Debugging, optimization and profiling - which happens at which stage(s) (compilation and link)

[Tim Prince]

Tim wrote:
> Thanks! It's indeed a clever way.
> 
> Being still curious, I am waiting for some explanation on which happens at which stage.
> 
-pg both inserts calls to profiling library functions at compile time, 
and adds the corresponding libraries at link time, possibly also 
substituting -pg built libraries for certain run-time libraries.
Certain compilers change run-time libraries to match options such as 
-march, so, although those gcc options may affect only compiler 
optimization passes, it needn't be that way forever.