[DannyBee]

"It's going to kill performance, but it's legal to do."

Sure, but it's going to cause the optimizer to do different things than it would have to that variable. As I said, this essentially changes what the compiler is allowed to do, and will expose or hide bugs (usually hide if it hurts the optimizer) :)

One only has to look at the bugzilla's of gcc and llvm to discover all sorts of fun things that barriers hide/expose.

[skybrian]

It's clearly not useful for tracking down compiler bugs, but might still be useful for more ordinary bugs in single-threaded user code.