org.apache.bcel.util
Class InstructionFinder
java.lang.Object
org.apache.bcel.util.InstructionFinder
public class InstructionFinder
extends java.lang.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
Regexp 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]);
...
}
$Id: InstructionFinder.java,v 1.1.1.1 2001/10/29 20:00:30 jvanzyl Exp $static interface | InstructionFinder.CodeConstraint - Code patterns found may be checked using an additional
user-defined constraint object whether they really match the needed criterion.
|
InstructionFinder
public InstructionFinder(InstructionList il)
il
- instruction list to search for given patterns
getInstructionList
public final InstructionList getInstructionList()
- 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 search(String pattern)
Start search beginning from the start of the given instruction list.
pattern
- the instruction pattern to search for, where case is ignored
- iterator of matches where e.nextElement()
returns an array of instruction handles describing the matched
area
search
public final Iterator search(String pattern,
InstructionHandle from)
Start search beginning from `from'.
pattern
- the instruction pattern to search for, where case is ignoredfrom
- where to start the search in the instruction list
- iterator of matches where e.nextElement() returns an array of instruction handles
describing the matched area
search
public final Iterator 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.
pattern
- the instruction pattern to search for, where case is ignoredfrom
- where to start the search in the instruction listconstraint
- optional CodeConstraint to check the found code pattern for
user-defined constraints
- iterator of matches where e.nextElement() returns an array of instruction handles
describing the matched area
search
public final Iterator search(String pattern,
InstructionFinder.CodeConstraint constraint)
Start search beginning from the start of the given instruction list.
Check found matches with the constraint object.
pattern
- the instruction pattern to search for, case is ignoredconstraint
- constraints to be checked on matching code
- instruction handle or `null' if the match failed