The dump verbosity has the following options
Print information when an optimization is successfully applied. It is up to a pass to decide which information is relevant. For example, the vectorizer passes print the source location of loops which got successfully vectorized.
Print information about missed optimizations. Individual passes control which information to include in the output. For example,
gcc -O2 -ftree-vectorize -fopt-info-vec-missed
will print information about missed optimization opportunities from vectorization passes on stderr.
Print verbose information about optimizations, such as certain transformations, more detailed messages about decisions etc.
Print detailed optimization information. This includes optimized, missed, and note.