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Catalog of Compiler Construction Tools
The resource overview includes compiler construction kits, lexer and parser generators, attribute grammar systems, transformation tools, front- and back-end generators, program analysis and optimization, environment generators, infrastructure/components/tools and compiler construction with Java.
catalog.compilertools.net/

Free Compiler Construction Tools
List of lexers, parser generators, code optimizers (optimizer generators), and other compiler construction kits.
www.thefreecountry.com/

Eli: An Integrated Toolset for Compiler Construction
Eli is a domain-specific programming environment designed to generate compilers for programming languages from specifications. Eli contains a vastlibrary with precoined solutions and reusable components and is Open Source.
eli-project.sourceforge.net/

Relational Meta-Language (RML)
Generation of efficient compilers and interpreters from Natural Semantics Specifications. Semantics for real programming languages like Java, Pascal, Modelica were developed.
www.ida.liu.se/

LLVM
A compiler infrastructure designed for compile-time, link-time, runtime, and "idle-time" optimization of programs from arbitrary programming languages. LLVM is written in C++. It currently supports compilation of C and C++ programs, using front-ends derived from GCC 3.4 to SPARC v9 and X86 architectures, a back-end which emits C, and a Just-In-Time compiler for X86 and SPARC v9 processors. [University of Illinois Open Source License]
llvm.cs.uiuc.edu/

Zephyr
Its philosophy: build compilers from parts, which might include front ends, back ends, optimizers, and the glue that holds all these pieces together. You might even generate parts automatically from compact specifications.
www.cs.virginia.edu/

CoSy
A flexible compiler development system for languages like C, DSP-C and Java, enabling architecture and compiler developers to generate and reconfigure efficient and robust compilers quickly for their existing and future cores.
www.ace.nl/

Gentle
A compiler construction system that supports language recognition, definition of abstract syntax trees, construction of tree walkers based on pattern matching, smart traversal, simple unparsing for source-to-source translation, and optimal code selection for microprocessors.
gentle.compilertools.net/

Cetus
An infrastructure for writing source-to-source compilers for C, C++, or similar languages.
peak.ecn.purdue.edu/

SUIF
Extensible compiler system that supports parallelization, object-oriented programming languages, scalar optimizations and machine-specific optimizations.
suif.stanford.edu/