Add the ability to declare Expr to be immutable at construction time.

This is currently not enforced (it really should be). So right now it
only amounts to a promise by the client that the Expr will not be modified
after it is constructed. We should actually enforce this by protecting
various fields of the Expr classes so they can't be changed if an Expr
is constructed as Immutable.

The motivation for doing this is it allows the value of GetHashCode()
to be cached. Expr classes now implement ComputeHashCode() to do the
actuall hash code computation.

1 files changed, 168 insertions, 32 deletions

diff --git a/Source/Core/AbsyExpr.cs b/Source/Core/AbsyExpr.cs
index 4a7db752..7b4900f2 100644
--- a/Source/Core/AbsyExpr.cs
+++ b/Source/Core/AbsyExpr.cs
@@ -31,9 +31,10 @@ namespace Microsoft.Boogie {
 

   [ContractClass(typeof(ExprContracts))]

   public abstract class Expr : Absy {

-    public Expr(IToken/*!*/ tok)

+    public Expr(IToken/*!*/ tok, bool immutable)

       : base(tok) {

       Contract.Requires(tok != null);

+      this.Immutable = immutable;

     }

 

     public void Emit(TokenTextWriter stream) {

@@ -41,6 +42,32 @@ namespace Microsoft.Boogie {
       Emit(stream, 0, false);

     }

 

+    /// <summary>

+    /// If true the client is making a promise that this Expr will be

+    /// treated immutably (i.e. once constructed it is never changed).

+    /// This is currently not enforced but it should be!

+    ///

+    /// This allows the Expr's hash code to be cached making calls to

+    /// GetHashCode() very cheap.

+    /// </summary>

+    /// <value><c>true</c> if immutable; otherwise, <c>false</c>.</value>

+    public bool Immutable {

+      get;

+      private set;

+    }

+

+    /// <summary>

+    /// Computes the hash code of this Expr skipping any cache.

+    ///

+    /// Sub classes should place their implementation of computing their hashcode

+    /// here (making sure to call ComputeHashCode() and not GetHashCode() on Expr)

+    /// and have GetHashCode() use a cached result from ComputeHashCode() if the

+    /// Expr was constructed to be immutable.

+    /// </summary>

+    /// <returns>The hash code.</returns>

+    public abstract int ComputeHashCode();

+    protected int CachedHashCode = 0;

+

     public abstract void Emit(TokenTextWriter/*!*/ wr, int contextBindingStrength, bool fragileContext);

 

     [Pure]

@@ -424,7 +451,7 @@ namespace Microsoft.Boogie {
   }

   [ContractClassFor(typeof(Expr))]

   public abstract class ExprContracts : Expr {

-    public ExprContracts() :base(null){

+    public ExprContracts() :base(null, /*immutable=*/ false){

 

     }

     public override void Emit(TokenTextWriter wr, int contextBindingStrength, bool fragileContext) {

@@ -456,11 +483,13 @@ namespace Microsoft.Boogie {
     /// </summary>

     /// <param name="tok"></param>

     /// <param name="b"></param>

-    public LiteralExpr(IToken/*!*/ tok, bool b)

-      : base(tok) {

+    public LiteralExpr(IToken/*!*/ tok, bool b, bool immutable=false)

+      : base(tok, immutable) {

       Contract.Requires(tok != null);

       Val = b;

       Type = Type.Bool;

+      if (immutable)

+        CachedHashCode = ComputeHashCode();

     }

 

     /// <summary>

@@ -468,11 +497,13 @@ namespace Microsoft.Boogie {
     /// </summary>

     /// <param name="tok"></param>

     /// <param name="v"></param>

-    public LiteralExpr(IToken/*!*/ tok, BigNum v)

-      : base(tok) {

+    public LiteralExpr(IToken/*!*/ tok, BigNum v, bool immutable=false)

+      : base(tok, immutable) {

       Contract.Requires(tok != null);

       Val = v;

       Type = Type.Int;

+      if (immutable)

+        CachedHashCode = ComputeHashCode();

     }

 

     /// <summary>

@@ -480,22 +511,26 @@ namespace Microsoft.Boogie {
     /// </summary>

     /// <param name="tok"></param>

     /// <param name="v"></param>

-    public LiteralExpr(IToken/*!*/ tok, BigDec v)

-      : base(tok) {

+    public LiteralExpr(IToken/*!*/ tok, BigDec v, bool immutable=false)

+      : base(tok, immutable) {

       Contract.Requires(tok != null);

       Val = v;

       Type = Type.Real;

+      if (immutable)

+        CachedHashCode = ComputeHashCode();

     }

 

     /// <summary>

     /// Creates a literal expression for the bitvector value "v".

     /// </summary>

-    public LiteralExpr(IToken/*!*/ tok, BigNum v, int b)

-      : base(tok) {

+    public LiteralExpr(IToken/*!*/ tok, BigNum v, int b, bool immutable=false)

+      : base(tok, immutable) {

       Contract.Requires(tok != null);

       Contract.Requires(0 <= b);

       Val = new BvConst(v, b);

       Type = Type.GetBvType(b);

+      if (immutable)

+        CachedHashCode = ComputeHashCode();

     }

 

     [Pure]

@@ -509,10 +544,20 @@ namespace Microsoft.Boogie {
       LiteralExpr other = (LiteralExpr)obj;

       return object.Equals(this.Val, other.Val);

     }

+

     [Pure]

     public override int GetHashCode() {

+      if (Immutable)

+        return this.CachedHashCode;

+      else

+        return ComputeHashCode();

+    }

+

+    [Pure]

+    public override int ComputeHashCode() {

       return this.Val.GetHashCode();

     }

+

     public override void Emit(TokenTextWriter stream, int contextBindingStrength, bool fragileContext) {

       //Contract.Requires(stream != null);

       stream.SetToken(this);

@@ -686,6 +731,7 @@ namespace Microsoft.Boogie {
   }

 

   public class IdentifierExpr : Expr {

+    // FIXME: Protect these fields

     public string/*!*/ Name;    // identifier symbol

     public Variable Decl;   // identifier declaration

     [ContractInvariantMethod]

@@ -701,11 +747,13 @@ namespace Microsoft.Boogie {
     /// </summary>

     /// <param name="tok"></param>

     /// <param name="name"></param>

-    internal IdentifierExpr(IToken/*!*/ tok, string/*!*/ name)

-      : base(tok) {

+    internal IdentifierExpr(IToken/*!*/ tok, string/*!*/ name, bool immutable=false)

+      : base(tok, immutable) {

       Contract.Requires(tok != null);

       Contract.Requires(name != null);

       Name = name;

+      if (immutable)

+        CachedHashCode = ComputeHashCode();

     }

     /// <summary>

     /// Creates an unresolved identifier expression.

@@ -713,13 +761,15 @@ namespace Microsoft.Boogie {
     /// <param name="tok"></param>

     /// <param name="name"></param>

     /// <param name="type"></param>

-    public IdentifierExpr(IToken/*!*/ tok, string/*!*/ name, Type/*!*/ type)

-      : base(tok) {

+    public IdentifierExpr(IToken/*!*/ tok, string/*!*/ name, Type/*!*/ type, bool immutable=false)

+      : base(tok, immutable) {

       Contract.Requires(tok != null);

       Contract.Requires(name != null);

       Contract.Requires(type != null);

       Name = name;

       Type = type;

+      if (immutable)

+        CachedHashCode = ComputeHashCode();

     }

 

     /// <summary>

@@ -727,13 +777,15 @@ namespace Microsoft.Boogie {
     /// </summary>

     /// <param name="tok"></param>

     /// <param name="d"></param>

-    public IdentifierExpr(IToken/*!*/ tok, Variable/*!*/ d)

-      : base(tok) {

+    public IdentifierExpr(IToken/*!*/ tok, Variable/*!*/ d, bool immutable=false)

+      : base(tok, immutable) {

       Contract.Requires(tok != null);

       Contract.Requires(d != null);

       Name = cce.NonNull(d.Name);

       Decl = d;

       Type = d.TypedIdent.Type;

+      if (immutable)

+        CachedHashCode = ComputeHashCode();

     }

     [Pure]

     [Reads(ReadsAttribute.Reads.Nothing)]

@@ -746,12 +798,22 @@ namespace Microsoft.Boogie {
       IdentifierExpr other = (IdentifierExpr)obj;

       return object.Equals(this.Name, other.Name) && object.Equals(this.Decl, other.Decl);

     }

+

     [Pure]

     public override int GetHashCode() {

+      if (Immutable)

+        return this.CachedHashCode;

+      else

+        return ComputeHashCode();

+    }

+

+    [Pure]

+    public override int ComputeHashCode() {

       int h = this.Name == null ? 0 : this.Name.GetHashCode();

       h ^= this.Decl == null ? 0 : this.Decl.GetHashCode();

       return h;

     }

+

     public override void Emit(TokenTextWriter stream, int contextBindingStrength, bool fragileContext) {

       //Contract.Requires(stream != null);

       if (CommandLineOptions.Clo.PrintWithUniqueASTIds && !stream.UseForComputingChecksums) {

@@ -848,17 +910,20 @@ namespace Microsoft.Boogie {
 

   public class OldExpr : Expr

   {

+    // FIXME: protect this field

     public Expr/*!*/ Expr;

     [ContractInvariantMethod]

     void ObjectInvariant() {

       Contract.Invariant(Expr != null);

     }

 

-    public OldExpr(IToken/*!*/ tok, Expr/*!*/ expr)

-      : base(tok) {

+    public OldExpr(IToken/*!*/ tok, Expr/*!*/ expr, bool immutable=false)

+      : base(tok, immutable) {

       Contract.Requires(tok != null);

       Contract.Requires(expr != null);

       Expr = expr;

+      if (immutable)

+        CachedHashCode = ComputeHashCode();

     }

     [Pure]

     [Reads(ReadsAttribute.Reads.Nothing)]

@@ -873,8 +938,16 @@ namespace Microsoft.Boogie {
     }

     [Pure]

     public override int GetHashCode() {

-      return this.Expr == null ? 0 : this.Expr.GetHashCode();

+      if (Immutable)

+        return this.CachedHashCode;

+      else

+        return ComputeHashCode ();

+    }

+    public override int ComputeHashCode() {

+      // FIXME: This is wrong, it's as if the OldExpr node isn't there at all

+      return this.Expr == null ? 0 : this.Expr.ComputeHashCode();

     }

+

     public override void Emit(TokenTextWriter stream, int contextBindingStrength, bool fragileContext) {

       //Contract.Requires(stream != null);

       stream.Write(this, "old(");

@@ -2110,8 +2183,10 @@ namespace Microsoft.Boogie {
   public class NAryExpr : Expr {

     [Additive]

     [Peer]

+    // FIXME: Protect these fields

     public IAppliable/*!*/ Fun;

-    public List<Expr>/*!*/ Args;

+    public List<Expr> Args;

+

     [ContractInvariantMethod]

     void ObjectInvariant() {

       Contract.Invariant(Fun != null);

@@ -2124,14 +2199,16 @@ namespace Microsoft.Boogie {
     public TypeParamInstantiation TypeParameters = null;

 

     [Captured]

-    public NAryExpr(IToken/*!*/ tok, IAppliable/*!*/ fun, List<Expr>/*!*/ args)

-      : base(tok) {

+    public NAryExpr(IToken/*!*/ tok, IAppliable/*!*/ fun, List<Expr>/*!*/ args, bool immutable=false)

+      : base(tok, immutable) {

       Contract.Requires(tok != null);

       Contract.Requires(fun != null);

       Contract.Requires(args != null);

       Fun = fun;

       Args = args;

       Contract.Assert(Contract.ForAll(0, args.Count, index => args[index] != null));

+      if (immutable)

+        CachedHashCode = ComputeHashCode();

     }

     [Pure]

     [Reads(ReadsAttribute.Reads.Nothing)]

@@ -2144,13 +2221,22 @@ namespace Microsoft.Boogie {
       NAryExpr other = (NAryExpr)obj;

       return object.Equals(this.Fun, other.Fun) && this.Args.SequenceEqual(other.Args);

     }

+    

     [Pure]

     public override int GetHashCode() {

+      if (Immutable)

+        return this.CachedHashCode;

+      else

+        return ComputeHashCode();

+    }

+

+    [Pure]

+    public override int ComputeHashCode() {

       int h = this.Fun.GetHashCode();

       // DO NOT USE Args.GetHashCode() because that uses Object.GetHashCode() which uses references

       // We want structural equality

       foreach (var arg in Args) {

-        h = (97*h) + arg.GetHashCode();

+        h = (97*h) + arg.ComputeHashCode();

       }

       return h;

     }

@@ -2658,15 +2744,39 @@ namespace Microsoft.Boogie {
       Contract.Invariant(cce.NonNullElements(Blocks));

     }

 

-    public CodeExpr(List<Variable>/*!*/ localVariables, List<Block/*!*/>/*!*/ blocks)

-      : base(Token.NoToken) {

+    public CodeExpr(List<Variable>/*!*/ localVariables, List<Block/*!*/>/*!*/ blocks, bool immutable=false)

+      : base(Token.NoToken, immutable) {

       Contract.Requires(localVariables != null);

       Contract.Requires(cce.NonNullElements(blocks));

       Contract.Requires(0 < blocks.Count);

       LocVars = localVariables;

       Blocks = blocks;

+      if (immutable)

+        CachedHashCode = ComputeHashCode();

+    }

+

+    // FIXME: This seems wrong we don't want reference equality, we want structural equality

+    [Pure]

+    public override bool Equals(object obj)

+    {

+      return base.Equals(obj);

+    }

+

+    [Pure]

+    public override int GetHashCode()

+    {

+      if (Immutable)

+        return CachedHashCode;

+      else

+        return ComputeHashCode();

+    }

+

+    [Pure]

+    public override int ComputeHashCode() {

+      return base.GetHashCode();

     }

 

+

     public override void ComputeFreeVariables(Set /*Variable*/ freeVars) {

       //Contract.Requires(freeVars != null);

       // Treat a BlockEexpr as if it has no free variables at all

@@ -2748,6 +2858,7 @@ namespace Microsoft.Boogie {
   }

 

   public class BvExtractExpr : Expr {

+    // FIXME: Protect these fields

     public /*readonly--except in StandardVisitor*/ Expr/*!*/ Bitvector;

     [ContractInvariantMethod]

     void ObjectInvariant() {

@@ -2756,13 +2867,15 @@ namespace Microsoft.Boogie {
 

     public readonly int Start, End;

 

-    public BvExtractExpr(IToken/*!*/ tok, Expr/*!*/ bv, int end, int start)

-      : base(tok) {

+    public BvExtractExpr(IToken/*!*/ tok, Expr/*!*/ bv, int end, int start, bool immutable=false)

+      : base(tok, immutable) {

       Contract.Requires(tok != null);

       Contract.Requires(bv != null);

       Bitvector = bv;

       Start = start;

       End = end;

+      if (immutable)

+        CachedHashCode = ComputeHashCode();

     }

 

     [Pure]

@@ -2777,9 +2890,18 @@ namespace Microsoft.Boogie {
       return object.Equals(this.Bitvector, other.Bitvector) &&

         this.Start.Equals(other.Start) && this.End.Equals(other.End);

     }

+

     [Pure]

     public override int GetHashCode() {

-      int h = this.Bitvector.GetHashCode();

+      if (Immutable)

+        return CachedHashCode;

+      else

+        return ComputeHashCode();

+    }

+    

+    [Pure]

+    public override int ComputeHashCode() {

+      int h = this.Bitvector.ComputeHashCode();

       h ^= Start * 17 ^ End * 13;

       return h;

     }

@@ -2847,6 +2969,7 @@ namespace Microsoft.Boogie {
   }

 

   public class BvConcatExpr : Expr {

+    // FIXME: Protect these fields

     public /*readonly--except in StandardVisitor*/ Expr/*!*/ E0, E1;

     [ContractInvariantMethod]

     void ObjectInvariant() {

@@ -2855,13 +2978,15 @@ namespace Microsoft.Boogie {
     }

 

 

-    public BvConcatExpr(IToken/*!*/ tok, Expr/*!*/ e0, Expr/*!*/ e1)

-      : base(tok) {

+    public BvConcatExpr(IToken/*!*/ tok, Expr/*!*/ e0, Expr/*!*/ e1, bool immutable=false)

+      : base(tok, immutable) {

       Contract.Requires(tok != null);

       Contract.Requires(e0 != null);

       Contract.Requires(e1 != null);

       E0 = e0;

       E1 = e1;

+      if (immutable)

+        CachedHashCode = ComputeHashCode();

     }

 

     [Pure]

@@ -2875,11 +3000,22 @@ namespace Microsoft.Boogie {
       BvConcatExpr other = (BvConcatExpr)obj;

       return object.Equals(this.E0, other.E0) && object.Equals(this.E1, other.E1);

     }

+

     [Pure]

-    public override int GetHashCode() {

-      int h = this.E0.GetHashCode() ^ this.E1.GetHashCode() * 17;

+    public override int GetHashCode()

+    {

+      if (Immutable)

+        return CachedHashCode;

+      else

+        return ComputeHashCode();

+    }

+

+    [Pure]

+    public override int ComputeHashCode() {

+      int h = this.E0.ComputeHashCode() ^ this.E1.ComputeHashCode() * 17;

       return h;

     }

+

     public override void Emit(TokenTextWriter stream, int contextBindingStrength, bool fragileContext) {

       //Contract.Requires(stream != null);

       stream.SetToken(this);