Add a variable to indicate the latest standard known to be supported for
each language:
* `CMAKE_C_STANDARD_LATEST`
* `CMAKE_CXX_STANDARD_LATEST`
* `CMAKE_CUDA_STANDARD_LATEST`
* `CMAKE_HIP_STANDARD_LATEST`
* `CMAKE_OBJC_STANDARD_LATEST`
* `CMAKE_OBJCXX_STANDARD_LATEST`
These variables, more generally referred to as
`CMAKE_<LANG>_STANDARD_LATEST`, are assigned an integer value which
represents the minimum between the latest version of the associated
language standard supported by the current compiler and the latest
version supported by CMake.
Add documentation for these variables in a new page called
`CMAKE_<LANG>_STANDARD_LATEST` was added under the "Variables for
Languages" section of the `cmake-variables(7)` page.
Update each compiler-specific CMake script under
`${CMAKE_ROOT}\Modules\Compiler` to manually define the relevant
`CMAKE_<LANG>_STANDARD_LATEST` variable as necessary. This will
require updating and maintaining as newer compiler versions become
recognized by CMake.
Closes: #25717
Revert commit 74b1c9fc8e (Explicitly specify language flag when source
LANGUAGE property is set, 2020-06-01, v3.19.0-rc1~722^2) and the lookup
tables from its two immediate ancestors. The purpose of that change was
to convert an explicit `LANGUAGE` source file property into an explicit
language specification compiler flag like `-x c`. This seems reasonable
since the property is documented as meaning "indicate what programming
language the source file is". It is also needed to help compilers deal
with non-standard source file extensions they don't recognize.
However, some projects have been setting `LANGUAGE C` on `.S` assembler
source files to mean "use the C compiler". Passing `-x c` for them
breaks the build because the `.S` sources are not written in C. These
projects should be updated to use `enable_language(ASM)`, for which
CMake often chooses the C compiler as the assembler when using
toolchains that support it (which would have to be the case for projects
using the approach).
Revert the change for now to preserve the old behavior for such projects.
We can re-introduce it with a policy in a future version of CMake.
Fixes: #21469
Issue: #14516, #20716
In commit 6555286c55 (XL: Add C and C++ language level flags,
2017-04-27, v3.9.0-rc1~184^2) we added support for both the traditional
XL compiler and the Clang-based variant used on Linux. The latter is
now handled by `Modules/Compiler/XLClang-{C,CXX}.cmake` using the
`XLClang` compiler id. Drop the corresponding content from the
traditional XL compiler modules.
The valid settings to pass to the IBM XL compiler for the -qhalt flag
vary widely by language and platform. Based on existing documentation,
the following table shows which error levels are valid to pass to
-qhalt= since -qhalt=e is not always available.
OS | xlc | xlC | xlf |
---------|-------|------------------
AIX | iwes | iw s | ilwesu |
BlueGene | iwes | iwes | ilwesu |
OS X | iwesu | iwesu | ilwesu |
Linux | w | w | ilwesu |
Document these variables.
Change our convention for setting these variables from:
set(CMAKE_C_FLAGS_INIT "...")
to
string(APPEND CMAKE_C_FLAGS_INIT " ...")
so that any value previously set by a toolchain file will be used.
Automate the conversion with:
sed -i 's/set *(\(CMAKE_\(C\|CXX\|Fortran\|RC\|ASM\|${[^}]\+}\)_FLAGS\(_[^_]\+\)\?_INIT \+"\)/string(APPEND \1 /' \
Modules/Compiler/*.cmake Modules/Platform/*.cmake
and follow up with some manual fixes (e.g. to cases that already
meant to append). Also revert the automated changes to contexts
that are not protected from running multiple times.
This was added without explanation by commit v2.8.2~1138 (Add initial XL
C compiler flags for safer builds, 2009-09-30). It is not consistent
with our default C++ flags for XL and disables several optimizations, so
drop it from our default flags for C.
Suggested-by: Todd Gamblin <tgamblin@llnl.gov>
Factor duplicate information out of Compiler/XL-<lang>.cmake modules
into a macro in a new Compiler/XL.cmake module. Invoke it from the
per-language files to produce the original settings.
This commit adds some default initial C flags for the XL compiler. The
most important is "-qhalt=e" which causes the compiler to error-out on
non-severe error messages. This is necessary to get try-compiles to
fail when bad arguments are passed to a function.
This moves platform-independent XL compiler flags into separate
"Compiler/XL-<lang>.cmake" modules. Platform-specific flags go in
"Platform/<os>-XL-<lang>.cmake" modules.
IBM rebranded its VisualAge compiler to XL starting at version 8.0. We
use the compiler id "XL" for newer versions and "VisualAge" for older
versions. We now also recognize the "z/OS" compiler, which is distinct
from XL.
