Comment # 13 on bug 1042090 from Hendrik Woltersdorf

I'm currently experimenting with a branched Thunderbird package.
I see the following build commands for i586 (example):

/usr/bin/g++ -std=gnu++11 -o PluginWidgetChild.o -c
-I/home/abuild/rpmbuild/BUILD/obj/dist/stl_wrappers
-I/home/abuild/rpmbuild/BUILD/obj/dist/system_wrappers -include
/home/abuild/rpmbuild/BUILD/thunderbird/mozilla/config/gcc_hidden.h -DNDEBUG=1
-DTRIMMED=1 -DOS_POSIX=1 -DOS_LINUX=1 -DFORCE_PR_LOG -DSTATIC_EXPORTABLE_JS_API
-DMOZ_HAS_MOZGLUE -DMOZILLA_INTERNAL_API -DIMPL_LIBXUL
-I/home/abuild/rpmbuild/BUILD/thunderbird/mozilla/dom/plugins/ipc
-I/home/abuild/rpmbuild/BUILD/obj/dom/plugins/ipc
-I/home/abuild/rpmbuild/BUILD/obj/ipc/ipdl/_ipdlheaders
-I/home/abuild/rpmbuild/BUILD/thunderbird/mozilla/ipc/chromium/src
-I/home/abuild/rpmbuild/BUILD/thunderbird/mozilla/ipc/glue
-I/home/abuild/rpmbuild/BUILD/thunderbird/mozilla/dom/plugins/base
-I/home/abuild/rpmbuild/BUILD/thunderbird/mozilla/xpcom/base
-I/home/abuild/rpmbuild/BUILD/obj/dist/include  -I/usr/include/nspr4
-I/usr/include/nss3       -fPIC  -DMOZILLA_CLIENT -include
/home/abuild/rpmbuild/BUILD/obj/mozilla-config.h -MD -MP -MF
.deps/PluginWidgetChild.o.pp  -Wall -Wc++11-compat -Wempty-body
-Wignored-qualifiers -Woverloaded-virtual -Wpointer-arith -Wsign-compare
-Wtype-limits -Wunreachable-code -Wwrite-strings -Wno-invalid-offsetof
-Wc++14-compat -Wc++1z-compat -Wimplicit-fallthrough
-Wno-error=maybe-uninitialized -Wno-error=deprecated-declarations
-Wno-error=array-bounds -fno-lifetime-dse -fomit-frame-pointer
-fmessage-length=0 -grecord-gcc-switches -O2 -Wall -D_FORTIFY_SOURCE=2
-fstack-protector-strong -funwind-tables -fasynchronous-unwind-tables -g
-fno-strict-aliasing -fno-delete-null-pointer-checks -Os -fno-exceptions
-fno-strict-aliasing -fno-rtti -ffunction-sections -fdata-sections
-fno-exceptions -fno-math-errno -pthread -pipe  -pipe -fno-omit-frame-pointer  
-I/home/abuild/rpmbuild/BUILD/thunderbird/mozilla/widget/gtk/compat -pthread
-I/usr/include/gtk-2.0 -I/usr/include/gtk-unix-print-2.0 -I/usr/include/gtk-2.0
-I/usr/include/atk-1.0 -I/usr/include/gtk-2.0 -I/usr/lib/gtk-2.0/include
-I/usr/include/pango-1.0 -I/usr/include/harfbuzz -I/usr/include/pango-1.0
-I/usr/include/cairo -I/usr/include/pixman-1 -I/usr/include/freetype2
-I/usr/include/libdrm -I/usr/include/libpng16 -I/usr/include/gdk-pixbuf-2.0
-I/usr/include/libpng16 -I/usr/include/glib-2.0 -I/usr/lib/glib-2.0/include
-I/home/abuild/rpmbuild/BUILD/obj/dist/include/cairo -Wno-error=shadow 
/home/abuild/rpmbuild/BUILD/thunderbird/mozilla/dom/plugins/ipc/PluginWidgetChild.cpp


In this long list there are two optimizer switches: "O2" and "Os". According to
the gcc documentation the last one (Os) wins.