protected bool IsCopyAlwaysUnnecessaryForAssignmentTarget(JSExpression target)
{
target = JSReferenceExpression.Strip(target);
var targetDot = target as JSDotExpressionBase;
// The assignment is performing a write into an element proxy, so a copy is unnecessary
// because the element proxy immediately unpacks the value into the array.
if ((targetDot != null) && PackedArrayUtil.IsElementProxy(targetDot.Target))
{
return(true);
}
return(false);
}
public void VisitNode(JSNewBoxedVariable nbv)
{
GenericParameter relevantParameter;
var initialValue = nbv.InitialValue;
var initialValueDerefed = initialValue;
initialValueDerefed = JSReferenceExpression.Strip(initialValueDerefed);
var initialValueType = initialValueDerefed.GetActualType(TypeSystem);
if (!nbv.SuppressClone &&
IsCopyNeeded(nbv.InitialValue, out relevantParameter) &&
// We don't need to make a copy if the source value is a reference (like T& this)
!((initialValueType) != null && initialValueType.IsByReference)
)
{
nbv.ReplaceChild(nbv.InitialValue, new JSStructCopyExpression(nbv.InitialValue));
}
VisitChildren(nbv);
}
protected bool IsCopyNeededForAssignmentTarget(JSExpression target)
{
target = JSReferenceExpression.Strip(target);
if (!OptimizeCopies)
{
return(true);
}
if (IsImmutable(target))
{
return(false);
}
var variable = target as JSVariable;
if (variable != null)
{
return(SecondPass.IsVariableModified(variable.Name));
}
return(true);
}
protected bool IsImmutable(JSExpression target)
{
target = JSReferenceExpression.Strip(target);
var fieldAccess = target as JSFieldAccess;
if (fieldAccess != null)
{
return(fieldAccess.Field.Field.Metadata.HasAttribute("JSIL.Meta.JSImmutable"));
}
var dot = target as JSDotExpressionBase;
if (dot != null)
{
if (IsImmutable(dot.Target))
{
return(true);
}
else if (IsImmutable(dot.Member))
{
return(true);
}
}
var indexer = target as JSIndexerExpression;
if (indexer != null)
{
if (IsImmutable(indexer.Target))
{
return(true);
}
}
return(false);
}
protected bool IsCopyNeeded(
JSExpression value,
out GenericParameter relevantParameter,
bool allowImmutabilityOptimizations = true
)
{
relevantParameter = null;
if ((value == null) || (value.IsNull))
{
return(false);
}
value = JSReferenceExpression.Strip(value);
var sce = value as JSStructCopyExpression;
if (sce != null)
{
return(false);
}
var valueType = value.GetActualType(TypeSystem);
var valueTypeDerefed = TypeUtil.DereferenceType(valueType) ?? valueType;
var cte = value as JSChangeTypeExpression;
var cast = value as JSCastExpression;
TypeReference originalType;
int temp;
if (cte != null)
{
originalType = cte.Expression.GetActualType(TypeSystem);
}
else if (cast != null)
{
originalType = cast.Expression.GetActualType(TypeSystem);
}
else
{
originalType = null;
}
if (originalType != null)
{
originalType = TypeUtil.FullyDereferenceType(originalType, out temp);
if (!IsStructOrGenericParameter(valueTypeDerefed) && !IsStructOrGenericParameter(originalType))
{
return(false);
}
relevantParameter = (originalType as GenericParameter) ?? (valueTypeDerefed as GenericParameter);
}
else
{
if (!IsStructOrGenericParameter(valueTypeDerefed))
{
return(false);
}
relevantParameter = (valueTypeDerefed as GenericParameter);
}
if (value is JSValueOfNullableExpression)
{
return(true);
}
if (IsTypeExcludedFromCopies(valueType))
{
return(false);
}
if (
(value is JSLiteral) ||
(value is JSNewExpression) ||
(value is JSPassByReferenceExpression) ||
(value is JSNewBoxedVariable) ||
(value is JSDefaultValueLiteral) ||
(value is JSFieldOfExpression)
)
{
return(false);
}
if (!OptimizeCopies)
{
return(true);
}
if (IsImmutable(value) && allowImmutabilityOptimizations)
{
return(false);
}
var valueDot = value as JSDotExpressionBase;
// The value is being read out of an element proxy, so no copy is necessary - the read unpacks the value
// on demand from the packed array.
if (
(valueDot != null) &&
PackedArrayUtil.IsElementProxy(valueDot.Target)
)
{
// return false;
}
var valueTypeInfo = TypeInfo.GetExisting(valueType);
if ((valueTypeInfo != null) && valueTypeInfo.IsImmutable && allowImmutabilityOptimizations)
{
return(false);
}
// If the expression is a parameter that is only used once and isn't aliased,
// we don't need to copy it.
var rightVar = value as JSVariable;
if (rightVar != null)
{
int referenceCount;
if (
ReferenceCounts.TryGetValue(rightVar.Identifier, out referenceCount) &&
(referenceCount == 1) &&
!rightVar.IsReference &&
rightVar.IsParameter &&
!SecondPass.VariableAliases.ContainsKey(rightVar.Identifier)
)
{
if (TraceElidedCopies)
{
Console.WriteLine(String.Format("Returning false from IsCopyNeeded for parameter {0} because reference count is 1 and it has no aliases", value));
}
return(false);
}
}
return(true);
}
