Class SSAPiInstruction

java.lang.Object
com.ibm.wala.ssa.SSAInstruction
com.ibm.wala.ssa.SSAAbstractUnaryInstruction
com.ibm.wala.ssa.SSAUnaryOpInstruction
com.ibm.wala.ssa.SSAPiInstruction
public class SSAPiInstruction extends SSAUnaryOpInstruction
A Pi instruction is a dummy assignment inserted at the tail of a basic block, in order to get a new variable name to associate with some flow-insensitive dataflow fact. You can build an IR with or without Pi instructions, depending on SSAOptions selected.

A Pi instruction is linked to its "cause" instruction, which is usually a conditional branch.

For example, the following pseudo-code 

    boolean condition = (x instanceof Integer);
    if (condition) {
       S1;
    else {
       S2;
    }

could be translated roughly as follows: 

    boolean condition = (x instanceof Integer);
    LABEL1: if (condition) {
       x_1 = pi(x, LABEL1);
       S1;
    else {
       x_2 = pi(x, LABEL2);
       S2;
    }

  • Constructor Details

    • SSAPiInstruction

      public SSAPiInstruction(int iindex, int result, int val, int piBlock, int successorBlock, SSAInstruction cause)
      Parameters:
      successorBlock - the successor block; this PI assignment happens on the transition between this basic block and the successor block.

  • Method Details

    • copyForSSA

      public SSAInstruction copyForSSA(SSAInstructionFactory insts, int[] defs, int[] uses)
      Description copied from class: SSAInstruction
      This method is meant to be used during SSA conversion for an IR that is not in SSA form. It creates a new SSAInstruction of the same type as the receiver, with a combination of the receiver's uses and defs and those from the method parameters.

      In particular, if the 'defs' parameter is null, then the new instruction has the same defs as the receiver. If 'defs' is not null, it must be an array with a size equal to the number of defs that the receiver instruction has. In this case, the new instruction has defs taken from the array. The uses of the new instruction work in the same way with the 'uses' parameter.

      Note that this only applies to CAst-based IR translation, since Java bytecode-based IR generation uses a different SSA construction mechanism.

      TODO: move this into the SSAInstructionFactory

      Overrides:
      copyForSSA in class SSAUnaryOpInstruction

    • toString

      public String toString(SymbolTable symbolTable)
      Overrides:
      toString in class SSAUnaryOpInstruction

    • visit

      public void visit(SSAInstruction.IVisitor v)
      Description copied from class: SSAInstruction
      Apply an IVisitor to this instruction. We invoke the appropriate IVisitor method according to the type of this instruction.
      Overrides:
      visit in class SSAUnaryOpInstruction
      See Also:

    • getSuccessor

      public int getSuccessor()

    • getPiBlock

      public int getPiBlock()

    • getCause

      public SSAInstruction getCause()

    • getVal

      public int getVal()