Package org.apache.bcel.util

Class InstructionFinder

java.lang.Object
org.apache.bcel.util.InstructionFinder
public class InstructionFinder extends Object
InstructionFinder is a tool to search for given instructions patterns, i.e., match sequences of instructions in an instruction list via regular expressions. This can be used, e.g., in order to implement a peep hole optimizer that looks for code patterns and replaces them with faster equivalents.

This class internally uses the java.util.regex package to search for regular expressions. A typical application would look like this: 



   InstructionFinder f   = new InstructionFinder(il);
   String            pat = "IfInstruction ICONST_0 GOTO ICONST_1 NOP (IFEQ|IFNE)";

   for (Iterator i = f.search(pat, constraint); i.hasNext(); ) {
   InstructionHandle[] match = (InstructionHandle[])i.next();
   ...
   il.delete(match[1], match[5]);
   ...
   }
See Also:

  • Constructor Details

  • Method Details

    • getInstructionList

      public final InstructionList getInstructionList()
      Returns:
      the inquired instruction list

    • reread

      public final void reread()
      Reread the instruction list, e.g., after you've altered the list upon a match.

    • search

      public final Iterator<InstructionHandle[]> search(String pattern)
      Start search beginning from the start of the given instruction list.
      Parameters:
      pattern - the instruction pattern to search for, where case is ignored
      Returns:
      iterator of matches where e.nextElement() returns an array of instruction handles describing the matched area

    • search

      public final Iterator<InstructionHandle[]> search(String pattern, InstructionFinder.CodeConstraint constraint)
      Start search beginning from the start of the given instruction list. Check found matches with the constraint object.
      Parameters:
      pattern - the instruction pattern to search for, case is ignored
      constraint - constraints to be checked on matching code
      Returns:
      instruction handle or 'null' if the match failed

    • search

      public final Iterator<InstructionHandle[]> search(String pattern, InstructionHandle from)
      Start search beginning from 'from'.
      Parameters:
      pattern - the instruction pattern to search for, where case is ignored
      from - where to start the search in the instruction list
      Returns:
      iterator of matches where e.nextElement() returns an array of instruction handles describing the matched area

    • search

      public final Iterator<InstructionHandle[]> search(String pattern, InstructionHandle from, InstructionFinder.CodeConstraint constraint)
      Search for the given pattern in the instruction list. You can search for any valid opcode via its symbolic name, e.g. "istore". You can also use a super class or an interface name to match a whole set of instructions, e.g. "BranchInstruction" or "LoadInstruction". "istore" is also an alias for all "istore_x" instructions. Additional aliases are "if" for "ifxx", "if_icmp" for "if_icmpxx", "if_acmp" for "if_acmpxx". Consecutive instruction names must be separated by white space which will be removed during the compilation of the pattern. For the rest the usual pattern matching rules for regular expressions apply.

      Example pattern: 

       search("BranchInstruction NOP ((IfInstruction|GOTO)+ ISTORE Instruction)*");

      If you alter the instruction list upon a match such that other matching areas are affected, you should call reread() to update the finder and call search() again, because the matches are cached.

      Parameters:
      pattern - the instruction pattern to search for, where case is ignored
      from - where to start the search in the instruction list
      constraint - optional CodeConstraint to check the found code pattern for user-defined constraints
      Returns:
      iterator of matches where e.nextElement() returns an array of instruction handles describing the matched area