[PATCH] D109354: [LoopBoundSplit] Check the split condition with its AddRec start value

[Max Kazantsev via Phabricator via llvm-commits]

mkazantsev requested changes to this revision.
mkazantsev added inline comments.
This revision now requires changes to proceed.


================
Comment at: llvm/lib/Transforms/Scalar/LoopBoundSplit.cpp:273
+    const SCEV *SplitAddRecStartSCEV =
+        dyn_cast<SCEVAddRecExpr>(SplitCandidateCond.AddRecSCEV)->getStart();
+    if (SE.isKnownPredicate(
----------------
This should either be `cast` instead of `dyn_cast` (if it never fails), or there should be a null check (if it may fail).


================
Comment at: llvm/lib/Transforms/Scalar/LoopBoundSplit.cpp:274
+        dyn_cast<SCEVAddRecExpr>(SplitCandidateCond.AddRecSCEV)->getStart();
+    if (SE.isKnownPredicate(
+            ICmpInst::getInversePredicate(SplitCandidateCond.Pred),
----------------
And what if both direct and inverted predicates are not known? It may be false, but SCEV is just not smart enough to prove it.

I think the correct (conservative) check should be like

```
if (!isKnownPredicate(SplitCandidateCond.Pred, SplitAddRecStartSCEV, SplitCandidateCond.BoundSCEV))
  continue;
```


CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D109354/new/

https://reviews.llvm.org/D109354