Compiler Support for Compiler Support for

Profiling Profiling

C++ C++ Template Template

MetaprogramsMetaprogramsJózsef Mihalicza, Norbert Pataki, Zoltán Porkoláb

Eötvös Loránd University

Faculty of Informatics

Dept. Of Programming Languages and Compilers

SPLST’11

OutlineOutline

Templates in C++Templates in C++

Template metaprogramsTemplate metaprograms

EfficiencEfficiencyy problems with C++ problems with C++

templates templates

Earlier efforts / Related worksEarlier efforts / Related works

Our solutionOur solution

ExamplesExamples

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C++ templatesC++ templates

Parametric polymorphismParametric polymorphism

Fundamental tools for generic Fundamental tools for generic

programmingprogramming

UnconstrainedUnconstrained

Implemented by instantiationImplemented by instantiation

Typical solution: multiply header filesTypical solution: multiply header files

Examples: standard library, inlc. STLExamples: standard library, inlc. STL

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Template metaprogramsTemplate metaprograms

Unruh 1994: prime numbersUnruh 1994: prime numbers

Has been proved to be Turing-Has been proved to be Turing-

completecomplete

Functional programming paradigmFunctional programming paradigm Recursion + pattern matchingRecursion + pattern matching

Referential transparencyReferential transparency

No assignmentNo assignment

(Almost) no i/o(Almost) no i/o

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Template metaprograms Template metaprograms

22template <int N>template <int N>

struct Factorialstruct Factorial

{{

enum { value = Factorial<N-1>::value * N }; enum { value = Factorial<N-1>::value * N };

};};

template <>template <>

struct Factorial<0>struct Factorial<0>

{{

enum { value = 1 };enum { value = 1 };

};};

int main()int main()

{{

int fact5 = Factorial<5>::value;int fact5 = Factorial<5>::value;

}}

SPLST’11

Template metaprogram Template metaprogram

usageusage Expression templates (blitz++, …)Expression templates (blitz++, …)

Parser generators (boost::spirit, …)Parser generators (boost::spirit, …)

Static interface checking (boost::concept, Static interface checking (boost::concept,

…)…)

Configuration management (boost::math, Configuration management (boost::math,

…)…)

Active libraries (…)Active libraries (…)

DSL integration (Porkolab-DSL integration (Porkolab-

Sinkovics,GPCE2010)Sinkovics,GPCE2010)

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Efficiency issuesEfficiency issues

Recursive header inclusionsRecursive header inclusions

Data structures (recursive templates)Data structures (recursive templates)

Imitating data manipulationsImitating data manipulations

Complex, unclear syntaxComplex, unclear syntax

Compilers was not optimized for TMPsCompilers was not optimized for TMPs

Hard to predict compilation time and Hard to predict compilation time and

memory usagememory usage

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Earlier effortsEarlier efforts Veldhuizen (1996- )Veldhuizen (1996- )

Ad-hoc measurement, non-standard tools Ad-hoc measurement, non-standard tools

Gurtovoy – Abrahams (2004)Gurtovoy – Abrahams (2004) Measuring full programs to identify idiomsMeasuring full programs to identify idioms

Porkolab-MihaliczaPorkolab-Mihalicza Debugging (GPCE 2006) + Profiling (Splst 2007)Debugging (GPCE 2006) + Profiling (Splst 2007)

Steven Watanabe (2008)Steven Watanabe (2008) Boost library extensionBoost library extension

Compilers was not optimized for TMPsCompilers was not optimized for TMPs

Hard to predict compilation time and memory Hard to predict compilation time and memory

usageusage

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Measuring compilation Measuring compilation

unitsunits AdvantagesAdvantages

Easy, platform and compiler independentEasy, platform and compiler independent

Get the big picture, understand behaviourGet the big picture, understand behaviour

Statistically correctStatistically correct

DrawbacksDrawbacks Artificial problemsArtificial problems

Not revealing details in complex programsNot revealing details in complex programs

Overheads (code generation, preprocessor)Overheads (code generation, preprocessor)

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Preprocessor overheadPreprocessor overhead

Instrumentation Instrumentation

frameworkframework

Code instrumentationCode instrumentation

Code instrumentation 2Code instrumentation 2

Warning generationWarning generation

OverheadOverhead

Deviation of Deviation of

overheadoverhead

Modified compilerModified compiler

SummarySummary

We have to measure template metaprogramsWe have to measure template metaprograms(and perhaps all large projects with many (and perhaps all large projects with many templates)templates)

Measuring compilation units are not feasible in Measuring compilation units are not feasible in real-world industrial projectsreal-world industrial projects

Preprocessing step has a significant overheadPreprocessing step has a significant overhead Instrumentation has a linear distortionInstrumentation has a linear distortion Modification of compiler can eliminate warning Modification of compiler can eliminate warning

overheadoverhead Template metaprogram profiling is still learnedTemplate metaprogram profiling is still learned

Thank you for your Thank you for your

attention!attention!Questions?

József Mihalicza, Norbert Pataki, Zoltán Porkoláb

jmihalicza@gmail.hu, patakino@elte.hu, gsd@elte.hu