public override Expr VisitNAryExpr(NAryExpr node)
{
// Try to do direct map indexing
// FIXME: If there are nested mapselects but they don't end on a variable
// then we'll do a lot of unnecessary work every time we traverse into a map select down.
var asMapSelect = ExprUtil.AsMapSelect(node);
if (asMapSelect != null)
{
// Gather the indices. They will be backwards as we traversing top down so have to
// reverse at the end.
//
// Here's an example showing this:
//
// var m:[int][int]bool;
// y:= m[0][1]
//
// The indicies we want are [0][1], but when traverse we will visit them backwards as
// we start at the root of the expression tree.
//
// The structure of this is
//
// mapselect
// / \
// mapselect 1
// / \
// m 0
var indices = new List <Expr>();
Expr firstArg = null;
do
{
// Traverse multi-arity arguments in reverse because later on we reverse them.
for (int index = asMapSelect.Args.Count - 1; index >= 1; --index)
{
// Don't do index variable mapping here because we might
// need to throw away what we've done
indices.Add(asMapSelect.Args[index]);
}
firstArg = asMapSelect.Args[0];
asMapSelect = ExprUtil.AsMapSelect(firstArg);
} while (asMapSelect != null);
// Hopefully a map variable we can write to
var asId = ExprUtil.AsIdentifer(firstArg);
if (asId != null && asId.Decl.TypedIdent.Type.IsMap)
{
// Do a remapping if necessary
// FIXME: This sucks. Fix boogie instead!
Variable V = null;
if (preReplacementReMap.ContainsKey(asId.Decl))
{
V = preReplacementReMap[asId.Decl];
}
else
{
V = asId.Decl;
}
// We need to make sure that the map variable isn't bound and that
// Note: that map is being fully indexed into and not partially
if ((!BoundVariables.Contains(V)) &&
indices.Count == MapProxy.ComputeIndicesRequireToDirectlyIndex(asId.Decl.TypedIdent.Type))
{
// Put indices in correct order
indices.Reverse();
// Expand the indices so variables are mapped
var expandedIndices = new List <Expr>();
foreach (var index in indices)
{
expandedIndices.Add((Expr)this.Visit(index));
}
var valueFromMap = State.ReadMapVariableInScopeAt(V, expandedIndices);
return(valueFromMap);
}
}
}
// Handle all other NAryExpr and fall back when we encounter a mapselect we can't support
// (e.g. the map variable being used is not known).
return(base.VisitNAryExpr(node));
}
// Only returns true if the indices definitely only alias up to one indice stored
// in StoresAtSymbolicNonAliasingIndices. i.e.
//
// returns true iff
//
// the indices do not alias anything in StoresAtSymbolicNonAliasingIndices
// OR
// the indices alias a single element in StoresAtSymbolicNonAliasingIndices
// which ok because this tells us which element to overwrite.
//
// Note that if this method returns false it means that the indices "might" alias.
private bool AliasesZeroOrOneSymbolicNonAliasingIndices(IList <Expr> indices)
{
if (indices.Count > 1)
{
// Our alias analysis is very primitive and we only allow a single index
return(false);
}
var indexExpr = indices[0];
// Analysis: We consider the follow expressions to not alias
// <sym_var>
// <constant> + <sym_var>
//
// Note sym_var must be the same
// Try single variable
var asId = ExprUtil.AsIdentifer(indexExpr);
if (asId != null)
{
if (SymVariable == null)
{
// We haven't picked a variable for use in our non aliasing symbolci expressions yet
// use this one
Debug.Assert(StoresAtSymbolicNonAliasingIndices.Count == 0);
SymVariable = asId.Decl;
return(true);
}
else
{
// We have an existing symbolic variable that we are using
if (SymVariable.Equals(asId.Decl))
{
return(true);
}
return(false);
}
}
// We are relying on the expression simplification of the expression builder to always
// but the constant on the left child
// <constant> + <sym_var>
var asAdd = ExprUtil.AsAdd(indexExpr);
if (asAdd != null)
{
var lhsAsLit = ExprUtil.AsLiteral(asAdd.Args[0]);
if (lhsAsLit != null)
{
var rhsAsId = ExprUtil.AsIdentifer(asAdd.Args[1]);
if (rhsAsId != null)
{
if (SymVariable == null)
{
// We haven't picked a variable for use in our non aliasing symbolci expressions yet
// use this one
Debug.Assert(StoresAtSymbolicNonAliasingIndices.Count == 0);
SymVariable = rhsAsId.Decl;
return(true);
}
else
{
// We have an existing symbolic variable that we are using
if (SymVariable.Equals(rhsAsId.Decl))
{
return(true);
}
return(false);
}
}
}
}
// The indicies might alias something we already have stored.
return(false);
}