AdaSlicer: An Ada Program Slicer

1
AdaSlicer An Ada Program Slicer

• Ricky E. Sward
• Department of Computer Science
• USAF Academy, CO
• ricky.sward_at_usafa.edu

A.T. Chamillard Computer Science Department
University of Colorado Spring, CO
chamillard_at_cs.uccs.edu
2
Overview

• Background
• Global Variables
• Identifying Globals
• Annotating Globals
• Re-engineering Globals
• ASIS
• Conclusions

3
Background

• Identifying global variables is well-defined
• Discussed in programming language texts
• Tools available to identify global variables
• Useful to identify during re-engineering
• In SPARK, globals are allowed, must annotate
• Goal is to convert to parameters

4
Overview

• Background
• Global Variables
• Identifying Globals
• Annotating Globals
• Re-engineering Globals
• ASIS
• Conclusions

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Global Variables

• In Ada, each variable must be declared
• Scope defines where a variable is visible
• A and B are local variables

procedure Local is A Integer 0 B
Integer 3 begin A B 2 end Local
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Global Variables

• A non-local variable is defined outside scope
• A global variable is non-local and also visible
  to entire program

procedure Outer_Procedure is A Integer
0 procedure Inner_Procedure is B
Integer 1 begin A A
B end Inner_Procedure begin A A
1 end Outer_Procedure
A is global
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Global Variables

• A package variable is in package global scope
• A package variable is a good global

package One_Global is X Integer 10
procedure Outera (A in out Integer) end
One_Global package body One_Global is
procedure Outera (A in out Integer) is
begin X X 1 end Outera end
One_Global
Package var X
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Overview

• Background
• Global Variables
• Identifying Globals
• Annotating Globals
• Re-engineering Globals
• ASIS
• Conclusions

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Identifying Global Variables

• Using static analysis consider the scope of
  variables
• Ignore local variables and parameters

package One_Global is X Integer 10
procedure Outera (A in out Integer) end
One_Global package body One_Global is
procedure Outera (A in out Integer) is
Y Integer 0 procedure Innerb (B
in out Integer) is begin
B X X X 1
end Innerb begin Y A
Innerb(A) end Outera end One_Global
Y is local
A is a parameter
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Identifying Global Variables

• Using static analysis consider the scope of
  variables
• Ignore local variables and parameters

package One_Global is X Integer 10
procedure Outera (A in out Integer) end
One_Global package body One_Global is
procedure Outera (A in out Integer) is
Y Integer 0 procedure Innerb (B
in out Integer) is begin
B X X X 1
end Innerb begin Y A
Innerb(A) end Outera end One_Global
X is global
B is a parameter
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Identifying Global Variables

• Access declaration information in symbol table
• Ok if package variable and procedure in outer
  scope

package One_Global is X Integer 10
procedure Outera (A in out Integer) end
One_Global package body One_Global is
procedure Outera (A in out Integer) is
Y Integer 0 procedure Innerb (B
in out Integer) is begin
B X X X 1
end Innerb begin Y A
Innerb(A) end Outera end One_Global
Symbol Table
Variable Scope Nesting
Y Outera 1
X One_Global 0
... ... ...
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Overview

• Background
• Global Variables
• Identifying Globals
• Annotating Globals
• Re-engineering Globals
• ASIS
• Conclusions

13
Annotating Global Variables

• One option in our tool is to add SPARK annotation
• -- global ltmodegt ltvariable namegt

package One_Global is X Integer 10
procedure Outera (A in out Integer) end
One_Global package body One_Global is
procedure Outera (A in out Integer) is
Y Integer 0 procedure Innerb (B
in out Integer) is -- global in out
X begin B X
X X 1 end Innerb
begin Y A Innerb(A)
end Outera end One_Global
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Annotating Global Variables

• To determine mode of global, look at DEF and REF

package One_Global is X Integer 10
procedure Outera (A in out Integer) end
One_Global package body One_Global is
procedure Outera (A in out Integer) is
Y Integer 0 procedure Innerb (B
in out Integer) is -- global in out
X begin B X
X X 1 end Innerb
begin Y A Innerb(A)
end Outera end One_Global
REF set B, X
DEF set B, X
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Overview

• Background
• Global Variables
• Identifying Globals
• Annotating Globals
• Re-engineering Globals
• ASIS
• Conclusions

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Re-engineering Global Variables

• Add global as formal parameter
• Add global as actual parameter in call
• Use the global definition of the variable to
  build the parameter
• Use the DEF and REF set to build the mode
• Appears only in REF, build as in parameter
• Appears only in DEF, build as out parameter
• Appears in both DEF and REF, build as in out
  using conservative approach
• For example...

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Re-engineering Global Variables
package One_Global_New is X Integer
10 procedure Outera (A in out
Integer) end One_Global package body
One_Global_New is procedure Outera (A in
out Integer) is Y Integer 0
procedure Innerb ( B in out
Integer X in out Integer ) is
begin B X
X X 1 end Innerb begin
Y A Innerb(B gt A, X gt
X) end Outera end One_Global_New
Add as formal
Add as actual
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Re-engineering Global Variables

• What if a global is nested deeper?
• May need to change two or more procedures
• Add global as formal parameter
• Add global as actual parameter
• Check to see if actual is global
• For example...

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Re-engineering Global Variables
package body Two_Globals is procedure Outera (
A in out Integer ) is procedure Innerb
( B in out Integer ) is
procedure Innerc ( C in out
Integer ) is begin C Y
Y Y 1 end Innerc
begin B B 1 Innerc(C gt
B) end Innerb begin Innerb(B gt
A) end Outera end Two_Globals
Y is a global
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Re-engineering Global Variables
package body Two_Globals_new is procedure
Outera ( A in out Integer ) is
procedure Innerb ( B in out
Integer) is procedure Innerc (
C in out Integer Y in out
Integer ) is begin C Y
Y Y 1 end Innerc
begin B B 1 Innerc(C gt
B, Y gt Y) end Innerb begin
Innerb(B gt A) end Outera end
Two_Globals_new
Need Y here
Y is a global
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Re-engineering Global Variables
package body Two_Globals_new is procedure
Outera ( A in out Integer ) is
procedure Innerb ( B in out
Integer Y in out Integer) is
procedure Innerc ( C in out
Integer Y in out Integer ) is
begin C Y Y
Y 1 end Innerc begin
B B 1 Innerc(C gt B, Y gt Y)
end Innerb begin Innerb(B gt A, Y gt
Y) end Outera end Two_Globals_new
Add Y as formal
Add Y as formal
Add Y as actual
Add Y as actual
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Overview

• Background
• Global Variables
• Identifying Globals
• Annotating Globals
• Re-engineering Globals
• ASIS
• Conclusions

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Ada Semantic Interface Specification (ASIS)

• Procedures for accessing Ada program structure
• Used ASIS 3.15a1 GNAT Ada Compiler 3.15a1
• Reasonable learning curve
• Examples provided with ASIS are great
• Very powerful tool

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Conclusions

• Need to develop a graphical user interface
• Target re-engineering efforts
• Also automatic refactoring applications