Am 19.11.19 um 22:51 schrieb Craig Scott:
On Tue, Nov 19, 2019 at 10:36 PM Eric Doenges <[email protected]
<mailto:[email protected]>> wrote:
Am 19.11.19 um 12:09 schrieb Stéphane Ancelot:
Hi,
I have a particular target (using swig / jni) that must not have
-O3 -NDEBUG flags from Relase build type
How can I overload this target flags ?
Since CMAKE_<lang>_FLAGS_RELEASE does not map to a user-visible
target property, you cannot override it directly (anything added
to the COMPILE_FLAGS property is appended to the command line and
does not replace any of the compiler flags CMake sets by itself).
However, you can redefine this variable before you create your
special target(s), and then restore it so that other targets are
not affected:
set(_CMAKE_CXX_FLAGS_RELEASE_SAVE ${CMAKE_CXX_FLAGS_RELEASE})
set(CMAKE_CXX_FLAGS_RELEASE)
< add your target(s) here >
set(CMAKE_CXX_FLAGS_RELEASE ${_CMAKE_CXX_FLAGS_RELEASE_SAVE})
This assumes your target is C++; if it is C, simply replace the
_CXX_ with _C_.
Actually, no, that's not how it works. This is actually a great
example of why projects shouldn't generally try to avoid manipulating
CMAKE_CXX_FLAGS and should instead prefer to modify target or
directory properties instead (not possible here for the original
problem, but worth highlighting nonetheless). The (often surprising)
behavior at play in the proposed example above is that it is not the
value of the CMAKE_CXX_FLAGS_RELEASE variable at the time the target
is created that matters, it's the variable's value /at the end of the
directory scope/. You can change the variable's value as much as you
like along the way before or after creating targets, but only the
final value at the end of the scope will actually be used in the build
command lines for targets created in that directory scope. This is
rarely what developers expect, but that's how it works, for better or
worse. When you start adding in calls to add_subdirectory(), it can
get really confusing what value is getting used where, so take great
care if your project really must modify these variables.
Very interesting, thanks for pointing that out. In our case things work
because all the actual targets are in fact created in subdirectories. I
think CMake really needs some straightforward way to allow you to
override flags on a per-target and per-file basis (in our case, we need
to be able to reduce the optimization level for individual source files
to work around bugs in the Intel compiler's optimizer).
--
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