[llvm] [SLP] Bail out on store-to-load forwarding hazards (PR #199606)

[Alexey Bataev via llvm-commits]

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@@ -28885,6 +28903,156 @@ bool SLPVectorizerPass::runImpl(Function &F, ScalarEvolution *SE_,
   return Changed;
 }
 
+/// Returns the constant loop-carried byte stride of \p Ptr in \p L, i.e. the
+/// step of its affine SCEV recurrence, or std::nullopt when \p Ptr is not a
+/// simple affine recurrence in \p L with a constant step. This is the same
+/// notion as LoopAccessAnalysis's CommonStride; it is computed here directly
+/// from ScalarEvolution rather than via getPtrStride, whose no-wrap versioning
+/// and PredicatedScalarEvolution machinery is meant for legality, not costing.
+static std::optional<int64_t>
+getConstantLoopStrideInBytes(Value *Ptr, ScalarEvolution &SE, const Loop *L) {
+  const auto *AR = dyn_cast<SCEVAddRecExpr>(SE.getSCEV(Ptr));
+  if (!AR || AR->getLoop() != L)
+    return std::nullopt;
+  const auto *Step = dyn_cast<SCEVConstant>(AR->getStepRecurrence(SE));
+  if (!Step)
+    return std::nullopt;
+  const APInt &StepVal = Step->getAPInt();
+  if (StepVal.getSignificantBits() > 64)
+    return std::nullopt;
+  return StepVal.getSExtValue();
+}
+
+bool BoUpSLP::findStoreLoadForwardingConflict(StoreInst *BaseStore,
+                                              unsigned VF) {
+  if (!BaseStore)
+    return false;
+
+  StoreInst *FirstStore = BaseStore;
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alexey-bataev wrote:

Remove FirstStore, use BaseStore instead

https://github.com/llvm/llvm-project/pull/199606