Which optimizations cause violation of SESE blocks ?

[Siddhartha Shivshankar <sshivsh at unity dot ncsu dot edu>]

Hello, hope you're doing fine. Before anything else thank you for
your work in enhancing, supporting and maintaining gcc. Your
work is truly admirable.

I work at the Center for Embedded systems research at NC State
University. We are trying to use gcc for the atmel avr micro-controller
platform, and our work requires assembly code produced by gcc
to be structured. (single entry single exit blocks, no side entries, exits from
loops, conditionals with clear merge points, etc. ) We would like to
turn off gcc optimizations that cause such code to be produced.

Is it possible to define such a set of optimizations at all at the outset ?

Have the folks at gcc.gnu had to address such an issue before ?
If so, what optimizations did they identify ?

I realize that this might be an involved question to answer if it has not
already been investigated. Please dont bother if that is the case.

Thanks,
-Siddhartha.