[llvm] [SLP] Add store-to-load forwarding conflict cost for widened store chains (PR #199606)

[Simon Pilgrim via llvm-commits]

================
@@ -676,6 +676,11 @@ class LLVM_ABI TargetTransformInfoImplBase {
   }
 
   virtual unsigned getCacheLineSize() const { return 0; }
+
+  virtual InstructionCost getStoreLoadForwardingConflictCost(
+      Type *VecTy, TargetTransformInfo::TargetCostKind CostKind) const {
+    return 0;
----------------
RKSimon wrote:

```suggestion
    return TTI::TCC_Free;
```
or TTI::TCC_Basic?

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