machine-dependent Passes on GIMPLE/SSA Tree's?

[Markus Franke]

Dear GCC Developers,

I am currently trying to get familiar with basic functionalities (and
their implementation) of the GCC (cc1).
After generating the GIMPLE representation of the Input-Parse-Tree a
huge number of optimisation passes takes place. These passes are said to
be hardware independent. However I am wondering, whether there are maybe
also some passes which make use of machine descriptions. I am thinking
about some Loop-Optimisations which can be performed much better if the
appropriate optimisation pass knows if there are vector machine
instructions. This would allow to parallelize the loop. (Tree level
if-conversion for vectorizer)
Are there also some other optimisation passes working on the GIMPLE/SSA
representation which make use of any machine-dependent features?

Thanks for help,

Markus Franke