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//-----------------------------------------------------------------------------
//
// Copyright (C) Microsoft Corporation. All Rights Reserved.
//
//-----------------------------------------------------------------------------
using System.Diagnostics.Contracts;
namespace Microsoft.AbstractInterpretationFramework {
using System.Collections;
using System.Diagnostics;
//using System.Compiler.Analysis;
public class NullnessLattice : MicroLattice {
readonly INullnessFactory/*!*/ factory;
[ContractInvariantMethod]
void ObjectInvariant() {
Contract.Invariant(factory != null);
}
public NullnessLattice(INullnessFactory/*!*/ factory) {
Contract.Requires(factory != null);
this.factory = factory;
// base();
}
enum Value {
Bottom,
NotNull,
Null,
MayBeNull
}
private class Elt : Element {
public Value value;
public Elt(Value v) {
this.value = v;
}
[Pure]
public override System.Collections.Generic.ICollection<IVariable/*!*/>/*!*/ FreeVariables() {
Contract.Ensures(cce.NonNullElements(Contract.Result<System.Collections.Generic.ICollection<IVariable>>()));
return cce.NonNull(new System.Collections.Generic.List<IVariable/*!*/>()).AsReadOnly();
}
public override Element/*!*/ Clone() {
Contract.Ensures(Contract.Result<Element>() != null);
return new Elt(this.value);
}
}
public override Element/*!*/ Top {
get {
Contract.Ensures(Contract.Result<Element>() != null);
return new Elt(Value.MayBeNull);
}
}
public override Element/*!*/ Bottom {
get {
Contract.Ensures(Contract.Result<Element>() != null);
return new Elt(Value.Bottom);
}
}
public static Element/*!*/ Null {
get {
Contract.Ensures(Contract.Result<Element>() != null);
return new Elt(Value.Null);
}
}
public static Element/*!*/ NotNull {
get {
Contract.Ensures(Contract.Result<Element>() != null);
return new Elt(Value.NotNull);
}
}
public override bool IsTop(Element/*!*/ element) {
//Contract.Requires(element != null);
Elt e = (Elt)element;
return e.value == Value.MayBeNull;
}
public override bool IsBottom(Element/*!*/ element) {
//Contract.Requires(element != null);
Elt e = (Elt)element;
return e.value == Value.Bottom;
}
public override Lattice.Element/*!*/ NontrivialJoin(Element/*!*/ first, Element/*!*/ second) {
//Contract.Requires(second != null);
//Contract.Requires(first != null);
Contract.Ensures(Contract.Result<Lattice.Element>() != null);
Elt a = (Elt)first;
Elt b = (Elt)second;
return (a.value == b.value) ? a : (Elt)Top;
}
public override Lattice.Element/*!*/ NontrivialMeet(Element/*!*/ first, Element/*!*/ second) {
//Contract.Requires(second != null);
//Contract.Requires(first != null);
Contract.Ensures(Contract.Result<Lattice.Element>() != null);
Elt a = (Elt)first;
Elt b = (Elt)second;
return (a.value == b.value) ? a : (Elt)Bottom;
}
public override Element/*!*/ Widen(Element/*!*/ first, Element/*!*/ second) {
//Contract.Requires(second != null);
//Contract.Requires(first != null);
Contract.Ensures(Contract.Result<Element>() != null);
return Join(first, second);
}
protected override bool AtMost(Element/*!*/ first, Element/*!*/ second) // this <= that
{
//Contract.Requires(first != null);
//Contract.Requires(second != null);
Elt a = (Elt)first;
Elt b = (Elt)second;
return a.value == b.value;
}
public override IExpr/*!*/ ToPredicate(IVariable/*!*/ var, Element/*!*/ element) {
//Contract.Requires(element != null);
//Contract.Requires(var != null);
Contract.Ensures(Contract.Result<IExpr>() != null);
Elt e = (Elt)element;
if (e.value == Value.NotNull) {
return factory.Neq(var, factory.Null);
}
if (e.value == Value.Null) {
return factory.Eq(var, factory.Null);
}
{
Contract.Assert(false);
throw new cce.UnreachableException();
}
throw new System.Exception();
}
public override IExpr GetFoldExpr(Element/*!*/ e) {
//Contract.Requires(e != null);
Elt elt = (Elt)e;
if (elt.value == Value.Null) {
return factory.Null;
} else {
// can't fold into an expression
return null;
}
}
public override bool Understands(IFunctionSymbol/*!*/ f, IList/*<IExpr!>*//*!*/ args) {
//Contract.Requires(args != null);
//Contract.Requires(f != null);
if (f.Equals(Microsoft.AbstractInterpretationFramework.Value.Eq) ||
f.Equals(Microsoft.AbstractInterpretationFramework.Value.Neq)) {
Contract.Assert(args.Count == 2);
IExpr/*!*/ arg0 = (IExpr/*!*/)cce.NonNull(args[0]);
IExpr/*!*/ arg1 = (IExpr/*!*/)cce.NonNull(args[1]);
// Look for "x OP null" or "null OP x" where OP is "==" or "!=".
if (arg0 is IVariable && arg1 is IFunApp && ((IFunApp)arg1).FunctionSymbol == Ref.Null) {
return true;
} else if (arg1 is IVariable && arg0 is IFunApp && ((IFunApp)arg0).FunctionSymbol == Ref.Null) {
return true;
}
}
return false;
}
public override Element/*!*/ EvaluatePredicate(IExpr/*!*/ e) {
//Contract.Requires(e != null);
Contract.Ensures(Contract.Result<Element>() != null);
IFunApp nary = e as IFunApp;
if (nary != null) {
bool isEq = nary.FunctionSymbol.Equals(Microsoft.AbstractInterpretationFramework.Value.Eq);
if (isEq || nary.FunctionSymbol.Equals(Microsoft.AbstractInterpretationFramework.Value.Neq)) {
IList/*<IExpr!>*//*!*/ args = nary.Arguments;
Contract.Assert(args != null);
Contract.Assert(args.Count == 2);
IExpr/*!*/ arg0 = (IExpr/*!*/)cce.NonNull(args[0]);
IExpr/*!*/ arg1 = (IExpr/*!*/)cce.NonNull(args[1]);
// Look for "x OP null" or "null OP x" where OP is "==" or "!=".
IVariable var = null;
if (arg0 is IVariable && arg1 is IFunApp && ((IFunApp)arg1).FunctionSymbol == Ref.Null) {
var = (IVariable)arg0;
} else if (arg1 is IVariable && arg0 is IFunApp && ((IFunApp)arg0).FunctionSymbol == Ref.Null) {
var = (IVariable)arg1;
}
if (var != null) // found the pattern
{
return isEq ? Null : NotNull;
}
}
}
return Top;
}
}
#if false
public class NullnessMicroLattice : MicroLattice
{
public override MicroLatticeElement Top { get { return NullnessLatticeElement.Top; } }
public override MicroLatticeElement Bottom { get { return NullnessLatticeElement.Bottom; } }
public override MicroLatticeElement EvaluateExpression (Expr e, LookupValue lookup)
{
if (e is LiteralExpr && ((LiteralExpr)e).Val == null)
{
return NullnessLatticeElement.Null;
}
return Top;
}
public override MicroLatticeElement EvaluatePredicate (Expr e, LookupValue lookup)
{
NAryExpr nary = e as NAryExpr;
if (nary != null &&
(nary.Fun.FunctionName.Equals("==") || nary.Fun.FunctionName.Equals("!=")))
{
Debug.Assert(nary.Args.Length == 2);
Expr arg0 = nary.Args[0], arg1 = nary.Args[1];
Variable var = null;
// Look for "x OP null" or "null OP x" where OP is "==" or "!=".
if (arg0 is IdentifierExpr && arg1 is LiteralExpr && ((LiteralExpr)arg1).Val == null)
{
var = ((IdentifierExpr)arg0).Decl;
}
else if (arg1 is IdentifierExpr && arg0 is LiteralExpr && ((LiteralExpr)arg0).Val == null)
{
var = ((IdentifierExpr)arg1).Decl;
}
if (var != null) // found the pattern
{
return nary.Fun.FunctionName.Equals("==") ?
NullnessLatticeElement.Null :
NullnessLatticeElement.NotNull;
}
}
return Top;
}
}
#endif
}
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