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java.lang.Objectorg.apache.bcel.util.InstructionFinder
public class InstructionFinder
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]); ... }
Instruction
,
InstructionList
Nested Class Summary | |
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static interface |
InstructionFinder.CodeConstraint
Code patterns found may be checked using an additional user-defined constraint object whether they really match the needed criterion. |
Field Summary | |
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private InstructionHandle[] |
handles
|
private InstructionList |
il
|
private String |
il_string
|
private static Map |
map
|
private static int |
NO_OPCODES
|
private static int |
OFFSET
|
Constructor Summary | |
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InstructionFinder(InstructionList il)
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Method Summary | |
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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. |
InstructionList |
getInstructionList()
|
private InstructionHandle[] |
getMatch(int matched_from,
int match_length)
|
private static char |
makeChar(short opcode)
Convert opcode number to char. |
private static String |
mapName(String pattern)
Map symbolic instruction names like "getfield" to a single character. |
private static String |
pattern2string(String pattern)
|
private static String |
pattern2string(String pattern,
boolean make_string)
|
private static String |
precompile(short from,
short to,
short extra)
|
void |
reread()
Reread the instruction list, e.g., after you've altered the list upon a match. |
Iterator |
search(String pattern)
Start search beginning from the start of the given instruction list. |
Iterator |
search(String pattern,
InstructionFinder.CodeConstraint constraint)
Start search beginning from the start of the given instruction list. |
Iterator |
search(String pattern,
InstructionHandle from)
Start search beginning from `from'. |
Iterator |
search(String pattern,
InstructionHandle from,
InstructionFinder.CodeConstraint constraint)
Search for the given pattern in the instruction list. |
Methods inherited from class java.lang.Object |
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clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait |
Field Detail |
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private static final int OFFSET
private static final int NO_OPCODES
private static final Map map
private InstructionList il
private String il_string
private InstructionHandle[] handles
Constructor Detail |
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public InstructionFinder(InstructionList il)
il
- instruction list to search for given patternsMethod Detail |
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public final void reread()
private static final String mapName(String pattern)
pattern
- instruction pattern in lower case
private static final String compilePattern(String pattern)
pattern
- The pattern to compile
private InstructionHandle[] getMatch(int matched_from, int match_length)
public final Iterator search(String pattern, InstructionHandle from, InstructionFinder.CodeConstraint constraint)
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
public final Iterator search(String pattern)
pattern
- the instruction pattern to search for, where case is ignored
public final Iterator search(String pattern, InstructionHandle from)
pattern
- the instruction pattern to search for, where case is ignoredfrom
- where to start the search in the instruction list
public final Iterator search(String pattern, InstructionFinder.CodeConstraint constraint)
pattern
- the instruction pattern to search for, case is ignoredconstraint
- constraints to be checked on matching code
private static final char makeChar(short opcode)
public final InstructionList getInstructionList()
private static String precompile(short from, short to, short extra)
private static final String pattern2string(String pattern)
private static final String pattern2string(String pattern, boolean make_string)
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