[llvm] [LAA] Rewrite findForkedPointer (NFCI) (PR #140298)

[Florian Hahn via llvm-commits]

================
@@ -1088,29 +1092,49 @@ static void findForkedSCEVs(
   }
 }
 
-static SmallVector<PointerIntPair<const SCEV *, 1, bool>>
-findForkedPointer(PredicatedScalarEvolution &PSE,
-                  const DenseMap<Value *, const SCEV *> &StridesMap, Value *Ptr,
-                  const Loop *L) {
-  ScalarEvolution *SE = PSE.getSE();
-  assert(SE->isSCEVable(Ptr->getType()) && "Value is not SCEVable!");
-  SmallVector<PointerIntPair<const SCEV *, 1, bool>> Scevs;
-  findForkedSCEVs(SE, L, Ptr, Scevs, MaxForkedSCEVDepth);
-
-  // For now, we will only accept a forked pointer with two possible SCEVs
-  // that are either SCEVAddRecExprs or loop invariant.
-  if (Scevs.size() == 2 &&
----------------
fhahn wrote:

Rigth, this wasnt related to the freeze issue, but the current code should reject if we have forked pointers that result in more than 2 SCEVs. I think there might be test coverage missing for the case, as there are no test failures when doing something like

```
diff --git a/llvm/lib/Analysis/LoopAccessAnalysis.cpp b/llvm/lib/Analysis/LoopAccessAnalysis.cpp
index 2a322a69a0db..7a7f1c68d8fe 100644
--- a/llvm/lib/Analysis/LoopAccessAnalysis.cpp
+++ b/llvm/lib/Analysis/LoopAccessAnalysis.cpp
@@ -1099,18 +1099,20 @@ findForkedPointer(PredicatedScalarEvolution &PSE,

   // For now, we will only accept a forked pointer with two possible SCEVs
   // that are either SCEVAddRecExprs or loop invariant.
-  if (Scevs.size() == 2 &&
-      (isa<SCEVAddRecExpr>(get<0>(Scevs[0])) ||
-       SE->isLoopInvariant(get<0>(Scevs[0]), L)) &&
-      (isa<SCEVAddRecExpr>(get<0>(Scevs[1])) ||
+  if (Scevs.size() < 2)
+  return {{replaceSymbolicStrideSCEV(PSE, StridesMap, Ptr), false}};
+  if (
+      !(isa<SCEVAddRecExpr>(get<0>(Scevs[0])) ||
+       SE->isLoopInvariant(get<0>(Scevs[0]), L)) ||
+      !(isa<SCEVAddRecExpr>(get<0>(Scevs[1])) ||
        SE->isLoopInvariant(get<0>(Scevs[1]), L))) {
+  return {{replaceSymbolicStrideSCEV(PSE, StridesMap, Ptr), false}};
+  }
     LLVM_DEBUG(dbgs() << "LAA: Found forked pointer: " << *Ptr << "\n");
     LLVM_DEBUG(dbgs() << "\t(1) " << *get<0>(Scevs[0]) << "\n");
     LLVM_DEBUG(dbgs() << "\t(2) " << *get<0>(Scevs[1]) << "\n");
     return Scevs;
-  }

-  return {{replaceSymbolicStrideSCEV(PSE, StridesMap, Ptr), false}};
 }

 bool AccessAnalysis::createCheckForAccess(
```

https://github.com/llvm/llvm-project/pull/140298