# g++49 -v
Using built-in specs.
COLLECT_GCC=g++49
COLLECT_LTO_WRAPPER=/usr/local/libexec/gcc49/gcc/i386-portbld-freebsd8.4/4.9.3/lto-wrapper
Target: i386-portbld-freebsd8.4
Configured with: ./../gcc-4.9-20150204/configure --with-build-config=bootstrap-debug --disable-nls --enable-gnu-indirect-function --libdir=/usr/local/lib/gcc49 --libexecdir=/usr/local/libexec/gcc49 --program-suffix=49 --with-as=/usr/local/bin/as --with-gmp=/usr/local --with-gxx-include-dir=/usr/local/lib/gcc49/include/c++/ --with-ld=/usr/local/bin/ld --with-libiconv-prefix=/usr/local --with-pkgversion='FreeBSD Ports Collection' --with-system-zlib --with-ecj-jar=/usr/local/share/java/ecj-4.5.jar --enable-languages=c,c++,objc,fortran,java --prefix=/usr/local --mandir=/usr/local/man --infodir=/usr/local/info/gcc49 --build=i386-portbld-freebsd8.4
Thread model: posix
gcc version 4.9.3 20150204 (prerelease) (FreeBSD Ports Collection) 


When compiling at the -Os optimization level, g++ 4.9 sometimes leaves undefined symbols in the resulting .o file.  In the example below, this causing a fatal linker error when trying to build a shared library that includes this .o file.  This problem does not occur when compiling with -O0 optimization, and does not occur with g++ 4.8.

In this example, the following class methods are inline:
  KeyListenerMultiplexer::acquire()
  FocusListenerMultiplexer::acquire()
  MouseListenerMultiplexer::acquire()
  PaintListenerMultiplexer::acquire()
  WindowListenerMultiplexer::acquire()
  MouseMotionListenerMultiplexer::acquire()

When the code is compiled with g++ 4.9 and -Os, the .o file contains undefined
symbols for them.  This does not happen with g++ 4.8 or when compiling with -O0.

Broken:

# g++49 -fPIC -fmessage-length=0 -fno-common -fno-strict-aliasing -fno-use-cxa-atexit -fvisibility-inlines-hidden -fvisibility=hidden -fexceptions -fno-enforce-eh-specs -Os -c fmgridif.ii -Wall -o fmgridif.o
# nm fmgridif.o | grep 'ListenerMultiplexer'              U _ZThn24_N22KeyListenerMultiplexer7acquireEv
         U _ZThn24_N24FocusListenerMultiplexer7acquireEv
         U _ZThn24_N24MouseListenerMultiplexer7acquireEv
         U _ZThn24_N24PaintListenerMultiplexer7acquireEv
         U _ZThn24_N25WindowListenerMultiplexer7acquireEv
         U _ZThn24_N30MouseMotionListenerMultiplexer7acquireEv
#


Works:

# g++49 -fPIC -fmessage-length=0 -fno-common -fno-strict-aliasing -fno-use-cxa-atexit -fvisibility-inlines-hidden -fvisibility=hidden -fexceptions -fno-enforce-eh-specs -O0 -c fmgridif.ii -Wall -o fmgridif.o
# nm fmgridif.o | grep 'ListenerMultiplexer'
#

Works:

# g++48 -fPIC -fmessage-length=0 -fno-common -fno-strict-aliasing -fno-use-cxa-atexit -fvisibility-inlines-hidden -fvisibility=hidden -fexceptions -fno-enforce-eh-specs -Os -c fmgridif.ii -Wall -o fmgridif.o
# nm fmgridif.o | grep 'ListenerMultiplexer'
#