Displaying 2 results from an estimated 2 matches for "backedge_condit".
2017 Mar 31
2
Dereferenceable load semantics & LICM
Hi all,
I have a question about dereferenceable metadata on load instruction. I
have a patch (https://reviews.llvm.org/D31539) for LICM that hoists loads
with !invariant.group.
The motivation example is devirtualization:
struct A {
virtual void foo();
};
int bar();
void indirect(A &a) {
while(bar())
a.foo();
}
With -O2 -fstrict-vtable-pointers we get:
define void
2017 Mar 31
2
Dereferenceable load semantics & LICM
...iant.group load, GVN
> > hoists the second load and I am not sure why it is legal then.
>
> I suspect what's going on is that we first canonicalize the loop to:
>
> if (precondition) {
> do {
> vptr = load vtable;
> fptr = *vptr;
> ...
> } while (backedge_condition);
> }
>
> after which it is safe to transform the program to (modulo aliasing):
>
> if (precondition) {
> vptr = load vtable;
> fptr = *vptr;
> do {
> ...
> } while (backedge_condition);
> }
>
> since the we moved a load from a ("strongly&q...