Robust/src/IR/Flat/BuildFlat.java

   1 package IR.Flat;
   2 import IR.*;
   3 import IR.Tree.*;
   4 import java.util.*;
   5
   6 public class BuildFlat {
   7     State state;
   8     Hashtable temptovar;
   9
  10     public BuildFlat(State st) {
  11         state=st;
  12         temptovar=new Hashtable();
  13     }
  14
  15     public Hashtable getMap() {
  16         return temptovar;
  17     }
  18
  19     public void buildFlat() {
  20         Iterator it=state.getClassSymbolTable().getDescriptorsIterator();
  21         while(it.hasNext()) {
  22             ClassDescriptor cn=(ClassDescriptor)it.next();
  23             flattenClass(cn);
  24         }
  25     }
  26
  27     private void flattenClass(ClassDescriptor cn) {
  28         Iterator methodit=cn.getMethods();
  29         while(methodit.hasNext()) {
  30             MethodDescriptor md=(MethodDescriptor)methodit.next();
  31             BlockNode bn=state.getMethodBody(md);
  32             FlatNode fn=flattenBlockNode(bn).getBegin();
  33             FlatMethod fm=new FlatMethod(md, fn);
  34             if (!md.isStatic())
  35                 fm.addParameterTemp(getTempforVar(md.getThis()));
  36             for(int i=0;i<md.numParameters();i++) {
  37                 fm.addParameterTemp(getTempforVar(md.getParameter(i)));
  38             }
  39             System.out.println(fm.printMethod());
  40             state.addFlatCode(md,fm);
  41         }
  42     }
  43
  44     private NodePair flattenBlockNode(BlockNode bn) {
  45         FlatNode begin=null;
  46         FlatNode end=null;
  47         for(int i=0;i<bn.size();i++) {
  48             NodePair np=flattenBlockStatementNode(bn.get(i));
  49             FlatNode np_begin=np.getBegin();
  50             FlatNode np_end=np.getEnd();
  51             if (begin==null) {
  52                 begin=np_begin;
  53             }
  54             if (end==null) {
  55                 end=np_end;
  56             } else {
  57                 end.addNext(np_begin);
  58                 end=np_end;
  59             }
  60         }
  61         if (begin==null) {
  62             end=begin=new FlatNop();
  63         }
  64         return new NodePair(begin,end);
  65     }
  66
  67     private NodePair flattenBlockExpressionNode(BlockExpressionNode en) {
  68         TempDescriptor tmp=TempDescriptor.tempFactory("neverused",en.getExpression().getType());
  69         return flattenExpressionNode(en.getExpression(),tmp);
  70     }
  71
  72     private NodePair flattenCastNode(CastNode cn,TempDescriptor out_temp) {
  73         TempDescriptor tmp=TempDescriptor.tempFactory("tocast",cn.getExpression().getType());
  74         NodePair np=flattenExpressionNode(cn.getExpression(), tmp);
  75         FlatCastNode fcn=new FlatCastNode(cn.getType(), tmp, out_temp);
  76         np.getEnd().addNext(fcn);
  77         return new NodePair(np.getBegin(),fcn);
  78     }
  79
  80     private NodePair flattenLiteralNode(LiteralNode ln,TempDescriptor out_temp) {
  81         FlatLiteralNode fln=new FlatLiteralNode(ln.getType(), ln.getValue(), out_temp);
  82         return new NodePair(fln,fln);
  83     }
  84
  85     private NodePair flattenCreateObjectNode(CreateObjectNode con,TempDescriptor out_temp) {
  86         TypeDescriptor td=con.getType();
  87         if (!td.isArray()) {
  88             FlatNew fn=new FlatNew(td, out_temp);
  89             TempDescriptor[] temps=new TempDescriptor[con.numArgs()];
  90             FlatNode last=fn;
  91             //Build arguments
  92             for(int i=0;i<con.numArgs();i++) {
  93                 ExpressionNode en=con.getArg(i);
  94                 TempDescriptor tmp=TempDescriptor.tempFactory("arg",en.getType());
  95                 temps[i]=tmp;
  96                 NodePair np=flattenExpressionNode(en, tmp);
  97                 last.addNext(np.getBegin());
  98                 last=np.getEnd();
  99             }
 100             MethodDescriptor md=con.getConstructor();
 101             //Call to constructor
 102             FlatCall fc=new FlatCall(md, null, out_temp, temps);
 103             last.addNext(fc);
 104             return new NodePair(fn,fc);
 105         } else {
 106             FlatNode first=null;
 107             FlatNode last=null;
 108             TempDescriptor[] temps=new TempDescriptor[con.numArgs()];
 109             for (int i=0;i<con.numArgs();i++) {
 110                 ExpressionNode en=con.getArg(i);
 111                 TempDescriptor tmp=TempDescriptor.tempFactory("arg",en.getType());
 112                 temps[i]=tmp;
 113                 NodePair np=flattenExpressionNode(en, tmp);
 114                 if (first==null)
 115                     first=np.getBegin();
 116                 else
 117                     last.addNext(np.getBegin());
 118                 last=np.getEnd();
 119
 120                 TempDescriptor tmp2=(i==0)?
 121                     out_temp:
 122                 TempDescriptor.tempFactory("arg",en.getType());
 123             }
 124             FlatNew fn=new FlatNew(td, out_temp, temps[0]);
 125             last.addNext(fn);
 126             NodePair np=generateNewArrayLoop(temps, td.dereference(), out_temp, 0);
 127             fn.addNext(np.getBegin());
 128             return new NodePair(first,np.getEnd());
 129         }
 130     }
 131
 132     private NodePair generateNewArrayLoop(TempDescriptor[] temparray, TypeDescriptor td, TempDescriptor tmp, int i) {
 133         TempDescriptor index=TempDescriptor.tempFactory("index",new TypeDescriptor(TypeDescriptor.INT));
 134         TempDescriptor tmpone=TempDescriptor.tempFactory("index",new TypeDescriptor(TypeDescriptor.INT));
 135         FlatNop fnop=new FlatNop();//last node
 136
 137         //index=0
 138         FlatLiteralNode fln=new FlatLiteralNode(index.getType(),new Integer(0),index);
 139         //tmpone=1
 140         FlatLiteralNode fln2=new FlatLiteralNode(tmpone.getType(),new Integer(1),tmpone);
 141
 142         TempDescriptor tmpbool=TempDescriptor.tempFactory("comp",new TypeDescriptor(TypeDescriptor.BOOLEAN));
 143
 144         FlatOpNode fcomp=new FlatOpNode(tmpbool,index,temparray[i],new Operation(Operation.LT));
 145         FlatCondBranch fcb=new FlatCondBranch(tmpbool);
 146         //is index<temp[i]
 147         TempDescriptor new_tmp=TempDescriptor.tempFactory("tmp",td);
 148         FlatNew fn=new FlatNew(td, new_tmp, temparray[i+1]);
 149         FlatSetElementNode fsen=new FlatSetElementNode(tmp,index,new_tmp);
 150         // index=index+1
 151         FlatOpNode fon=new FlatOpNode(index,index,tmpone,new Operation(Operation.ADD));
 152         //jump out
 153         fln.addNext(fln2);
 154         fln2.addNext(fcomp);
 155         fcomp.addNext(fcb);
 156         fcb.addTrueNext(fn);
 157         fcb.addFalseNext(fnop);
 158         fn.addNext(fsen);
 159         //Recursive call here
 160         if ((i+1)<temparray.length) {
 161             NodePair np2=generateNewArrayLoop(temparray, td.dereference(), new_tmp, i+1);
 162             fsen.addNext(np2.getBegin());
 163             np2.getEnd().addNext(fon);
 164         } else {
 165             fsen.addNext(fon);
 166         }
 167         fon.addNext(fcomp);
 168         return new NodePair(fln, fnop);
 169     }
 170
 171     private NodePair flattenMethodInvokeNode(MethodInvokeNode min,TempDescriptor out_temp) {
 172         TempDescriptor[] temps=new TempDescriptor[min.numArgs()];
 173         FlatNode first=null;
 174         FlatNode last=null;
 175         TempDescriptor thisarg=null;
 176
 177         if (min.getExpression()!=null) {
 178             thisarg=TempDescriptor.tempFactory("thisarg",min.getExpression().getType());
 179             NodePair np=flattenExpressionNode(min.getExpression(),thisarg);
 180             first=np.getBegin();
 181             last=np.getEnd();
 182         }
 183
 184         //Build arguments
 185         for(int i=0;i<min.numArgs();i++) {
 186             ExpressionNode en=min.getArg(i);
 187             TempDescriptor td=TempDescriptor.tempFactory("arg",en.getType());
 188             temps[i]=td;
 189             NodePair np=flattenExpressionNode(en, td);
 190             if (first==null)
 191                 first=np.getBegin();
 192             else
 193                 last.addNext(np.getBegin());
 194             last=np.getEnd();
 195         }
 196
 197         MethodDescriptor md=min.getMethod();
 198
 199         //Call to constructor
 200
 201         FlatCall fc;
 202         if(md.getReturnType()==null||md.getReturnType().isVoid())
 203             fc=new FlatCall(md, null, thisarg, temps);
 204         else
 205             fc=new FlatCall(md, out_temp, thisarg, temps);
 206         if (first==null) {
 207             first=fc;
 208         } else
 209             last.addNext(fc);
 210         return new NodePair(first,fc);
 211     }
 212
 213     private NodePair flattenFieldAccessNode(FieldAccessNode fan,TempDescriptor out_temp) {
 214         TempDescriptor tmp=TempDescriptor.tempFactory("temp",fan.getExpression().getType());
 215         NodePair npe=flattenExpressionNode(fan.getExpression(),tmp);
 216         FlatFieldNode fn=new FlatFieldNode(fan.getField(),tmp,out_temp);
 217         npe.getEnd().addNext(fn);
 218         return new NodePair(npe.getBegin(),fn);
 219     }
 220
 221     private NodePair flattenAssignmentNode(AssignmentNode an,TempDescriptor out_temp) {
 222         // Two cases:
 223         // left side is variable
 224         // left side is field
 225
 226         Operation base=an.getOperation().getBaseOp();
 227         TempDescriptor src_tmp=TempDescriptor.tempFactory("src",an.getSrc().getType());
 228         NodePair np_src=flattenExpressionNode(an.getSrc(),src_tmp);
 229         FlatNode last=np_src.getEnd();
 230         if (base!=null) {
 231             TempDescriptor src_tmp2=TempDescriptor.tempFactory("tmp", an.getDest().getType());
 232             NodePair np_dst_init=flattenExpressionNode(an.getDest(),src_tmp2);
 233             last.addNext(np_dst_init.getBegin());
 234             TempDescriptor dst_tmp=TempDescriptor.tempFactory("dst_tmp",an.getDest().getType());
 235             FlatOpNode fon=new FlatOpNode(dst_tmp, src_tmp,src_tmp2, base);
 236             np_dst_init.getEnd().addNext(fon);
 237             last=fon;
 238             src_tmp=dst_tmp;
 239         }
 240
 241         if (an.getDest().kind()==Kind.FieldAccessNode) {
 242             FieldAccessNode fan=(FieldAccessNode)an.getDest();
 243             ExpressionNode en=fan.getExpression();
 244             TempDescriptor dst_tmp=TempDescriptor.tempFactory("dst",en.getType());
 245             NodePair np_baseexp=flattenExpressionNode(en, dst_tmp);
 246             last.addNext(np_baseexp.getBegin());
 247             FlatSetFieldNode fsfn=new FlatSetFieldNode(dst_tmp, fan.getField(), src_tmp);
 248             np_baseexp.getEnd().addNext(fsfn);
 249             return new NodePair(np_src.getBegin(), fsfn);
 250         } else if (an.getDest().kind()==Kind.NameNode) {
 251             NameNode nn=(NameNode)an.getDest();
 252             if (nn.getExpression()!=null) {
 253                 FieldAccessNode fan=(FieldAccessNode)nn.getExpression();
 254                 ExpressionNode en=fan.getExpression();
 255                 TempDescriptor dst_tmp=TempDescriptor.tempFactory("dst",en.getType());
 256                 NodePair np_baseexp=flattenExpressionNode(en, dst_tmp);
 257                 last.addNext(np_baseexp.getBegin());
 258                 FlatSetFieldNode fsfn=new FlatSetFieldNode(dst_tmp, fan.getField(), src_tmp);
 259                 np_baseexp.getEnd().addNext(fsfn);
 260                 return new NodePair(np_src.getBegin(), fsfn);
 261             } else {
 262                 if (nn.getField()!=null) {
 263                     FlatSetFieldNode fsfn=new FlatSetFieldNode(getTempforVar(nn.getVar()), nn.getField(), src_tmp);
 264                     last.addNext(fsfn);
 265                     return new NodePair(np_src.getBegin(), fsfn);
 266                 } else {
 267                     FlatOpNode fon=new FlatOpNode(getTempforVar(nn.getVar()), src_tmp, null, new Operation(Operation.ASSIGN));
 268                     last.addNext(fon);
 269                     return new NodePair(np_src.getBegin(),fon);
 270                 }
 271             }
 272         }
 273         throw new Error();
 274     }
 275
 276     private NodePair flattenNameNode(NameNode nn,TempDescriptor out_temp) {
 277         if (nn.getExpression()!=null) {
 278             /* Hack - use subtree instead */
 279             return flattenExpressionNode(nn.getExpression(),out_temp);
 280         } else if (nn.getField()!=null) {
 281             TempDescriptor tmp=getTempforVar(nn.getVar());
 282             FlatFieldNode ffn=new FlatFieldNode(nn.getField(), tmp, out_temp);
 283             return new NodePair(ffn,ffn);
 284         } else {
 285             TempDescriptor tmp=getTempforVar(nn.getVar());
 286             FlatOpNode fon=new FlatOpNode(out_temp, tmp, null, new Operation(Operation.ASSIGN));
 287             return new NodePair(fon,fon);
 288         }
 289     }
 290
 291     private NodePair flattenOpNode(OpNode on,TempDescriptor out_temp) {
 292         TempDescriptor temp_left=TempDescriptor.tempFactory("leftop",on.getLeft().getType());
 293         TempDescriptor temp_right=null;
 294
 295         Operation op=on.getOp();
 296         if (op.getOp()==Operation.POSTINC||
 297             op.getOp()==Operation.POSTDEC||
 298             op.getOp()==Operation.PREINC||
 299             op.getOp()==Operation.PREDEC) {
 300             LiteralNode ln=new LiteralNode("int",new Integer(1));
 301             ln.setType(new TypeDescriptor(TypeDescriptor.INT));
 302             AssignmentNode an=new AssignmentNode(on.getLeft(),ln,
 303                                new AssignOperation((op.getOp()==Operation.POSTINC||op.getOp()==Operation.PREINC)?AssignOperation.PLUSEQ:AssignOperation.MINUSEQ));
 304             if (op.getOp()==Operation.POSTINC||
 305                 op.getOp()==Operation.POSTDEC) {
 306                 NodePair left=flattenExpressionNode(on.getLeft(),out_temp);
 307                 NodePair assign=flattenAssignmentNode(an,temp_left);
 308                 left.getEnd().addNext(assign.getBegin());
 309                 return new NodePair(left.getBegin(),assign.getEnd());
 310             } else {
 311                 NodePair assign=flattenAssignmentNode(an,out_temp);
 312                 return assign;
 313             }
 314         }
 315
 316         NodePair left=flattenExpressionNode(on.getLeft(),temp_left);
 317         NodePair right;
 318         if (on.getRight()!=null) {
 319             temp_right=TempDescriptor.tempFactory("rightop",on.getRight().getType());
 320             right=flattenExpressionNode(on.getRight(),temp_right);
 321         } else {
 322             FlatNop nop=new FlatNop();
 323             right=new NodePair(nop,nop);
 324         }
 325
 326         if (op.getOp()==Operation.LOGIC_OR) {
 327             /* Need to do shortcircuiting */
 328             FlatCondBranch fcb=new FlatCondBranch(temp_left);
 329             FlatOpNode fon1=new FlatOpNode(out_temp,temp_left,null,new Operation(Operation.ASSIGN));
 330             FlatOpNode fon2=new FlatOpNode(out_temp,temp_right,null,new Operation(Operation.ASSIGN));
 331             FlatNop fnop=new FlatNop();
 332             left.getEnd().addNext(fcb);
 333             fcb.addFalseNext(right.getBegin());
 334             right.getEnd().addNext(fon2);
 335             fon2.addNext(fnop);
 336             fcb.addTrueNext(fon1);
 337             fon1.addNext(fnop);
 338             return new NodePair(left.getBegin(), fnop);
 339         } else if (op.getOp()==Operation.LOGIC_AND) {
 340             /* Need to do shortcircuiting */
 341             FlatCondBranch fcb=new FlatCondBranch(temp_left);
 342             FlatOpNode fon1=new FlatOpNode(out_temp,temp_left,null,new Operation(Operation.ASSIGN));
 343             FlatOpNode fon2=new FlatOpNode(out_temp,temp_right,null,new Operation(Operation.ASSIGN));
 344             FlatNop fnop=new FlatNop();
 345             left.getEnd().addNext(fcb);
 346             fcb.addTrueNext(right.getBegin());
 347             right.getEnd().addNext(fon2);
 348             fon2.addNext(fnop);
 349             fcb.addFalseNext(fon1);
 350             fon1.addNext(fnop);
 351             return new NodePair(left.getBegin(), fnop);
 352         }
 353
 354         FlatOpNode fon=new FlatOpNode(out_temp,temp_left,temp_right,op);
 355         left.getEnd().addNext(right.getBegin());
 356         right.getEnd().addNext(fon);
 357         return new NodePair(left.getBegin(),fon);
 358     }
 359
 360     private NodePair flattenExpressionNode(ExpressionNode en, TempDescriptor out_temp) {
 361         switch(en.kind()) {
 362         case Kind.AssignmentNode:
 363             return flattenAssignmentNode((AssignmentNode)en,out_temp);
 364         case Kind.CastNode:
 365             return flattenCastNode((CastNode)en,out_temp);
 366         case Kind.CreateObjectNode:
 367             return flattenCreateObjectNode((CreateObjectNode)en,out_temp);
 368         case Kind.FieldAccessNode:
 369             return flattenFieldAccessNode((FieldAccessNode)en,out_temp);
 370         case Kind.LiteralNode:
 371             return flattenLiteralNode((LiteralNode)en,out_temp);
 372         case Kind.MethodInvokeNode:
 373             return flattenMethodInvokeNode((MethodInvokeNode)en,out_temp);
 374         case Kind.NameNode:
 375             return flattenNameNode((NameNode)en,out_temp);
 376         case Kind.OpNode:
 377             return flattenOpNode((OpNode)en,out_temp);
 378         }
 379         throw new Error();
 380     }
 381
 382     private NodePair flattenDeclarationNode(DeclarationNode dn) {
 383         VarDescriptor vd=dn.getVarDescriptor();
 384         TempDescriptor td=getTempforVar(vd);
 385         if (dn.getExpression()!=null)
 386             return flattenExpressionNode(dn.getExpression(),td);
 387         else {
 388             FlatNop fn=new FlatNop();
 389             return new NodePair(fn,fn);
 390         }
 391     }
 392
 393     private TempDescriptor getTempforVar(VarDescriptor vd) {
 394         if (temptovar.containsKey(vd))
 395             return (TempDescriptor)temptovar.get(vd);
 396         else {
 397             TempDescriptor td=TempDescriptor.tempFactory(vd.getName(),vd.getType());
 398             temptovar.put(vd,td);
 399             return td;
 400         }
 401     }
 402
 403     private NodePair flattenIfStatementNode(IfStatementNode isn) {
 404         TempDescriptor cond_temp=TempDescriptor.tempFactory("condition",new TypeDescriptor(TypeDescriptor.BOOLEAN));
 405         NodePair cond=flattenExpressionNode(isn.getCondition(),cond_temp);
 406         FlatCondBranch fcb=new FlatCondBranch(cond_temp);
 407         NodePair true_np=flattenBlockNode(isn.getTrueBlock());
 408         NodePair false_np;
 409         FlatNop nopend=new FlatNop();
 410
 411         if (isn.getFalseBlock()!=null)
 412             false_np=flattenBlockNode(isn.getFalseBlock());
 413         else {
 414             FlatNop nop=new FlatNop();
 415             false_np=new NodePair(nop,nop);
 416         }
 417
 418         cond.getEnd().addNext(fcb);
 419         fcb.addTrueNext(true_np.getBegin());
 420         fcb.addFalseNext(false_np.getBegin());
 421         true_np.getEnd().addNext(nopend);
 422         false_np.getEnd().addNext(nopend);
 423         return new NodePair(cond.getBegin(), nopend);
 424     }
 425
 426     private NodePair flattenLoopNode(LoopNode ln) {
 427         if (ln.getType()==LoopNode.FORLOOP) {
 428             NodePair initializer=flattenBlockNode(ln.getInitializer());
 429             TempDescriptor cond_temp=TempDescriptor.tempFactory("condition", new TypeDescriptor(TypeDescriptor.BOOLEAN));
 430             NodePair condition=flattenExpressionNode(ln.getCondition(),cond_temp);
 431             NodePair update=flattenBlockNode(ln.getUpdate());
 432             NodePair body=flattenBlockNode(ln.getBody());
 433             FlatNode begin=initializer.getBegin();
 434             FlatCondBranch fcb=new FlatCondBranch(cond_temp);
 435             FlatNop nopend=new FlatNop();
 436
 437             initializer.getEnd().addNext(condition.getBegin());
 438             body.getEnd().addNext(update.getBegin());
 439             update.getEnd().addNext(condition.getBegin());
 440             condition.getEnd().addNext(fcb);
 441             fcb.addFalseNext(nopend);
 442             fcb.addTrueNext(body.getBegin());
 443             return new NodePair(begin,nopend);
 444         } else if (ln.getType()==LoopNode.WHILELOOP) {
 445             TempDescriptor cond_temp=TempDescriptor.tempFactory("condition", new TypeDescriptor(TypeDescriptor.BOOLEAN));
 446             NodePair condition=flattenExpressionNode(ln.getCondition(),cond_temp);
 447             NodePair body=flattenBlockNode(ln.getBody());
 448             FlatNode begin=condition.getBegin();
 449             FlatCondBranch fcb=new FlatCondBranch(cond_temp);
 450             FlatNop nopend=new FlatNop();
 451
 452             body.getEnd().addNext(condition.getBegin());
 453             condition.getEnd().addNext(fcb);
 454             fcb.addFalseNext(nopend);
 455             fcb.addTrueNext(body.getBegin());
 456             return new NodePair(begin,nopend);
 457         } else if (ln.getType()==LoopNode.DOWHILELOOP) {
 458             TempDescriptor cond_temp=TempDescriptor.tempFactory("condition", new TypeDescriptor(TypeDescriptor.BOOLEAN));
 459             NodePair condition=flattenExpressionNode(ln.getCondition(),cond_temp);
 460             NodePair body=flattenBlockNode(ln.getBody());
 461             FlatNode begin=body.getBegin();
 462             FlatCondBranch fcb=new FlatCondBranch(cond_temp);
 463             FlatNop nopend=new FlatNop();
 464
 465             body.getEnd().addNext(condition.getBegin());
 466             condition.getEnd().addNext(fcb);
 467             fcb.addFalseNext(nopend);
 468             fcb.addTrueNext(body.getBegin());
 469             return new NodePair(begin,nopend);
 470         } else throw new Error();
 471     }
 472
 473     private NodePair flattenReturnNode(ReturnNode rntree) {
 474         TempDescriptor retval=null;
 475         NodePair cond=null;
 476         if (rntree.getReturnExpression()!=null) {
 477             retval=TempDescriptor.tempFactory("ret_value", rntree.getReturnExpression().getType());
 478             cond=flattenExpressionNode(rntree.getReturnExpression(),retval);
 479         }
 480
 481         FlatReturnNode rnflat=new FlatReturnNode(retval);
 482
 483         if (cond!=null) {
 484             cond.getEnd().addNext(rnflat);
 485             return new NodePair(cond.getBegin(),rnflat);
 486         } else
 487             return new NodePair(rnflat,rnflat);
 488
 489     }
 490
 491     private NodePair flattenSubBlockNode(SubBlockNode sbn) {
 492         return flattenBlockNode(sbn.getBlockNode());
 493     }
 494
 495     private NodePair flattenBlockStatementNode(BlockStatementNode bsn) {
 496         switch(bsn.kind()) {
 497         case Kind.BlockExpressionNode:
 498             return flattenBlockExpressionNode((BlockExpressionNode)bsn);
 499
 500         case Kind.DeclarationNode:
 501             return flattenDeclarationNode((DeclarationNode)bsn);
 502
 503         case Kind.IfStatementNode:
 504             return flattenIfStatementNode((IfStatementNode)bsn);
 505
 506         case Kind.LoopNode:
 507             return flattenLoopNode((LoopNode)bsn);
 508
 509         case Kind.ReturnNode:
 510             return flattenReturnNode((IR.Tree.ReturnNode)bsn);
 511
 512         case Kind.SubBlockNode:
 513             return flattenSubBlockNode((SubBlockNode)bsn);
 514
 515         }
 516         throw new Error();
 517     }
 518 }