Glossary

General

LLVM backend
A (Clang) compiler backend that converts the LLVM Intermediate Representation (IR) to code for a specified machine or other languages. In the case of Emscripten, the specified target is JavaScript.
Load-store consistency

Load-Store Consistency (LSC), is the requirement that after a value with a specific type is written to a memory location, loads from that memory location will be of the same type. So if a variable contains a 32-bit floating point number, then both loads and stores to that variable will be of 32-bit floating point values, and not 16-bit unsigned integers or anything else.

Note

This definition is taken from Emscripten: An LLVM-to-JavaScript Compiler (section 2.1.1). There is additional detail in that paper.

Minifying
Minification in JavaScript is the process of removing all unnecessary characters from source code without changing its functionality. At higher optimisation levels Emscripten uses the Closure Compiler to minify Emscripten code.
Relooping
Recreate high-level loop and if structures from the low-level labels and branches that appear in LLVM assembly (definition taken from this paper).
SDL
Simple DirectMedia Layer (SDL) is a cross-platform development library designed to provide low level access to audio, keyboard, mouse, joystick, and graphics hardware via OpenGL and Direct3D.
Typed Arrays Mode 2

Typed Arrays Mode 2 is the name of the approach used for the current Emscripten memory representation. This is the only memory model supported by the (current) Fastcomp compiler and is the default memory model for the old compiler.

The original compiler supported a number of other memory models and compilation modes (see Code Generation Modes) but Typed Arrays Mode 2 proved to have, among other benefits, the greatest support for arbitrary code.

XHR
Contraction of XMLHttpRequest. Emscripten uses XHRs for asynchronously downloading binary data.

Emscripten tools and dependencies

Clang
Clang is a compiler front end for C, C++, and other programming languages that uses LLVM as its back end.
Closure Compiler
The closure compiler is used to minify Emscripten-generated code at higher optimisations.
Compiler Configuration File
The Compiler Configuration File stores the active tools and SDKs as defined using emsdk activate.
emcc
The Emscripten Compiler Frontend (emcc). Emscripten’s drop-in replacement for a compiler like gcc.
Emscripten Command Prompt
The Emscripten Windows Command Prompt (emcmdprompt.bat) is used to call Emscripten tools from the command line on Windows.
Fastcomp
Fastcomp is Emscripten’s current compiler core.
Git
Git is a distributed revision control system. Emscripten is hosted on Github and can be updated and modified using a git client.
Github

GitHub is a Git repository web-based hosting service that also offers project-based collaboration features including wikis, task management, and bug tracking.

The Emscripten project is hosted on Github.

Java
Java is a programming language and computing platform. It is used by Emscripten for the code that performs some advanced optimisations. The required version is listed in the toolchain requirements.
JavaScript

JavaScript (ECMAScript) is a programming language that is primarily used as part of a web browser, providing programmatic access to objects within a host environment. With node.js, it is also being used in server-side network programming.

The asm.js subset of JavaScript is Emscripten’s target output language.

lli
LLVM Interpreter

The LLVM interpreter (LLI) executes programs from LLVM bitcode. This tool is not maintained and has odd errors and crashes.

Emscripten provides an alternative tool, the LLVM Nativizer.

LLVM
LLVM is a compiler infrastructure designed to allow optimization of programs written in arbitrary programming languages.
LLVM Nativizer

The LLVM Nativizer (tools/nativize_llvm.py) compiles LLVM bitcode to a native executable. This links to the host libraries, so comparisons of output with Emscripten builds will not necessarily be identical.

It performs a similar role to the LLVM Interpreter.

Note

Sometimes the output of the this tool will crash or fail. This tool is intended for developers fixing bugs in Emscripten.

node.js
Node.js is a cross-platform runtime environment for server-side and networking applications written in JavaScript. Essentially it allows you to run JavaScript applications outside of a browser context.
Python
Python is a scripting language used to write many of Emscripten’s tools. The required version is listed in the toolchain requirements.
vs-tool

vs-tool is a Visual Studio 2010 plugin for integrating MinGW, Clang and Emscripten into the VS IDE. The plugin is automatically added by the Windows NSIS Installer Emscripten SDK if Visual Studio 2010 is present on the target system.

Note

At time of writing this only supports Visual Studio 2010 (check here to see if VS 2012 support has been added).

SDK Terms

The following terms are used when referring to the SDK and Emscripten SDK (emsdk):

emsdk
The Emscripten SDK (emsdk) is used to perform all SDK maintenance and can install, update, add, remove and activate SDKs and tools. Most operations are of the form ./emsdk command. To access the emsdk script, launch the Emscripten Command Prompt.
Tool
The basic unit of software bundled in the SDK. A Tool has a name and a version. For example, clang-3.2-32bit is a tool that contains the 32-bit version of the Clang v3.2 compiler. Other tools used by Emscripten include Java, Git, node.js, etc.
SDK

A set of tools. For example, sdk-1.5.6-32bit is an SDK consisting of the tools: clang-3.2-32bit, node-0.10.17-32bit, python-2.7.5.1-32bit and emscripten-1.5.6.

There are a number of different Emscripten SDK packages, including the Portable Emscripten SDK and Windows NSIS Installer Emscripten SDK. SDKs can be downloaded from here.

Active Tool/SDK
The emsdk can store multiple versions of tools and SDKs. The active tools/SDK is the set of tools that are used by default on the Emscripten Command Prompt. This compiler configuration is stored in a user-specific persistent file (~/.emscripten) and can be changed using emsdk.
Portable Emscripten SDK
A portable no-installer version of the SDK package. It is identical to the NSIS SDK installer, except that it does not interact with the Windows registry. This allows Emscripten to be used on a computer without administrative privileges, and means that the installation can be migrated from one location (directory or computer) to another by simply copying/zipping up the directory contents.
Windows NSIS Installer Emscripten SDK
A Windows NSIS installer of the Emscripten SDK. This registers the Emscripten SDK as a ‘standard’ Windows application, allowing it to be installed and removed from Windows like any other app. This installer also automatically deploys vs-tool if Visual Studio 2010 is present on the target system.
emsdk root directory
The emsdk can manage any number of tools and SDKs, and these are stored in subdirectories of the emsdk root directory. The emsdk root is the directory specified when you first installed an SDK.
SDK root directory
The emsdk can store any number of tools and SDKs. The SDK root directory is the directory used to store a particular SDK. It is located as follows, with respect to the emsdk root directory: <emsdk root>\emscripten\<sdk root directory>\

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