ocamlopt - The OCaml native-code compiler
ocamlopt [ options ] filename ...
ocamlopt.opt (same options)
The OCaml high-performance native-code compiler ocamlopt(1) compiles OCaml source files to
native code object files and link these object files to produce standalone executables.
The ocamlopt(1) command has a command-line interface very close to that of ocamlc(1). It
accepts the same types of arguments and processes them sequentially:
Arguments ending in .mli are taken to be source files for compilation unit interfaces.
Interfaces specify the names exported by compilation units: they declare value names with
their types, define public data types, declare abstract data types, and so on. From the
file x.mli, the ocamlopt(1) compiler produces a compiled interface in the file x.cmi. The
interface produced is identical to that produced by the bytecode compiler ocamlc(1).
Arguments ending in .ml are taken to be source files for compilation unit implementations.
Implementations provide definitions for the names exported by the unit, and also contain
expressions to be evaluated for their side-effects. From the file x.ml, the ocamlopt(1)
compiler produces two files: x.o, containing native object code, and x.cmx, containing
extra information for linking and optimization of the clients of the unit. The compiled
implementation should always be referred to under the name x.cmx (when given a .o file,
ocamlopt(1) assumes that it contains code compiled from C, not from OCaml).
The implementation is checked against the interface file x.mli (if it exists) as described
in the manual for ocamlc(1).
Arguments ending in .cmx are taken to be compiled object code. These files are linked
together, along with the object files obtained by compiling .ml arguments (if any), and
the OCaml standard library, to produce a native-code executable program. The order in
which .cmx and .ml arguments are presented on the command line is relevant: compilation
units are initialized in that order at run-time, and it is a link-time error to use a com-
ponent of a unit before having initialized it. Hence, a given x.cmx file must come before
all .cmx files that refer to the unit x.
Arguments ending in .cmxa are taken to be libraries of object code. Such a library packs
in two files lib.cmxa and lib.a a set of object files (.cmx/.o files). Libraries are build
with ocamlopt -a (see the description of the -a option below). The object files contained
in the library are linked as regular .cmx files (see above), in the order specified when
the library was built. The only difference is that if an object file contained in a
library is not referenced anywhere in the program, then it is not linked in.
Arguments ending in .c are passed to the C compiler, which generates a .o object file.
This object file is linked with the program.
Arguments ending in .o or .a are assumed to be C object files and libraries. They are
linked with the program.
The output of the linking phase is a regular Unix executable file. It does not need ocaml-
run(1) to run.
ocamlopt.opt is the same compiler as ocamlopt, but compiled with itself instead of with
the bytecode compiler ocamlc(1). Thus, it behaves exactly like ocamlopt, but compiles
faster. ocamlopt.opt is not available in all installations of OCaml.
The following command-line options are recognized by ocamlopt(1).
-a Build a library (.cmxa/.a file) with the object files (.cmx/.o files) given on the
command line, instead of linking them into an executable file. The name of the
library must be set with the -o option.
If -cclib or -ccopt options are passed on the command line, these options are
stored in the resulting .cmxa library. Then, linking with this library automati-
cally adds back the -cclib and -ccopt options as if they had been provided on the
command line, unless the -noautolink option is given.
-annot Dump detailed information about the compilation (types, bindings, tail-calls, etc).
The information for file src.ml is put into file src.annot. In case of a type
error, dump all the information inferred by the type-checker before the error. The
src.annot file can be used with the emacs commands given in emacs/caml-types.el to
display types and other annotations interactively.
Has been deprecated. Please use -annot instead.
-c Compile only. Suppress the linking phase of the compilation. Source code files are
turned into compiled files, but no executable file is produced. This option is use-
ful to compile modules separately.
Use ccomp as the C linker called to build the final executable and as the C com-
piler for compiling .c source files.
Pass the -llibname option to the linker. This causes the given C library to be
linked with the program.
Pass the given option to the C compiler and linker. For instance, -ccopt -Ldir
causes the C linker to search for C libraries in directory dir.
Optimize the produced code for space rather than for time. This results in smaller
but slightly slower programs. The default is to optimize for speed.
Print the version number of ocamlopt(1) and a detailed summary of its configura-
tion, then exit.
Generate an object file (.cmx and .o files) that can later be included as a sub-
module (with the given access path) of a compilation unit constructed with -pack.
For instance, ocamlopt -for-pack P -c A.ml will generate a.cmx and a.o files that
can later be used with ocamlopt -pack -o P.cmx a.cmx.
-g Add debugging information while compiling and linking. This option is required in
order to produce stack backtraces when the program terminates on an uncaught excep-
tion (see ocamlrun(1)).
-i Cause the compiler to print all defined names (with their inferred types or their
definitions) when compiling an implementation (.ml file). No compiled files (.cmo
and .cmi files) are produced. This can be useful to check the types inferred by
the compiler. Also, since the output follows the syntax of interfaces, it can help
in writing an explicit interface (.mli file) for a file: just redirect the standard
output of the compiler to a .mli file, and edit that file to remove all declara-
tions of unexported names.
Add the given directory to the list of directories searched for compiled interface
files (.cmi) and compiled object code files (.cmo). By default, the current direc-
tory is searched first, then the standard library directory. Directories added with
-I are searched after the current directory, in the order in which they were given
on the command line, but before the standard library directory.
If the given directory starts with +, it is taken relative to the standard library
directory. For instance, -I +labltk adds the subdirectory labltk of the standard
library to the search path.
Set aggressiveness of inlining to n, where n is a positive integer. Specifying
-inline 0 prevents all functions from being inlined, except those whose body is
smaller than the call site. Thus, inlining causes no expansion in code size. The
default aggressiveness, -inline 1, allows slightly larger functions to be inlined,
resulting in a slight expansion in code size. Higher values for the -inline option
cause larger and larger functions to become candidate for inlining, but can result
in a serious increase in code size.
Compile the file filename as an interface file, even if its extension is not .mli.
Recognize file names ending with string as interface files (instead of the default
Labels are not ignored in types, labels may be used in applications, and labelled
parameters can be given in any order. This is the default.
Force all modules contained in libraries to be linked in. If this flag is not
given, unreferenced modules are not linked in. When building a library (-a flag),
setting the -linkall flag forces all subsequent links of programs involving that
library to link all the modules contained in the library.
Do not compile assertion checks. Note that the special form assert false is always
compiled because it is typed specially. This flag has no effect when linking
When linking .cmxa libraries, ignore -cclib and -ccopt options potentially con-
tained in the libraries (if these options were given when building the libraries).
This can be useful if a library contains incorrect specifications of C libraries or
C options; in this case, during linking, set -noautolink and pass the correct C
libraries and options on the command line.
Allow the compiler to use some optimizations that are valid only for code that is
Ignore non-optional labels in types. Labels cannot be used in applications, and
parameter order becomes strict.
Specify the name of the output file produced by the linker. The default output name
is a.out, in keeping with the Unix tradition. If the -a option is given, specify
the name of the library produced. If the -pack option is given, specify the name of
the packed object file produced. If the -output-obj option is given, specify the
name of the output file produced. If the -shared option is given, specify the name
of plugin file produced.
Cause the linker to produce a C object file instead of an executable file. This is
useful to wrap OCaml code as a C library, callable from any C program. The name of
the output object file must be set with the -o option. This option can also be
used to produce a compiled shared/dynamic library (.so extension).
-p Generate extra code to write profile information when the program is executed. The
profile information can then be examined with the analysis program gprof(1). The
-p option must be given both at compile-time and at link-time. Linking object
files not compiled with -p is possible, but results in less precise profiling.
See the gprof(1) man page for more information about the profiles.
Full support for gprof(1) is only available for certain platforms (currently: Intel
x86/Linux and Alpha/Digital Unix). On other platforms, the -p option will result
in a less precise profile (no call graph information, only a time profile).
-pack Build an object file (.cmx and .o files) and its associated compiled interface
(.cmi) that combines the .cmx object files given on the command line, making them
appear as sub-modules of the output .cmx file. The name of the output .cmx file
must be given with the -o option. For instance, ocam-
lopt -pack -o P.cmx A.cmx B.cmx C.cmx generates compiled files P.cmx, P.o and P.cmi
describing a compilation unit having three sub-modules A, B and C, corresponding to
the contents of the object files A.cmx, B.cmx and C.cmx. These contents can be
referenced as P.A, P.B and P.C in the remainder of the program.
The .cmx object files being combined must have been compiled with the appropriate
-for-pack option. In the example above, A.cmx, B.cmx and C.cmx must have been com-
piled with ocamlopt -for-pack P.
Multiple levels of packing can be achieved by combining -pack with -for-pack. See
The OCaml user's manual, chapter "Native-code compilation" for more details.
Cause the compiler to call the given command as a preprocessor for each source
file. The output of command is redirected to an intermediate file, which is com-
piled. If there are no compilation errors, the intermediate file is deleted after-
Check information path during type-checking, to make sure that all types are
derived in a principal way. All programs accepted in -principal mode are also
accepted in default mode with equivalent types, but different binary signatures.
Allow arbitrary recursive types during type-checking. By default, only recursive
types where the recursion goes through an object type are supported. Note that once
you have created an interface using this flag, you must use it again for all depen-
Add suffix to the name of the runtime library that will be used by the program. If
OCaml was configured with option -with-debug-runtime, then the d suffix is sup-
ported and gives a debug version of the runtime.
-S Keep the assembly code produced during the compilation. The assembly code for the
source file x.ml is saved in the file x.s.
Build a plugin (usually .cmxs) that can be dynamically loaded with the Dynlink mod-
ule. The name of the plugin must be set with the -o option. A plugin can include a
number of OCaml modules and libraries, and extra native objects (.o, .a files).
Building native plugins is only supported for some operating system. Under some
systems (currently, only Linux AMD 64), all the OCaml code linked in a plugin must
have been compiled without the -nodynlink flag. Some constraints might also apply
to the way the extra native objects have been compiled (under Linux AMD 64, they
must contain only position-independent code).
The left-hand part of a sequence must have type unit.
Compile or link multithreaded programs, in combination with the system threads
library described in The OCaml user's manual.
Turn bound checking off for array and string accesses (the v.(i)ands.[i] con-
structs). Programs compiled with -unsafe are therefore faster, but unsafe: anything
can happen if the program accesses an array or string outside of its bounds. Addi-
tionally, turn off the check for zero divisor in integer division and modulus oper-
ations. With -unsafe, an integer division (or modulus) by zero can halt the pro-
gram or continue with an unspecified result instead of raising a Division_by_zero
-v Print the version number of the compiler and the location of the standard library
directory, then exit.
Print all external commands before they are executed, in particular invocations of
the assembler, C compiler, and linker.
Print the version number of the compiler in short form (e.g. "3.11.0"), then exit.
Enable, disable, or mark as errors the warnings specified by the argument warn-
ing-list. See ocamlc(1) for the syntax of warning-list.
Mark as errors the warnings specified in the argument warning-list. The compiler
will stop with an error when one of these warnings is emitted. The warning-list
has the same meaning as for the -w option: a + sign (or an uppercase letter) turns
the corresponding warnings into errors, a - sign (or a lowercase letter) turns them
back into warnings, and a @ sign both enables and marks the corresponding warnings.
Note: it is not recommended to use the -warn-error option in production code,
because it will almost certainly prevent compiling your program with later versions
of OCaml when they add new warnings.
The default setting is -warn-error -a (none of the warnings is treated as an
-where Print the location of the standard library, then exit.
- file Process file as a file name, even if it starts with a dash (-) character.
-help or --help
Display a short usage summary and exit.
OPTIONS FOR THE IA32 ARCHITECTURE
The IA32 code generator (Intel Pentium, AMD Athlon) supports the following additional
Use the IA32 instructions to compute trigonometric and exponential functions,
instead of calling the corresponding library routines. The functions affected are:
atan, atan2, cos, log, log10, sin, sqrt and tan. The resulting code runs faster,
but the range of supported arguments and the precision of the result can be
reduced. In particular, trigonometric operations cos, sin, tan have their range
reduced to [-2^64, 2^64].
OPTIONS FOR THE AMD64 ARCHITECTURE
The AMD64 code generator (64-bit versions of Intel Pentium and AMD Athlon) supports the
following additional options:
-fPIC Generate position-independent machine code. This is the default.
Generate position-dependent machine code.
OPTIONS FOR THE SPARC ARCHITECTURE
The Sparc code generator supports the following additional options:
Generate SPARC version 8 code.
Generate SPARC version 9 code.
The default is to generate code for SPARC version 7, which runs on all SPARC processors.
The OCaml user's manual, chapter "Native-code compilation".