PostgreSQL's JIT
implementation can inline the bodies of functions
of types C and internal, as well as
operators based on such functions. To do so for functions in extensions,
the definitions of those functions need to be made available.
When using PGXS to build an extension
against a server that has been compiled with LLVM JIT support, the
relevant files will be built and installed automatically.
The relevant files have to be installed into
$pkglibdir/bitcode/$extension/ and a summary of them
into $pkglibdir/bitcode/$extension.index.bc, where
$pkglibdir is the directory returned by
pg_config --pkglibdir and $extension
is the base name of the extension's shared library.
For functions built into PostgreSQL itself,
the bitcode is installed into
$pkglibdir/bitcode/postgres.
PostgreSQL provides a JIT implementation based on LLVM. The interface to the JIT provider is pluggable and the provider can be changed without recompiling (although currently, the build process only provides inlining support data for LLVM). The active provider is chosen via the setting jit_provider.
A JIT provider is loaded by dynamically loading the
named shared library. The normal library search path is used to locate
the library. To provide the required JIT provider
callbacks and to indicate that the library is actually a
JIT provider, it needs to provide a C function named
_PG_jit_provider_init. This function is passed a
struct that needs to be filled with the callback function pointers for
individual actions:
struct JitProviderCallbacks
{
JitProviderResetAfterErrorCB reset_after_error;
JitProviderReleaseContextCB release_context;
JitProviderCompileExprCB compile_expr;
};
extern void _PG_jit_provider_init(JitProviderCallbacks *cb);