constantselect.java

一种将c高级语言转化给VHDL的编译器

/*
 *
 LA-CC 05-135 Trident 0.7.1

Copyright Notice
Copyright 2006 (c) the Regents of the University of California.

This Software was produced under a U.S. Government contract
(W-7405-ENG-36) by Los Alamos National Laboratory, which is operated
by the University of California for the U.S. Department of Energy. The
U.S. Government is licensed to use, reproduce, and distribute this
Software. Permission is granted to the public to copy and use this
Software without charge, provided that this Notice and any statement
of authorship are reproduced on all copies. Neither the Government nor
the University makes any warranty, express or implied, or assumes any
liability or responsibility for the user of this Software.


 */


package fp.passes;
import fp.flowgraph.*;
import java.util.*;
 
public class ConstantSelect extends Pass implements BlockPass {
 
  /*
    The purpose of this pass is to use constants to eliminate 
    select instructions.
  */
   
 
  public ConstantSelect(PassManager pm) {
    super(pm);
  }
 
  public boolean optimize(BlockNode node) {
    // For example, in the following instruction:
    // %a5 = select %TRUE %a3 %a4 predicate
    // This instruction can be removed and then
    // substitute %a3 for %a5 hereafter.

    // The predicate can be ignored, because a
    // subsequent use of %a5, for example, would 
    // be using the same predicate, or one that is
    // more inclusive.

    // Store substitution pair in a hash map.
    boolean steadyState = false;

    while (!steadyState) {

      steadyState = true;
      HashMap subsMap = new HashMap();  

      ArrayList list = node.getInstructions();
      ArrayList instRemovalList = new ArrayList();

      for(Iterator iter = list.iterator(); iter.hasNext(); ) {
	Instruction inst = (Instruction) iter.next(); 
	// Examine select instructions for constant condition value.
	if (Select.conforms(inst)) {
	  BooleanOperand bool = Select.getCondition(inst);
	  if (bool == BooleanOperand.TRUE) {
	    //System.out.println("Found a select with a TRUE");
	    Operand res = Select.getResult(inst);
	    Operand val1 = Select.getVal1(inst);
	    subsMap.put(res, val1);
	    instRemovalList.add(inst);
	    steadyState = false;
	  } else if (bool == BooleanOperand.FALSE) {
	    //System.out.println("Found a select with a FALSE");
	    Operand res = Select.getResult(inst);
	    Operand val2 = Select.getVal2(inst);
	    subsMap.put(res, val2);
	    instRemovalList.add(inst);
	    steadyState = false;
	  }
	}
      }

      for(Iterator iter = instRemovalList.iterator(); iter.hasNext(); ) {
	Instruction inst = (Instruction) iter.next(); 
	node.removeInstruction(inst);
      }

      boolean change;
      do {
	change = false;
	if (subsMap.size() > 0) {
	  HashMap instMap = new HashMap();

	  for(Iterator iter = list.iterator(); iter.hasNext(); ) {
	    Instruction inst = (Instruction) iter.next(); 

	    // Check uses for any substitutions.
	    int numDefs = inst.getNumberOfDefs();
	    int numUses = inst.getNumberOfUses();
	    for(int i = numDefs; i < (numDefs + numUses); i++) {
	      Operand use = inst.getOperand(i);
	      Operand useSub = (Operand)(subsMap.get(use));

	      // Record the substitution we will make later
	      if (useSub != null) {
	  	instMap.put(inst, use);
	      }
	    }
	  }

	  Set instSet = instMap.keySet();

	  // Remove all the instructions that need substitutions 
	  for(Iterator iter = instSet.iterator(); iter.hasNext(); ) {
	    Instruction inst = (Instruction) iter.next(); 
	    node.removeInstruction(inst);
	  }

	  // make the substitution
	  for(Iterator iter = instSet.iterator(); iter.hasNext(); ) {
	    Instruction inst = (Instruction) iter.next(); 
	    Operand use = (Operand)instMap.get(inst);
	    Operand useSub = (Operand)(subsMap.get(use));
	    inst.replaceOperand(use, useSub);
	    node.addInstruction(inst);
	    change = true;
	  }
	}
      } while(change == true);
    }
    
    return true;
  }
 
  public String name() {
    return "ConstantSelect";
  }
 
 
}