On 07/09/2016 06:36 PM, Timon Gehr wrote:
Undefined behaviour means the language semantics don't define a
successor state for a computation that has not terminated. Do you agree
with that definition? If not, what /is/ UB in D, and why is it called UB?
Yah, I was joking with Walter that effectively the moment you define
undefined behavior it's not undefined any longer :o). It happens to the
best of us. I think we're all aligned here.
There's some interesting interaction here. Consider:
int fun(int x)
{
int[10] y;
...
return ++y[9 >> x];
}
Now, under the "shift by negative numbers is undefined" rule, the
compiler is free to eliminate the bounds check from the indexing because
it's always within bounds for all defined programs. If it isn't, memory
corruption may ensue. However, if the compiler says "shift by negative
numbers is implementation-specified", the the compiler cannot portably
eliminate the bounds check.
It's a nice example illustrating how things that seem to have nothing
with memory corruption do effect it.
Andrei
