Declarative Intraprocedural Flow Analysis of Java Source Code

Transcription

1 Declarative Intraprocedural Flow Analysis of Java Source Code Emma Nilsson-Nyman Torbjörn Ekman Görel Hedin Eva Magnusson Dept of Computer Science Lund University Programming Tools Group University of Oxford

2 Goals Source code analysis is useful Refactorings Errors Optimizations Simplify its implementation Intraprocedural control flow and data flow Normally: Three address code This paper: Declarative AST computations

3 Tool: Compiler Compiler CFG DF Application LOC Java 1.4 Compiler built using JastAdd Attribute grammars - declarative AST computations Synthesized and inherited attributes Modern extensions Reference attributes Super-imposed graphs Collection attributes Circular attributes Non-terminal attributes

4 Tool: Compiler Compiler CFG DF Application LOC Java 1.4 Compiler built using JastAdd Attribute grammars - declarative AST computations Synthesized and inherited attributes Modern extensions Reference attributes Super-imposed graphs Collection attributes Circular attributes Non-terminal attributes

5 Tool: Compiler Compiler CFG DF Application LOC Java 1.4 Compiler built using JastAdd Attribute grammars - declarative AST computations Synthesized and inherited attributes Modern extensions Reference attributes Super-imposed graphs Collection attributes Circular attributes Non-terminal attributes

6 Intraprocedural Control Flow Compiler CFG DF Application Traditional control flow graphs (CFG) Three address code Basic blocks Successors, predecessors Entry and exit blocks Entry Exit

7 Intraprocedural Control Flow CFG Our control flow graphs Basic blocks -> Statements AST: Entry MethodDecl Block WhileStmt Stmt

8 Intraprocedural Control Flow CFG AST: Our control flow graphs Basic blocks -> Statements MethodDecl Entry and exit nodes Entry Block Exit WhileStmt Stmt

9 Intraprocedural Control Flow CFG AST: Our control flow graphs Basic blocks -> Statements MethodDecl Entry and exit nodes Reference attributes Entry Block Exit Successors WhileStmt Stmt

10 Intraprocedural Control Flow CFG AST: Our control flow graphs Basic blocks -> Statements MethodDecl Entry and exit nodes Reference attributes Entry Block Exit Successors Predecessors WhileStmt Stmt

11 Intraprocedural Control Flow CFG AST: Defining successors: syn Set Stmt.succ(); eq Stmt.succ() = following(); eq WhileStmt.succ() = following().union(getstmt());... Entry MethodDecl Block WhileStmt Exit Stmt

12 Intraprocedural Control Flow CFG AST: Defining predecessors: coll Set Stmt.pred() [empty()] with add; Stmt contributes this to Stmt.pred() for each succ(); Entry MethodDecl Block WhileStmt Exit Stmt

13 Intraprocedural Control Flow Compiler CFG DF Application LOC 300 LOC Approx 240 LOC for Java exceptions Control Flow API: Stmt Stmt entry() Stmt exit() Set succ() Set pred()

14 Intraprocedural Data Flow Compiler CFG DF Application Data Flow (DF) Live variables a = 0; b = 0; a = b + 5; b = a + b;...

15 Intraprocedural Data Flow DF Live variables a = 0; b = 0; a = b + 5; b = a + b;... Definition: in(s) = use(s) (out(s) \ def(s)) out(s) = in(x) x succ(s)

16 Intraprocedural Data Flow DF Live variables a = 0; b = 0; a = b + 5; b = a + b;... Definition: in(s) = use(s) (out(s) \ def(s)) out(s) = in(x) x succ(s)

17 Intraprocedural Data Flow DF Live variables a = 0; b = 0; a = b + 5; b = a + b;... Definition: in(s) = use(s) (out(s) \ def(s)) out(s) = in(x) x succ(s)

18 Intraprocedural Data Flow DF Live variables a = 0; in=, out= b = 0; in=, out= {b} a = b + 5; in= {b}, out= {a,b} b = a + b; in= {a,b}, out= {...}... Definition: in(s) = use(s) (out(s) \ def(s)) out(s) = in(x) x succ(s)

19 Intraprocedural Data Flow DF Live variables a = 0; in=, out= def= {a}, use= b = 0; in=, out= {b} def= {b}, use= a = b + 5; in= {b}, out= {a,b} def= {a}, use= {b} b = a + b; in= {a,b}, out= {...} def= {b}, use= {a,b}... Definition: in(s) = use(s) (out(s) \ def(s)) out(s) = in(x) x succ(s)

20 Intraprocedural Data Flow DF Live variables a = 0; in=, out= def= {a}, use= b = 0; in=, out= {b} def= {b}, use= a = b + 5; in= {b}, out= {a,b} def= {a}, use= {b} b = a + b; in= {a,b}, out= {...} def= {b}, use= {a,b}... Definition: in(s) = use(s) (out(s) \ def(s)) out(s) = in(x) x succ(s)

21 Intraprocedural Data Flow DF in(s) = use(s) (out(s) \ def(s)) syn Set Stmt.in() circular [empty()]; eq Stmt.in() = use().union(out().compl(def())); out(s) = x succ(s) in(x) coll Set Stmt.out() circular [empty()] with add; Stmt contributes in() to Stmt.out() for each pred();

22 Intraprocedural Data Flow DF in(s) = use(s) (out(s) \ def(s)) syn Set Stmt.in() circular [empty()]; eq Stmt.in() = use().union(out().compl(def())); out(s) = x succ(s) in(x) coll Set Stmt.out() circular [empty()] with add; Stmt contributes in() to Stmt.out() for each pred();

23 Intraprocedural Data Flow Compiler CFG DF Application LOC 300 LOC 30 LOC Data Flow API: Stmt Set in() Set out() Set def() Set use()

24 Application: Dead Assignment Compiler CFG DF Application Dead assignment Dead! a = 0; b = 0; a = b + 5; b = a + b;...

25 Application: Dead Assignment DA Dead? a = 0; b = 0; a = b + 5; b = a + b;... true false false... not def(s) out(s) syn boolean Stmt.isDead(); eq Stmt.isDead() =!def().subset(out());

26 Application: Dead Assignment DA Dead? a = 0; true def= {a} out= b = 0; false def= {b} out= {b} a = b + 5; false def= {a} out= {a,b} b = a + b;... def= {b} out= {...}... not def(s) out(s) syn boolean Stmt.isDead(); eq Stmt.isDead() =!def().subset(out());

27 Application: Dead Assignment DA Dead? a = 0; true def= {a} out= b = 0; false def= {b} out= {b} a = b + 5; false def= {a} out= {a,b} b = a + b;... def= {b} out= {...}... not def(s) out(s) syn boolean Stmt.isDead(); eq Stmt.isDead() =!def().subset(out());

28 Application: Dead Assignment Compiler CFG DF Application LOC 300 LOC 30 LOC 10 LOC Dead Assignment API: Stmt boolean isdead()

29 Practical Experience Compilation Time (s) Imperative (s) kloc Declarative (s) Dead Assigns junit antlr bloat jigsaw

30 Practical Experience Compilation Time (s) Imperative (s) kloc Declarative (s) Dead Assigns junit antlr bloat jigsaw

31 Practical Experience Compilation Time (s) Imperative (s) kloc Declarative (s) Dead Assigns junit antlr bloat jigsaw

32 Practical Experience Seconds junit bloat antlr jigsaw Compilation Declarative Imperative kloc

33 Conclusions Concise - close to mathematical definitions Composable modules Source code instead of three address code Extensible Resonable execution times

34 Future Work Additional Analyses Interprocedural control flow and data flow Preliminary work: metrics (Chidamber & Kemerer), call graphs SSA graphs Additional Applications Bug detection Refactorings On going work...

35 The End Thanks for listening! Questions?

36 Exceptions Propagate down (inh) MethodDecl enclosingtrystmt() hasenclosingfinally() Propagate up (syn) Entry Block Exit containsreturn() TryStmt Block Finally TryStmt Block Finally ReturnStmt

37 Intraprocedural Data Flow DF def(s) coll Set Stmt.def() [empty()] with add; VarAccess contributes decl() when isdest() && decl().islocalvariable() to Stmt.def() for enclosingstmt(); use(s) coll Set Stmt.use() [empty()] with add; VarAccess contributes decl() when issource() && decl().islocalvariable() to Stmt.use() for enclosingstmt();