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Seminar: Automation, Compilers, and Code-Generation

Chair: High Performance and Automatic Computing

RWTH AACHEN UNIVERSITY

Safdar Dabeer Khan

Outline

yOverview yStatic Compilation yVirtual machines yTraditional Approaches yJIT yDefining JIT yJIT: A Combination of two traditional approaches yWorking Mechanism yConceptual Idea yTechnical steps yAdvantages & Drawbacks yApplications yExploring JIT & java yCompilation in java yVM & JVM yJIT in JVM yRuntime optimizations by JIT yStartup Delay and Possible Optimizations yJava HotSpot

Compiler and Interpreter

Basic conceptual view of both techniques, remember they are not mutually exclusive.

Interpreter

Source

program

Compiler

Input parameters

Output

Source

program

Platform

Target Program

Output

Produce machine code directly executable by computer hardware.

Generates a stand-alone machine code program.

Can make almost all conversions from source to the machine level at once.

Performs actions described by high level program.

Generate machine code and then walk a parse tree for execution OR Generate and execute intermediate software-defined instructions. Perform some conversion work every time a statement or function is executed

Hybrid Compilation/Interpretation

Intermediate

Representation

Source

code

Platform

Compiler Phase 1

Platform

Interpreter Phase 2

Which one is better ?

Compilation

Interpretation

Hybrid

Static Compilation

Source

code yTranslate from high level language to machine code. yAll bindings are done at compile time. yLinking is done during the creation of an executable. yLinker resolves the referenced symbols. yRobust, better security, before hand optimization, reduced start-up cost yCompatibility concerns, Less opportunity for performance improvement, dynamic traits exploitation, infeasible speculative optimization

Static

library object code

Binary Executable

Compiler

Assembler

Linker

Ahead of Time Compilation (AOT)

yTrade offs: y Memory y Starting time yPortability yOptimizations

Compiler

High level language

Intermediate language

OR

Native machine code /

System dependent binary

Outline

yOverview yStatic Compilation yVirtual machines yTraditional Approaches yJIT yDefining JIT yJIT: A Combination of two traditional approaches yWorking Mechanism yConceptual Idea yTechnical steps yAdvantages & Drawbacks yApplications yExploring JIT & java yCompilation in java yVM & JVM yJIT in JVM yRuntime optimizations by JIT yStartup Delay and Possible Optimizations yJava HotSpot

Defining JIT

—•--In-Time (JIT) compilation, also known as dynamic translation, is compilation done during execution of a program at run time rather

JIT: A combination of approaches

yJIT compiler represents a hybrid approach. yCombining two approaches brings pros and cons of both techniques. Selectively compile the most frequently executing methods to native code during execution. AOT

Interpretation

Combining

two approaches yields JIT Cont.

Conceptual view of JIT

yTranslate continuously. yPerform caching of compiled code. yMinimizes lag on future execution of same code during a given run. AOT compilation

Intermediate

code Byte code

Dynamic

Compilation

Machine

code

Outline

yOverview yStatic Compilation yVirtual machines yTraditional Approaches yJIT yDefining JIT yJIT: A Combination of two traditional approaches yWorking Mechanism yConceptual Idea yTechnical steps yAdvantages & Drawbacks yApplications yExploring JIT & java yCompilation in java yVM & JVM yJIT in JVM yRuntime optimizations by JIT yStartup Delay and Possible Optimizations yJava HotSpot

Conceptual Idea

yCompiler

Cont..

yInterpreter Cont. yJIT Cont. yJIT [1]

Technical Steps

yWe can divide JIT into distinct phases mainly: yMachine code creation at runtime . yMachine code execution at runtime. yMachine code creation yThis step is similar to what every compiler does with slight difference. yCreate machine code at program run time. yUse building blocks for keeping code in memory for execution later. yEasier to write

Intermediate code Machine code at runtime

yMachine code execution (involved roughly three main steps): yAllocate a readable, writable and executable chunk of memory on the heap. yCopy the machine code implementing intermediate code into this chunk. yExecute code from this chunk by casting it to a function pointer and calling through it.

Example: (for details, please visit link)

1 2 3 4

Advantages and Drawbacks

Faster execution.

Easier handling of late bound data types.

Enforce security guarantees.

Can be optimized to targeted CPU and operating system

Portable byte code.

Can use profile information to perform optimizations. Can perform other many different runtime optimizations.

Startup delay.

Limited AOT optimizations because of time.

Compiler should be packaged inside virtual machine. Can not perform complex optimizations which are possible with static compilation.

Maintenance and debugging can be a headache.

Security concerns

Outline

yOverview yStatic Compilation yVirtual machines yTraditional Approaches yJIT yDefining JIT yJIT: A Combination of two traditional approaches yWorking Mechanism yConceptual Idea yTechnical steps yAdvantages & Drawbacks yApplications yExploring JIT & java yCompilation in java yVM & JVM yJIT in JVM yRuntime optimizations by JIT yStartup Delay and Possible Optimizations yJava HotSpot

Applications

Many different companies/organizations have adopted JIT in there tools, some of renown are: yOracle Java that improves the performance of Java applications at run time. yMicrosoft .NET Framework yThe JIT compiler is part of the Common Language Runtime (CLR). The CLR manages the execution of all .NET applications. yJIT in web browsers yTrace Monkey is a trace based JIT compiler used by Mozilla Firefox browser to run

JavaScript programs

yLLVM yintro

Outline

yOverview yStatic Compilation yVirtual machines yTraditional Approaches yJIT yDefining JIT yJIT: A Combination of two traditional approaches yWorking Mechanism yConceptual Idea yTechnical steps yAdvantages & Drawbacks yApplications yExploring JIT & java yCompilation in java yVM & JVM yJIT in JVM yRuntime optimizations by JIT yStartup Delay and Possible Optimizations yJava HotSpot

Compilation in java

Conceptual view of code compilation in java.

Java compiler Java source

code JVM

Java compiler Java byte code

Operating System (OS)

Hardware

JIT placed inside JVM

Java source code is compiled by java compiler

resulting in JVM readable java byte code.

JVM performs following two main steps:

Compiles byte code at runtime into

machine readable instructions

Execute compiled machine readable code

Virtual Machine

yDifferent kind of virtual machines provide different functions. ySome of the important goals of VM to consider: yPortability. yBridge the gap between compilers and interpreters. yA virtual machine need at least following three basic components: yInterpreter yRuntime Supporting System yCollection of librariesquotesdbs_dbs11.pdfusesText_17

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