[PATCH] D94717: [LoopNest] Consider loop nest with inner loop guard using outer loop induction variable to be perfect

[Whitney Tsang via Phabricator via llvm-commits]

Whitney added inline comments.


================
Comment at: llvm/lib/Analysis/LoopInfo.cpp:405
+  // otherwise return nullptr.
+  if (&LoopNest::skipEmptyBlockUntil(ExitFromLatchSucc, GuardOtherSucc) ==
+      GuardOtherSucc)
----------------
bmahjour wrote:
> AFAICS `skipEmptyBlockUntil` doesn't check that the unique successor blocks have unique predecessors. Don't we need to check for that too?
I thought about that too, but it seems to be questionable...

```
if (cond)
  goto label;
if (0 < N) {
  for (int i = 0; i < N; ++i) {...}
label:  
}
```
Should we consider `if (0 < N)` to be a loop guard? It actually guarded the loop, but it is not a single entry single exit region.


If we decided to check for unique predecessor, it may make sense to do it in `skipEmptyBlockUntil`.


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  https://reviews.llvm.org/D94717/new/

https://reviews.llvm.org/D94717