User Agent: Mozilla/5.0 (Windows NT 6.2; rv:49.0) Gecko/20100101 Firefox/49.0 Steps to reproduce: 1. emerge firefox 50.0 (libyuv 1602) when 49.0 (libyuv 971) is installed, using the gcc 4.9.3 on the x86 Gentoo 2. wait near the 1/4-1/3 estimated emerge time 3. see the error "'asm' operand has impossible constraints ); ^" and then fail of the building Actual results: I Saw the text from the emerge output: "efox-50.0/work/firefox-50.0/ipc/glue -I/var/tmp/portage/www-client/firefox-50.0/ work/firefox-50.0/ff/dist/include -fPIC -DMOZILLA_CLIENT -include /var/tmp/p ortage/www-client/firefox-50.0/work/firefox-50.0/ff/mozilla-config.h -MD -MP -MF .deps/Unified_cpp_media_libyuv1.o.pp -Wall -Wc++11-compat -Wempty-body -Wignor ed-qualifiers -Woverloaded-virtual -Wpointer-arith -Wsign-compare -Wtype-limits -Wunreachable-code -Wwrite-strings -Wno-invalid-offsetof -Wno-error=maybe-uninit ialized -Wno-error=deprecated-declarations -Wno-error=array-bounds -march=native -fno-exceptions -fno-strict-aliasing -fno-rtti -fno-exceptions -fno-math-errno -pthread -pipe -O2 -fomit-frame-pointer -m32 -mmmx /var/tmp/portage/www-client /firefox-50.0/work/firefox-50.0/ff/media/libyuv/libyuv_libyuv/Unified_cpp_media_ libyuv1.cpp In file included from /var/tmp/portage/www-client/firefox-50.0/work/firefox-50.0 /ff/media/libyuv/libyuv_libyuv/Unified_cpp_media_libyuv1.cpp:47:0: /var/tmp/portage/www-client/firefox-50.0/work/firefox-50.0/media/libyuv/source/r ow_gcc.cc: In function 'void libyuv::I422AlphaToARGBRow_SSSE3(const uint8*, cons t uint8*, const uint8*, const uint8*, uint8*, const libyuv::YuvConstants*, int)' : /var/tmp/portage/www-client/firefox-50.0/work/firefox-50.0/media/libyuv/source/r ow_gcc.cc:1803:4: error: 'asm' operand has impossible constraints ); ^ /var/tmp/portage/www-client/firefox-50.0/work/firefox-50.0/config/rules.mk:934: recipe for target 'Unified_cpp_media_libyuv1.o' failed make[4]: *** [Unified_cpp_media_libyuv1.o] Error 1" and the emerge was broken Expected results: The emerge must be succesfully finished as it was with the earlier (<=49) firefox versions.

Related upstream bugs: https://bugs.chromium.org/p/libyuv/issues/detail?id=517 https://bugs.chromium.org/p/libyuv/issues/detail?id=532 https://bugs.chromium.org/p/libyuv/issues/detail?id=602

Sorry, i forgot to include may be an important detail: in part of make.conf, the among others build options: CFLAGS="-O2 -march=native -mmmx -msse -msse2 -msse3 -mssse3" CXXFLAGS="${CFLAGS}"

After trying to build 51.0 firefox where the libyuv is the same version as in firefox of 50.0, i.e. the 1602, with the new stable in Gentoo version of gcc 4.9.4 (the previous one was 4.9.3), it succeed. I'm closing the bug.