Profiling in the .NET Framework 4.5
In previous versions of the .NET Framework, profilers could instrument Common Intermediate Language code (CIL) only when the CIL was just-in-time (JIT) compiled for the first time. In the .NET Framework 4.5, the profiler can request code that was previously JIT-compiled to be JIT-compiled again. JIT recompilation enables the profiler to instrument CIL at any time during the execution of the profiled application. Note that JIT recompilation may not be used by profilers that dynamically attach to a running program.
See Using the JIT Recompilation Methods to Add Instrumentation for a description of how a profiler can recompile instrumented code.