On the AtariAge forums, Tursi mentioned that C99 (I think) placed an EVEN after all string constants, which annoyed him. I can see why they did that, since I did the same thing in GCC. I'm not going to get to that right now, but I wanted to make a note of that so I wouldn't forget.
Currently, I'm looking into more bugs Lucien2 found while writing Rush Hour.
There was a problem with an "unrecognizable instruction" which was a nice easy fix. The problem here is that there was a pattern for comparisons against zero (X == 0), which called for a scratch register. This extra register is useful to handle cases where we need to compare against a post-incremented pointer (*r1+), or indexed addresses (@5(r1)). In these cases we can emit an instruction like "mov *r1+, r0" or "mov @5(r1), r0" which is smaller, faster, and has no side-effects.
If the need for a zero compare is made early enough, this scratch register request is ignored, and everything is fine. If this happens later, as the result of an optimization, GCC looks for an exact match. This fails, because of the scratch register request, which doesn't exist at this point.
This was fixed by making a second, unnamed pattern which compares against zero, but uses no scratch register. In this case, we emit an instruction like "mov @5(r1), @5(r1)", and disallow post-incremented pointers. This is not as efficient, but will work just fine.