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18.1 Native-Compilation Functions

Native-Compilation is implemented as a side effect of byte-compilation (see 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 (see 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 both the corresponding .elc file with byte code and 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 (see Native-Compilation Variables).

When Emacs is run non-interactively, messages produced by native-compilation are reported by calling message (see Displaying Messages), and are usually displayed on the standard error stream of the terminal from which Emacs was invoked.

Function: native-compile function-or-file &optional output

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.

Function: batch-native-compile &optional for-tarball

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 (see 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 see Native-Compilation Variables for more details.

Function: native-compile-async files &optional recursively load selector

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 (see Native-Compilation Variables).

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

Function: 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.

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