how to instrument??

[smartgong]

hi,everyone

   I am a totally newer to the GCC. But I have browsed the maillist for a while.:)
   I think my question maybe is very silly. but I really appreciate your hints:)

  Could anyone tell something about instrumentation. I know it is necessary to profile and optimization. But how to instrument some code to some place?
  
  How could I locate the beinstrumented place? If I add the instrumentation code( I think it should be RTX, right?), should compiler reallocate the register or how to find the register for instrumentation code?how and where to allocate the memory for the instrumentation code? And after I add the code, How Could i keep/change control flow?

  en , My teacher press me to give a presentation tomorrow about instrumentation.

  oho, My god, Gcc is very interesting and GCC is too large, and I just look at this week.
   Could  anyone  help me? thanks

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