gcc - Debugging optimization problems -

i've written code (fortran, fwiw), , compiled gfortran without optimisation. runs, , produces expected output. if recompile -o2 or -o3, runs , exits normally, produces no output.

presumably, output-producing section of code somehow being optimized away. bug in gfortran - or silly in code.

so: start debugging this? there tools can use understand optimizer doing, , why?