[not2b]

If the flow graph doesn't have a clean nested structure, this impedes compiler optimization. It can be possible to normalize it, but this may require the compiler to clone the code. Compilers are pretty good these days; if you've experienced a C compiler "inappropriately" optimizing something away the most likely cause these days is not a compiler bug, but a software developer who doesn't understand rules related to aliasing or undefined behavior.

I do agree that the specific use of goto to jump cleanly out of several loops is appropriate: the problem is that C lacks clean constructs for exiting named blocks. That would be preferable to general goto and doesn't harm optimization, the flow graph is still easy to analyze, convert to SSA form and the like.