[llvm] [SLP] Avoid seeding related affine loop address computations (PR #226220)

[Tim Besard via llvm-commits]

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@@ -1003,6 +1007,88 @@ bool isOnceUsedSeed(const Instruction *I) {
       I);
 }
 
+/// Returns true if \p Ptr is only used by scalar loads and stores, directly or
+/// through getelementptrs with constant offsets.
+static bool onlyFeedsScalarAccesses(Value *Ptr, bool ReVec,
+                                    unsigned Depth = 0) {
+  constexpr unsigned MaxDepth = 2;
+  if (Ptr->use_empty() || Ptr->hasNUsesOrMore(UsesLimit))
+    return false;
+  return all_of(Ptr->users(), [&](User *U) {
+    if (isa<LoadInst>(U))
+      return !getValueType(U, ReVec)->isVectorTy();
+    if (auto *Store = dyn_cast<StoreInst>(U))
+      return Store->getPointerOperand() == Ptr &&
+             !getValueType(Store, ReVec)->isVectorTy();
+    if (auto *GEP = dyn_cast<GetElementPtrInst>(U))
+      return Depth < MaxDepth && GEP->getPointerOperand() == Ptr &&
+             GEP->hasAllConstantIndices() &&
+             onlyFeedsScalarAccesses(GEP, ReVec, Depth + 1);
+    return false;
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maleadt wrote:

Applied. The `&& Op != Ptr` sat inside `match(...)` in the suggestion, so I moved it out of the call.

https://github.com/llvm/llvm-project/pull/226220