// note. pattern #1:
// * ref = atom
// * read(ref)
// conditions:
// 1) ref is read only once after it had been assigned
// 2) atom isn't reassigned before read(ref) takes place
// 3) if ref is CF$XXXX then atom can be of any node type (not only an atom)
// transformed into:
// * read(atom)
private static bool TryMatchPattern1(DfaHelper dfa, Expression atom)
{
var p1_ref = atom as Ref;
if (p1_ref == null) return false;
var p1_lastass = dfa.Writes(p1_ref).LastOrDefault();
if (p1_lastass == null) return false;
var p1_ref_onlyread_afterass = dfa.Reads(p1_ref).SingleOrDefault2(
r => dfa.ExecOrderOfStmt(r) >= dfa.ExecOrderOfStmt(p1_lastass));
if (p1_ref_onlyread_afterass == null) return false;
var p1_atom = p1_lastass.Rhs;
if (!p1_ref.Sym.Name.StartsWith("CF$") &&
!p1_ref.Sym.Name.StartsWith("CS$"))
{
if (!p1_atom.IsAtom()) return false;
var p1_atom_reasses = dfa.Writes(p1_atom).Where(w =>
dfa.ExecOrderOfStmt(p1_lastass) <= dfa.ExecOrderOfStmt(w) &&
dfa.ExecOrderOfStmt(w) <= dfa.ExecOrderOfStmt(p1_ref_onlyread_afterass));
if (p1_atom_reasses.IsNotEmpty()) return false;
}
dfa.Remove(p1_lastass);
var p1_ref_onlyread_stmt = p1_ref_onlyread_afterass.Stmt();
dfa.ReplaceRecursive(p1_ref_onlyread_stmt, p1_ref, p1_atom);
return true;
}
// note. pattern #2:
// * atom = atom op any
// transformed into:
// * atom [op=] any
private static bool TryMatchPattern2(DfaHelper dfa, Expression atom)
{
var p2_atom = atom;
foreach (var p2_ass in dfa.Writes(atom))
{
if (!(p2_ass.Rhs is BinaryOperator)) continue;
var binary = p2_ass.Rhs as BinaryOperator;
if (!p2_atom.Equiv(binary.Lhs)) continue;
var p2_opeq = p2_atom.CreateOpPreAssign(binary.OperatorType, binary.Rhs);
if (p2_opeq == null) return false;
dfa.Replace(p2_ass, p2_opeq);
return true;
}
return false;
}
