Remove CallExp::implicitCastTo altogether.

The pure -> immutable case is checked in implicitConvTo as well,
and since it yields MATCHexact, the castTo() in
Expression::implicitCastTo is a no-op anyway.

src/cast.c

@@ -610,27 +610,6 @@ MATCH AssocArrayLiteralExp::implicitConvTo(Type *t)
         return Expression::implicitConvTo(t);
 }
 
-Expression *CallExp::implicitCastTo(Scope *sc, Type *t)
-{
-    //printf("CallExp::implicitCastTo(%s of type %s) => %s\n", toChars(), type->toChars(), t->toChars());
-
-    /* Allow the result of strongly pure functions to
-     * convert to immutable
-     */
-    if (f && f->isolateReturn() &&
-        type->immutableOf()->equals(t))
-    {
-        /* Avoid emitting CastExp for:
-         *  T[] make() pure { ...  }
-         *  immutable T[] arr = make();  // unique return
-         */
-        Expression *e = copy();
-        e->type = t;
-        return e;
-    }
-    return Expression::implicitCastTo(sc, t);
-}
-
 MATCH CallExp::implicitConvTo(Type *t)
 {
 #if 0

src/expression.h

@@ -1103,7 +1103,6 @@ class CallExp : public UnaExp
     int isLvalue();
     Expression *toLvalue(Scope *sc, Expression *e);
     Expression *addDtorHook(Scope *sc);
-    Expression *implicitCastTo(Scope *sc, Type *t);
     MATCH implicitConvTo(Type *t);
 
     Expression *doInline(InlineDoState *ids);