Teach CMake to prefer the system default compiler automatically when no
compiler is specified. By default use "cc" for C, "CC" for C++, and
"f95" for Fortran. Load a new Platform/<os>-<lang>.cmake module to
allow each platform to specify for each language its system compiler
name(s) and/or exclude certain names.
Create Platform/(CYGWIN|Darwin|Linux|Windows)-CXX.cmake modules to
specify "c++" as the system C++ compiler name for these platforms. On
systems that use case-insensitive filesystems exclude C++ compiler names
that are distinguished from C compiler names only by case.
This will change the default compiler selection for existing build
scripts that do not specify a compiler when run on machines with
separate system and GNU compilers both installed in the PATH. We do not
make this change in default behavior lightly. However:
(1) If a given build really needs specific compilers one should specify
them explicitly e.g. by setting CC, CXX, and FC in the environment.
(2) The motivating case is to prefer the system Clang on newer OS X
systems over the older GNU compilers typically also installed. On
such systems the names "cc" and "c++" link to Clang. This is the
first platform known to CMake on which "c++" is not a GNU compiler.
The old behavior selected "gcc" for C and "c++" C++ and therefore
chooses GNU for C and Clang for C++ by default. The new behavior
selects GNU or Clang consistently for both languages on older or
newer OS X systems, respectively.
(3) Other than the motivating OS X case the conditions under which the
behavior changes do not tend to exist in default OS installations.
They typically occur only on non-GNU systems with manually-installed
GNU compilers.
(4) The consequences of the new behavior are not dire. At worst the
project fails to compile with the system compiler when it previously
worked with the non-system GNU compiler. Such failure is easy to
work around (see #1).
In short this change creates a more sensible default behavior everywhere
and fixes poor default behavior on a widely-used platform at the cost of
a modest change in behavior in less-common conditions.
The compiler candidate list selection and search code for C, C++, ASM,
and Fortran languages was duplicated across four modules. To look for
compilers adjacent to already-enabled languages the C and CXX modules
each used _CMAKE_USER_(C|CXX)_COMPILER_PATH and the ASM module used
_CMAKE_TOOLCHAIN_LOCATION. Since commit 4debb7ac (Bias Fortran compiler
search with C/C++ compilers, 2009-09-09) CMake prefers Fortran compilers
matching the vendor and directory of an enabled C or C++ compiler.
Factor out the common functionality among the four languages into a new
CMakeDetermineCompiler module. Generalize the Fortran implementation so
that all languages may each use the vendor and directory of the other
languages that have already been enabled. For now do not list any
vendor-specific names for C, C++, or ASM so that only the directory
preference is used for these languages (existing behavior).
This commit changes the way how the assembler support works in cmake.
The language "ASM" now always uses the C/Cxx compiler instead
of the assembler directly. This fixes#8392, assembler files are
not preprocessed.
If one wants to use the assembler directly, the specific
assembler "dialect" has to be enabled. I.e. to get as/gas,
you have to use now ASM-ATT, the same way for ASM_MASM and ASM_NASM.
Implemented this now for gcc.
SunStudio, IBM, HP and Intel still todo.
Alex
The TI DSP compiler predefines "__TI_COMPILER_VERSION__". Use this to
identify the C and C++ compilers. For assembler language the C compiler
executable is used:
$ cl6x -h
TMS320C6x C/C++ Compiler v6.1.11
Tools Copyright (c) 1996-2009 Texas Instruments Incorporated
Use this command-line option and output to recognize the assembler.
CMakeDetermineASMCompiler.cmake relied on that somebody else (usually
during enabling C or CXX) already included that file, and broke if that
was not the case.
Thanks to Louis for the patch
Alex
For assembler, the "compiler ID" cannot be detected by "compiling" a
source file, since there is not source file all assemblers understand.
Instead the function CMAKE_DETERMINE_COMPILER_ID_VENDOR() is used to
run the assembler and check its output.
For this the CMAKE_DETERMINE_COMPILER_ID_VENDOR() function had to be
extended so that it creates the run directory if it doesn't exist yet.
In CMakeASMInformation.cmake now also CMAKE_ASM_COMPILER_ID is used
(but there are no such files yet, will come with the support for the
IAR toolchain).
Alex
This adds copyright/license notification blocks CMake's non-find
modules. Most of the modules had no notices at all. Some had notices
referring to the BSD license already. This commit normalizes existing
notices and adds missing notices.
Brad King
Alex Neundorf
Wojciech Migda
Todd Gamblin