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//-----------------------------------------------------------------------------
//
// Copyright (C) Microsoft Corporation. All Rights Reserved.
//
//-----------------------------------------------------------------------------
using Microsoft.Contracts;
namespace Microsoft.AbstractInterpretationFramework
{
using System.Collections;
using System.Diagnostics;
using System.Compiler.Analysis;
public class NullnessLattice : MicroLattice
{
readonly INullnessFactory! factory;
public NullnessLattice(INullnessFactory! factory) {
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()
{
return (!) (new System.Collections.Generic.List<IVariable!>()).AsReadOnly();
}
public override Element! Clone()
{
return new Elt(this.value);
}
}
public override Element! Top
{
get { return new Elt(Value.MayBeNull); }
}
public override Element! Bottom
{
get { return new Elt(Value.Bottom); }
}
public static Element! Null
{
get { return new Elt(Value.Null); }
}
public static Element! NotNull
{
get { return new Elt(Value.NotNull); }
}
public override bool IsTop (Element! element)
{
Elt e = (Elt) element;
return e.value == Value.MayBeNull;
}
public override bool IsBottom (Element! element)
{
Elt e = (Elt) element;
return e.value == Value.Bottom;
}
public override Lattice.Element! NontrivialJoin (Element! first, Element! second)
{
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)
{
Elt a = (Elt) first;
Elt b = (Elt) second;
return (a.value == b.value) ? a : (Elt)Bottom;
}
public override Element! Widen (Element! first, Element! second)
{
return Join(first,second);
}
protected override bool AtMost (Element! first, Element! second) // this <= that
{
Elt a = (Elt) first;
Elt b = (Elt) second;
return a.value == b.value;
}
public override IExpr! ToPredicate(IVariable! var, Element! element) {
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);
}
assert false;
throw new System.Exception();
}
public override IExpr GetFoldExpr(Element! e) {
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) {
if (f.Equals(Microsoft.AbstractInterpretationFramework.Value.Eq) ||
f.Equals(Microsoft.AbstractInterpretationFramework.Value.Neq)) {
assert args.Count == 2;
IExpr! arg0 = (IExpr!)args[0];
IExpr! arg1 = (IExpr!)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) {
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;
assert args.Count == 2;
IExpr! arg0 = (IExpr!)args[0];
IExpr! arg1 = (IExpr!)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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