[clang] [compiler-rt] [Sanitizer] add signed-integer-wrap sanitizer (PR #80089)

[Kees Cook via cfe-commits]

kees wrote:

> > > > > Why not just enforce -fsanitize=signed-integer-overflow with -fwrapv? I suspect it's just overlook, and not intentional behavior.
> > > > 
> > > > 
> > > > +1
> > > > We should consider this direction
> > > 
> > > 
> > > The UB-vs-non-UB seemed to be a really specific goal in the existing code. i.e. that the sanitizer was disabled didn't look like an accident. For people using this to find _only_ UB, this would be a behavioral change, so to me it seems like a separate name makes the most sense. Anyone wanting wrap-around checking can use -wrap, and anyone wanting UB checking can use -overflow.
> > 
> > 
> > Isn't this still UB even with -fwrapv? UB is a language feature, not compiler.
> 
> `-fwrapv` is essentially a language dialect that defines the behavior of integer wraparound. It is no longer UB in compilations using that mode.

Right. `-fwrapv` defines the signed integer overflow resolution strategy. Without `-fwrapv` it is undefined (default language feature). With `-fwrapv` it is defined as 2s-complement wrap-around (and is well defined, like unsigned integer overflow).

https://github.com/llvm/llvm-project/pull/80089