Native-Compilation is implemented as a side effect of byte-compilation (Byte Compilation). Thus, compiling Lisp code natively always produces its byte code as well, and therefore all the rules and caveats of preparing Lisp code for byte compilation (Compilation Functions) are valid for native-compilation as well. You can natively-compile either a single function or macro definition, or a whole file of Lisp code, with the native-compile function. Natively-compiling a file will produce the .eln file with native code. Native compilation might produce warning or error messages; these are normally recorded in the buffer called *Native-compile-Log*. In interactive sessions, it uses the special LIMPLE mode (native-comp-limple-mode), which sets up font-lock as appropriate for this log, and is otherwise the same as Fundamental mode. Logging of messages resulting from native-compilation can be controlled by the native-comp-verbose variable (Native-Compilation Variables). When Emacs is run non-interactively, messages produced by native-compilation are reported by calling message (Displaying Messages), and are usually displayed on the standard error stream of the terminal from which Emacs was invoked.

native-compile

This function compiles function-or-file into native code. The argument function-or-file can be a function symbol, a Lisp form, or a name (a string) of the file which contains the Emacs Lisp source code to compile. If the optional argument output is provided, it must be a string specifying the name of the file to write the compiled code into. Otherwise, if function-or-file is a function or a Lisp form, this function returns the compiled object, and if function-or-file is a file name, the function returns the full absolute name of the file it created for the compiled code. The output file is by default given the .eln extension. This function runs the final phase of the native compilation, which invokes GCC via libgccjit, in a separate subprocess, which invokes the same Emacs executable as the process that called this function.

batch-native-compile

This function runs native-compilation on files specified on the Emacs command line in batch mode. It must be used only in a batch execution of Emacs, as it kills Emacs upon completion of the compilation. If one or more of the files fail to compile, the Emacs process will attempt to compile all the other files, and will terminate with a non-zero status code. The optional argument for-tarball, if non-nil, tells the function to place the resulting .eln files in the last directory mentioned in native-comp-eln-load-path (Library Search); this is meant to be used as part of building an Emacs source tarball for the first time, when the natively-compiled files, which are absent from the source tarball, should be generated in the build tree instead of the user's cache directory.

Native compilation can be run entirely asynchronously, in a subprocess of the main Emacs process. This leaves the main Emacs process free to use while the compilation runs in the background. This is the method used by Emacs to natively-compile any Lisp file or byte-compiled Lisp file that is loaded into Emacs, when no natively-compiled file for it is available. Note that because of this use of a subprocess, native compilation may produce warning and errors which byte-compilation does not, and Lisp code may thus need to be modified to work correctly. See native-comp-async-report-warnings-errors in Native-Compilation Variables for more details.

native-compile-async

This function compiles the named files asynchronously. The argument files should be a single file name (a string) or a list of one or more file and/or directory names. If directories are present in the list, the optional argument recursively should be non-nil to cause the compilation to recurse into those directories. If load is non-nil, Emacs will load each file that it succeeded to compile. The optional argument selector allows control of which of files will be compiled; it can have one of the following values:

nil or omitted

Select all the files and directories in files.

a regular expression string

Select the files and directories whose names match the regexp.

a function

A predicate function, which will be called with each file and directory in files, and should return non-nil if the file or the directory should be selected for compilation.

On systems with multiple CPU execution units, when files names more than one file, this function will normally start several compilation subprocesses in parallel, under the control of native-comp-async-jobs-number (Native-Compilation Variables).

Command emacs-lisp-native-compile

This command compiles the file visited by the current buffer into native code, if the file was changed since the last time it was natively-compiled.

Command emacs-lisp-native-compile-and-load

This command compiles the file visited by the current buffer into native code, like emacs-lisp-native-compile, but it also loads the native code when the compilation finishes.

The following function allows Lisp programs to test whether native-compilation is available at runtime.

native-comp-available-p

This function returns non-nil if the running Emacs process has the native-compilation support compiled into it. On systems that load libgccjit dynamically, it also makes sure that library is available and can be loaded. Lisp programs that need to know up front whether native-compilation is available should use this predicate.

By default, asynchronous native compilation writes the *.eln files it produces to a subdirectory of the first writable directory specified by the native-comp-eln-load-path variable (Native-Compilation Variables). You can change this by using the following function in your startup files:

startup-redirect-eln-cache

This function arranges for the asynchronous native compilation to write the produced *.eln files to cache-directory, which must be a single directory, a string. It also destructively modifies native-comp-eln-load-path such that its first element is cache-directory. If cache-directory is not an absolute file name, it is interpreted relative to user-emacs-directory (Init File).

This section documents the variables that control native-compilation.

native-comp-speed

This variable specifies the optimization level for native compilation. Its value should be a number between −1 and 3. Values between 0 and 3 specify the optimization levels equivalent to the corresponding compiler -O0, -O1, etc. command-line options of the compiler. The value −1 means disable native-compilation: functions and files will be only byte-compiled; however, the *.eln files will still be produced, they will just contain the compiled code in bytecode form. (This can be achieved at function granularity by using the (declare (speed -1)) form, Declare Form.) The default value is 2.

native-comp-debug

This variable specifies the level of debugging information produced by native-compilation. Its value should be a number between zero and 3, with the following meaning:

0

No debugging output. This is the default.

1

Emit debugging symbols with the native code. This allows easier debugging of the native code with debuggers such as gdb.

2

Like 1, and in addition dump pseudo-C code.

3

Like 2, and in addition dump the GCC intermediate passes and libgccjit log file.

native-comp-verbose

This variable controls the verbosity of native-compilation by suppressing some or all of the log messages emitted by it. If its value is zero, the default, all of the log messages are suppressed. Setting it to a value between 1 and 3 will allow logging of the messages whose level is above the value. The values have the following interpretations:

0

No logging. This is the default.

1

Log the final LIMPLE representation of the code.

2

Log the LAP, the final LIMPLE, and some additional pass info.

3

Maximum verbosity: log everything.

native-comp-async-jobs-number

This variable determines the maximum number of native-compilation subprocesses that will be started simultaneously. It should be a non-negative number. The default value is zero, which means use half the number of the CPU execution units, or 1 if the CPU has only one execution unit.

native-comp-async-report-warnings-errors

If this variable's value is non-nil, warnings and errors from asynchronous native-compilation subprocesses are reported in the main Emacs session in a buffer named *Warnings*. The default value t means display the resulting buffer. To log warnings without popping up the *Warnings* buffer, set this variable to silent. A common cause for asynchronous native-compilation to produce warnings is compiling a file that is missing some require of a necessary feature. The feature may be loaded into the main emacs, but because native compilation always starts from a subprocess with a pristine environment, that may not be true for the subprocess.

native-comp-async-query-on-exit

If this variable's value is non-nil, Emacs will query upon exiting whether to exit and kill any asynchronous native-compilation subprocesses that are still running, thus preventing the corresponding .eln files from being written. If the value is nil, the default, Emacs will kill these subprocesses without querying.

The variable native-comp-eln-load-path holds the list of directories where Emacs looks for the *.eln files (Library Search); in that role it is the equivalent of load-path used to look for *.el and *.elc files. The directories in this list are also used for writing the *.eln files produced by asynchronous native-compilation; specifically, Emacs will write these files into the first writable directory in the list. Thus, you can control where native-compilation stores the results by changing the value of this variable.

native-comp-jit-compilation

This variable, if non-nil, enables asynchronous (a.k.a. just-in-time, or JIT) native compilation of the *.elc files loaded by Emacs for which the corresponding *.eln files do not already exist. This JIT compilation uses separate Emacs sub-processes running in batch mode, according to the value of native-comp-async-jobs-number. When the JIT compilation of a Lisp file finishes successfully, the resulting .eln file is loaded and its code replaces the definition of functions provided by the .elc file.

Setting the value of native-comp-jit-compilation to nil disables JIT native compilation. However, even when JIT native compilation is disabled, Emacs might still need to start asynchronous native compilation subprocesses to produce trampolines. To control this, use a separate variable, described below.

native-comp-enable-subr-trampolines

This variable controls generation of trampolines. A trampoline is a small piece of native code required to allow calling Lisp primitives, which were advised or redefined, from Lisp code that was natively-compiled with native-comp-speed set to 2 or greater. Emacs stores the generated trampolines on separate *.eln files. By default, this variable's value is t, which enables the generation of trampoline files; setting it to nil disables the generation of trampolines. Note that if a trampoline needed for advising or redefining a primitive is not available and cannot be generated, calls to that primitive from natively-compiled Lisp will ignore redefinitions and advices, and will behave as if the primitive was called directly from C. Therefore, we don't recommend disabling the trampoline generation, unless you know that all the trampolines needed by your Lisp programs are already compiled and accessible to Emacs. The value of this variable can also be a string, in which case it specifies the name of a directory in which to store the generated trampoline *.eln files, overriding the directories in native-comp-eln-load-path. This is useful if you want the trampolines to be generated as needed, but don't want to store them under the user's HOME directory or in the other public directories where *.eln files are kept. However, unlike with directories in native-comp-eln-load-path, the trampolines will be stored in the directory given by the value of this variable, not in its version-specific subdirectory. If the name of this directory is not absolute, it is interpreted relative to invocation-directory (System Environment) If this variable is non-nil, and Emacs needs to produce a trampoline, but it cannot find any writable directory to store the trampoline, it will store it inside temporary-file-directory (Unique File Names). Trampolines produced when no writable directory is found to store them, or when this variable is a string, will only be available for the duration of the current Emacs session, because Emacs doesn't look for trampolines in either of these places.