/GC[:(allocation|lifetime) Enable managed memory profiling. It is possible to enable tracing of allocations only (/GC:allocation) ...

/GC[:(allocation|lifetime)]
                Enable managed memory profiling. It is possible to enable
                tracing of allocations only (/GC:allocation) or allocations
                and lifetime of objects (/GC:lifetime).  Default is
                allocations only.
                Use only with /Launch.  To attach to an application and
                collect .NET memory data, use the VSPerfClrEnv
                tool to configure the profiler.