Download and build GCC MELT
with GCC MELT examples

Get files for GCC MELT top

Download GCC MELT plugin source releases for GCC 4.8 or 4.9 or 5.x

Please use the latest release, or, if brave enough, a recent snapshot (under GPLv3+ license and FSF copyright). Please report bugs on gcc-melt list and on the MELT SourceForge Tickets system (also known as MELT-SFT).

Latest source release of GCC MELT plugin

The MELT plugin 1.3.0 release candidate 2 (for GCC 5 or GCC 6 is available (since may 11th, 2016) from melt-1.3-rc2-plugin-for-gcc-5-or-6.tar.bz2 as a bzip2-ed tar source file of md5sum eb4df214b293caabec07be4a672eda4e and of 4013849 bytes (3.9 Megabytes), extracted from MELT branch svn revision 236128. It brings significant bugs fixes and compatibility w.r.t. both GCC 5 and GCC 6. See this message. Please upgrade.

The MELT plugin 1.2.0 release (for GCC GCC 4.9 or GCC 5.*) is available (since july 24th, 2015) from melt-1.2.0-plugin-for-gcc-4.9-or-5.tar.bz2 as a bzip2-ed tar source file of md5sum e718e8686a947f801d7fba4f3e699f80, and of 4075486 bytes (4.0 Megabytes), extracted from MELT branch svn revision 226151.. It brings significant features and bug fixes, see this message. Please upgrade.

The MELT plugin 1.1.3 release (for GCC 4.8 or 4.9) is available (since november 13th, 2014) from melt-plugin-1.1.3-for-gcc-4.8-or-4.9.tar.bz2 as a bzip2-ed tar source file of md5sum 258116d9403bad6b7a65e4ab1a4bbc59, and of 4124848 bytes (4.0 Megabytes), extracted from MELT branch svn revision 217521.. It brings significant features and bug fixes (see here). Please upgrade.

The MELT plugin 1.1.2 release (for GCC 4.8 or 4.9) is available (since august 31th, 2014) from melt-1.1.2-plugin-for-gcc-4.8-or-4.9.tar.bz2 as a bzip2-ed tar source file of md5sum fab80bfaee76abea1513c69f504ab49f, and of 3936275 bytes (3.8 Megabytes), extracted from MELT branch svn revision 214717. It brings bug fixes with respect to MELT 1.1.1 (so you should upgrade, see this message for details).

The MELT plugin 1.1.1 release (for GCC 4.8 or 4.9) is available (since august 11th, 2014) from melt-1.1.1-plugin-for-gcc-4.8-or-4.9.tar.bz2 as a bzip2-ed tar source file of md5sum 5879dd6931d169bb64384b33537624e2, and of 3899914 bytes (3.8 Megabytes), extracted from MELT branch svn revision 213809. It brings bug fixes with respect to MELT 1.1 (so you should upgrade, see this message for details).

The MELT plugin 1.1 release (for GCC 4.8 or 4.9) is available (since july 27th, 2014) from melt-1.1-plugin-for-gcc-4.8-or-4.9.tar.bz2 as a bzip2-ed tar source file of md5sum dcd4332f91140f12bee51ae4d33f66f0, and of 3891501 bytes (3.8 Megabytes), extracted from MELT branch svn revision 213094. It brings significant new features (see this message for details) with respect to MELT 1.0.2 (but the probe is becoming deprecated).

The MELT plugin 1.0.2 release (for GCC 4.7, 4.8 or better) is available (since december 18th, 2013) from melt-1.0.2-plugin-for-gcc-4.7-or-4.8.tar.bz2 as a bzip2-ed tar source file of md5sum 07926d9d3ee18f7d0db523725fa7d709, and of 3756363 bytes (3.6Megabytes); this bug-fixing release is obtained from MELT 1.0.1 (which was extracted from MELT branch svn revision 204522) corrected with the patch-melt-plugin-1.0.1-to-1.0.2.diff (so this release is not simply and directly extracted from the MELT branch). With respect to MELT 1.0.1 it brings a bug fix (related to -fplugin-arg-melt-mode=findgimple mode), see MELT-SFT-7, so update is recommended.

The MELT plugin 1.0.1 release (for GCC 4.7, 4.8 or better) is available from melt-1.0.1-plugin-for-gcc-4.7-or-4.8.tar.bz2 as a bzip2-ed tar source file of md5sum c7c3dbf3edd4e5747ddcf4a30dad41c4, and of 3754405 bytes (3.6 Megabytes) extracted from MELT branch svn revision 204522 on november 07th 2013. With respect to MELT 1.0 it brings some bug fixes (see this message for details), so update is recommended.

The MELT plugin 1.0 release (for GCC 4.7, 4.8 or better) is available from melt-1.0-plugin-for-gcc-4.7-or-4.8.tar.bz2 as a bzip2-ed source tarball of 3754482 bytes (3.6Mbytes) of md5sum fe07c9204e31c3a61931181737903d7e; it is extracted from MELT branch svn 204149 on october 29th 2013. It brings major features and enhancements (working macros, better diagnostics, useful modes for exploring Gimple, etc, etc...), see this message.

GCC MELT plugin releases are also downloadable (a few days after their release here) on SourceForge, even when this site is unavailable.

Thanks to Alexandre Lissy, some Ubuntu binary packages (also usable on Debian and derived distributions) of MELT 0.9.8 plugin are available on See this message.

Experimental snapshot

From time to time, a MELT plugin snapshot tarball might be available as melt-plugin-snapshot.tar.bz2.

This snapshot is extracted from the MELT branch, it may be buggy, unstable, and might even fail to build. Use at your own risk. Sometimes, it could even be older than the latest release. Snapshots may be announced on

Previous releases.

You probably don't want to use old releases. This is for historical reference only.

The MELT plugin 0.9.9 release (for GCC 4.6, 4.7 and 4.8) is available as a bzip2-ed source tarball from melt-0.9.9-plugin-for-gcc-4.6-or-4.7-or-4.8.tar.bz2 of 3706132 bytes (3.6Mbytes) of md5sum ce50c55d64b6c906a5787818f078c86d and/or as a gzip-ed source tarball from melt-0.9.9-plugin-for-gcc-4.6-or-4.7-or-4.8.tar.gz of 5865547 bytes (5.6Mbytes) of md5sum b3c2a10787485202ad1e8b057d8170d2, extracted from MELT branch svn rev. 200300 on june 22th 2013. This brings many significant language features (notably hooks, module variables, nested expression and code chunks, etc...), many runtime improvements (more plugin events, ...), enabling an even more powerful mixture of C++ and MELT code; see this message for details. This MELT 0.9.9 is a release bringing major features and improvements (hooks, static module variables, improved pass installation, better tuned garbage collector, better working eval, and interactive read-eval-print-loop, etc.). MELT 0.9.9 is the last MELT plugin working for GCC 4.6 (future versions will only work for GCC 4.7 or better).
(the version number 0.9.9 of the MELT plugin is not related to the version 4.6, 4.7 or 4.8 of the GCC compiler able to use it)

The MELT plugin 0.9.8 release (for GCC 4.6, 4.7 and future 4.8) is available from melt-0.9.8-plugin-for-gcc-4.6-or-4.7-or-4.8.tar.gz as a gzipped source tarball of 5377928 bytes of md5sum 6c0721202857c44a8edb1ae2252605e8 extracted from MELT branch svn rev. 194693 on december 22nd 2012. This brings several significant language features (the :auto c-type annotations, the box, constant_box, unbox syntactic constructs), the ability to evaluate a file with the evalfile mode, and much more; see this message for details.
(the version number 0.9.8 of the MELT plugin is not related to the version 4.6, 4.7 or future 4.8 of the GCC compiler able to use it)

The MELT plugin 0.9.7 release (for GCC 4.6, 4.7 and future 4.8) is available from melt-0.9.7-plugin-for-gcc-4.6-or-4.7-or-4.8.tar.gz a gnu-zipped source tar file of 5193713 bytes of md5sum 9873b7cb1363c3638457fe775a402aa9 extracted from the MELT branch of GCC svn rev. 192291 on october 10th 2012. This brings a read-eval-print loop and an evaluator to MELT and many new things. See this message for more. (the version number 0.9.7 of the MELT plugin is not related to the version 4.6, 4.7 of the GCC compiler able to use it)

Older releases are not shown.

Debian/Ubuntu packages for GCC MELT plugin

Thanks to Alexandre Lissy, Ubuntu .deb packages of the GCC MELT plugin are available on Source of the Debian packaging of GCC MELT plugin is available on Gitorious, thanks to Alexandre Lissy. See this message.

Building the GCC MELT plugin on GNU/Linux top

Audience: you are expected to be familiar with building free software from source code on GNU/Linux systems on the command line (so at ease with g++, make, bash, awk), and you should have root access to your computer. Please read this entire section before starting the build. If your GCC compiler is not invoked by gcc or g++, replace these appropriately (e.g. with /usr/local/bin/g++-4.9 if your systam has that).

Prerequisites for compiling (and using) GCC MELT

A recent GCC compiler (version 4.8, 4.9, 5. or later) is required. Check with gcc -v and g++ -v that you have a 4.8 or later version of the compiler, and (with gcc -v 2>&1 | grep plugin) that your compiler has enabled plugins.

Don't expect to make GCC MELT run on an earlier version of GCC (like 4.7). If your gcc or g++ configuration, as reported by e.g. g++ -v, does not say Configured with: .... --enable-plugin complain to your Linux vendor and recompile your GCC compiler from a recent FSF source release, preferably 4.8 or later. This might not be easy, and probably takes hours.

You should be sure that your gcc and g++ commands are running the real GCC compiler. Remember that on some systems the gcc (or g++) command is actually using a ccache or a distcc utility. Please disable such things on your system, perhaps by using a full path like /usr/bin/gcc-4.9 or whatever.

Some Gnu/Linux distributions are overloading their gcc command with ccache. Double-check that this is not the case on your system (because GCC MELT often compiles an empty file to get some other things done).

Please use a powerful computer to build the GCC MELT plugin. You need at least 6Gbytes of RAM, and 9Gbytes of disk space. A successful build of GCC MELT plugin may take more than 15 - 30 minutes on the clock.

Building GCC MELT needs some resources, mostly because the building process is translating MELTC++ the MELT translator several times, and because the generated C++ code contain very long initialization routines, which take time and memory to be compiled to dlopen-able shared objects.

Ensure that you have all the dependencies to build GCC plugins, which also requires the dependencies to build the GCC compiler itself. If you have a recent Debian or compatible (Ubuntu, Mint, ....) distribution, run as root apt-get build-dep g++-4.9 gcc-4.9-plugin-dev then apt-get install g++-4.9 gcc-4.9 gcc-4.9-plugin-dev. If you have some other distribution, try to find the equivalent commands to get the build dependencies, and the binary packages, of the g++ compiler (if you don't have a g++-4.9 but a g++-5 replace 4.9 by 5 in these commands). These dependencies are also needed to use MELT, because MELT is routinely emitting C++ code suited for your compiler, then make-ing some shared object from that emitted code, and at last dlopen-ing that shared object module.

If you cannot get help from your distribution to have the build dependencies of your compiler installed, you'll need to install a lot of (GNU or other) utilities, notably make, gcc, g++, bash, autotools, awk, indent, sed, perl, svn, binutils (i.e. ld and as), autogen, m4, ed, texinfo, texi2html, unifdef, astyle etc. You'll also need the required libraries -in development form- for your compiler, perhaps PPL and/or ISL, CLOOG, GMP, and more. Run gcc -v to understand how your particular GCC compiler was configured and built, then install all the build dependencies.

Compiling and installing the GCC MELT plugin

Since GCC MELT is a [meta-]plugin, it is installed in the directory for plugins, as obtained by gcc -print-file-name=plugin. Ensure that the path obtained by this command is a absolute file path to a directory containing a non empty include sub-directory by running successfully ls -l $(gcc -print-file-name=plugin)/include/gcc-plugin.h. Since GCC MELT is installed in a plugin/ sub-tree suited for your GCC compiler it does not need any configure step.

We say (pedantically) that GCC MELT is a meta-plugin since it is a plugin for gcc which itself dynamically loads, with dlopen, other shared object modules.

Optional: The GCC MELT build may notify you about some important steps. If you like (Gnome/Kde/Xfce4) desktop "bubble" notifications, you may want to set your GCCMELT_BUILD_NOTIFICATION environment variable to some script accessible thru your $PATH, like e.g. my $HOME/bin/meltbuild-notification containing

#file meltbuild-notification
# first arg title, second arg message
if [ "$DISPLAY" = ":0.0" -a -n "$DESKTOP_SESSION" -a $(which notify-send) ]; then
   notify-send -t 3500 -i info "MELT BUILD: $1" "$2"
   logger -t meltbuild -p "$1=" "$2"

But this is only eye candy. You don't need that meltbuild-notification script. If you want it,
export GCCMELT_BUILD_NOTIFICATION=$HOME/bin/meltbuild-notification or similar. The GCC MELT building won't notify you if you don't have any GCCMELT_BUILD_NOTIFICATION environment variable.

Notice that MELT should be built in a fresh directory, independent (and outside of...) of the source or installed binary of the gcc compiler you are building it for. Often, you'll build MELT in a fresh subdirectory of /tmp/ or of your $HOME/tmp/. You don't need to be root to compile MELT (but you probably need to be root to install it...). Be aware that MELT is tightly coupled with GCC and should have a version compatible with your particular gcc and g++ (etc..., perhaps named gcc-4.8 and so on...) compilers.. Some MELT plugin for GCC 4.7 and 4.8 at most cannot work with a GCC 4.9.

  1. You should download (e.g. with cd /tmp; wget or whatever is appropriate) and un-tar your GCC MELT plugin source archive (perhaps with tar xjvf melt-1.1.3-plugin-for-4.8-or-4.9.tar.gz) in some fresh directory to obtain a directory (such as melt-1.1.3-plugin-for-4.8-or-4.9/, perhaps /tmp/melt-1.1.3-plugin-for-4.8-or-4.9/ etc...) containing (amongst others) two files melt-runtime.{h,cc} and a sub-directory melt/ with notably melt/generated/meltrunsup.h and melt/warmelt-outobj.melt (and many other files, etc...). This directory also contains MELT-Plugin-Makefile which is symlinked from Makefile.
  2. Go into that directory with e.g. cd melt-1.1.3-plugin-for-4.8-or-4.9/ then list it with ls -lF and carefully read the README-MELT-PLUGIN file there using your favorite pager (less, ...) or editor (emacs, vim, gedit etc....). Your README-MELT-PLUGIN file may contain additional installation instructions or caveats.
  3. Inspect the Makefile (it is a symlink), and edit it if you want. You probably don't need to change anything in that file, but you could (e.g. you might want to change the MELTGCC_PLUGIN_DIR make variable to have MELT installed elsewhere).
  4. If your GCC compiler is a cross-compiler, set your environment variable MELTGCC_NO_CHECK_RUNTIME with export MELTGCC_NO_CHECK_RUNTIME=yes to avoid having the melt-runtime.c be checked by an existing MELT pass. Most users have a straight compiler (not a cross-compiler) so should not have any MELTGCC_NO_CHECK_RUNTIME environment variable.
  5. compile your GCC MELT plugin: run make all; you don't need to be root for that. You could specify the particular compiler you want to extend with e.g. make CC=/usr/bin/gcc-4.9 CXX=/usr/bin/g++-4.9 or something similar (read the Makefile please). This make should not be parallel (no make -j) and takes some time (e.g. more than 20 minutes). The last dozen of output lines should say that MELT plugin compilation completed and may give additional advice.
  6. Installation step: run (without being root) make install DESTDIR=/tmp/meltpluginst (where the given DESTDIR is some fresh installation temporary directory (outside of your GCC or MELT source or build or installation directories!) then copy as root (e.g. using sudo) that directory, e.g. with sudo cp -r -v -p /tmp/meltpluginst/. /.). Actually, only the $(gcc -print-file-name=plugin) directory (and perhaps some documentation directory) will be filled.
  7. (much later) optional uninstallation: the $(gcc -print-file-name=plugin) directory contains files and subdirectories named melt*. You can remove them. Notice that is actually a symlink (e.g. to Advanced users might explicit their particular version of the GCC MELT plugin with options like gcc -fplugin=melt-1.1.3 (so in principle you could have several MELT versions for the same GCC compiler version, even if this is adventurous).

You should rebuild (from a pristine MELT source code tree) your GCC MELT plugin at every change (even very minor ones!) of your GCC compiler, even a minor "patchlevel" evolution from gcc-4.9.1 to gcc-4.9.2.

The installed GCC MELT plugin contains notably the MELT source code, a Makefile fragment, and its C++ translation in some melt-sources/ sub-directory (containing e.g. warmelt-outobj.melt, and warmelt-outobj+meltdesc.c and, etc....), and many shared object MELT modules in some melt-modules/ sub-directory. All are needed to run GCC MELT. The modules shared object file names contain an MD5 signature in their path, like e.g. - of course, the actual MD5 checksum may differ, it is the checksum of the catenation of generated C++ files.

The experimental MELT branch top

GCC MELT is a GCC plugin and also an experimental GCC development branch (free software GPLv3 licensed and FSF copyrighted), and most users want the MELT plugin. The MELT branch is mostly useful for potential contributors to GCC MELT willing to improve MELT itself. The MELT plugin source code is extracted from the MELT branch. You could get the latest code snapshot of the experimental MELT branch using subversion: svn co svn:// gcc-melt and you can browse that branch at

You probably need 4 gigabytes of disk space, and dozens of minutes, to retrieve the MELT branch using the above svn command. You should build a gcc-melt compiler as you build the GCC trunk, in a build tree outside of the source tree.

To get the source tarball for a GCC MELT plugin, run contrib/ $PWD /tmp/meltpluginsource from inside the MELT branch source code to get the /tmp/meltpluginsource.tar.gz tarball. A similar command is used to get every MELT plugin release tarball.

The GCC trunk (on which the GCC community actively works to prepare the next release of GCC) is often merged (usually once a week) into the MELT branch. So that MELT branch may be unstable. You probably want to pass --program-suffix=-melt to ..../gcc-melt/configure when building that branch (outside of its source tree).

MELT examples top

Small tutorial examples

Simple tutorial examples are available on melt-examples at GitHub, notably

Software written in MELT

Pierre Vittet has developped Talpo (available on Gitorious) using GCC MELT. Talpo is a MELT extension giving some warnings about your code (e.g. find misuse of untested fopen-s). This is a GSOC 2011 project on Customizable warnings with a GCC plugin

My colleague Emmanuel Haucourt (CEA, LIST, DILS) is using MELT to interface his Alcool tool to GCC.


Most of GCC MELT is coded MELT itself. In particular, files melt/warmelt-*.melt contain the MELTC++ translator, and files melt/xtramelt-*.melt contain other things (notably the probe, most of the glue between Gimple and Tree internal GCC representations, a pass to check the GCC MELT runtime against its coding rules, and some simple other passes).