= CompileTimeOptions

MLton's compile-time options control the name of the output file, the
verbosity of compile-time messages, and whether or not certain
optimizations are performed.  They also can specify which intermediate
files are saved and can stop the compilation process early, at some
intermediate pass, in which case compilation can be resumed by passing
the generated files to MLton.  MLton uses the input file suffix to
determine the type of input program.  The possibilities are `.c`,
`.mlb`, `.o`, `.s`, and `.sml`.

With no arguments, MLton prints the version number and exits.  For a
usage message, run MLton with an invalid switch, e.g.  `mlton -z`.  In
the explanation below and in the usage message, for flags that take a
number of choices (e.g. `{true|false}`), the first value listed is the
default.


== Options

* ``-align __n__``
+
Aligns object in memory by the specified alignment (`4` or `8`).
The default varies depending on architecture.

* ``-as-opt __option__``
+
Pass _option_ to `cc` when compiling assembler code.  If you wish to
pass an option to the assembler, you must use `cc`&rsquo;s `-Wa,` syntax.

* ``-cc __cc__``
+
Specify the executable for the C compiler.  The C compiler is also invoked to
compile assembly (`.s` files) to object code (`.o` files) and to link object
code into an executable.

* ``-cc-opt __option__``
+
Pass _option_ to `cc` when compiling C code.

* ``-codegen {native|amd64|c|llvm|x86}``
+
Generate native object code via amd64 assembly, C code, LLVM code, or
x86 code or C code.  With `-codegen native` (`-codegen amd64` or
`-codegen x86`), MLton typically compiles more quickly and generates
better code.

* ``-const __name__ __value__``
+
Set the value of a compile-time constant.  Here is a list of
available constants, their default values, and what they control.
+
** ``Exn.keepHistory {false|true}``
+
Enable `MLton.Exn.history`.  See <<MLtonExn#>> for details.  There is a
performance cost to setting this to `true`, both in memory usage of
exceptions and in run time, because of additional work that must be
performed at each exception construction, raise, and handle.

* ``-default-ann __ann__``
+
Specify default <<MLBasisAnnotations#,ML Basis annotations>>.  For
example, `-default-ann 'warnUnused true'` causes unused variable
warnings to be enabled by default.  A default is overridden by the
corresponding annotation in an ML Basis file.

* ``-default-type __type__``
+
Specify the default binding for a primitive type.  For example,
`-default-type word64` causes the top-level type `word` and the
top-level structure `Word` in the <<BasisLibrary#,Basis Library>> to be
equal to `Word64.word` and `Word64:WORD`, respectively.  Similarly,
`-default-type intinf` causes the top-level type `int` and the
top-level structure `Int` in the <<BasisLibrary#,Basis Library>> to be
equal to `IntInf.int` and `IntInf:INTEGER`, respectively.

* ``-disable-ann __ann__``
+
Ignore the specified <<MLBasisAnnotations#,ML Basis annotation>> in
every ML Basis file.  For example, to see _all_ match and unused
warnings, compile with
+
----
-default-ann 'warnUnused true'
-disable-ann forceUsed
-disable-ann nonexhaustiveMatch
-disable-ann redundantMatch
-disable-ann warnUnused
----

* ``-export-header __file__``
+
Write C prototypes to _file_ for all of the functions in the program
<<CallingFromCToSML#,exported from SML to C>>.

* ``-ieee-fp {false|true}``
+
Cause the x86 native code generator to be pedantic about following the
IEEE floating point standard.  By default, it is not, because of the
performance cost.  This only has an effect with `-codegen x86`.

* ``-inline __n__``
+
Set the inlining threshold used in the optimizer.  The threshold is an
approximate measure of code size of a procedure.  The default is
`320`.

* ``-keep {g|o}``
+
Save intermediate files.  If no `-keep` argument is given, then only
the output file is saved.
+
[cols="^25%,<75%"]
|===
| `g` | generated `.c` and `.s` files passed to `cc` and generated `.ll` files passed to `llvm-as`
| `o` | object (`.o`) files
|===

* ``-link-opt __option__``
+
Pass _option_ to `cc` when linking.  You can use this to specify
library search paths, e.g. `-link-opt -Lpath`, and libraries to link
with, e.g., `-link-opt -lfoo`, or even both at the same time,
e.g. `-link-opt '-Lpath -lfoo'`.  If you wish to pass an option to the
linker, you must use `cc`&rsquo;s `-Wl,` syntax, e.g.,
`-link-opt '-Wl,--export-dynamic'`.

* ``-llvm-as __llvm-as__``
+
Specify the executable for the LLVM `.ll` to `.bc` assembler;
can be used to select a specific version of the tool (e.g., `-llvm-as llvm-as-14`).

* ``-llvm-as-opt __option__``
+
Pass _option_ to `llvm-as` when assembling (`.ll` to `.bc`) LLVM code.

* ``-llvm-llc __llc__``
+
Specify the executable for the LLVM `.bc` to `.o` system compiler;
can be used to select a specific version of the tool (e.g., `-llvm-as llc-14`).

* ``-llvm-llc-opt __option__``
+
Pass _option_ to `llc` when compiling (`.bc` to `.o`) LLVM code.

* ``-llvm-opt __opt__``
+
Specify the executable for the LLVM `.bc` to `.bc` optimizer;
can be used to select a specific version of the tool (e.g., `-llvm-opt opt-14`).

* ``-llvm-opt-opt __option__``
+
Pass _option_ to `opt` when optimizing (`.bc` to `.bc`) LLVM code.

* ``-mlb-path-map __file__``
+
Use _file_ as an <<MLBasisPathMap#,ML Basis path map>> to define
additional MLB path variables.  Multiple uses of `-mlb-path-map` and
`-mlb-path-var` are allowed, with variable definitions in later path
maps taking precedence over earlier ones.

* ``-mlb-path-var __name__ __value__``
+
Define an additional MLB path variable.  Multiple uses of
`-mlb-path-map` and `-mlb-path-var` are allowed, with variable
definitions in later path maps taking precedence over earlier ones.

* ``-output __file__``
+
Specify the name of the final output file. The default name is the
input file name with its suffix removed and an appropriate, possibly
empty, suffix added.

* ``-profile {no|alloc|count|time}``
+
Produce an executable that gathers <<Profiling#,profiling>> data.  When
such an executable is run, it produces an `mlmon.out` file.

* ``-profile-branch {false|true}``
+
If true, the profiler will separately gather profiling data for each
branch of a function definition, `case` expression, and `if`
expression.

* ``-profile-stack {false|true}``
+
If `true`, the executable will gather profiling data for all functions
on the stack, not just the currently executing function.  See
<<ProfilingTheStack#>>.

* ``-profile-val {false|true}``
+
If `true`, the profiler will separately gather profiling data for each
(expansive) `val` declaration.

* ``-runtime __arg__``
+
Pass argument to the runtime system via `@MLton`.  See
<<RunTimeOptions#>>.  The argument will be processed before other
`@MLton` command line switches.  Multiple uses of `-runtime` are
allowed, and will pass all the arguments in order.  If the same
runtime switch occurs more than once, then the last setting will take
effect.  There is no need to supply the leading `@MLton` or the
trailing `--`; these will be supplied automatically.
+
An argument to `-runtime` may contain spaces, which will cause the
argument to be treated as a sequence of words by the runtime.  For
example the command line:
+
----
mlton -runtime 'ram-slop 0.4' foo.sml
----
+
will cause `foo` to run as if it had been called like:
+
----
foo @MLton ram-slop 0.4 --
----
+
An executable created with `-runtime stop` doesn't process any
`@MLton` arguments.  This is useful to create an executable, e.g.,
`echo`, that must treat `@MLton` like any other command-line argument.
+
----
% mlton -runtime stop echo.sml
% echo @MLton --
@MLton --
----

* ``-show-basis __file__``
+
Pretty print to _file_ the basis defined by the input program.  See
<<ShowBasis#>>.

* ``-show-def-use __file__``
+
Output def-use information to _file_.  Each identifier that is defined
appears on a line, followed on subsequent lines by the position of
each use.

* ``-stop {f|g|o|tc}``
+
Specify when to stop.
+
[cols="^25%,<75%"]
|===
| `f` | list of files on stdout (only makes sense when input is `foo.mlb`)
| `g` | generated `.c` and `.s` files
| `o` | object (`.o`) files
| `tc` | after type checking
|===
+
If you compile with `-stop g` or `-stop o`, you can resume compilation
by running MLton on the generated `.c` and `.s` or `.o` files.

* ``-target {self|__...__}``
+
Generate an executable that runs on the specified platform.  The
default is `self`, which means to compile for the machine that MLton
is running on.  To use any other target, you must first install a
<<CrossCompiling#,cross compiler>>.

* ``-target-as-opt __target__ __option__``
+
Like `-as-opt`, this passes _option_ to `cc` when compliling
assembler code, except it only passes _option_ when the target
architecture, operating system, or arch-os pair is _target_.

* ``-target-cc-opt __target__ __option__``
+
Like `-cc-opt`, this passes _option_ to `cc` when compiling C code,
except it only passes _option_ when the target architecture, operating
system, or arch-os pair is _target_.

* ``-target-link-opt __target__ __option__``
+
Like `-link-opt`, this passes _option_ to `cc` when linking, except
it only passes _option_ when the target architecture, operating
system, or arch-os pair is _target_.

* ``-verbose {0|1|2|3}``
+
How verbose to be about what passes are running.  The default is `0`.
+
[cols="^25%,<75%"]
|===
| `0` | silent
| `1` | calls to compiler, assembler, and linker
| `2` | 1, plus intermediate compiler passes
| `3` | 2, plus some data structure sizes
|===
