Presence-Condition Simplification: Problem, Solutions, Applications - PowerPoint PPT Presentation

Presence-Condition Simplification: Problem, Solutions, Applications Alexander von Rhein, Alexander Grebhahn, Sven Apel, Norbert Siegmund, Dirk Beyer, and Thorsten Berger University of Passau, Germany

Alexander von Rhein Presence-Condition Simplification Simplification + Thermodynamics + Friction + Turbocharging + …  This picture would be  Imagine I will speak about much more focused. the pistons in a diesel engine. FOSD meeting 2014 2

Alexander von Rhein Presence-Condition Simplification Presence Conditions  In analysis reports  Verification  Type checking  Dataflow analysis  In source code  #ifdefs  In internal code representations  Variability-aware AST in TypeChef FOSD meeting 2014 3

Alexander von Rhein Presence-Condition Simplification Presence-Condition Simplification Presence Condition Context VariabilityModel = base ⋀ (decrypt ⇔ encrypt) ⋀ (sign ⇔ verify) ⋀ (encrypt ⇒ keys) ⋀ (sign ⇒ keys) simp (Presence Condition, Context) FOSD meeting 2014 4

Alexander von Rhein Presence-Condition Simplification Scenario 2: Variability Model Synthesis Hierarchy Cross-tree constraints  VM synthesis [She, ICSE11] generates models from expressions  Problem: eliminating redundant facts from CTC  Solution:  Presence condition := cross-tree constraints  Context := hierarchy constraints FOSD meeting 2014 5

Alexander von Rhein Presence-Condition Simplification Formal Problem Definition  Given a presence condition 𝑞 and its context 𝑛 : (both given as boolean expressions)  we seek x = simp( 𝑞 , 𝑛 ) such that 1. 𝑛 → (x ≡ 𝑞 ) If 𝑛 holds, we can replace 𝑞 by 𝑦 . 2. 𝑦 should be “smaller” than 𝑞 . We define the size of an expression as the number of its operators. FOSD meeting 2014 6

Alexander von Rhein Presence-Condition Simplification Solutions  R ESTRICT (Coudert & Madre, 1989)  Based on binary decision diagrams  Heuristic to minimize the node count in the BDD  DAG traversal / comparison  Two-level logic minimization (1980s)  Input: an expression and a don’t care set DC  DC states for which variable assignments we don’t care about the value of x  Our don’t care set is ¬ 𝑛  Q UINE -M C C LUSKEY (1956)  E SPRESSO (1986) FOSD meeting 2014 7

Alexander von Rhein Presence-Condition Simplification Experiments  E1 “Classification of Variants”  Presence conditions from Norbert’s ICSE12 paper  E2 “Defect-Location Reporting”  Presence conditions from Sven’s ICSE13 paper  E3 “Code Simplification”  21 #ifdef projects  Almost no condition-simplification potential  E4 “AST Simplification”  Presence conditions from T YPE C HEF AST for Linux kernel  E5 “Scaling” with VM synthesis  Generated variability models from SPLOT  Models with 20 to 90 options FOSD meeting 2014 8

Alexander von Rhein Presence-Condition Simplification E1 “Classification of Variants” size ( simp 𝑞 , 𝑛 ) ReductionFactor = lower is better size ( p ) FOSD meeting 2014 9

Alexander von Rhein Presence-Condition Simplification E5 “Scaling” Care-set: DNF-clauses needed to express p ∧ 𝑛 and ¬p ∧ 𝑛 Can increase with larger variability models FOSD meeting 2014 10

Alexander von Rhein Presence-Condition Simplification Conclusion  Presence-condition simplification  has many application scenarios (reporting, code conditions, …)  is effective (can make conditions much smaller)  is efficient (fast as long as conditions/contexts can be expressed in BDDs)  Future work  Other application scenarios  Specialized algorithms? FOSD meeting 2014 11

Alexander von Rhein Presence-Condition Simplification Christian’s Application? “Order of Feature Interactions” Presence Condition Context Bug-triggering condition (e.g. Linux) Variability model ⋀ other global conditions VariabilityModel = base ⋀ (decrypt ⇔ encrypt) ⋀ (sign ⇔ verify) ⋀ (encrypt ⇒ keys) ⋀ (sign ⇒ keys) simp (Presence Condition, Context) Heuristics! count variables in simplified condition 2 variables left -> 2-way interaction FOSD meeting 2014 12