Package org.apache.bcel.util
Class InstructionFinder
- java.lang.Object
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- org.apache.bcel.util.InstructionFinder
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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 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:
Instruction
,InstructionList
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Nested Class Summary
Nested Classes Modifier and Type Class Description 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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Field Summary
Fields Modifier and Type Field Description private InstructionHandle[]
handles
private InstructionList
il
private java.lang.String
ilString
private static java.util.Map<java.lang.String,java.lang.String>
map
private static int
NO_OPCODES
private static int
OFFSET
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Constructor Summary
Constructors Constructor Description InstructionFinder(InstructionList il)
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Method Summary
All Methods Static Methods Instance Methods Concrete Methods Modifier and Type Method Description private static java.lang.String
compilePattern(java.lang.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 java.lang.String
mapName(java.lang.String pattern)
Map symbolic instruction names like "getfield" to a single character.private static java.lang.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.java.util.Iterator<InstructionHandle[]>
search(java.lang.String pattern)
Start search beginning from the start of the given instruction list.java.util.Iterator<InstructionHandle[]>
search(java.lang.String pattern, InstructionHandle from)
Start search beginning from `from'.java.util.Iterator<InstructionHandle[]>
search(java.lang.String pattern, InstructionHandle from, InstructionFinder.CodeConstraint constraint)
Search for the given pattern in the instruction list.java.util.Iterator<InstructionHandle[]>
search(java.lang.String pattern, InstructionFinder.CodeConstraint constraint)
Start search beginning from the start of the given instruction list.
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Field Detail
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OFFSET
private static final int OFFSET
- See Also:
- Constant Field Values
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NO_OPCODES
private static final int NO_OPCODES
- See Also:
- Constant Field Values
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map
private static final java.util.Map<java.lang.String,java.lang.String> map
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il
private final InstructionList il
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ilString
private java.lang.String ilString
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handles
private InstructionHandle[] handles
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Constructor Detail
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InstructionFinder
public InstructionFinder(InstructionList il)
- Parameters:
il
- instruction list to search for given patterns
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Method Detail
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reread
public final void reread()
Reread the instruction list, e.g., after you've altered the list upon a match.
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mapName
private static java.lang.String mapName(java.lang.String pattern)
Map symbolic instruction names like "getfield" to a single character.- Parameters:
pattern
- instruction pattern in lower case- Returns:
- encoded string for a pattern such as "BranchInstruction".
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compilePattern
private static java.lang.String compilePattern(java.lang.String pattern)
Replace symbolic names of instructions with the appropiate character and remove all white space from string. Meta characters such as +, * are ignored.- Parameters:
pattern
- The pattern to compile- Returns:
- translated regular expression string
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getMatch
private InstructionHandle[] getMatch(int matched_from, int match_length)
- Returns:
- the matched piece of code as an array of instruction (handles)
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search
public final java.util.Iterator<InstructionHandle[]> search(java.lang.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 ignoredfrom
- where to start the search in the instruction listconstraint
- 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
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search
public final java.util.Iterator<InstructionHandle[]> search(java.lang.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
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search
public final java.util.Iterator<InstructionHandle[]> search(java.lang.String pattern, InstructionHandle from)
Start search beginning from `from'.- Parameters:
pattern
- the instruction pattern to search for, where case is ignoredfrom
- 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
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search
public final java.util.Iterator<InstructionHandle[]> search(java.lang.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 ignoredconstraint
- constraints to be checked on matching code- Returns:
- instruction handle or `null' if the match failed
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makeChar
private static char makeChar(short opcode)
Convert opcode number to char.
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getInstructionList
public final InstructionList getInstructionList()
- Returns:
- the inquired instruction list
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precompile
private static java.lang.String precompile(short from, short to, short extra)
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