ocamlopt - The OCaml native-code compiler
The OCaml high-performance native-code compiler ocamlopt
OCaml source files to native code object files and link these object files to
produce standalone executables.
(1) command has a command-line interface very close to that
(1). It accepts the same types of arguments and processes them
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
(1) compiler produces a compiled interface in the file
.cmi. The interface produced is identical to that produced by the
bytecode compiler ocamlc
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:
.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
.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
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 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
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
(1) to run.
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
- 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 automatically adds back the
-cclib and -ccopt options as if they had been
provided on the command line, unless the -noautolink option is
given. Additionally, a substring $CAMLORIGIN inside a
-ccopt options will be replaced by the full path to the
.cma library, excluding the filename.
- Show absolute filenames in error messages.
- 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.
- Dump detailed information about the compilation (types, bindings,
tail-calls, etc) in binary format. The information for file src.ml
is put into file src.cmt. In case of a type error, dump all the
information inferred by the type-checker before the error. The annotation
files produced by -bin-annot contain more information and are much
more compact than the files produced by -annot.
- 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 modules separately.
- -cc ccomp
- Use ccomp as the C linker called to build the final executable and
as the C compiler for compiling .c source files.
- -cclib -llibname
- Pass the -llibname option to the linker. This causes the
given C library to be linked with the program.
- -ccopt option
- 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
- Print the version number of ocamlopt(1) and a detailed summary of
its configuration, then exit.
- -for-pack module-path
- 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.
- 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)).
- 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
- -I directory
- Add the given directory to the list of directories searched for compiled
interface files (.cmi), compiled object code files (.cmx), and libraries
(.cmxa). 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 library directory. See also option
If the given directory starts with +, it is taken relative to the
standard library directory. For instance, -I +compiler-libs
adds the subdirectory compiler-libs of the standard library to the
- -impl filename
- Compile the file filename as an implementation file, even if its
extension is not .ml.
- -inline n
- 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
- -intf filename
- Compile the file filename as an interface file, even if its
extension is not .mli.
- -intf-suffix string
- Recognize file names ending with string as interface files (instead
of the default .mli).
- Keep documentation strings in generated .cmi files.
- Keep locations in generated .cmi files.
- 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 record dependencies for module aliases.
- Deactivates the applicative behaviour of functors. With this option, each
functor application generates new types in its result and applying the
same functor twice to the same argument yields two incompatible
- 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
- 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
- Allow the compiler to use some optimizations that are valid only for code
that is never dynlinked.
- Do not automatically add the standard library directory the list of
directories searched for compiled interface files (.cmi), compiled object
code files (.cmx), and libraries (.cmxa). See also option -I.
- Ignore non-optional labels in types. Labels cannot be used in
applications, and parameter order becomes strict.
- -o exec-file
- 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. This can also be used when compiling an
interface or implementation file, without linking, in which case it sets
the name of the cmi or cmo file, and also sets the module name to the file
name up to the first dot.
- -open module
- Opens the given module before processing the interface or implementation
files. If several -open options are given, they are processed in
order, just as if the statements open! module1;; ... open! moduleN;; were
added at the top of each file.
- 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).
- 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).
- 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
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 OCaml user's manual, chapter
"Native-code compilation" for more details.
- -pp command
- 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.
- -ppx command
- After parsing, pipe the abstract syntax tree through the preprocessor
command. The module Ast_mapper(3) implements the external
interface of a preprocessor.
- 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 dependencies.
- -runtime-variant suffix
- 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 supported and
gives a debug version of the runtime.
- Keep the assembly code produced during the compilation. The assembly code
for the source file x.ml is saved in the file x.s.
- Enforce the separation between types
string and bytes, thereby making strings
read-only. This will become the default in a future version of OCaml.
- 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 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
- When a type is visible under several module-paths, use the shortest one
when printing the type's name in inferred interfaces and error and warning
- 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] 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 exception.
- Identify the types string and bytes, thereby
making strings writable. For reasons of backward compatibility, this is
the default setting for the moment, but this will change in a future
version of OCaml.
- 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.
- -version or -vnum
- Print the version number of the compiler in short form (e.g.
"3.11.0"), then exit.
- -w warning-list
- Enable, disable, or mark as fatal the warnings specified by the argument
warning-list. See ocamlc(1) for the syntax of
- -warn-error warning-list
- Mark as fatal 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) marks the corresponding
warnings as fatal, a - sign (or a lowercase letter) turns them back
into non-fatal warnings, and a @ sign both enables and marks as
fatal 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 or modify
The default setting is -warn-error -a (all warnings are
- Show the description of all available warning numbers.
- 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.
The IA32 code generator (Intel Pentium, AMD Athlon) supports the following
- 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].
The AMD64 code generator (64-bit versions of Intel Pentium and AMD Athlon)
supports the following additional options:
- Generate position-independent machine code. This is the default.
- Generate position-dependent machine code.
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
The ARM code generator supports the following additional options:
- Select the ARM target architecture
- Select the floating-point hardware
- Generate position-independent machine code.
- Generate position-dependent machine code. This is the default.
- Enable Thumb/Thumb-2 code generation
- Disable Thumb/Thumb-2 code generation
The default values for target architecture, floating-point hardware and thumb
usage were selected at configure-time when building ocamlopt
This configuration can be inspected using ocamlopt -config
Target architecture depends on the "model" setting, while
floating-point hardware and thumb support are determined from the ABI setting
in "system" ( linux_eabi
The OCaml user's manual
, chapter "Native-code