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*
* Copyright (c) Microsoft Corporation.
*
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* copy of the license can be found in the License.html file at the root of this distribution. If
* you cannot locate the Microsoft Public License, 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 Microsoft Public License.
*
* You must not remove this notice, or any other, from this software.
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* ***************************************************************************/
using System;
using System.Collections.Generic;
using System.Collections.ObjectModel;
using System.Diagnostics;
using System.Dynamic.Utils;
using System.Reflection;
using System.Runtime.CompilerServices;
#if SILVERLIGHT
using System.Core;
#endif
#if CLR2
namespace Microsoft.Scripting.Ast.Compiler{
#else
namespace System.Linq.Expressions.Compiler {
#endif
/// <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 partial class StackSpiller {
// Is the evaluation stack empty?
private enum Stack {
Empty,
NonEmpty
};
// Should the parent nodes be rewritten, and in what way?
// Designed so bitwise-or produces the correct result when merging two
// subtrees. In particular, SpillStack is preferred over Copy which is
// preferred over None.
//
// Values:
// None -> no rewrite needed
// Copy -> copy into a new node
// SpillStack -> spill stack into temps
[Flags]
private enum RewriteAction {
None = 0,
Copy = 1,
SpillStack = 3,
}
// Result of a rewrite operation. Always contains an action and a node.
private struct Result {
internal readonly RewriteAction Action;
internal readonly Expression Node;
internal Result(RewriteAction action, Expression node) {
Action = action;
Node = node;
}
}
/// <summary>
/// The source of temporary variables
/// </summary>
private readonly TempMaker _tm = new TempMaker();
/// <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 guarentee 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
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
// (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, newBody);
}
// Clone the lambda, replacing the body & variables
return new Expression<T>(newBody, lambda.Name, lambda.TailCall, lambda.Parameters);
}
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;
}
// DynamicExpression
[System.Diagnostics.CodeAnalysis.SuppressMessage("Microsoft.Usage", "CA1801:ReviewUnusedParameters", MessageId = "stack")]
private Result RewriteDynamicExpression(Expression expr, Stack stack) {
var node = (DynamicExpression)expr;
// CallSite is on the stack
IArgumentProvider argNode = (IArgumentProvider)node;
ChildRewriter cr = new ChildRewriter(this, Stack.NonEmpty, argNode.ArgumentCount);
cr.AddArguments(argNode);
if (cr.Action == RewriteAction.SpillStack) {
RequireNoRefArgs(node.DelegateType.GetMethod("Invoke"));
}
return cr.Finish(cr.Rewrite ? node.Rewrite(cr[0, -1]) : expr);
}
private Result RewriteIndexAssignment(BinaryExpression node, Stack stack) {
IndexExpression index = (IndexExpression)node.Left;
ChildRewriter cr = new ChildRewriter(this, stack, 2 + index.Arguments.Count);
cr.Add(index.Object);
cr.Add(index.Arguments);
cr.Add(node.Right);
if (cr.Action == RewriteAction.SpillStack) {
RequireNotRefInstance(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) {
BinaryExpression 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);
}
// BinaryExpression
private Result RewriteBinaryExpression(Expression expr, Stack stack) {
BinaryExpression node = (BinaryExpression)expr;
ChildRewriter 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);
}
// variable assignment
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 = Expression.Assign(node.Left, right.Node);
}
return new Result(right.Action, node);
}
private Result RewriteAssignBinaryExpression(Expression expr, Stack stack) {
var node = (BinaryExpression)expr;
switch (node.Left.NodeType) {
case ExpressionType.Index:
return RewriteIndexAssignment(node, stack);
case ExpressionType.MemberAccess:
return RewriteMemberAssignment(node, stack);
case ExpressionType.Parameter:
return RewriteVariableAssignment(node, stack);
case ExpressionType.Extension:
return RewriteExtensionAssignment(node, stack);
default:
throw Error.InvalidLvalue(node.Left.NodeType);
}
}
private Result RewriteExtensionAssignment(BinaryExpression node, Stack stack) {
node = Expression.Assign(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);
}
// LambdaExpression
[System.Diagnostics.CodeAnalysis.SuppressMessage("Microsoft.Usage", "CA1801:ReviewUnusedParameters", MessageId = "stack")]
private static Result RewriteLambdaExpression(Expression expr, Stack stack) {
LambdaExpression 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);
}
// ConditionalExpression
private Result RewriteConditionalExpression(Expression expr, Stack stack) {
ConditionalExpression 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 = Expression.Condition(test.Node, ifTrue.Node, ifFalse.Node, node.Type);
}
return new Result(action, expr);
}
// member assignment
private Result RewriteMemberAssignment(BinaryExpression node, Stack stack) {
MemberExpression lvalue = (MemberExpression)node.Left;
ChildRewriter 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 unchaged.
cr.Add(lvalue.Expression);
cr.Add(node.Right);
if (cr.Action == RewriteAction.SpillStack) {
RequireNotRefInstance(lvalue.Expression);
}
if (cr.Rewrite) {
return cr.Finish(
new AssignBinaryExpression(
MemberExpression.Make(cr[0], lvalue.Member),
cr[1]
)
);
}
return new Result(RewriteAction.None, node);
}
// MemberExpression
private Result RewriteMemberExpression(Expression expr, Stack stack) {
MemberExpression 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.MemberType == MemberTypes.Property) {
// Only need to validate propreties 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);
}
//RewriteIndexExpression
private Result RewriteIndexExpression(Expression expr, Stack stack) {
IndexExpression node = (IndexExpression)expr;
ChildRewriter cr = new ChildRewriter(this, stack, node.Arguments.Count + 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.Add(node.Arguments);
if (cr.Action == RewriteAction.SpillStack) {
RequireNotRefInstance(node.Object);
}
if (cr.Rewrite) {
expr = new IndexExpression(
cr[0],
node.Indexer,
cr[1, -1]
);
}
return cr.Finish(expr);
}
// MethodCallExpression
private Result RewriteMethodCallExpression(Expression expr, Stack stack) {
MethodCallExpression node = (MethodCallExpression)expr;
ChildRewriter cr = new ChildRewriter(this, stack, node.Arguments.Count + 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) {
RequireNotRefInstance(node.Object);
RequireNoRefArgs(node.Method);
}
return cr.Finish(cr.Rewrite ? node.Rewrite(cr[0], cr[1, -1]) : expr);
}
// NewArrayExpression
private Result RewriteNewArrayExpression(Expression expr, Stack stack) {
NewArrayExpression 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.
}
ChildRewriter cr = new ChildRewriter(this, stack, node.Expressions.Count);
cr.Add(node.Expressions);
if (cr.Rewrite) {
Type element = node.Type.GetElementType();
if (node.NodeType == ExpressionType.NewArrayInit) {
expr = Expression.NewArrayInit(element, cr[0, -1]);
} else {
expr = Expression.NewArrayBounds(element, cr[0, -1]);
}
}
return cr.Finish(expr);
}
// InvocationExpression
private Result RewriteInvocationExpression(Expression expr, Stack stack) {
InvocationExpression 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.Arguments.Count);
cr.Add(node.Arguments);
if (cr.Action == RewriteAction.SpillStack) {
RequireNoRefArgs(Expression.GetInvokeMethod(node.Expression));
}
// 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 InvocationExpression(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.Arguments.Count + 1);
// first argument starts on stack as provided
cr.Add(node.Expression);
// rest of arguments have non-empty stack (delegate instance on the stack)
cr.Add(node.Arguments);
if (cr.Action == RewriteAction.SpillStack) {
RequireNoRefArgs(Expression.GetInvokeMethod(node.Expression));
}
return cr.Finish(cr.Rewrite ? new InvocationExpression(cr[0], cr[1, -1], node.Type) : expr);
}
// NewExpression
private Result RewriteNewExpression(Expression expr, Stack stack) {
NewExpression node = (NewExpression)expr;
// The first expression starts on a stack as provided by parent,
// rest are definitely non-emtpy (which ChildRewriter guarantees)
ChildRewriter cr = new ChildRewriter(this, stack, node.Arguments.Count);
cr.AddArguments(node);
if (cr.Action == RewriteAction.SpillStack) {
RequireNoRefArgs(node.Constructor);
}
return cr.Finish(cr.Rewrite ? new NewExpression(node.Constructor, cr[0, -1], node.Members) : expr);
}
// TypeBinaryExpression
private Result RewriteTypeBinaryExpression(Expression expr, Stack stack) {
TypeBinaryExpression node = (TypeBinaryExpression)expr;
// The expression is emitted on top of current stack
Result expression = RewriteExpression(node.Expression, stack);
if (expression.Action != RewriteAction.None) {
if (node.NodeType == ExpressionType.TypeIs) {
expr = Expression.TypeIs(expression.Node, node.TypeOperand);
} else {
expr = Expression.TypeEqual(expression.Node, node.TypeOperand);
}
}
return new Result(expression.Action, expr);
}
// Throw
private Result RewriteThrowUnaryExpression(Expression expr, Stack stack) {
UnaryExpression node = (UnaryExpression)expr;
// Throw statement itself does not care about the stack
// but it will empty the stack and it may cause stack misbalance
// 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 = Expression.Throw(value.Node, node.Type);
}
return new Result(action, expr);
}
// UnaryExpression
private Result RewriteUnaryExpression(Expression expr, Stack stack) {
UnaryExpression 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);
}
// RewriteListInitExpression
private Result RewriteListInitExpression(Expression expr, Stack stack) {
ListInitExpression node = (ListInitExpression)expr;
//ctor runs on initial stack
Result newResult = RewriteExpression(node.NewExpression, stack);
Expression rewrittenNew = newResult.Node;
RewriteAction action = newResult.Action;
ReadOnlyCollection<ElementInit> inits = node.Initializers;
ChildRewriter[] cloneCrs = new ChildRewriter[inits.Count];
for (int i = 0; i < inits.Count; i++) {
ElementInit init = inits[i];
//initializers all run on nonempty stack
ChildRewriter 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[inits.Count];
for (int i = 0; i < inits.Count; i++) {
ChildRewriter cr = cloneCrs[i];
if (cr.Action == RewriteAction.None) {
newInits[i] = inits[i];
} else {
newInits[i] = Expression.ElementInit(inits[i].AddMethod, cr[0, -1]);
}
}
expr = Expression.ListInit((NewExpression)rewrittenNew, new TrueReadOnlyCollection<ElementInit>(newInits));
break;
case RewriteAction.SpillStack:
RequireNotRefInstance(node.NewExpression);
ParameterExpression tempNew = MakeTemp(rewrittenNew.Type);
Expression[] comma = new Expression[inits.Count + 2];
comma[0] = Expression.Assign(tempNew, rewrittenNew);
for (int i = 0; i < inits.Count; i++) {
ChildRewriter cr = cloneCrs[i];
Result add = cr.Finish(Expression.Call(tempNew, inits[i].AddMethod, cr[0, -1]));
comma[i + 1] = add.Node;
}
comma[inits.Count + 1] = tempNew;
expr = MakeBlock(comma);
break;
default:
throw ContractUtils.Unreachable;
}
return new Result(action, expr);
}
// RewriteMemberInitExpression
private Result RewriteMemberInitExpression(Expression expr, Stack stack) {
MemberInitExpression node = (MemberInitExpression)expr;
//ctor runs on original stack
Result result = RewriteExpression(node.NewExpression, stack);
Expression rewrittenNew = result.Node;
RewriteAction action = result.Action;
ReadOnlyCollection<MemberBinding> bindings = node.Bindings;
BindingRewriter[] bindingRewriters = new BindingRewriter[bindings.Count];
for (int i = 0; i < bindings.Count; i++) {
MemberBinding binding = bindings[i];
//bindings run on nonempty stack
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[bindings.Count];
for (int i = 0; i < bindings.Count; i++) {
newBindings[i] = bindingRewriters[i].AsBinding();
}
expr = Expression.MemberInit((NewExpression)rewrittenNew, new TrueReadOnlyCollection<MemberBinding>(newBindings));
break;
case RewriteAction.SpillStack:
RequireNotRefInstance(node.NewExpression);
ParameterExpression tempNew = MakeTemp(rewrittenNew.Type);
Expression[] comma = new Expression[bindings.Count + 2];
comma[0] = Expression.Assign(tempNew, rewrittenNew);
for (int i = 0; i < bindings.Count; i++) {
BindingRewriter cr = bindingRewriters[i];
Expression initExpr = cr.AsExpression(tempNew);
comma[i + 1] = initExpr;
}
comma[bindings.Count + 1] = tempNew;
expr = MakeBlock(comma);
break;
default:
throw ContractUtils.Unreachable;
}
return new Result(action, expr);
}
#endregion
#region Statements
// Block
private Result RewriteBlockExpression(Expression expr, Stack stack) {
BlockExpression 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);
}
// LabelExpression
private Result RewriteLabelExpression(Expression expr, Stack stack) {
LabelExpression node = (LabelExpression)expr;
Result expression = RewriteExpression(node.DefaultValue, stack);
if (expression.Action != RewriteAction.None) {
expr = Expression.Label(node.Target, expression.Node);
}
return new Result(expression.Action, expr);
}
// LoopStatement
private Result RewriteLoopExpression(Expression expr, Stack stack) {
LoopExpression 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);
}
// GotoExpression
// 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) {
GotoExpression 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);
}
// SwitchStatement
private Result RewriteSwitchExpression(Expression expr, Stack stack) {
SwitchExpression 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 guarenteed 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);
if (clone == null) {
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);
}
// TryStatement
private Result RewriteTryExpression(Expression expr, Stack stack) {
TryExpression 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 varaible 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);
if (clone == null) {
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 vaues 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:
/// NewExpression,
/// MethodCallExpression,
/// InvocationExpression,
/// 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:
/// MethodCallExpression,
/// MemberExpression (for properties),
/// IndexExpression,
/// ListInitExpression,
/// MemberInitExpression,
/// assign to MemberExpression,
/// assign to IndexExpression.
/// </summary>
/// <remarks>
/// We could support this if spilling happened later in the compiler.
/// </remarks>
private static void RequireNotRefInstance(Expression instance) {
// Primitive value types are okay because they are all readonly,
// but we can't rely on this for non-primitive types. So we throw
// NotSupported.
if (instance != null && instance.Type.IsValueType && Type.GetTypeCode(instance.Type) == TypeCode.Object) {
throw Error.TryNotSupportedForValueTypeInstances(instance.Type);
}
}
}
}
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