Variables optimized out at -O0

[Ryan Johnson <scovich@xxxxxxxxx>]

Hi,

My distribution (nixos 17.03) recently upgraded to gcc-5.4.0, and I find 
now that the distribution's gdb-7.12.1 very frequently reports variables 
as <optimized out> and inline functions as not available. I'm trying to 
isolate a small test case, but meanwhile I wanted to double check 
whether I'm doing something silly with my compile flags, or if this is a 
known/expected behavior. The compilation command (filtering out -D, -M 
and -W flags is):

g++ -o build/unoptimized/foo.o -c src/foo.cpp -fPIC -g -march=corei7 
-std=c++11 -pthread -fwrapv  -O0 -fno-omit-frame-pointer

g++ -o install/unoptimized/lib/libFoo.so -shared 
-Wl,--no-copy-dt-needed-entries -g -pthread -fuse-ld=gold -rdynamic 
'-Wl,-rpath,$ORIGIN' '-Wl,-rpath,$ORIGIN/../lib' $OBJECT_FILES 
-Wl,-z,defs -Wl,-soname=libFoo.so

Sadly, I can't switch to a more recent version of gcc for this 
particular task...

Thoughts?
Ryan