GDC(1) GNU GDC(1)
NAME
gdc - A GCC-based compiler for the D language
SYNOPSIS
gdc [-c|-S] [-g] [-pg]
[-Olevel] [-Wwarn...]
[-Idir...] [-Ldir...]
[-foption...] [-mmachine-option...]
[-o outfile] [@file] infile...
Only the most useful options are listed here; see below for the
remainder.
DESCRIPTION
The gdc command is the GNU compiler for the D language and supports
many of the same options as gcc. This manual only documents the
options specific to gdc.
OPTIONS
Input and Output files
For any given input file, the file name suffix determines what kind of
compilation is done. The following kinds of input file names are
supported:
file.d
D source files.
file.dd
Ddoc source files.
file.di
D interface files.
You can specify more than one input file on the gdc command line, each
being compiled separately in the compilation process. If you specify a
"-o file" option, all the input files are compiled together, producing
a single output file, named file. This is allowed even when using "-S"
or "-c".
A D interface file contains only what an import of the module needs,
rather than the whole implementation of that module. They can be
created by gdc from a D source file by using the "-H" option. When the
compiler resolves an import declaration, it searches for matching .di
files first, then for .d.
A Ddoc source file contains code in the D macro processor language. It
is primarily designed for use in producing user documentation from
embedded comments, with a slight affinity towards HTML generation. If
a .d source file starts with the string "Ddoc" then it is treated as
general purpose documentation, not as a D source file.
Runtime Options
These options affect the runtime behavior of programs compiled with
gdc.
-fall-instantiations
Generate code for all template instantiations. The default
template emission strategy is to not generate code for declarations
that were either instantiated speculatively, such as from
"__traits(compiles, ...)", or that come from an imported module not
being compiled.
-fno-assert
Turn off code generation for "assert" contracts.
-fno-bounds-check
Turns off array bounds checking for all functions, which can
improve performance for code that uses arrays extensively. Note
that this can result in unpredictable behavior if the code in
question actually does violate array bounds constraints. It is
safe to use this option if you are sure that your code never throws
a "RangeError".
-fbounds-check=value
An alternative to -fbounds-check that allows more control as to
where bounds checking is turned on or off. The following values
are supported:
on Turns on array bounds checking for all functions.
safeonly
Turns on array bounds checking only for @safe functions.
off Turns off array bounds checking completely.
-fno-builtin
Don't recognize built-in functions unless they begin with the
prefix __builtin_. By default, the compiler will recognize when a
function in the "core.stdc" package is a built-in function.
-fcheckaction=value
This option controls what code is generated on an assertion, bounds
check, or final switch failure. The following values are
supported:
context
Throw an "AssertError" with extra context information.
halt
Halt the program execution.
throw
Throw an "AssertError" (the default).
-fdebug
-fdebug=value
Turn on compilation of conditional "debug" code into the program.
The -fdebug option itself sets the debug level to 1, while -fdebug=
enables "debug" code that are identified by any of the following
values:
level
Sets the debug level to level, any "debug" code <= level is
compiled into the program.
ident
Turns on compilation of any "debug" code identified by ident.
-fno-druntime
Implements <https://dlang.org/spec/betterc.html>. Assumes that
compilation targets an environment without a D runtime library.
This is equivalent to compiling with the following options:
gdc -nophoboslib -fno-exceptions -fno-moduleinfo -fno-rtti
-fextern-std=standard
Sets the C++ name mangling compatibility to the version identified
by standard. The following values are supported:
c++98
c++03
Sets "__traits(getTargetInfo, "cppStd")" to 199711.
c++11
Sets "__traits(getTargetInfo, "cppStd")" to 201103.
c++14
Sets "__traits(getTargetInfo, "cppStd")" to 201402.
c++17
Sets "__traits(getTargetInfo, "cppStd")" to 201703. This is
the default.
c++20
Sets "__traits(getTargetInfo, "cppStd")" to 202002.
-fno-invariants
Turns off code generation for class "invariant" contracts.
-fmain
Generates a default "main()" function when compiling. This is
useful when unittesting a library, as it enables running the
unittests in a library without having to manually define an entry-
point function. This option does nothing when "main" is already
defined in user code.
-fno-moduleinfo
Turns off generation of the "ModuleInfo" and related functions that
would become unreferenced without it, which may allow linking to
programs not written in D. Functions that are not be generated
include module constructors and destructors ("static this" and
"static ~this"), "unittest" code, and "DSO" registry functions for
dynamically linked code.
-fonly=filename
Tells the compiler to parse and run semantic analysis on all
modules on the command line, but only generate code for the module
specified by filename.
-fno-postconditions
Turns off code generation for postcondition "out" contracts.
-fno-preconditions
Turns off code generation for precondition "in" contracts.
-fpreview=id
Turns on an upcoming D language change identified by id. The
following values are supported:
all Turns on all upcoming D language features.
dip1000
Implements
<https://github.com/dlang/DIPs/blob/master/DIPs/other/DIP1000.md>
(Scoped pointers).
dip1008
Implements
<https://github.com/dlang/DIPs/blob/master/DIPs/other/DIP1008.md>
(Allow exceptions in @nogc code).
dip1021
Implements
<https://github.com/dlang/DIPs/blob/master/DIPs/accepted/DIP1021.md>
(Mutable function arguments).
dip25
Implements
<https://github.com/dlang/DIPs/blob/master/DIPs/archive/DIP25.md>
(Sealed references).
dtorfields
Turns on generation for destructing fields of partially
constructed objects.
fieldwise
Turns on generation of struct equality to use field-wise
comparisons.
fixaliasthis
Implements new lookup rules that check the current scope for
"alias this" before searching in upper scopes.
in Implements "in" parameters to mean "scope const [ref]" and
accepts rvalues.
inclusiveincontracts
Implements "in" contracts of overridden methods to be a
superset of parent contract.
intpromote
Implements C-style integral promotion for unary "+", "-" and
"~" expressions.
nosharedaccess
Turns off and disallows all access to shared memory objects.
rvaluerefparam
Implements rvalue arguments to "ref" parameters.
shortenedmethods
Implements use of "=>" for methods and top-level functions in
addition to lambdas.
-frelease
Turns on compiling in release mode, which means not emitting
runtime checks for contracts and asserts. Array bounds checking is
not done for @system and @trusted functions, and assertion failures
are undefined behavior.
This is equivalent to compiling with the following options:
gdc -fno-assert -fbounds-check=safe -fno-invariants \
-fno-postconditions -fno-preconditions -fno-switch-errors
-frevert=
Turns off a D language feature identified by id. The following
values are supported:
all Turns off all revertable D language features.
dip25
Reverts
<https://github.com/dlang/DIPs/blob/master/DIPs/archive/DIP25.md>
(Sealed references).
dtorfields
Turns off generation for destructing fields of partially
constructed objects.
markdown
Turns off Markdown replacements in Ddoc comments.
-fno-rtti
Turns off generation of run-time type information for all user
defined types. Any code that uses features of the language that
require access to this information will result in an error.
-fno-switch-errors
This option controls what code is generated when no case is matched
in a "final switch" statement. The default run time behavior is to
throw a "SwitchError". Turning off -fswitch-errors means that
instead the execution of the program is immediately halted.
-funittest
Turns on compilation of "unittest" code, and turns on the
"version(unittest)" identifier. This implies -fassert.
-fversion=value
Turns on compilation of conditional "version" code into the program
identified by any of the following values:
level
Sets the version level to level, any "version" code >= level is
compiled into the program.
ident
Turns on compilation of "version" code identified by ident.
-fno-weak-templates
Turns off emission of declarations that can be defined in multiple
objects as weak symbols. The default is to emit all public symbols
as weak, unless the target lacks support for weak symbols.
Disabling this option means that common symbols are instead put in
COMDAT or become private.
Options for Directory Search
These options specify directories to search for files, libraries, and
other parts of the compiler:
-Idir
Specify a directory to use when searching for imported modules at
compile time. Multiple -I options can be used, and the paths are
searched in the same order.
-Jdir
Specify a directory to use when searching for files in string
imports at compile time. This switch is required in order to use
"import(file)" expressions. Multiple -J options can be used, and
the paths are searched in the same order.
-Ldir
When linking, specify a library search directory, as with gcc.
-Bdir
This option specifies where to find the executables, libraries,
source files, and data files of the compiler itself, as with gcc.
-fmodule-file=module=spec
This option manipulates file paths of imported modules, such that
if an imported module matches all or the leftmost part of module,
the file path in spec is used as the location to search for D
sources. This is used when the source file path and names are not
the same as the package and module hierarchy. Consider the
following examples:
gdc test.d -fmodule-file=A.B=foo.d -fmodule-file=C=bar
This will tell the compiler to search in all import paths for the
source file foo.d when importing A.B, and the directory bar/ when
importing C, as annotated in the following D code:
module test;
import A.B; // Matches A.B, searches for foo.d
import C.D.E; // Matches C, searches for bar/D/E.d
import A.B.C; // No match, searches for A/B/C.d
-imultilib dir
Use dir as a subdirectory of the gcc directory containing target-
specific D sources and interfaces.
-iprefix prefix
Specify prefix as the prefix for the gcc directory containing
target-specific D sources and interfaces. If the prefix represents
a directory, you should include the final '/'.
-nostdinc
Do not search the standard system directories for D source and
interface files. Only the directories that have been specified
with -I options (and the directory of the current file, if
appropriate) are searched.
Code Generation
In addition to the many gcc options controlling code generation, gdc
has several options specific to itself.
-H Generates D interface files for all modules being compiled. The
compiler determines the output file based on the name of the input
file, removes any directory components and suffix, and applies the
.di suffix.
-Hd dir
Same as -H, but writes interface files to directory dir. This
option can be used with -Hf file to independently set the output
file and directory path.
-Hf file
Same as -H but writes interface files to file. This option can be
used with -Hd dir to independently set the output file and
directory path.
-M Output the module dependencies of all source files being compiled
in a format suitable for make. The compiler outputs one make rule
containing the object file name for that source file, a colon, and
the names of all imported files.
-MM Like -M but does not mention imported modules from the D standard
library package directories.
-MF file
When used with -M or -MM, specifies a file to write the
dependencies to. When used with the driver options -MD or -MMD,
-MF overrides the default dependency output file.
-MG This option is for compatibility with gcc, and is ignored by the
compiler.
-MP Outputs a phony target for each dependency other than the modules
being compiled, causing each to depend on nothing.
-MT target
Change the target of the rule emitted by dependency generation to
be exactly the string you specify. If you want multiple targets,
you can specify them as a single argument to -MT, or use multiple
-MT options.
-MQ target
Same as -MT, but it quotes any characters which are special to
make.
-MD This option is equivalent to -M -MF file. The driver determines
file by removing any directory components and suffix from the input
file, and then adding a .deps suffix.
-MMD
Like -MD but does not mention imported modules from the D standard
library package directories.
-X Output information describing the contents of all source files
being compiled in JSON format to a file. The driver determines
file by removing any directory components and suffix from the input
file, and then adding a .json suffix.
-Xf file
Same as -X, but writes all JSON contents to the specified file.
-fdoc
Generates "Ddoc" documentation and writes it to a file. The
compiler determines file by removing any directory components and
suffix from the input file, and then adding a .html suffix.
-fdoc-dir=dir
Same as -fdoc, but writes documentation to directory dir. This
option can be used with -fdoc-file=file to independently set the
output file and directory path.
-fdoc-file=file
Same as -fdoc, but writes documentation to file. This option can
be used with -fdoc-dir=dir to independently set the output file and
directory path.
-fdoc-inc=file
Specify file as a Ddoc macro file to be read. Multiple -fdoc-inc
options can be used, and files are read and processed in the same
order.
-fdump-c++-spec=file
For D source files, generate corresponding C++ declarations in
file.
-fdump-c++-spec-verbose
In conjunction with -fdump-c++-spec= above, add comments for
ignored declarations in the generated C++ header.
-fsave-mixins=file
Generates code expanded from D "mixin" statements and writes the
processed sources to file. This is useful to debug errors in
compilation and provides source for debuggers to show when
requested.
Warnings
Warnings are diagnostic messages that report constructions that are not
inherently erroneous but that are risky or suggest there is likely to
be a bug in the program. Unless -Werror is specified, they do not
prevent compilation of the program.
-Wall
Turns on all warnings messages. Warnings are not a defined part of
the D language, and all constructs for which this may generate a
warning message are valid code.
-Walloca
This option warns on all uses of "alloca" in the source.
-Walloca-larger-than=n
Warn on unbounded uses of alloca, and on bounded uses of alloca
whose bound can be larger than n bytes. -Wno-alloca-larger-than
disables -Walloca-larger-than warning and is equivalent to
-Walloca-larger-than=SIZE_MAX or larger.
-Wcast-result
Warn about casts that will produce a null or zero result.
Currently this is only done for casting between an imaginary and
non-imaginary data type, or casting between a D and C++ class.
-Wno-deprecated
Do not warn about usage of deprecated features and symbols with
"deprecated" attributes.
-Werror
Turns all warnings into errors.
-Wspeculative
List all error messages from speculative compiles, such as
"__traits(compiles, ...)". This option does not report messages as
warnings, and these messages therefore never become errors when the
-Werror option is also used.
-Wtemplates
Warn when a template instantiation is encountered. Some coding
rules disallow templates, and this may be used to enforce that
rule.
-Wunknown-pragmas
Warn when a "pragma()" is encountered that is not understood by
gdc. This differs from -fignore-unknown-pragmas where a pragma
that is part of the D language, but not implemented by the
compiler, won't get reported.
-Wno-varargs
Do not warn upon questionable usage of the macros used to handle
variable arguments like "va_start".
-fignore-unknown-pragmas
Turns off errors for unsupported pragmas.
-fmax-errors=n
Limits the maximum number of error messages to n, at which point
gdc bails out rather than attempting to continue processing the
source code. If n is 0 (the default), there is no limit on the
number of error messages produced.
-fsyntax-only
Check the code for syntax errors, but do not actually compile it.
This can be used in conjunction with -fdoc or -H to generate files
for each module present on the command-line, but no other output
file.
-ftransition=id
Report additional information about D language changes identified
by id. The following values are supported:
all List information on all D language transitions.
complex
List all usages of complex or imaginary types.
field
List all non-mutable fields which occupy an object instance.
in List all usages of "in" on parameter.
nogc
List all hidden GC allocations.
templates
List statistics on template instantiations.
tls List all variables going into thread local storage.
vmarkdown
List instances of Markdown replacements in Ddoc.
Options for Linking
These options come into play when the compiler links object files into
an executable output file. They are meaningless if the compiler is not
doing a link step.
-defaultlib=libname
Specify the library to use instead of libphobos when linking.
Options specifying the linkage of libphobos, such as
-static-libphobos or -shared-libphobos, are ignored.
-debuglib=libname
Specify the debug library to use instead of libphobos when linking.
This option has no effect unless the -g option was also given on
the command line. Options specifying the linkage of libphobos,
such as -static-libphobos or -shared-libphobos, are ignored.
-nophoboslib
Do not use the Phobos or D runtime library when linking. Options
specifying the linkage of libphobos, such as -static-libphobos or
-shared-libphobos, are ignored. The standard system libraries are
used normally, unless -nostdlib or -nodefaultlibs is used.
-shared-libphobos
On systems that provide libgphobos and libgdruntime as a shared and
a static library, this option forces the use of the shared version.
If no shared version was built when the compiler was configured,
this option has no effect.
-static-libphobos
On systems that provide libgphobos and libgdruntime as a shared and
a static library, this option forces the use of the static version.
If no static version was built when the compiler was configured,
this option has no effect.
Developer Options
This section describes command-line options that are primarily of
interest to developers or language tooling.
-fdump-d-original
Output the internal front-end AST after the "semantic3" stage.
This option is only useful for debugging the GNU D compiler itself.
-v Dump information about the compiler language processing stages as
the source program is being compiled. This includes listing all
modules that are processed through the "parse", "semantic",
"semantic2", and "semantic3" stages; all "import" modules and their
file paths; and all "function" bodies that are being compiled.
SEE ALSO
gpl(7), gfdl(7), fsf-funding(7), gcc(1) and the Info entries for gdc
and gcc.
COPYRIGHT
Copyright (c) 2006-2022 Free Software Foundation, Inc.
Permission is granted to copy, distribute and/or modify this document
under the terms of the GNU Free Documentation License, Version 1.3 or
any later version published by the Free Software Foundation; with no
Invariant Sections, no Front-Cover Texts, and no Back-Cover Texts. A
copy of the license is included in the man page gfdl(7).
gcc-12 2022-08-19 GDC(1)
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