Ubuntu Manpage: ocamlopt - The OCaml native-code compiler

name
synopsis
description
options
options for the flambda middle-end
options for the amd64 architecture
see also

NAME

       ocamlopt - The OCaml native-code compiler

SYNOPSIS

       ocamlopt [ options ] filename ...

       ocamlopt.opt (same options)

DESCRIPTION

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, after all options have been processed:

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 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 OCaml.

OPTIONS

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 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.

-absname
Show absolute filenames in error messages.

-no-absname
Do not try to show absolute filenames in error messages.

-annot Deprecated since OCaml 4.11. Please use -bin-annot instead.

-bin-annot
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.

-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 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.

-color mode
Enable or disable colors in compiler messages (especially warnings and errors). The following
modes are supported:

auto use heuristics to enable colors only if the output supports them (an ANSI-compatible tty
terminal);

always enable colors unconditionally;

never disable color output.

The environment variable "OCAML_COLOR" is considered if -color is not provided. Its values are
auto/always/never as above.

If -color is not provided, "OCAML_COLOR" is not set and the environment variable "NO_COLOR" is
set, then color output is disabled. Otherwise, the default setting is auto, and the current
heuristic checks that the "TERM" environment variable exists and is not empty or "dumb", and that
isatty(stderr) holds.

-error-style mode
Control the way error messages and warnings are printed. The following modes are supported:

short only print the error and its location;

contextual like "short", but also display the source code snippet corresponding to the location of
the error.

The default setting is contextual.

The environment variable "OCAML_ERROR_STYLE" is considered if -error-style is not provided. Its
values are short/contextual as above.

-compact
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.

-config
Print the version number of ocamlopt(1) and a detailed summary of its configuration, then exit.

-config-var
Print the value of a specific configuration variable from the -config output, then exit. If the
variable does not exist, the exit code is non-zero.

-depend ocamldep-args
Compute dependencies, as ocamldep would do.

-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.

-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)).

-no-g Do not record debugging information (default).

-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.

-cmi-file filename
Type-check the source implementation to be compiled against the specified interface file (by-
passes the normal lookup for .mli and .cmi files).

-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 -nostdlib.

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
search path.

-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 size.

-insn-sched
Enables the instruction scheduling pass in the compiler backend.

-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-docs
Keep documentation strings in generated .cmi files.

-keep-locs
Keep locations in generated .cmi files.

-labels
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.

-linkall
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. When compiling a module (option -c), setting the -linkall option ensures that this
module will always be linked if it is put in a library and this library is linked.

-linscan
Use linear scan register allocation. Compiling with this allocator is faster than with the usual
graph coloring allocator, sometimes quite drastically so for long functions and modules. On the
other hand, the generated code can be a bit slower.

-match-context-rows
Set number of rows of context used during pattern matching compilation. Lower values cause faster
compilation, but less optimized code. The default value is 32.

-no-alias-deps
Do not record dependencies for module aliases.

-no-app-funct
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 structures.

-noassert
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.

-noautolink
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.

-nodynlink
Allow the compiler to use some optimizations that are valid only for code that is never dynlinked.

-no-insn-sched
Disables the instruction scheduling pass in the compiler backend.

-nostdlib
Do not automatically add the standard library directory to the list of directories searched for
compiled interface files (.cmi), compiled object code files (.cmx), and libraries (.cmxa). See
also option -I.

-nolabels
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.

-opaque
When compiling a .mli interface file, this has the same effect as the -opaque option of the
bytecode compiler. When compiling a .ml implementation file, this produces a .cmx file without
cross-module optimization information, which reduces recompilation on module change.

-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.

-output-obj
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). -output-complete-obj Same as -output-obj except the object file produced
includes the runtime and autolink libraries.

-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 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.

-principal
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.

-no-principal
Do not check principality of type inference. This is the default.

-rectypes
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.

-no-rectypes
Do no allow arbitrary recursive types during type-checking. This is the default.

-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.

-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.

-safe-string
Enforce the separation between types string and bytes, thereby making strings read-only. This is
the default.

-safer-matching
Do not use type information to optimize pattern-matching. This allows to detect match failures
even if a pattern-matching was wrongly assumed to be exhaustive. This only impacts GADT and
polymorphic variant compilation.

-save-ir-after pass
Save intermediate representation after the given compilation pass. The currently supported passes
are: scheduling.

-shared
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 code).

-short-paths
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 messages.

-stop-after pass
Stop compilation after the given compilation pass. The currently supported passes are: parsing,
typing, scheduling, emit.

-strict-sequence
The left-hand part of a sequence must have type unit.

-no-strict-sequence
Left-hand part of a sequence need not have type unit. This is the default.

-unboxed-types
When a type is unboxable (i.e. a record with a single argument or a concrete datatype with a
single constructor of one argument) it will be unboxed unless annotated with [@@ocaml.boxed].

-no-unboxed-types
When a type is unboxable it will be boxed unless annotated with [@@ocaml.unboxed]. This is the
default.

-unsafe
Turn bound checking off for array and string accesses (the v.(i) and s.[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.

-unsafe-string
Identify the types string and bytes, thereby making strings writable. This is intended for
compatibility with old source code and should not be used with new software.

-v Print the version number of the compiler and the location of the standard library directory, then
exit.

-verbose
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 warning-list.

-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 existing warnings.

The default setting is -warn-error -a (no warning is fatal).

-warn-help
Show the description of all available warning numbers.

-where Print the location of the standard library, then exit.

-with-runtime
Include the runtime system in the generated program. This is the default.

-without-runtime
The compiler does not include the runtime system (nor a reference to it) in the generated program;
it must be supplied separately.

- 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 FLAMBDA MIDDLE-END

       When the Flambda code generator has been enabled at configuration time, its behavior may be tuned up with
       the following additional options:

       -02    Perform more optimisation than usual. Compilation times may be lengthened.

       -03    Perform  even  more  optimisation than usual, possibly including unrolling of recursive functions.
              Compilation times may be significantly lengthened.

       -Oclassic
              Makes inlining decisions at the point of definition of a function rather than at the call site(s).
              This mirrors the behaviour of OCaml compilers not using Flambda. Compared to compilation using the
              new Flambda inlining heuristics (for example at -O2)  it  produces  smaller  .cmx  files,  shorter
              compilation times and code that probably runs rather slower.

       -inlining-report
              Emit .inlining files (one per round of optimisation) showing all of the inliner's decisions.

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.

       -fno-PIC
              Generate position-dependent machine code.