Profile-guided optimization

[Andrew Haley]

Juan Antonio Farré Basurte wrote:

> I want to use profile-guided optimization in my current development project. I have a doubt for which I can't find an answer
> anywhere.
> 
> The basic idea of PGO is:
> 1. Build instrumented code
> 2. Run real-world representative tests to generate profile
> info.
> 3. Build code using profile info for optimizations.
> 
> My doubt is whether I should build instrumented code (step 1) already
> with the same optimization options I want to finally use in step 3, or I'd get more realistical profile info if I compile step 1 without any
> optimization (or may be some intermediate option).
> 
> Does anybody have any hints about this question?

It's an interative process.  You start with compiling your code with a
best guess set of optimization options and then rebuild with PGO, and
then profile again.  Measure every time, make sure you're getting an
improvement.

Andrew.