I'm upgrading Boost in an iOS project form 1.53 to 1.55, and getting the following error: cc1plus: error in backend: Couldn't allocate input reg for constraint 'Q'! cc1plus: error in backend: Couldn't allocate input reg for constraint 'Q'! lipo: can't figure out the architecture type of: /var/folders/j1/9fz1wymd0xs91683nq8gzwhr0000gn/T//ccBue08f.out "/Applications/Xcode.app/Contents/Developer/Platforms/iPhoneOS.platform/Developer/usr/bin/llvm-g++" -ftemplate-depth-128 -O3 -finline-functions -Wno-inline -Wall -pedantic -gdwarf-2 -fexceptions -isysroot /Applications/Xcode.app/Contents/Developer/Platforms/iPhoneOS.platform/Developer/SDKs/iPhoneOS6.1.sdk -pthread -arch arm -Wextra -Wno-long-long -Wno-variadic-macros -Wunused-function -arch armv7 -arch armv7s -fpermissive -pedantic -DBOOST_ALL_NO_LIB=1 -DBOOST_ATOMIC_STATIC_LINK=1 -DBOOST_SYSTEM_STATIC_LINK=1 -DBOOST_THREAD_BUILD_LIB=1 -DBOOST_THREAD_DONT_USE_CHRONO -DBOOST_THREAD_POSIX -DNDEBUG -D_LITTLE_ENDIAN -I"." -c -o "bin.v2/libs/thread/build/darwin-6.1~iphone/release/architecture-arm/link-static/macosx-version-iphone-6.1/target-os-iphone/threading-multi/pthread/once.o" "libs/thread/src/pthread/once.cpp" Is it a known issue? Is there a workaround? Thanks.