>You may find calls to functions from the standard library to be converted in surprising ways, while touching undefined behavior can eliminate evaluations, branches, function calls and more.

Yes, things like memcpy and printf are (in most cases) built-in in compilers. Not surprising really.

Undefined behavioral is bad programming, if your ask me. Almost all examples of it, that i ran across, are in really ugly code that only a "smart" programmer would write.

Clangs static analyzer points out undefined behavior, and gcc is close to getting a "-Wundefined" flag that points that out at compile time.

A optimizing C compiler can change the resulting code even more then just doing dead code elimination. But the point still stands, that C maps well to assembly and that languages that do things like their own memory allocation are not even comparable to what the cpu provides (only automatic memory allocation that a cpu somewhat provides is the stack, and C exposes even that).

Deterministically locating all undefined behavior is undecidable. Static analyzers can only locate a subset of it.

Commonly-used type punning techniques frequently exhibit undefined behavior due to strict aliasing: https://blog.regehr.org/archives/1307 .

"Deterministically locating all undefined behavior is undecidable. Static analyzers can only locate a subset of it."

It might be true but barely matters when we have tools like KCC. It's built on an executable semantics of C that runs in a framework on top of Maude rewrite engine.

http://www.kframework.org/index.php/Main_Page

https://github.com/kframework/c-semantics

http://fsl.cs.illinois.edu/FSL/papers/2015/hathhorn-ellison-...

That's fascinating; thank you for that. I often find academic papers are too densely written to me to read, but the authors of that paper have gone out of their way to describe everything in a straightforward manner.