Comment by gpderetta
4 days ago
Casting a char pointer to a vector pointer and doing vector loads doesn't violate provenance, although it might violate TBAA.
Regarding provenance, consider this:
void bar();
int foo() {
int * ptr = malloc(sizeof(int));
*ptr = 10;
bar();
int result = *ptr;
free(ptr);
return result;
}
If the compiler can track the lifetime of the dynamically allocated int, it can remove the allocation and covert this function to simply
int foo() {
bar();
return 10;
}
It can't if arbitrary code (for example inside bar()) can forge pointers to that memory location. The code can seem silly, but you could end up with something similar after inlining.
Then show me the compiler which tells the user that it removed this dead code. There is even an assignment removed, which violates all expectations
> It can't if arbitrary code (for example inside bar()) can forge pointers to that memory location.
Yes. It absolutely can. What are you even talking about?
C is not the Windows Start Menu. This habit of thinking it needs to do what it thinks I might expect instead of what I told it is deeply psychotic.
I litterally have no idea what are you trying to say. Do you mean that bar should be allowed to access *ptr with impunity or not?
I'm not trying to say anything. I said and meant exactly what I said. No more, no less. Your logic is obviously flawed. There is nothing preventing that optimization in the presence of a forged pointer in bar().
3 replies →