4.1 Working on the JIT library ¶

Having checked out the source code (to “src”), you can configure and build the JIT library like this:

mkdir build
mkdir install
PREFIX=$(pwd)/install
cd build
../src/configure \
   --enable-host-shared \
   --enable-languages=jit,c++ \
   --disable-bootstrap \
   --enable-checking=release \
   --prefix=$PREFIX
nice make -j4 # altering the "4" to however many cores you have

This should build a libgccjit.so within jit/build/gcc:

[build] $ file gcc/libgccjit.so*
gcc/libgccjit.so:       symbolic link to `libgccjit.so.0'
gcc/libgccjit.so.0:     symbolic link to `libgccjit.so.0.0.1'
gcc/libgccjit.so.0.0.1: ELF 64-bit LSB shared object, x86-64, version 1 (SYSV), dynamically linked, not stripped

Here’s what those configuration options mean:

Option: --enable-host-shared ¶

Configuring with this option means that the compiler is built as position-independent code, which incurs a slight performance hit, but it necessary for a shared library.

Option: --enable-languages=jit,c++ ¶

This specifies which frontends to build. The JIT library looks like a frontend to the rest of the code.

The C++ portion of the JIT test suite requires the C++ frontend to be enabled at configure-time, or you may see errors like this when running the test suite:

xgcc: error: /home/david/jit/src/gcc/testsuite/jit.dg/test-quadratic.cc: C++ compiler not installed on this system
c++: error trying to exec 'cc1plus': execvp: No such file or directory

Option: --disable-bootstrap ¶

For hacking on the “jit” subdirectory, performing a full bootstrap can be overkill, since it’s unused by a bootstrap. However, when submitting patches, you should remove this option, to ensure that the compiler can still bootstrap itself.

Option: --enable-checking=release ¶

The compile can perform extensive self-checking as it runs, useful when debugging, but slowing things down.

For maximum speed, configure with --enable-checking=release to disable this self-checking.