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<div class="moz-cite-prefix">Am 19.11.19 um 22:51 schrieb Craig
Scott:<br>
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<div dir="ltr" class="gmail_attr">On Tue, Nov 19, 2019 at
10:36 PM Eric Doenges <<a href="mailto:doenges@mvtec.com"
moz-do-not-send="true">doenges@mvtec.com</a>> wrote:<br>
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<div>Am 19.11.19 um 12:09 schrieb Stéphane Ancelot:<br>
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<p>Hi,</p>
<p>I have a particular target (using swig / jni) that
must not have -O3 -NDEBUG flags from Relase build type</p>
<p>How can I overload this target flags ?</p>
</blockquote>
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:<br>
<p>set(_CMAKE_CXX_FLAGS_RELEASE_SAVE
${CMAKE_CXX_FLAGS_RELEASE})<br>
set(CMAKE_CXX_FLAGS_RELEASE)<br>
< add your target(s) here ><br>
set(CMAKE_CXX_FLAGS_RELEASE
${_CMAKE_CXX_FLAGS_RELEASE_SAVE})<br>
</p>
<p>This assumes your target is C++; if it is C, simply
replace the _CXX_ with _C_.</p>
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<div>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 <i>at the end
of the directory scope</i>. 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.</div>
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</blockquote>
<p>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).<br>
</p>
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