On Friday, 29 August 2014 at 08:50:59 UTC, Ola Fosheim Grøstad
wrote:
On Friday, 29 August 2014 at 08:29:50 UTC, deadalnix wrote:
Because, if you don't have undefined BEHAVIOR, you can't
change the BEHAVIOR. So you have to prove that store/loads
won't fault before doing anything with them. As per spec. Or
you'll change the BEHAVIOR.
By fault you mean trap an illegal address. I don't think that
should be required unless it is volatile, but that would depend
on the spec.
"Undefined behaviour" goes much further and can in theory
propagate all over the program…
Not only illegal address. You can trap for various reason, for
instance GC read/write barrier.
Indeed, undefined behavior can be anything, by definition, and
this cannot. Still, removing undefined behavior and replace it by
undefined values cause the optimizer to have to prove that
load/store won't fault, which is going to kill any expectation of
performance.
