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

[Florian Hahn via llvm-commits]

================
@@ -1207,29 +1207,46 @@ 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);
+/// Given \p ForkedSCEVs corresponding to \p Ptr, get AddRecs from \p Assume and
+/// \p StridesMap, and return SCEVs that could potentially be checked at runtime
+/// (AddRecs and loop-invariants). Returns an empty range as an early exit.
+static iterator_range<PointerIntPair<const SCEV *, 1, bool> *> getRTCheckPtrs(
+    PredicatedScalarEvolution &PSE, const Loop *L, Value *Ptr,
+    MutableArrayRef<PointerIntPair<const SCEV *, 1, bool>> ForkedSCEVs,
+    const DenseMap<Value *, const SCEV *> &StridesMap, bool Assume) {
+  for (auto &P : ForkedSCEVs) {
+    auto *AR = dyn_cast<SCEVAddRecExpr>(P.getPointer());
+    if (!AR && Assume)
+      AR = PSE.getAsAddRec(Ptr);
+
+    // Call replaceSymbolicStrideSCEV only after PSE.getAsAddRec, because
+    // assumptions might have been added to PSE, resulting in simplifications.
+    const SCEV *S = replaceSymbolicStrideSCEV(PSE, StridesMap, Ptr);
----------------
fhahn wrote:

Conceptually I am not sure if it make sense to call `replaceSymbolicStrideSCEV`; the pointer underlying IR pointer for the SCEV expression we are processing may be different than the original IR pointer, so using it here seems fragile for forked pointers.

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