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 386056 2006-03-15 11:31:56Z tcurdt $static interface | InstructionFinder.CodeConstraint - Code patterns found may be checked using an additional user-defined
constraint object whether they really match the needed criterion.
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private static String | compilePattern(String pattern) - Replace symbolic names of instructions with the appropiate character and
remove all white space from string.
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InstructionList | getInstructionList()
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private InstructionHandle[] | getMatch(int matched_from, int match_length)
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private static char | makeChar(short opcode) - Convert opcode number to char.
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private static String | mapName(String pattern) - Map symbolic instruction names like "getfield" to a single character.
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private static String | pattern2string(String pattern)
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private static String | pattern2string(String pattern, boolean make_string)
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private static String | precompile(short from, short to, short extra)
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void | reread() - Reread the instruction list, e.g., after you've altered the list upon a
match.
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Iterator | search(String pattern) - Start search beginning from the start of the given instruction list.
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Iterator | search(String pattern, InstructionHandle from) - Start search beginning from `from'.
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Iterator | search(String pattern, InstructionHandle from, InstructionFinder.CodeConstraint constraint) - Search for the given pattern in the instruction list.
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Iterator | search(String pattern, InstructionFinder.CodeConstraint constraint) - Start search beginning from the start of the given instruction list.
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NO_OPCODES
private static final int NO_OPCODES
OFFSET
private static final int OFFSET
il_string
private String il_string
map
private static final Map map
InstructionFinder
public InstructionFinder(InstructionList il)
il
- instruction list to search for given patterns
compilePattern
private static final String compilePattern(String pattern)
Replace symbolic names of instructions with the appropiate character and
remove all white space from string. Meta characters such as +, * are
ignored.
pattern
- The pattern to compile
- translated regular expression string
getInstructionList
public final InstructionList getInstructionList()
- the inquired instruction list
getMatch
private InstructionHandle[] getMatch(int matched_from,
int match_length)
- the matched piece of code as an array of instruction (handles)
makeChar
private static final char makeChar(short opcode)
Convert opcode number to char.
mapName
private static final String mapName(String pattern)
Map symbolic instruction names like "getfield" to a single character.
pattern
- instruction pattern in lower case
- encoded string for a pattern such as "BranchInstruction".
pattern2string
private static final String pattern2string(String pattern)
pattern2string
private static final String pattern2string(String pattern,
boolean make_string)
precompile
private static String precompile(short from,
short to,
short extra)
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