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// Licensed to the .NET Foundation under one or more agreements.
// The .NET Foundation licenses this file to you under the MIT license.
using System.Collections.Generic;
using System.Collections.ObjectModel;
using System.Diagnostics;
using System.Diagnostics.CodeAnalysis;
using System.Dynamic.Utils;
using System.Reflection;
using System.Runtime.CompilerServices;
namespace System.Linq.Expressions.Compiler
{
/// <summary>
/// Expression rewriting to spill the CLR stack into temporary variables
/// in order to guarantee some properties of code generation, for
/// example that we always enter try block on empty stack.
/// </summary>
internal sealed partial class StackSpiller
{
/// <summary>
/// Indicates whether the evaluation stack is empty.
/// </summary>
private enum Stack
{
Empty,
NonEmpty,
};
/// <summary>
/// Should the parent nodes be rewritten, and in what way?
/// </summary>
/// <remarks>
/// Designed so bitwise-or produces the correct result when merging two
/// subtrees. In particular, SpillStack is preferred over Copy which is
/// preferred over None.
/// </remarks>
[Flags]
private enum RewriteAction
{
/// <summary>
/// No rewrite needed.
/// </summary>
None = 0,
/// <summary>
/// Copy into a new node.
/// </summary>
Copy = 1,
/// <summary>
/// Spill stack into temps.
/// </summary>
SpillStack = 3,
}
/// <summary>
/// Result of a rewrite operation. Always contains an action and a node.
/// </summary>
private readonly struct Result
{
internal readonly RewriteAction Action;
internal readonly Expression Node;
internal Result(RewriteAction action, Expression node)
{
Action = action;
Node = node;
}
}
/// <summary>
/// Initial stack state. Normally empty, but when inlining the lambda
/// we might have a non-empty starting stack state.
/// </summary>
private readonly Stack _startingStack;
/// <summary>
/// Lambda rewrite result. We need this for inlined lambdas to figure
/// out whether we need to guarantee it an empty stack.
/// </summary>
private RewriteAction _lambdaRewrite;
/// <summary>
/// Analyzes a lambda, producing a new one that has correct invariants
/// for codegen. In particular, it spills the IL stack to temps in
/// places where it's invalid to have a non-empty stack (for example,
/// entering a try statement).
/// </summary>
internal static LambdaExpression AnalyzeLambda(LambdaExpression lambda)
{
return lambda.Accept(new StackSpiller(Stack.Empty));
}
private StackSpiller(Stack stack)
{
_startingStack = stack;
}
// Called by Expression<T>.Accept(StackSpiller).
internal Expression<T> Rewrite<T>(Expression<T> lambda)
{
VerifyTemps();
// Lambda starts with an empty stack.
Result body = RewriteExpressionFreeTemps(lambda.Body, _startingStack);
_lambdaRewrite = body.Action;
VerifyTemps();
if (body.Action != RewriteAction.None)
{
// Create a new scope for temps.
// Note that none of these will be hoisted so there is no closure impact.
Expression newBody = body.Node;
if (_tm.Temps.Count > 0)
{
newBody = Expression.Block(_tm.Temps, new TrueReadOnlyCollection<Expression>(newBody));
}
// Clone the lambda, replacing the body & variables.
return Expression<T>.Create(newBody, lambda.Name, lambda.TailCall, new ParameterList(lambda));
}
return lambda;
}
#region Expressions
[Conditional("DEBUG")]
private static void VerifyRewrite(Result result, Expression node)
{
Debug.Assert(result.Node != null);
// (result.Action == RewriteAction.None) if and only if (node == result.Node)
Debug.Assert((result.Action == RewriteAction.None) ^ (node != result.Node), "rewrite action does not match node object identity");
// if the original node is an extension node, it should have been rewritten
Debug.Assert(result.Node.NodeType != ExpressionType.Extension, "extension nodes must be rewritten");
// if we have Copy, then node type must match
Debug.Assert(
result.Action != RewriteAction.Copy || node.NodeType == result.Node.NodeType || node.CanReduce,
"rewrite action does not match node object kind"
);
// New type must be reference assignable to the old type
// (our rewrites preserve type exactly, but the rules for rewriting
// an extension node are more lenient, see Expression.ReduceAndCheck())
Debug.Assert(
TypeUtils.AreReferenceAssignable(node.Type, result.Node.Type),
"rewritten object must be reference assignable to the original type"
);
}
private Result RewriteExpressionFreeTemps(Expression? expression, Stack stack)
{
int mark = Mark();
Result result = RewriteExpression(expression, stack);
Free(mark);
return result;
}
private Result RewriteDynamicExpression(Expression expr)
{
var node = (IDynamicExpression)expr;
// CallSite is on the stack.
var cr = new ChildRewriter(this, Stack.NonEmpty, node.ArgumentCount);
cr.AddArguments(node);
if (cr.Action == RewriteAction.SpillStack)
{
RequireNoRefArgs(node.DelegateType.GetInvokeMethod());
}
return cr.Finish(cr.Rewrite ? node.Rewrite(cr[0, -1]!) : expr);
}
private Result RewriteIndexAssignment(BinaryExpression node, Stack stack)
{
var index = (IndexExpression)node.Left;
var cr = new ChildRewriter(this, stack, 2 + index.ArgumentCount);
cr.Add(index.Object);
cr.AddArguments(index);
cr.Add(node.Right);
if (cr.Action == RewriteAction.SpillStack)
{
cr.MarkRefInstance(index.Object);
}
if (cr.Rewrite)
{
node = new AssignBinaryExpression(
new IndexExpression(
cr[0], // Object
index.Indexer,
cr[1, -2]! // arguments
),
cr[-1]! // value
);
}
return cr.Finish(node);
}
// BinaryExpression: AndAlso, OrElse
private Result RewriteLogicalBinaryExpression(Expression expr, Stack stack)
{
var node = (BinaryExpression)expr;
// Left expression runs on a stack as left by parent
Result left = RewriteExpression(node.Left, stack);
// ... and so does the right one
Result right = RewriteExpression(node.Right, stack);
//conversion is a lambda. stack state will be ignored.
Result conversion = RewriteExpression(node.Conversion, stack);
RewriteAction action = left.Action | right.Action | conversion.Action;
if (action != RewriteAction.None)
{
// We don't have to worry about byref parameters here, because the
// factory doesn't allow it (it requires identical parameters and
// return type from the AndAlso/OrElse method)
expr = BinaryExpression.Create(
node.NodeType,
left.Node,
right.Node,
node.Type,
node.Method,
(LambdaExpression)conversion.Node
);
}
return new Result(action, expr);
}
private Result RewriteReducibleExpression(Expression expr, Stack stack)
{
Result result = RewriteExpression(expr.Reduce(), stack);
// It's at least Copy because we reduced the node.
return new Result(result.Action | RewriteAction.Copy, result.Node);
}
private Result RewriteBinaryExpression(Expression expr, Stack stack)
{
var node = (BinaryExpression)expr;
var cr = new ChildRewriter(this, stack, 3);
// Left expression executes on the stack as left by parent
cr.Add(node.Left);
// Right expression always has non-empty stack (left is on it)
cr.Add(node.Right);
// conversion is a lambda, stack state will be ignored
cr.Add(node.Conversion);
if (cr.Action == RewriteAction.SpillStack)
{
RequireNoRefArgs(node.Method);
}
return cr.Finish(cr.Rewrite ?
BinaryExpression.Create(
node.NodeType,
cr[0]!,
cr[1]!,
node.Type,
node.Method,
(LambdaExpression?)cr[2]) :
expr);
}
private Result RewriteVariableAssignment(BinaryExpression node, Stack stack)
{
// Expression is evaluated on a stack in current state.
Result right = RewriteExpression(node.Right, stack);
if (right.Action != RewriteAction.None)
{
node = new AssignBinaryExpression(node.Left, right.Node);
}
return new Result(right.Action, node);
}
private Result RewriteAssignBinaryExpression(Expression expr, Stack stack)
{
var node = (BinaryExpression)expr;
return node.Left.NodeType switch
{
ExpressionType.Index => RewriteIndexAssignment(node, stack),
ExpressionType.MemberAccess => RewriteMemberAssignment(node, stack),
ExpressionType.Parameter => RewriteVariableAssignment(node, stack),
ExpressionType.Extension => RewriteExtensionAssignment(node, stack),
_ => throw Error.InvalidLvalue(node.Left.NodeType),
};
}
private Result RewriteExtensionAssignment(BinaryExpression node, Stack stack)
{
node = new AssignBinaryExpression(node.Left.ReduceExtensions(), node.Right);
Result result = RewriteAssignBinaryExpression(node, stack);
// it's at least Copy because we reduced the node
return new Result(result.Action | RewriteAction.Copy, result.Node);
}
private static Result RewriteLambdaExpression(Expression expr)
{
var node = (LambdaExpression)expr;
// Call back into the rewriter
expr = AnalyzeLambda(node);
// If the lambda gets rewritten, we don't need to spill the stack,
// but we do need to rebuild the tree above us so it includes the new node.
RewriteAction action = (expr == node) ? RewriteAction.None : RewriteAction.Copy;
return new Result(action, expr);
}
private Result RewriteConditionalExpression(Expression expr, Stack stack)
{
var node = (ConditionalExpression)expr;
// Test executes at the stack as left by parent.
Result test = RewriteExpression(node.Test, stack);
// The test is popped by conditional jump so branches execute
// at the stack as left by parent too.
Result ifTrue = RewriteExpression(node.IfTrue, stack);
Result ifFalse = RewriteExpression(node.IfFalse, stack);
RewriteAction action = test.Action | ifTrue.Action | ifFalse.Action;
if (action != RewriteAction.None)
{
expr = ConditionalExpression.Make(test.Node, ifTrue.Node, ifFalse.Node, node.Type);
}
return new Result(action, expr);
}
private Result RewriteMemberAssignment(BinaryExpression node, Stack stack)
{
var lvalue = (MemberExpression)node.Left;
var cr = new ChildRewriter(this, stack, 2);
// If there's an instance, it executes on the stack in current state
// and rest is executed on non-empty stack.
// Otherwise the stack is left unchanged.
cr.Add(lvalue.Expression);
cr.Add(node.Right);
if (cr.Action == RewriteAction.SpillStack)
{
cr.MarkRefInstance(lvalue.Expression);
}
if (cr.Rewrite)
{
return cr.Finish(
new AssignBinaryExpression(
MemberExpression.Make(cr[0], lvalue.Member),
cr[1]!
)
);
}
return new Result(RewriteAction.None, node);
}
private Result RewriteMemberExpression(Expression expr, Stack stack)
{
var node = (MemberExpression)expr;
// Expression is emitted on top of the stack in current state.
Result expression = RewriteExpression(node.Expression, stack);
if (expression.Action != RewriteAction.None)
{
if (expression.Action == RewriteAction.SpillStack &&
node.Member is PropertyInfo)
{
// Only need to validate properties because reading a field
// is always side-effect free.
RequireNotRefInstance(node.Expression);
}
expr = MemberExpression.Make(expression.Node, node.Member);
}
return new Result(expression.Action, expr);
}
private Result RewriteIndexExpression(Expression expr, Stack stack)
{
var node = (IndexExpression)expr;
var cr = new ChildRewriter(this, stack, node.ArgumentCount + 1);
// For instance methods, the instance executes on the
// stack as is, but stays on the stack, making it non-empty.
cr.Add(node.Object);
cr.AddArguments(node);
if (cr.Action == RewriteAction.SpillStack)
{
cr.MarkRefInstance(node.Object);
}
if (cr.Rewrite)
{
expr = new IndexExpression(
cr[0],
node.Indexer,
cr[1, -1]!
);
}
return cr.Finish(expr);
}
private Result RewriteMethodCallExpression(Expression expr, Stack stack)
{
MethodCallExpression node = (MethodCallExpression)expr;
var cr = new ChildRewriter(this, stack, node.ArgumentCount + 1);
// For instance methods, the instance executes on the
// stack as is, but stays on the stack, making it non-empty.
cr.Add(node.Object);
cr.AddArguments(node);
if (cr.Action == RewriteAction.SpillStack)
{
cr.MarkRefInstance(node.Object);
cr.MarkRefArgs(node.Method, startIndex: 1);
}
if (cr.Rewrite)
{
if (node.Object != null)
{
expr = new InstanceMethodCallExpressionN(node.Method, cr[0]!, cr[1, -1]!);
}
else
{
expr = new MethodCallExpressionN(node.Method, cr[1, -1]!);
}
}
return cr.Finish(expr);
}
[UnconditionalSuppressMessage("ReflectionAnalysis", "IL3050:RequiresDynamicCode",
Justification = "A NewArrayExpression has already been created. The original creator will get a warning that it is not trim compatible.")]
private Result RewriteNewArrayExpression(Expression expr, Stack stack)
{
var node = (NewArrayExpression)expr;
if (node.NodeType == ExpressionType.NewArrayInit)
{
// In a case of array construction with element initialization
// the element expressions are never emitted on an empty stack because
// the array reference and the index are on the stack.
stack = Stack.NonEmpty;
}
else
{
// In a case of NewArrayBounds we make no modifications to the stack
// before emitting bounds expressions.
}
var cr = new ChildRewriter(this, stack, node.Expressions.Count);
cr.Add(node.Expressions);
if (cr.Rewrite)
{
expr = NewArrayExpression.Make(node.NodeType, node.Type, new TrueReadOnlyCollection<Expression>(cr[0, -1]!));
}
return cr.Finish(expr);
}
private Result RewriteInvocationExpression(Expression expr, Stack stack)
{
var node = (InvocationExpression)expr;
ChildRewriter cr;
// See if the lambda will be inlined.
LambdaExpression? lambda = node.LambdaOperand;
if (lambda != null)
{
// Arguments execute on current stack.
cr = new ChildRewriter(this, stack, node.ArgumentCount);
cr.AddArguments(node);
if (cr.Action == RewriteAction.SpillStack)
{
cr.MarkRefArgs(Expression.GetInvokeMethod(node.Expression), startIndex: 0);
}
// Lambda body also executes on current stack.
var spiller = new StackSpiller(stack);
lambda = lambda.Accept(spiller);
if (cr.Rewrite || spiller._lambdaRewrite != RewriteAction.None)
{
node = new InvocationExpressionN(lambda, cr[0, -1]!, node.Type);
}
Result result = cr.Finish(node);
return new Result(result.Action | spiller._lambdaRewrite, result.Node);
}
cr = new ChildRewriter(this, stack, node.ArgumentCount + 1);
// First argument starts on stack as provided.
cr.Add(node.Expression);
// Rest of arguments have non-empty stack (the delegate instance is on the stack).
cr.AddArguments(node);
if (cr.Action == RewriteAction.SpillStack)
{
cr.MarkRefArgs(Expression.GetInvokeMethod(node.Expression), startIndex: 1);
}
return cr.Finish(cr.Rewrite ? new InvocationExpressionN(cr[0]!, cr[1, -1]!, node.Type) : expr);
}
private Result RewriteNewExpression(Expression expr, Stack stack)
{
var node = (NewExpression)expr;
// The first expression starts on a stack as provided by parent,
// rest are definitely non-empty (which ChildRewriter guarantees).
var cr = new ChildRewriter(this, stack, node.ArgumentCount);
cr.AddArguments(node);
if (cr.Action == RewriteAction.SpillStack)
{
cr.MarkRefArgs(node.Constructor!, startIndex: 0);
}
return cr.Finish(cr.Rewrite ? new NewExpression(node.Constructor, cr[0, -1]!, node.Members) : expr);
}
private Result RewriteTypeBinaryExpression(Expression expr, Stack stack)
{
var node = (TypeBinaryExpression)expr;
// The expression is emitted on top of current stack.
Result expression = RewriteExpression(node.Expression, stack);
if (expression.Action != RewriteAction.None)
{
expr = new TypeBinaryExpression(expression.Node, node.TypeOperand, node.NodeType);
}
return new Result(expression.Action, expr);
}
private Result RewriteThrowUnaryExpression(Expression expr, Stack stack)
{
var node = (UnaryExpression)expr;
// Throw statement itself does not care about the stack
// but it will empty the stack and it may cause stack imbalance
// it so we need to restore stack after unconditional throw to make JIT happy
// this has an effect of executing Throw on an empty stack.
Result value = RewriteExpressionFreeTemps(node.Operand, Stack.Empty);
RewriteAction action = value.Action;
if (stack != Stack.Empty)
{
action = RewriteAction.SpillStack;
}
if (action != RewriteAction.None)
{
expr = new UnaryExpression(ExpressionType.Throw, value.Node, node.Type, null);
}
return new Result(action, expr);
}
private Result RewriteUnaryExpression(Expression expr, Stack stack)
{
var node = (UnaryExpression)expr;
Debug.Assert(node.NodeType != ExpressionType.Quote, "unexpected Quote");
Debug.Assert(node.NodeType != ExpressionType.Throw, "unexpected Throw");
// Operand is emitted on top of the stack as-is.
Result expression = RewriteExpression(node.Operand, stack);
if (expression.Action == RewriteAction.SpillStack)
{
RequireNoRefArgs(node.Method);
}
if (expression.Action != RewriteAction.None)
{
expr = new UnaryExpression(node.NodeType, expression.Node, node.Type, node.Method);
}
return new Result(expression.Action, expr);
}
private Result RewriteListInitExpression(Expression expr, Stack stack)
{
var node = (ListInitExpression)expr;
// Constructor runs on initial stack.
Result newResult = RewriteExpression(node.NewExpression, stack);
Expression rewrittenNew = newResult.Node;
RewriteAction action = newResult.Action;
ReadOnlyCollection<ElementInit> inits = node.Initializers;
int count = inits.Count;
ChildRewriter[] cloneCrs = new ChildRewriter[count];
for (int i = 0; i < count; i++)
{
ElementInit init = inits[i];
// Initializers all run on non-empty stack (the list instance is on it).
var cr = new ChildRewriter(this, Stack.NonEmpty, init.Arguments.Count);
cr.Add(init.Arguments);
action |= cr.Action;
cloneCrs[i] = cr;
}
switch (action)
{
case RewriteAction.None:
break;
case RewriteAction.Copy:
ElementInit[] newInits = new ElementInit[count];
for (int i = 0; i < count; i++)
{
ChildRewriter cr = cloneCrs[i];
if (cr.Action == RewriteAction.None)
{
newInits[i] = inits[i];
}
else
{
newInits[i] = new ElementInit(inits[i].AddMethod, new TrueReadOnlyCollection<Expression>(cr[0, -1]!));
}
}
expr = new ListInitExpression((NewExpression)rewrittenNew, new TrueReadOnlyCollection<ElementInit>(newInits));
break;
case RewriteAction.SpillStack:
bool isRefNew = IsRefInstance(node.NewExpression);
var comma = new ArrayBuilder<Expression>(count + 2 + (isRefNew ? 1 : 0));
ParameterExpression tempNew = MakeTemp(rewrittenNew.Type);
comma.UncheckedAdd(new AssignBinaryExpression(tempNew, rewrittenNew));
ParameterExpression refTempNew = tempNew;
if (isRefNew)
{
refTempNew = MakeTemp(tempNew.Type.MakeByRefType());
comma.UncheckedAdd(new ByRefAssignBinaryExpression(refTempNew, tempNew));
}
for (int i = 0; i < count; i++)
{
ChildRewriter cr = cloneCrs[i];
Result add = cr.Finish(new InstanceMethodCallExpressionN(inits[i].AddMethod, refTempNew, cr[0, -1]!));
comma.UncheckedAdd(add.Node);
}
comma.UncheckedAdd(tempNew);
expr = MakeBlock(comma);
break;
default:
throw ContractUtils.Unreachable;
}
return new Result(action, expr);
}
private Result RewriteMemberInitExpression(Expression expr, Stack stack)
{
var node = (MemberInitExpression)expr;
// Constructor runs on initial stack.
Result result = RewriteExpression(node.NewExpression, stack);
Expression rewrittenNew = result.Node;
RewriteAction action = result.Action;
ReadOnlyCollection<MemberBinding> bindings = node.Bindings;
int count = bindings.Count;
BindingRewriter[] bindingRewriters = new BindingRewriter[count];
for (int i = 0; i < count; i++)
{
MemberBinding binding = bindings[i];
// Bindings run on non-empty stack (the object instance is on it).
BindingRewriter rewriter = BindingRewriter.Create(binding, this, Stack.NonEmpty);
bindingRewriters[i] = rewriter;
action |= rewriter.Action;
}
switch (action)
{
case RewriteAction.None:
break;
case RewriteAction.Copy:
MemberBinding[] newBindings = new MemberBinding[count];
for (int i = 0; i < count; i++)
{
newBindings[i] = bindingRewriters[i].AsBinding();
}
expr = new MemberInitExpression((NewExpression)rewrittenNew, new TrueReadOnlyCollection<MemberBinding>(newBindings));
break;
case RewriteAction.SpillStack:
bool isRefNew = IsRefInstance(node.NewExpression);
var comma = new ArrayBuilder<Expression>(count + 2 + (isRefNew ? 1 : 0));
ParameterExpression tempNew = MakeTemp(rewrittenNew.Type);
comma.UncheckedAdd(new AssignBinaryExpression(tempNew, rewrittenNew));
ParameterExpression refTempNew = tempNew;
if (isRefNew)
{
refTempNew = MakeTemp(tempNew.Type.MakeByRefType());
comma.UncheckedAdd(new ByRefAssignBinaryExpression(refTempNew, tempNew));
}
for (int i = 0; i < count; i++)
{
BindingRewriter cr = bindingRewriters[i];
Expression initExpr = cr.AsExpression(refTempNew);
comma.UncheckedAdd(initExpr);
}
comma.UncheckedAdd(tempNew);
expr = MakeBlock(comma);
break;
default:
throw ContractUtils.Unreachable;
}
return new Result(action, expr);
}
#endregion
#region Statements
private Result RewriteBlockExpression(Expression expr, Stack stack)
{
var node = (BlockExpression)expr;
int count = node.ExpressionCount;
RewriteAction action = RewriteAction.None;
Expression[]? clone = null;
for (int i = 0; i < count; i++)
{
Expression expression = node.GetExpression(i);
// All statements within the block execute at the
// same stack state.
Result rewritten = RewriteExpression(expression, stack);
action |= rewritten.Action;
if (clone == null && rewritten.Action != RewriteAction.None)
{
clone = Clone(node.Expressions, i);
}
if (clone != null)
{
clone[i] = rewritten.Node;
}
}
if (action != RewriteAction.None)
{
// Okay to wrap since we know no one can mutate the clone array.
expr = node.Rewrite(null, clone!);
}
return new Result(action, expr);
}
private Result RewriteLabelExpression(Expression expr, Stack stack)
{
var node = (LabelExpression)expr;
Result expression = RewriteExpression(node.DefaultValue, stack);
if (expression.Action != RewriteAction.None)
{
expr = new LabelExpression(node.Target, expression.Node);
}
return new Result(expression.Action, expr);
}
private Result RewriteLoopExpression(Expression expr, Stack stack)
{
var node = (LoopExpression)expr;
// The loop statement requires empty stack for itself, so it
// can guarantee it to the child nodes.
Result body = RewriteExpression(node.Body, Stack.Empty);
RewriteAction action = body.Action;
// However, the loop itself requires that it executes on an empty stack
// so we need to rewrite if the stack is not empty.
if (stack != Stack.Empty)
{
action = RewriteAction.SpillStack;
}
if (action != RewriteAction.None)
{
expr = new LoopExpression(body.Node, node.BreakLabel, node.ContinueLabel);
}
return new Result(action, expr);
}
// Note: goto does not necessarily need an empty stack. We could always
// emit it as a "leave" which would clear the stack for us. That would
// prevent us from doing certain optimizations we might want to do,
// however, like the switch-case-goto pattern. For now, be conservative.
private Result RewriteGotoExpression(Expression expr, Stack stack)
{
var node = (GotoExpression)expr;
// Goto requires empty stack to execute so the expression is
// going to execute on an empty stack.
Result value = RewriteExpressionFreeTemps(node.Value, Stack.Empty);
// However, the statement itself needs an empty stack for itself
// so if stack is not empty, rewrite to empty the stack.
RewriteAction action = value.Action;
if (stack != Stack.Empty)
{
action = RewriteAction.SpillStack;
}
if (action != RewriteAction.None)
{
expr = Expression.MakeGoto(node.Kind, node.Target, value.Node, node.Type);
}
return new Result(action, expr);
}
private Result RewriteSwitchExpression(Expression expr, Stack stack)
{
var node = (SwitchExpression)expr;
// The switch statement test is emitted on the stack in current state.
Result switchValue = RewriteExpressionFreeTemps(node.SwitchValue, stack);
RewriteAction action = switchValue.Action;
ReadOnlyCollection<SwitchCase> cases = node.Cases;
SwitchCase[]? clone = null;
for (int i = 0; i < cases.Count; i++)
{
SwitchCase @case = cases[i];
Expression[]? cloneTests = null;
ReadOnlyCollection<Expression> testValues = @case.TestValues;
for (int j = 0; j < testValues.Count; j++)
{
// All tests execute at the same stack state as the switch.
// This is guaranteed by the compiler (to simplify spilling).
Result test = RewriteExpression(testValues[j], stack);
action |= test.Action;
if (cloneTests == null && test.Action != RewriteAction.None)
{
cloneTests = Clone(testValues, j);
}
if (cloneTests != null)
{
cloneTests[j] = test.Node;
}
}
// And all the cases also run on the same stack level.
Result body = RewriteExpression(@case.Body, stack);
action |= body.Action;
if (body.Action != RewriteAction.None || cloneTests != null)
{
if (cloneTests != null)
{
testValues = new ReadOnlyCollection<Expression>(cloneTests);
}
@case = new SwitchCase(body.Node, testValues);
clone ??= Clone(cases, i);
}
if (clone != null)
{
clone[i] = @case;
}
}
// default body also runs on initial stack
Result defaultBody = RewriteExpression(node.DefaultBody, stack);
action |= defaultBody.Action;
if (action != RewriteAction.None)
{
if (clone != null)
{
// okay to wrap because we aren't modifying the array
cases = new ReadOnlyCollection<SwitchCase>(clone);
}
expr = new SwitchExpression(node.Type, switchValue.Node, defaultBody.Node, node.Comparison, cases);
}
return new Result(action, expr);
}
private Result RewriteTryExpression(Expression expr, Stack stack)
{
var node = (TryExpression)expr;
// Try statement definitely needs an empty stack so its
// child nodes execute at empty stack.
Result body = RewriteExpression(node.Body, Stack.Empty);
ReadOnlyCollection<CatchBlock> handlers = node.Handlers;
CatchBlock[]? clone = null;
RewriteAction action = body.Action;
if (handlers != null)
{
for (int i = 0; i < handlers.Count; i++)
{
RewriteAction curAction = body.Action;
CatchBlock handler = handlers[i];
Expression? filter = handler.Filter;
if (handler.Filter != null)
{
// Our code gen saves the incoming filter value and provides it as a variable so the stack is empty
Result rfault = RewriteExpression(handler.Filter, Stack.Empty);
action |= rfault.Action;
curAction |= rfault.Action;
filter = rfault.Node;
}
// Catch block starts with an empty stack (guaranteed by TryStatement).
Result rbody = RewriteExpression(handler.Body, Stack.Empty);
action |= rbody.Action;
curAction |= rbody.Action;
if (curAction != RewriteAction.None)
{
handler = Expression.MakeCatchBlock(handler.Test, handler.Variable, rbody.Node, filter);
clone ??= Clone(handlers, i);
}
if (clone != null)
{
clone[i] = handler;
}
}
}
Result fault = RewriteExpression(node.Fault, Stack.Empty);
action |= fault.Action;
Result @finally = RewriteExpression(node.Finally, Stack.Empty);
action |= @finally.Action;
// If the stack is initially not empty, rewrite to spill the stack
if (stack != Stack.Empty)
{
action = RewriteAction.SpillStack;
}
if (action != RewriteAction.None)
{
if (clone != null)
{
// Okay to wrap because we aren't modifying the array.
handlers = new ReadOnlyCollection<CatchBlock>(clone);
}
expr = new TryExpression(node.Type, body.Node, @finally.Node, fault.Node, handlers!);
}
return new Result(action, expr);
}
private Result RewriteExtensionExpression(Expression expr, Stack stack)
{
Result result = RewriteExpression(expr.ReduceExtensions(), stack);
// it's at least Copy because we reduced the node
return new Result(result.Action | RewriteAction.Copy, result.Node);
}
#endregion
#region Cloning
/// <summary>
/// Will clone an IList into an array of the same size, and copy
/// all values up to (and NOT including) the max index.
/// </summary>
/// <returns>The cloned array.</returns>
private static T[] Clone<T>(ReadOnlyCollection<T> original, int max)
{
Debug.Assert(original != null);
Debug.Assert(max < original.Count);
T[] clone = new T[original.Count];
for (int j = 0; j < max; j++)
{
clone[j] = original[j];
}
return clone;
}
#endregion
/// <summary>
/// If we are spilling, requires that there are no byref arguments to
/// the method call.
///
/// Used for:
/// DynamicExpression,
/// UnaryExpression,
/// BinaryExpression.
/// </summary>
/// <remarks>
/// We could support this if spilling happened later in the compiler.
/// Other expressions that can emit calls with arguments (such as
/// ListInitExpression and IndexExpression) don't allow byref arguments.
/// </remarks>
private static void RequireNoRefArgs(MethodBase? method)
{
if (method != null && method.GetParametersCached().Any(p => p.ParameterType.IsByRef))
{
throw Error.TryNotSupportedForMethodsWithRefArgs(method);
}
}
/// <summary>
/// Requires that the instance is not a value type (primitive types are
/// okay because they're immutable).
///
/// Used for:
/// MemberExpression (for properties).
/// </summary>
/// <remarks>
/// We could support this if spilling happened later in the compiler.
/// </remarks>
private static void RequireNotRefInstance(Expression? instance)
{
if (IsRefInstance(instance))
{
throw Error.TryNotSupportedForValueTypeInstances(instance.Type);
}
}
private static bool IsRefInstance([NotNullWhen(true)] Expression? instance)
{
// Primitive value types are okay because they are all read-only,
// but we can't rely on this for non-primitive types. So we have
// to either throw NotSupported or use ref locals.
return instance != null && instance.Type.IsValueType && instance.Type.GetTypeCode() == TypeCode.Object;
}
}
}
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