new OPT_DominatorsPhase().perform(ir);
new OPT_DominatorsPhase(true).perform(ir);
  void perform (OPT_IR ir) {    this.ir = ir;        if (ir.hasReachableExceptionHandlers()) return;    OPT_DefUse.computeDU (ir);    new OPT_Simple().perform(ir);    new OPT_BranchOptimizations(-1).perform(ir, true);    new OPT_CFGTransformations().perform(ir);    new OPT_DominatorsPhase().perform(ir);    OPT_DefUse.computeDU (ir);    ir.setInstructionScratchWord(0);        unrollLoops (ir);  }