Examples of wyil.lang.Code

wyil.lang.Code

Represents a WyIL bytecode. The Whiley Intermediate Language (WyIL) employs register-based bytecodes (as opposed to e.g. the Java Virtual Machine, which uses stack-based bytecodes). During execution, one can think of the "machine" as maintaining a call stack made up of "frames". For each function or method on the call stack, the corresponding frame consists of zero or more registers. Bytecodes may read/write values from registers. Like the Java Virtual Machine, WyIL uses unstructured control-flow. However, unlike the JVM, it also allows variables to be automatically retyped by runtime type tests. The following illustrates:

 function sum([int] data) => int: int r = 0 for item in data: r = r + item return r

This function is compiled into the following WyIL bytecode:

 function sum([int] data) => int: body: const %1 = 0          : int assign %2 = %0        : [int] forall %3 in %2 ()    : [int] assign %4 = %1    : int add %1 = %4, %3   : int return %1             : int

Here, we can see that every bytecode is associated with one (or more) types. These types are inferred by the compiler during type propagation.

Each bytecode has a binary format which identifies the opcode, registers used and pool items used (e.g. names, constants, etc). The generic organisation of a bytecode is as follows:

 +--------+-----------+------------+ | opcode | registers | pool items | +--------+-----------+------------+

The opcode is currently always 1 byte, whilst the remainder varies between instructions. Many bytecodes assign to a target register and read values from operand registers. Such bytecodes are organised as follows:

 +--------+--------+----------+------------+ | opcode | target | operands | pool items | +--------+--------+----------+------------+

@author David J. Pearce

  }


  @Override
  public Env propagate(int index, Entry entry, Env environment) {
    rewrites.put(index,null);
    Code code = entry.code;
    boolean isLive = true;
    environment = (Env) environment.clone();


    if (code instanceof Code.AbstractAssignable) {
      Code.AbstractAssignable aa = (Code.AbstractAssignable) code;

  protected BitSet infer(Code.Block block, int start, int end) {
    BitSet modified = new BitSet(block.numSlots());
    int size = block.size();
    for(int i=start;i<end;++i) {
      Code.Block.Entry entry = block.get(i);
      Code code = entry.code;


      if (code instanceof Code.AbstractAssignable) {
        Code.AbstractAssignable aa = (Code.AbstractAssignable) code;
        if(aa.target() != Codes.NULL_REG) {
          modified.set(aa.target());

      //String lin;
      String tag = "\t/* entry# " + idx + "*/";


      this.sourceTag = tag;
      bodyAddLineNL(  "// block.entry #" + idx  );
      Code cod = blkIn.code;
      tmp = this.writeSourceLineID(blkIn);
      bodyAddLine(tmp);


      String temp = cod.toString();
      bodyAddLineNL(  "//             Looks like " + safeString2(temp)  );


      String[] frags = temp.split(" ", 4);
      String opc = frags[0];
      if (cod instanceof Codes.Const) {

Related Classes of wyil.lang.Code

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