ocamlopt - The Objective Caml native-code compiler
ocamlopt [ options ] filename ...
ocamlopt.opt (same options)
The Objective Caml high-performance native-code compiler ocamlopt(1)
compiles Caml 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
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
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 Caml).
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 Caml Light 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 component 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 ocamlrun(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 Objective Caml.
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
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 automatically adds back the 0options
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
-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 useful to compile
Use ccomp as the C linker called to build the final executable
and as the C compiler 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 configuration, 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 exception (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 declarations 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 directory 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
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
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 .mli).
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 already-compiled files.
When linking .cmxa libraries, ignore -cclib and -ccopt options
potentially contained 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 never dynlinked.
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
Cause the linker to produce a C object file instead of an
executable file. This is useful to wrap Caml code as a C
library, callable from any C program. The name of the output
object file is camlprog.o by default; it can 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
See the gprof(1) man page for more information about the
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,
ocamlopt -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 compiled with
ocamlopt -for-pack P.
Multiple levels of packing can be achieved by combining -pack
with -for-pack. See The Objective Caml users 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 compiled. If there are no
compilation errors, the intermediate file is deleted afterwards.
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
-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 module. The name of the plugin must be set with
the -o option. A plugin can include a number of Caml 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 Caml
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).
Compile or link multithreaded programs, in combination with the
system threads library described in The Objective Caml users
Turn bound checking off for array and string accesses (the
v.(i)ands.[i] constructs). Programs compiled with -unsafe are
therefore faster, but unsafe: anything can happen if the program
accesses an array or string outside of its bounds. Additionally,
turn off the check for zero divisor in integer division and
modulus operations. With -unsafe, an integer division (or
modulus) by zero can halt the program 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 or disable warnings according to the argument
warning-list. The argument is a set of letters. If a letter is
uppercase, it enables the corresponding warnings; lowercase
disables the warnings. The correspondence is the following:
A all warnings
C start of comments that look like mistakes
D use of deprecated features
E fragile pattern matchings (matchings that will remain
complete even if additional constructors are added to one of the
variant types matched)
F partially applied functions (expressions whose result has
function type and is ignored)
L omission of labels in applications
M overriding of methods
P missing cases in pattern matchings (i.e. partial matchings)
S expressions in the left-hand side of a sequence that don’t
have type unit (and that are not functions, see F above)
U redundant cases in pattern matching (unused cases)
V overriding of instance variables
Y unused variables that are bound with let or as, and don’t
start with an underscore (_) character
Z all other cases of unused variables that don’t start with an
underscore (_) character
X warnings that don’t fit in the above categories (except A)
The default setting is -w Aelz, enabling all warnings except
fragile pattern matchings, omitted labels, and innocuous unused
variables. Note that warnings F and S are not always triggered,
depending on the internals of the type checker.
Turn the warnings indicated in the argument warning-list into
errors. 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: an uppercase character turns the
corresponding warning into an error, a lowercase character
leaves it as a warning. The default setting is -warn-error a
(none of the warnings is treated as an error).
-where Print the location of the standard library, then exit.
- file Process file as a file name, even if it starts with a dash (-)
-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 option:
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
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
The Objective Caml users manual, chapter "Native-code compilation".