qt5base-lts/mkspecs/features/ltcg.prf
Thiago Macieira 859eb2467d Add qmake config for controlling LTCG behavior for static libs
Static libraries may get installed and used by other builds, which may
be done with a different version or build of the compiler. So this
commit introduces two new flags:
 - no-static-ltcg: disables LTCG completely for static libraries
 - fat-static-lto: forces static libraries to produce fat LTO objects

fat-static-lto is useful for Linux distributions, since installed static
libraries should not carry LTO information, but that information is
useful during Qt's own build. This feature should be used alongside some
compiler-specific method of removing the LTO information from the
static libraries prior to installation, so only the regular part
remains.

For current GCC versions, this command suffices:
  strip -R '.gnu.lto*' -R '.gnu.debuglto*' libname.a

Otherwise, distributions can use "no-static-ltcg" to disable it
completely.

Change-Id: I495bc19409f348069f5bfffd155237ade9f4b42f
Reviewed-by: Jörg Bornemann <joerg.bornemann@qt.io>
2019-06-17 15:27:51 +00:00

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static:no-static-ltcg {
# Static library but no-static-ltcg enabled: skip LTCG
} else: CONFIG(release, debug|release) {
# We need fat object files when creating static libraries on some platforms
# so the linker will know to load a particular object from the library
# in the first place. On others, we have special ar and nm to create the symbol
# tables so the linker will know better. For other compilers, we disable LTCG
# for static libraries.
msvc {
# Nothing to do
} else {
!isEmpty(QMAKE_AR_LTCG): QMAKE_AR = $$QMAKE_AR_LTCG
!isEmpty(QMAKE_NM_LTCG): QMAKE_NM = $$QMAKE_NM_LTCG
equals(QMAKE_RANLIB_LTCG, true): QMAKE_RANLIB =
else: !isEmpty(QMAKE_RANLIB_LTCG): QMAKE_RANLIB = $$QMAKE_RANLIB_LTCG
static:isEmpty(QMAKE_AR_LTCG):isEmpty(QMAKE_RANLIB_LTCG) {
# We don't know how to create symbol tables for static libs with this
# compiler, so disable LTCG
QMAKE_CFLAGS_LTCG =
QMAKE_CXXFLAGS_LTCG =
QMAKE_LFLAGS_LTCG =
}
}
fat-lto|if(static:fat-static-lto) {
QMAKE_CFLAGS_LTCG += $$QMAKE_CFLAGS_LTCG_FATOBJECTS
QMAKE_CXXFLAGS_LTCG += $$QMAKE_CXXFLAGS_LTCG_FATOBJECTS
}
load(link_ltcg)
QMAKE_CFLAGS -= $$QMAKE_CFLAGS_LTCG
QMAKE_CFLAGS += $$QMAKE_CFLAGS_LTCG
QMAKE_CXXFLAGS -= $$QMAKE_CXXFLAGS_LTCG
QMAKE_CXXFLAGS += $$QMAKE_CXXFLAGS_LTCG
QMAKE_LFLAGS -= $$QMAKE_LFLAGS_LTCG
QMAKE_LFLAGS += $$QMAKE_LFLAGS_LTCG
}