Hi folks.
Maybe the one or another remembers the post I've wrote more than a month
ago. I was (and still am) new to the GCC codebase and had the evil plan
to add an optimization pass to do byte permutations (capturing all
home-brewed bswap things and all the other 23 possible byte-permutations
as well).
Well - I had a lot of time to kill during the last weeks, and I had a
lot of timeto read into the source. Business trips without internet
access are a perfect opportunity to read such stuf...
Anyway, after all this passive read-work, I've been able to add the
humble beginnings of my pass. I'm now able to and I've been able to run
a code that does a printf as soon as I find an structure in the SSA tree
that is a potential candidate for my optimization.
However, approaching this point has been very painfull and I'm far away
from chainging anything in the SSA.
Let's get to the point: The documentation sucks. If you want to learn
how things work the wiki and the documentation is of little help. You
have to read other code, step through other optimizations and do a lot
of reverse-engineering and code-reading to understand how all the
different things fit and relate to each other.
I think a well commented pseudo-pass (well document as: talk to someone
who know C but has no idea about the GCC magic..) that does something
stupid but valid like re-inventing the neg-operator by using not and
subtraction could act as be a very nice boilerplate code for people like me.
For someone who is into the SSA structures and the gcc internals should
be able to write up something within a day or an half.
Just an idea.. And just to let you know how hard it can be: Finding out
what GTY means *can* take half a day...
Nils
- Something general (beginner related) Nils Pipenbrinck
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