I would bet that a substantial fraction of the rumoured GCC 3 bugs were originally caused by undefined behaviour in the compiled source, as new advanced compile

I would bet that a substantial fraction of the rumoured GCC 3 bugs were originally caused by undefined behaviour in the compiled source, as new advanced compiler optimizations were being introduced in the GCC 3 series. (On the other hand, those newly introduced optimizations likely did have many bugs to begin with...) At the time of GCC 2.7, no one really expected pointer access through the wrong type or signed integer overflow to cause anything weird. The CPU would just read whatever was in memory at the pointed address, and integers would wrap around just like in assembly.