Link-Time Static Analysis for Efficient Separate Compilation of Object-Oriented Languages

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August Miles
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What is the name of the piece that describes the global compilation?
What type of tree is used?
What is the main purpose of global compilation?

1 Link-Time Static Analysis for Efficient Separate Compilation of Object-Oriented Languages Jean Privat Roland Ducournau LIRMM CNRS/Université Montpellier II France Program Analysis for Software Tools and Engineering Lisbon 2005 Privat, Ducournau (LIRMM) Link-Time Static Analysis PASTE 05 1 / 24

CNRS/Université Montpellier II France Program Analysis for Software Tools

2 Outline 1 Motivation 2 Global Techniques Type Analysis Coloring Binary Tree Dispatch 3 Separate Compilation 4 Benchmarks Description Results Privat, Ducournau (LIRMM) Link-Time Static Analysis PASTE 05 2 / 24

Compilation 4 Benchmarks Description Results

3 Outline 1 Motivation 2 Global Techniques Type Analysis Coloring Binary Tree Dispatch 3 Separate Compilation 4 Benchmarks Description Results Privat, Ducournau (LIRMM) Link-Time Static Analysis PASTE 05 3 / 24

4 Software Engineering Ideal Production of Modular Software Extensible software Reusable software components Object-Oriented Programming (inheritance + late binding) Production of Software in a Modular Way Small code modification small recompilation Shared software components are compiled only once Software components can be distributed in a compiled form Separate Compilation (compile components + link) Privat, Ducournau (LIRMM) Link-Time Static Analysis PASTE 05 4 / 24

modification small recompilation Shared software components are compiled only once Software components can be

5 Compilation of OO Programs Global Techniques Knowledge of the whole program more efficient implementation: Method invocation Access to attribute Subtyping test The Problem Previous works use global technique with global compilation Global compilation is incompatible with modular production Privat, Ducournau (LIRMM) Link-Time Static Analysis PASTE 05 5 / 24

Problem Previous works use global technique with global compilation Global compilation is

6 Our Proposition A Compromise A separate compilation framework that includes 3 global compilation techniques How To? Perform global techniques at link-time Privat, Ducournau (LIRMM) Link-Time Static Analysis PASTE 05 6 / 24

7 Outline 1 Motivation 2 Global Techniques Type Analysis Coloring Binary Tree Dispatch 3 Separate Compilation 4 Benchmarks Description Results Privat, Ducournau (LIRMM) Link-Time Static Analysis PASTE 05 7 / 24

8 Type Analysis Problems Most method invocations are actually monomorphic Implement them with a static direct call (no late binding) Many methods are dead Remove them How to? Approximate 3 sets: Live classes and methods Concrete type of each expression Called methods of each call site Many type analysis exist Privat, Ducournau (LIRMM) Link-Time Static Analysis PASTE 05 8 / 24

Approximate 3 sets: Live classes and methods Concrete type of each expression Called methods

9 Coloring Problem Overhead with standard VFT in multiple inheritance: Subobjects Many VFT (quadratic number, cubic size) Solution Simple inheritance implementation even in multiple inheritance How to? Assign an identifier by class Assign a color (index) by class, method and attribute Minimize size of the tables A NP-hard problem Privat, Ducournau (LIRMM) Link-Time Static Analysis PASTE 05 9 / 24

Assign an identifier by class Assign a color (index) by class, method and attribute Minimize size

10 Coloring (example) A Methods introduced in A A table B C B table Gap C table D D table Privat, Ducournau (LIRMM) Link-Time Static Analysis PASTE / 24

11 Binary Tree Dispatch Problem Prediction of conditional branching of modern processors does not work with VFT Solution Use static jumps instead of VFT How to? Perform a type analysis Assign an identifier by live class For each live call site, enumerate concrete type in a select tree Privat, Ducournau (LIRMM) Link-Time Static Analysis PASTE / 24

Perform a type analysis Assign an identifier by live class For each live call site,

12 Binary Tree Dispatch (Example) Compiling call site x.foo id is the class itentifier of the receiver x Concrete type of x is {A, B, C} Class A B C Identifier foo implementation A foo B foo C foo Generated Code if id <= 15 then if id <= 12 then call B foo else call C foo else call A foo Privat, Ducournau (LIRMM) Link-Time Static Analysis PASTE / 24

C Identifier 19 12 15 foo implementation A foo B foo C foo Generated Code if id <= 15 then

13 Outline 1 Motivation 2 Global Techniques Type Analysis Coloring Binary Tree Dispatch 3 Separate Compilation 4 Benchmarks Description Results Privat, Ducournau (LIRMM) Link-Time Static Analysis PASTE / 24

Compilation 4 Benchmarks Description Results Privat,

14 Separate Compilation Source code Compiled component... void foo() {... bar... } void bar() {... foo... }... local phase local phase metadata... call... metadata bar?... call foo?... global phase Final executable... call... call... 0x x05175 Two Phases Local phase compiles independently of future use Global phase links compiled components Privat, Ducournau (LIRMM) Link-Time Static Analysis PASTE / 24

... global phase Final executable... call.

15 Local Phase Source code Compiled component Local phase Metamodel Metamodel Internal model Input Source code of a class Outputs Metamodel of required classes Compiled version of the class (with unresolved symbols) Metadata : metamodel, internal model Privat, Ducournau (LIRMM) Link-Time Static Analysis PASTE / 24

classes Compiled version of the class (with unresolved symbols) Metadata :

16 Compiled Component Method Call Site Assign a unique symbol by call site Compile into a direct call Attribute Access and Subtype Test Assign a unique symbol by color and identifier Compile into a direct access: in the instance for attribute access in the subtyping table for subtype tests Privat, Ducournau (LIRMM) Link-Time Static Analysis PASTE / 24

identifier Compile into a direct access: in the instance for attribute access in the

17 Global phase Metadata Compiled component Live global Type analysis model Coloring Symbol substitution Final excutable 3 Stages Type analysis: based on the metadata Coloring: computes colors Symbol substitution: generates the final executable Method Call Site Symbols Substitute the address of: monomorphic the invoked method polymorphic w/ BTD a generated select tree polymorphic w/ VFT a generated table access Privat, Ducournau (LIRMM) Link-Time Static Analysis PASTE / 24

executable Method Call Site Symbols Substitute the address of: monomorphic the invoked method polymorphic w/ BTD a

18 Outline 1 Motivation 2 Global Techniques Type Analysis Coloring Binary Tree Dispatch 3 Separate Compilation 4 Benchmarks Description Results Privat, Ducournau (LIRMM) Link-Time Static Analysis PASTE / 24

19 Benchmarks Description Language and Compilers g++: Separate + VFT w/ subobjects SmartEiffel: Global + Binary Tree Dispatch prmc w/ VFT: Separate + Coloring + VFT prmc w/ BTD: Separate + Coloring + BTD Programs The same programs for all language 1 program per OO mechanism Small programs are generated by a script Privat, Ducournau (LIRMM) Link-Time Static Analysis PASTE / 24

Coloring + BTD Programs The same programs for all language 1 program per OO mechanism Small

20 Size of Executables Size of the Exec. (kb) g++ SmartEiffel prmc w/ btd prmc w/ vft Number of Classes Subobjects: many VTF an important overhead prmc: BTD VFT SmartEiffel: better dead code removal Privat, Ducournau (LIRMM) Link-Time Static Analysis PASTE / 24

40 50 60 70 Number of Classes Subobjects: many VTF an important overhead

21 Late Binding Time (s) g++ SmartEiffel prmc w/ btd prmc w/ vft Size of the Concrete Type of the Reicever Subobjects: constant overhead + cache misses Coloring: better on megamorphic calls BTD: better on oligomorphic calls Privat, Ducournau (LIRMM) Link-Time Static Analysis PASTE / 24

22 Attribute Access Time (s) g++ SmartEiffel prmc Size of the Concrete Type of Receiver Subobjects: constant overhead Coloring: constant attribute access SmartEiffel: can degenerate Privat, Ducournau (LIRMM) Link-Time Static Analysis PASTE / 24

23 Type Downcast Time (s) g++ SmartEiffel prmc Size of the Concrete Type of the Casted Expression g++: bad performances Coloring and BTD: equivalent and mainly constant Privat, Ducournau (LIRMM) Link-Time Static Analysis PASTE / 24

24 Summary Summary A separate compilation framework with global techniques for statically typed class-based languages Better modularity than global compilers Better performance than other separate compilers Outlook Shared libraries linked at load-time or dynamically loaded Time overhead of the global phase (link) Privat, Ducournau (LIRMM) Link-Time Static Analysis PASTE / 24

Link-Time Static Analysis for Efficient Separate Compilation of Object-Oriented Languages

Link-Time Static Analysis for Efficient Separate Compilation of Object-Oriented Languages Link-Time Static nalysis for Efficient Separate Compilation of Object-Oriented Languages Jean Privat privat@lirmm.fr LIRMM CNRS Université Montpellier II 161 rue da 34392 Montpellier cedex 5, France Roland

Link-Time Static Analysis for Efficient Separate Compilation of Object-Oriented Languages

What is the name of the piece that describes the global compilation?

What type of tree is used?

What is the main purpose of global compilation?