a == b
return LiftCSharpEqualityComparison(comp, ComparisonKind.Equality, trueInst)
?? LiftCSharpUserEqualityComparison(comp, ComparisonKind.Equality, trueInst);
} else if (falseInst.MatchLdcI4(1)) {
// (a.GetValueOrDefault() == b.GetValueOrDefault()) ? (a.HasValue != b.HasValue) : true
// => a != b
return LiftCSharpEqualityComparison(comp, ComparisonKind.Inequality, trueInst)
?? LiftCSharpUserEqualityComparison(comp, ComparisonKind.Inequality, trueInst);
} else if (IsGenericNewPattern(comp.Left, comp.Right, trueInst, falseInst)) {
// (default(T) == null) ? Activator.CreateInstance<T>() : default(T)
// => Activator.CreateInstance<T>()
return trueInst;
}
} else {
// Not (in)equality, but one of < <= > >=.
// Returns false unless all HasValue bits are true.
if (falseInst.MatchLdcI4(0) && AnalyzeCondition(trueInst)) {
// comp(lhs, rhs) ? (v1 != null && ... && vn != null) : false
// => comp.lifted[C#](lhs, rhs)
return LiftCSharpComparison(comp, comp.Kind);
} else if (trueInst.MatchLdcI4(0) && AnalyzeCondition(falseInst)) {
// comp(lhs, rhs) ? false : (v1 != null && ... && vn != null)
return LiftCSharpComparison(comp, comp.Kind.Negate());
}
}
}
ILVariable v;
// Handle equality comparisons with bool?:
if (MatchGetValueOrDefault(condition, out v)
&& NullableType.GetUnderlyingType(v.Type).IsKnownType(KnownTypeCode.Boolean))
{
if (MatchHasValueCall(trueInst, v) && falseInst.MatchLdcI4(0)) {
// v.GetValueOrDefault() ? v.HasValue : false
// ==> v == true
context.Step("NullableLiftingTransform: v == true", ifInst);
return new Comp(ComparisonKind.Equality, ComparisonLiftingKind.CSharp,
StackType.I4, Sign.None,
new LdLoc(v) { ILRange = trueInst.ILRange },
new LdcI4(1) { ILRange = falseInst.ILRange }
) { ILRange = ifInst.ILRange };
} else if (trueInst.MatchLdcI4(0) && MatchHasValueCall(falseInst, v)) {
// v.GetValueOrDefault() ? false : v.HasValue
// ==> v == false
context.Step("NullableLiftingTransform: v == false", ifInst);
return new Comp(ComparisonKind.Equality, ComparisonLiftingKind.CSharp,
StackType.I4, Sign.None,
new LdLoc(v) { ILRange = falseInst.ILRange },
trueInst // LdcI4(0)
) { ILRange = ifInst.ILRange };
} else if (MatchNegatedHasValueCall(trueInst, v) && falseInst.MatchLdcI4(1)) {
// v.GetValueOrDefault() ? !v.HasValue : true
// ==> v != true
context.Step("NullableLiftingTransform: v != true", ifInst);
return new Comp(ComparisonKind.Inequality, ComparisonLiftingKind.CSharp,
StackType.I4, Sign.None,
new LdLoc(v) { ILRange = trueInst.ILRange },
falseInst // LdcI4(1)
) { ILRange = ifInst.ILRange };
} else if (trueInst.MatchLdcI4(1) && MatchNegatedHasValueCall(falseInst, v)) {
// v.GetValueOrDefault() ? true : !v.HasValue
// ==> v != false
context.Step("NullableLiftingTransform: v != false", ifInst);
return new Comp(ComparisonKind.Inequality, ComparisonLiftingKind.CSharp,
StackType.I4, Sign.None,
new LdLoc(v) { ILRange = falseInst.ILRange },
new LdcI4(0) { ILRange = trueInst.ILRange }
) { ILRange = ifInst.ILRange };
}
}
// Handle & and | on bool?:
if (trueInst.MatchLdLoc(out v)) {
if (MatchNullableCtor(falseInst, out var utype, out var arg)
&& utype.IsKnownType(KnownTypeCode.Boolean) && arg.MatchLdcI4(0))
{
// condition ? v : (bool?)false
// => condition & v
context.Step("NullableLiftingTransform: 3vl.logic.and(bool, bool?)", ifInst);
return new ThreeValuedLogicAnd(condition, trueInst) { ILRange = ifInst.ILRange };
}
if (falseInst.MatchLdLoc(out var v2)) {
// condition ? v : v2
if (MatchThreeValuedLogicConditionPattern(condition, out var nullable1, out var nullable2)) {
// (nullable1.GetValueOrDefault() || (!nullable2.GetValueOrDefault() && !nullable1.HasValue)) ? v : v2
if (v == nullable1 && v2 == nullable2) {
context.Step("NullableLiftingTransform: 3vl.logic.or(bool?, bool?)", ifInst);
return new ThreeValuedLogicOr(trueInst, falseInst) { ILRange = ifInst.ILRange };
} else if (v == nullable2 && v2 == nullable1) {
context.Step("NullableLiftingTransform: 3vl.logic.and(bool?, bool?)", ifInst);
return new ThreeValuedLogicAnd(falseInst, trueInst) { ILRange = ifInst.ILRange };
}
}
}
} else if (falseInst.MatchLdLoc(out v)) {
if (MatchNullableCtor(trueInst, out var utype, out var arg)
&& utype.IsKnownType(KnownTypeCode.Boolean) && arg.MatchLdcI4(1)) {
// condition ? (bool?)true : v
// => condition | v
context.Step("NullableLiftingTransform: 3vl.logic.or(bool, bool?)", ifInst);
return new ThreeValuedLogicOr(condition, falseInst) { ILRange = ifInst.ILRange };
}
}
return null;
}
private bool IsGenericNewPattern(ILInstruction compLeft, ILInstruction compRight, ILInstruction trueInst, ILInstruction falseInst)
{
// (default(T) == null) ? Activator.CreateInstance<T>() : default(T)
return falseInst.MatchDefaultValue(out var type) &&
(trueInst is Call c && c.Method.FullName == "System.Activator.CreateInstance" && c.Method.TypeArguments.Count == 1) &&
type.Kind == TypeKind.TypeParameter &&
compLeft.MatchDefaultValue(out var type2) &&
type.Equals(type2) &&
compRight.MatchLdNull();
}
private bool MatchThreeValuedLogicConditionPattern(ILInstruction condition, out ILVariable nullable1, out ILVariable nullable2)
{
// Try to match: nullable1.GetValueOrDefault() || (!nullable2.GetValueOrDefault() && !nullable1.HasValue)
nullable1 = null;
nullable2 = null;
if (!condition.MatchLogicOr(out var lhs, out var rhs))
return false;
if (!MatchGetValueOrDefault(lhs, out nullable1))
return false;
if (!NullableType.GetUnderlyingType(nullable1.Type).IsKnownType(KnownTypeCode.Boolean))
return false;
if (!rhs.MatchLogicAnd(out lhs, out rhs))
return false;
if (!lhs.MatchLogicNot(out var arg))
return false;
if (!MatchGetValueOrDefault(arg, out nullable2))
return false;
if (!NullableType.GetUnderlyingType(nullable2.Type).IsKnownType(KnownTypeCode.Boolean))
return false;
if (!rhs.MatchLogicNot(out arg))
return false;
return MatchHasValueCall(arg, nullable1);
}
#endregion
#region CSharpComp
static bool MatchCompOrDecimal(ILInstruction inst, out CompOrDecimal result)
{
result = default(CompOrDecimal);
result.Instruction = inst;
if (inst is Comp comp && !comp.IsLifted) {
result.Kind = comp.Kind;
result.Left = comp.Left;
result.Right = comp.Right;
return true;
} else if (inst is Call call && call.Method.IsOperator && call.Arguments.Count == 2 && !call.IsLifted) {
switch (call.Method.Name) {
case "op_Equality":
result.Kind = ComparisonKind.Equality;
break;
case "op_Inequality":
result.Kind = ComparisonKind.Inequality;
break;
case "op_LessThan":
result.Kind = ComparisonKind.LessThan;
break;
case "op_LessThanOrEqual":
result.Kind = ComparisonKind.LessThanOrEqual;
break;
case "op_GreaterThan":
result.Kind = ComparisonKind.GreaterThan;
break;
case "op_GreaterThanOrEqual":
result.Kind = ComparisonKind.GreaterThanOrEqual;
break;
default:
return false;
}
result.Left = call.Arguments[0];
result.Right = call.Arguments[1];
return call.Method.DeclaringType.IsKnownType(KnownTypeCode.Decimal);
}
return false;
}
/// <summary>
/// Represents either non-lifted IL `Comp` or a call to one of the (non-lifted) 6 comparison operators on `System.Decimal`.
/// </summary>
struct CompOrDecimal
{
public ILInstruction Instruction;
public ComparisonKind Kind;
public ILInstruction Left;
public ILInstruction Right;
public IType LeftExpectedType {
get {
if (Instruction is Call call) {
return call.Method.Parameters[0].Type;
} else {
return SpecialType.UnknownType;
}
}
}
public IType RightExpectedType {
get {
if (Instruction is Call call) {
return call.Method.Parameters[1].Type;
} else {
return SpecialType.UnknownType;
}
}
}
internal ILInstruction MakeLifted(ComparisonKind newComparisonKind, ILInstruction left, ILInstruction right)
{
if (Instruction is Comp comp) {
return new Comp(newComparisonKind, ComparisonLiftingKind.CSharp, comp.InputType, comp.Sign, left, right) {
ILRange = Instruction.ILRange
};
} else if (Instruction is Call call) {
IMethod method;
if (newComparisonKind == Kind) {
method = call.Method;
} else if (newComparisonKind == ComparisonKind.Inequality && call.Method.Name == "op_Equality") {
method = call.Method.DeclaringType.GetMethods(m => m.Name == "op_Inequality")
.FirstOrDefault(m => ParameterListComparer.Instance.Equals(m.Parameters, call.Method.Parameters));
if (method == null)
return null;
} else {
return null;
}
return new Call(CSharp.Resolver.CSharpOperators.LiftUserDefinedOperator(method)) {
Arguments = { left, right },
ConstrainedTo = call.ConstrainedTo,
ILRange = call.ILRange,
ILStackWasEmpty = call.ILStackWasEmpty,
IsTail = call.IsTail
};
} else {
return null;
}
}
}
#endregion
#region Lift...Comparison
ILInstruction LiftCSharpEqualityComparison(CompOrDecimal valueComp, ComparisonKind newComparisonKind, ILInstruction hasValueTest)
{
Debug.Assert(newComparisonKind.IsEqualityOrInequality());
bool hasValueTestNegated = false;
while (hasValueTest.MatchLogicNot(out var arg)) {
hasValueTest = arg;
hasValueTestNegated = !hasValueTestNegated;
}
// The HasValue comparison must be the same operator as the Value comparison.
if (hasValueTest is Comp hasValueComp) {
// Comparing two nullables: HasValue comparison must be the same operator as the Value comparison
if ((hasValueTestNegated ? hasValueComp.Kind.Negate() : hasValueComp.Kind) != newComparisonKind)
return null;
if (!MatchHasValueCall(hasValueComp.Left, out ILVariable leftVar))
return null;
if (!MatchHasValueCall(hasValueComp.Right, out ILVariable rightVar))
return null;
nullableVars = new List<ILVariable> { leftVar };
var (left, leftBits) = DoLift(valueComp.Left);
nullableVars[0] = rightVar;
var (right, rightBits) = DoLift(valueComp.Right);
if (left != null && right != null && leftBits[0] && rightBits[0]
&& SemanticHelper.IsPure(left.Flags) && SemanticHelper.IsPure(right.Flags)
) {
context.Step("NullableLiftingTransform: C# (in)equality comparison", valueComp.Instruction);
return valueComp.MakeLifted(newComparisonKind, left, right);
}
} else if (newComparisonKind == ComparisonKind.Equality && !hasValueTestNegated && MatchHasValueCall(hasValueTest, out ILVariable v)) {
// Comparing nullable with non-nullable -> we can fall back to the normal comparison code.
nullableVars = new List<ILVariable> { v };
return LiftCSharpComparison(valueComp, newComparisonKind);
} else if (newComparisonKind == ComparisonKind.Inequality && hasValueTestNegated && MatchHasValueCall(hasValueTest, out v)) {
// Comparing nullable with non-nullable -> we can fall back to the normal comparison code.
nullableVars = new List<ILVariable> { v };
return LiftCSharpComparison(valueComp, newComparisonKind);
}
return null;
}
/// <summary>
/// Lift a C# comparison.
/// This method cannot be used for (in)equality comparisons where both sides are nullable
/// (these special cases are handled in LiftCSharpEqualityComparison instead).
///
/// The output instructions should evaluate to <c>false</c> when any of the <c>nullableVars</c> is <c>null</c>
/// (except for newComparisonKind==Inequality, where this case should evaluate to <c>true</c> instead).
/// Otherwise, the output instruction should evaluate to the same value as the input instruction.
/// The output instruction should have the same side-effects (incl. exceptions being thrown) as the input instruction.
/// This means unlike LiftNormal(), we cannot rely on the input instruction not being evaluated if
/// a variable is <c>null</c>.
/// </summary>
ILInstruction LiftCSharpComparison(CompOrDecimal comp, ComparisonKind newComparisonKind)
{
var (left, right, bits) = DoLiftBinary(comp.Left, comp.Right, comp.LeftExpectedType, comp.RightExpectedType);
// due to the restrictions on side effects, we only allow instructions that are pure after lifting.
// (we can't check this before lifting due to the calls to GetValueOrDefault())
if (left != null && right != null && SemanticHelper.IsPure(left.Flags) && SemanticHelper.IsPure(right.Flags)) {
if (!bits.All(0, nullableVars.Count)) {
// don't lift if a nullableVar doesn't contribute to the result
return null;
}
context.Step("NullableLiftingTransform: C# comparison", comp.Instruction);
return comp.MakeLifted(newComparisonKind, left, right);
}
return null;
}
Call LiftCSharpUserEqualityComparison(CompOrDecimal hasValueComp, ComparisonKind newComparisonKind, ILInstruction nestedIfInst)
{
// User-defined equality operator:
// if (comp(call get_HasValue(ldloca nullable1) == call get_HasValue(ldloca nullable2)))
// if (logic.not(call get_HasValue(ldloca nullable)))
// ldc.i4 1
// else
// call op_Equality(call GetValueOrDefault(ldloca nullable1), call GetValueOrDefault(ldloca nullable2)
// else
// ldc.i4 0
// User-defined inequality operator:
// if (comp(call get_HasValue(ldloca nullable1) != call get_HasValue(ldloca nullable2)))
// ldc.i4 1
// else
// if (call get_HasValue(ldloca nullable))
// call op_Inequality(call GetValueOrDefault(ldloca nullable1), call GetValueOrDefault(ldloca nullable2))
// else
// ldc.i4 0
if (!MatchHasValueCall(hasValueComp.Left, out ILVariable nullable1))
return null;
if (!MatchHasValueCall(hasValueComp.Right, out ILVariable nullable2))
return null;
if (!nestedIfInst.MatchIfInstructionPositiveCondition(out var condition, out var trueInst, out var falseInst))
return null;
if (!MatchHasValueCall(condition, out ILVariable nullable))
return null;
if (nullable != nullable1 && nullable != nullable2)
return null;
if (!falseInst.MatchLdcI4(newComparisonKind == ComparisonKind.Equality ? 1 : 0))
return null;
if (!(trueInst is Call call))
return null;
if (!(call.Method.IsOperator && call.Arguments.Count == 2))
return null;
if (call.Method.Name != (newComparisonKind == ComparisonKind.Equality ? "op_Equality" : "op_Inequality"))
return null;
var liftedOperator = CSharp.Resolver.CSharpOperators.LiftUserDefinedOperator(call.Method);
if (liftedOperator == null)
return null;
nullableVars = new List<ILVariable> { nullable1 };
var (left, leftBits) = DoLift(call.Arguments[0]);
nullableVars[0] = nullable2;
var (right, rightBits) = DoLift(call.Arguments[1]);
if (left != null && right != null && leftBits[0] && rightBits[0]
&& SemanticHelper.IsPure(left.Flags) && SemanticHelper.IsPure(right.Flags)
) {
context.Step("NullableLiftingTransform: C# user-defined (in)equality comparison", nestedIfInst);
return new Call(liftedOperator) {
Arguments = { left, right },
ConstrainedTo = call.ConstrainedTo,
ILRange = call.ILRange,
ILStackWasEmpty = call.ILStackWasEmpty,
IsTail = call.IsTail,
};
}
return null;
}
#endregion
#region LiftNormal / DoLift
/// <summary>
/// Performs nullable lifting.
///
/// Produces a lifted instruction with semantics equivalent to:
/// (v1 != null && ... && vn != null) ? trueInst : falseInst,
/// where the v1,...,vn are the <c>this.nullableVars</c>.
/// If lifting fails, returns <c>null</c>.
/// </summary>
ILInstruction LiftNormal(ILInstruction trueInst, ILInstruction falseInst, Interval ilrange)
{
if (trueInst.MatchIfInstructionPositiveCondition(out var nestedCondition, out var nestedTrue, out var nestedFalse)) {
// Sometimes Roslyn generates pointless conditions like:
// if (nullable.HasValue && (!nullable.HasValue || nullable.GetValueOrDefault() == b))
if (MatchHasValueCall(nestedCondition, out ILVariable v) && nullableVars.Contains(v)) {
trueInst = nestedTrue;
}
}
bool isNullCoalescingWithNonNullableFallback = false;
if (!MatchNullableCtor(trueInst, out var utype, out var exprToLift)) {
isNullCoalescingWithNonNullableFallback = true;
utype = context.TypeSystem.Compilation.FindType(trueInst.ResultType.ToKnownTypeCode());
exprToLift = trueInst;
if (nullableVars.Count == 1 && exprToLift.MatchLdLoc(nullableVars[0])) {
// v.HasValue ? ldloc v : fallback
// => v ?? fallback
context.Step("v.HasValue ? v : fallback => v ?? fallback", trueInst);
return new NullCoalescingInstruction(NullCoalescingKind.Nullable, trueInst, falseInst) {
UnderlyingResultType = NullableType.GetUnderlyingType(nullableVars[0].Type).GetStackType(),
ILRange = ilrange
};
} else if (trueInst is Call call && !call.IsLifted
&& CSharp.Resolver.CSharpOperators.IsComparisonOperator(call.Method)
&& falseInst.MatchLdcI4(call.Method.Name == "op_Inequality" ? 1 : 0))
{
// (v1 != null && ... && vn != null) ? call op_LessThan(lhs, rhs) : ldc.i4(0)
var liftedOperator = CSharp.Resolver.CSharpOperators.LiftUserDefinedOperator(call.Method);
if ((call.Method.Name == "op_Equality" || call.Method.Name == "op_Inequality") && nullableVars.Count != 1) {
// Equality is special (returns true if both sides are null), only handle it
// in the normal code path if we're dealing with only a single nullable var
// (comparing nullable with non-nullable).
liftedOperator = null;
}
if (liftedOperator != null) {
context.Step("Lift user-defined comparison operator", trueInst);
var (left, right, bits) = DoLiftBinary(call.Arguments[0], call.Arguments[1],
call.Method.Parameters[0].Type, call.Method.Parameters[1].Type);
if (left != null && right != null && bits.All(0, nullableVars.Count)) {
return new Call(liftedOperator) {
Arguments = { left, right },
ConstrainedTo = call.ConstrainedTo,
ILRange = call.ILRange,
ILStackWasEmpty = call.ILStackWasEmpty,
IsTail = call.IsTail
};
}
}
}
}
ILInstruction lifted;
if (nullableVars.Count == 1 && MatchGetValueOrDefault(exprToLift, nullableVars[0])) {
// v.HasValue ? call GetValueOrDefault(ldloca v) : fallback
// => conv.nop.lifted(ldloc v) ?? fallback
// This case is handled separately from DoLift() because
// that doesn't introduce nop-conversions.
context.Step("v.HasValue ? v.GetValueOrDefault() : fallback => v ?? fallback", trueInst);
var inputUType = NullableType.GetUnderlyingType(nullableVars[0].Type);
lifted = new LdLoc(nullableVars[0]);
if (!inputUType.Equals(utype) && utype.ToPrimitiveType() != PrimitiveType.None) {
// While the ILAst allows implicit conversions between short and int
// (because both map to I4); it does not allow implicit conversions
// between short? and int? (structs of different types).
// So use 'conv.nop.lifted' to allow the conversion.
lifted = new Conv(
lifted,
inputUType.GetStackType(), inputUType.GetSign(), utype.ToPrimitiveType(),
checkForOverflow: false,
isLifted: true
) {
ILRange = ilrange
};
}
} else {
context.Step("NullableLiftingTransform.DoLift", trueInst);
BitSet bits;
(lifted, bits) = DoLift(exprToLift);
if (lifted == null) {
return null;
}
if (!bits.All(0, nullableVars.Count)) {
// don't lift if a nullableVar doesn't contribute to the result
return null;
}
Debug.Assert(lifted is ILiftableInstruction liftable && liftable.IsLifted
&& liftable.UnderlyingResultType == exprToLift.ResultType);
}
if (isNullCoalescingWithNonNullableFallback) {
lifted = new NullCoalescingInstruction(NullCoalescingKind.NullableWithValueFallback, lifted, falseInst) {
UnderlyingResultType = exprToLift.ResultType,
ILRange = ilrange
};
} else if (!MatchNull(falseInst, utype)) {
// Normal lifting, but the falseInst isn't `default(utype?)`
// => use the `??` operator to provide the fallback value.
lifted = new NullCoalescingInstruction(NullCoalescingKind.Nullable, lifted, falseInst) {
UnderlyingResultType = exprToLift.ResultType,
ILRange = ilrange
};
}
return lifted;
}
/// <summary>
/// Recursive function that lifts the specified instruction.
/// The input instruction is expected to a subexpression of the trueInst
/// (so that all nullableVars are guaranteed non-null within this expression).
///
/// Creates a new lifted instruction without modifying the input instruction.
/// On success, returns (new lifted instruction, bitset).
/// If lifting fails, returns (null, null).
///
/// The returned bitset specifies which nullableVars were considered "relevant" for this instruction.
/// bitSet[i] == true means nullableVars[i] was relevant.
///
/// The new lifted instruction will have equivalent semantics to the input instruction
/// if all relevant variables are non-null [except that the result will be wrapped in a Nullable{T} struct].
/// If any relevant variable is null, the new instruction is guaranteed to evaluate to <c>null</c>
/// without having any other effect.
/// </summary>
(ILInstruction, BitSet) DoLift(ILInstruction inst)
{
if (MatchGetValueOrDefault(inst, out ILVariable inputVar)) {
// n.GetValueOrDefault() lifted => n.
BitSet foundIndices = new BitSet(nullableVars.Count);
for (int i = 0; i < nullableVars.Count; i++) {
if (nullableVars[i] == inputVar) {
foundIndices[i] = true;
}
}
if (foundIndices.Any())
return (new LdLoc(inputVar) { ILRange = inst.ILRange }, foundIndices);
else
return (null, null);
} else if (inst is Conv conv) {
var (arg, bits) = DoLift(conv.Argument);
if (arg != null) {
if (conv.HasDirectFlag(InstructionFlags.MayThrow) && !bits.All(0, nullableVars.Count)) {
// Cannot execute potentially-throwing instruction unless all
// the nullableVars are arguments to the instruction
// (thus causing it not to throw when any of them is null).
return (null, null);
}
var newInst = new Conv(arg, conv.InputType, conv.InputSign, conv.TargetType, conv.CheckForOverflow, isLifted: true) {
ILRange = conv.ILRange
};
return (newInst, bits);
}
} else if (inst is BitNot bitnot) {
var (arg, bits) = DoLift(bitnot.Argument);
if (arg != null) {
var newInst = new BitNot(arg, isLifted: true, stackType: bitnot.ResultType) {
ILRange = bitnot.ILRange
};
return (newInst, bits);
}
} else if (inst is BinaryNumericInstruction binary) {
var (left, right, bits) = DoLiftBinary(binary.Left, binary.Right, SpecialType.UnknownType, SpecialType.UnknownType);
if (left != null && right != null) {
if (binary.HasDirectFlag(InstructionFlags.MayThrow) && !bits.All(0, nullableVars.Count)) {
// Cannot execute potentially-throwing instruction unless all
// the nullableVars are arguments to the instruction
// (thus causing it not to throw when any of them is null).
return (null, null);
}
var newInst = new BinaryNumericInstruction(
binary.Operator, left, right,
binary.LeftInputType, binary.RightInputType,
binary.CheckForOverflow, binary.Sign,
isLifted: true
) {
ILRange = binary.ILRange
};
return (newInst, bits);
}
} else if (inst is Comp comp && !comp.IsLifted && comp.Kind == ComparisonKind.Equality
&& MatchGetValueOrDefault(comp.Left, out ILVariable v)
&& NullableType.GetUnderlyingType(v.Type).IsKnownType(KnownTypeCode.Boolean)
&& comp.Right.MatchLdcI4(0)
) {
// C# doesn't support ComparisonLiftingKind.ThreeValuedLogic,
// except for operator! on bool?.
var (arg, bits) = DoLift(comp.Left);
Debug.Assert(arg != null);
var newInst = new Comp(comp.Kind, ComparisonLiftingKind.ThreeValuedLogic, comp.InputType, comp.Sign, arg, comp.Right.Clone()) {
ILRange = comp.ILRange
};
return (newInst, bits);
} else if (inst is Call call && call.Method.IsOperator) {
// Lifted user-defined operators, except for comparison operators (as those return bool, not bool?)
var liftedOperator = CSharp.Resolver.CSharpOperators.LiftUserDefinedOperator(call.Method);
if (liftedOperator == null || !NullableType.IsNullable(liftedOperator.ReturnType))
return (null, null);
ILInstruction[] newArgs;
BitSet newBits;
if (call.Arguments.Count == 1) {
var (arg, bits) = DoLift(call.Arguments[0]);
newArgs = new[] { arg };
newBits = bits;
} else if (call.Arguments.Count == 2) {
var (left, right, bits) = DoLiftBinary(call.Arguments[0], call.Arguments[1],
call.Method.Parameters[0].Type, call.Method.Parameters[1].Type);
newArgs = new[] { left, right };
newBits = bits;
} else {
return (null, null);
}
if (newBits == null || !newBits.All(0, nullableVars.Count)) {
// all nullable vars must be involved when calling a method (side effect)
return (null, null);
}
var newInst = new Call(liftedOperator) {
ConstrainedTo = call.ConstrainedTo,
IsTail = call.IsTail,
ILStackWasEmpty = call.ILStackWasEmpty,
ILRange = call.ILRange
};
newInst.Arguments.AddRange(newArgs);
return (newInst, newBits);
}
return (null, null);
}
(ILInstruction, ILInstruction, BitSet) DoLiftBinary(ILInstruction lhs, ILInstruction rhs, IType leftExpectedType, IType rightExpectedType)
{
var (left, leftBits) = DoLift(lhs);
var (right, rightBits) = DoLift(rhs);
if (left != null && right == null && SemanticHelper.IsPure(rhs.Flags)) {
// Embed non-nullable pure expression in lifted expression.
right = NewNullable(rhs.Clone(), rightExpectedType);
}
if (left == null && right != null && SemanticHelper.IsPure(lhs.Flags)) {
// Embed non-nullable pure expression in lifted expression.
left = NewNullable(lhs.Clone(), leftExpectedType);
}
if (left != null && right != null) {
var bits = leftBits ?? rightBits;
if (rightBits != null)
bits.UnionWith(rightBits);
return (left, right, bits);
} else {
return (null, null, null);
}
}
private ILInstruction NewNullable(ILInstruction inst, IType underlyingType)
{
if (underlyingType == SpecialType.UnknownType)
return inst;
var nullable = context.TypeSystem.Compilation.FindType(KnownTypeCode.NullableOfT).GetDefinition();
var ctor = nullable?.Methods.FirstOrDefault(m => m.IsConstructor && m.Parameters.Count == 1);
if (ctor != null) {
ctor = ctor.Specialize(new TypeParameterSubstitution(new[] { underlyingType }, null));
return new NewObj(ctor) { Arguments = { inst } };
} else {
return inst;
}
}
#endregion
#region Match...Call
/// <summary>
/// Matches 'call get_HasValue(arg)'
/// </summary>
internal static bool MatchHasValueCall(ILInstruction inst, out ILInstruction arg)
{
arg = null;
if (!(inst is Call call))
return false;
if (call.Arguments.Count != 1)
return false;
if (call.Method.Name != "get_HasValue")
return false;
if (call.Method.DeclaringTypeDefinition?.KnownTypeCode != KnownTypeCode.NullableOfT)
return false;
arg = call.Arguments[0];
return true;
}
/// <summary>
/// Matches 'call get_HasValue(ldloca v)'
/// </summary>
internal static bool MatchHasValueCall(ILInstruction inst, out ILVariable v)
{
if (MatchHasValueCall(inst, out ILInstruction arg)) {
return arg.MatchLdLoca(out v);
}
v = null;
return false;
}
/// <summary>
/// Matches 'call get_HasValue(ldloca v)'
/// </summary>
internal static bool MatchHasValueCall(ILInstruction inst, ILVariable v)
{
return MatchHasValueCall(inst, out ILVariable v2) && v == v2;
}
/// <summary>
/// Matches 'logic.not(call get_HasValue(ldloca v))'
/// </summary>
static bool MatchNegatedHasValueCall(ILInstruction inst, ILVariable v)
{
return inst.MatchLogicNot(out var arg) && MatchHasValueCall(arg, v);
}
/// <summary>
/// Matches 'newobj Nullable{underlyingType}.ctor(arg)'
/// </summary>
internal static bool MatchNullableCtor(ILInstruction inst, out IType underlyingType, out ILInstruction arg)
{
underlyingType = null;
arg = null;
if (!(inst is NewObj newobj))
return false;
if (!newobj.Method.IsConstructor || newobj.Arguments.Count != 1)
return false;
if (newobj.Method.DeclaringTypeDefinition?.KnownTypeCode != KnownTypeCode.NullableOfT)
return false;
arg = newobj.Arguments[0];
underlyingType = NullableType.GetUnderlyingType(newobj.Method.DeclaringType);
return true;
}
/// <summary>
/// Matches 'call Nullable{T}.GetValueOrDefault(arg)'
/// </summary>
internal static bool MatchGetValueOrDefault(ILInstruction inst, out ILInstruction arg)
{
arg = null;
if (!(inst is Call call))
return false;
if (call.Method.Name != "GetValueOrDefault" || call.Arguments.Count != 1)
return false;
if (call.Method.DeclaringTypeDefinition?.KnownTypeCode != KnownTypeCode.NullableOfT)
return false;
arg = call.Arguments[0];
return true;
}
/// <summary>
/// Matches 'call Nullable{T}.GetValueOrDefault(ldloca v)'
/// </summary>
internal static bool MatchGetValueOrDefault(ILInstruction inst, out ILVariable v)
{
v = null;
return MatchGetValueOrDefault(inst, out ILInstruction arg)
&& arg.MatchLdLoca(out v);
}
/// <summary>
/// Matches 'call Nullable{T}.GetValueOrDefault(ldloca v)'
/// </summary>
internal static bool MatchGetValueOrDefault(ILInstruction inst, ILVariable v)
{
return MatchGetValueOrDefault(inst, out ILVariable v2) && v == v2;
}
static bool MatchNull(ILInstruction inst, out IType underlyingType)
{
underlyingType = null;
if (inst.MatchDefaultValue(out IType type)) {
underlyingType = NullableType.GetUnderlyingType(type);
return NullableType.IsNullable(type);
}
underlyingType = null;
return false;
}
static bool MatchNull(ILInstruction inst, IType underlyingType)
{
return MatchNull(inst, out var utype) && utype.Equals(underlyingType);
}
#endregion
}
class NullableLiftingStatementTransform : IStatementTransform
{
public void Run(Block block, int pos, StatementTransformContext context)
{
new NullableLiftingTransform(context).RunStatements(block, pos);
}
}
}