[llvm-commits] [Review] GVN Patch

[Eli Friedman]

On Fri, Oct 19, 2012 at 3:28 PM, Owen Anderson <resistor at mac.com> wrote:
>
> On Oct 19, 2012, at 3:22 PM, Bill Wendling <wendling at apple.com> wrote:
>
> Owen expressed doubt about that when I asked him because memdep uses caching
> and stuff. Owen, could you shed some light on what your concerns were?
>
>
> My concern here is that MemDep performs caching, which would then be
> invalidated if the set of unreachable blocks changes.  Perhaps this  is not
> an issue, if we're already having to invalidate the cache in those
> circumstances already; it's been a long time since I looked at it.

We don't invalidate that cache currently.  That said, the relevant
callback already exists, so we can just blow away a bit more state if
necessary.

Another issue with putting the check in GVN: if MemDep can look at
unreachable blocks, it can look through unreachable blocks, so we
could end up returning completely non-sensical results in reachable
blocks.

-Eli