Languages and Compiler Design II Project 4 Hints

1. Languages and Compiler Design IIProject 4 Hints Material provided by Prof. Jingke Li Stolen with pride and modified by Herb Mayer PSU Spring 2010 rev.: 5/19/2010 CS322

2. Agenda • Storage Model • Initial Setup • Top-Level Routines • Fetch-Execute Loop • Interpreting Statements • Evaluating Expressions • Handling Call Nodes • TestInterp.java CS322

3. Storage Model The interpreter organizes data in three storage categories: temps, stack, and heap. To allow an uniform access pattern, they are all mapped to a single integer array called mem[]. • Temps — mem[ 0 ]--mem[ maxTemp-1 ] TEMP nodes are mapped to temp memory using their indices (with a fixed offset). • Stack — mem[ maxTemp ]--mem[ maxStack-1 ] Function activation records are allocated and de-allocated on the stack • Heap — mem[ maxStack ]--mem[ maxMem-1 ] Calls to malloc result in space allocated in the heap CS322

4. Initial Setup public class Interp{ private static int maxMem = 4096, maxStack = 2048, maxTemp = 512, tempOffset = 100, wordSize = 1; private int[] mem; // memory array private int hp, sp, fp; // heap, stack, frame pointers private int retVal; // storage for return value private FUNClist funcs; // input program’s funcs } //end class Interp public Interp( PROG p ){ mem = new int[maxMem]; hp = maxMem - 1; fp = sp = maxStack - 1; retVal = 0; funcs = p.funcs; } //end Interp CS322

5. Top-Level Routines public void go() throws Exception{ interpFunc("main"); } //end go void interpFunc( String label ) throws Exception{ for( int i = 0; i < funcs.size(); i++ ) { FUNC f = (FUNC) funcs.elementAt(i); if( f.label.equals(label) ) { sp = sp - f.varCnt - f.argCnt - 1; interpStmts(f.stmts); sp = sp + f.varCnt + f.argCnt + 1; return; } //end if }//end for throw new InterpException("Can’t find function: " + label); } //end InterpFunc CS322

6. Fetch-Execute Loop public void interpStmts(STMTlist sl) throws Exception{ int i = 0; while( i < sl.size() ) { STMT s = (STMT) sl.elementAt( i ); if( s instanceof MOVE ) { interpMove((MOVE) s ); i++; } else if( s instanceof LABEL ) { i++; } else if( s instanceof CALLST ) { interpCallSt((CALLST) s ); i++; } else if( s instanceof RETURN ) { ...; return; } else if( s instanceof JUMP ) { i = genTarget((JUMP) s).target,sl); } else if( s instanceof CJUMP ) { if( evalCond((CJUMP) s ) ) i = getTarget(...); else i++; //end if }else{ throw new InterpException( "Illegal STMT: " + s ); } //end if } //end while } //end interpStmts CS322

7. Interpreting Statements private void interpMove( MOVE s ) throws Exception{ int idx; if( s.dst instanceof TEMP ) idx = ((TEMP) s.dst).num - tempOffset; else if( s.dst instanceof MEM ) idx = evaluate(((MEM) s.dst).exp); else if( s.dst instanceof MEMBER ) ... else if( s.dst instanceof PARAM ) ... else if( s.dst instanceof VAR ) ... else throw new InterpException("Wrong Address form"); mem[idx] = evaluate(s.src); } //end interpMove // search a STMTlist for a matching LABEL node private int genTarget( NAME n, STMTlist sl ) throws Exception{ for( int i = 0; i < sl.size(); i++ ) { if( ( sl.elementAt(i) instanceof LABEL ) && ...) return i+1; } //end for throw new InterpException( ... ); } //end genTarget // evaluate the CJUMP’s condition to a Boolean value private boolean evalCond( CJUMP s ) throws Exception{ int v1 = evaluate( s.left ), v2 = evaluate( s.right ); switch( s.op ) { ... } } //end evalCond CS322

8. Evaluating Expressions // Every expression is evaluated to an integer value public int evaluate( EXP e ) throws Exception{ if( e instanceof BINOP ) return evalBinop((BINOP) e); if( e instanceof CALL ) return evalCall((CALL) e); if( e instanceof MEM ) return mem[evaluate(((MEM) e).exp)]; if( e instanceof TEMP ) return mem[...]; if( e instanceof MEMBER ) return mem[...]; if( e instanceof PARAM ) return mem[fp + ...]; if( e instanceof VAR ) return mem[fp - ...]; if( e instanceof CONST ) return ((CONST) e).val; if( (e instanceof NAME ) && ((NAME) e).id.equals("wSZ")) return wordSize; throw new InterpException("Illegal EXP node for evaluate: " + e); } //end evaluate int evalBinop( BINOP e ) throws Exception{ int lval = evaluate(e.left), rval = evaluate(e.right); switch( e.op ) { ... } } //end evalBinop CS322

9. Handling Call Nodes private void interpCallSt( CALLST s ) throws Exception{ String fname = s.func.id; if( fname.equals("prInt") ) { System.out.println(evaluate(...)); } else if( fname.equals("prString")) { ... } else handleCall( fname, s.args ); } //end interpCallSt // evaluate args, place results in callee’s AR (through sp pointer) private void handleCall( String fname, EXPlist args) throws Exception{ ... mem[sp + ..] = ... mem[sp] = fp; fp = sp; interpFunc( fname ); sp = fp; fp = mem[sp]; ... } //end handleCall int evalCall( CALL e ) throws Exception{ ... return retVal; } //end evalCall CS322

10. TestInterp.java public class TestInterp{ public static void main( String [] args ) { try { PROG p = new irParser(System.in).Program(); Interp intp = new Interp(p); intp.go(); } //end try catch (InterpException e) { System.err.println(e.toString()); } //end catch catch (Exception e) { System.err.println(e.toString()); } //end catch } //end main } //end TestInterp CS322