[llvm] [TTI][CostModel] Add cost modeling for expandload and compressstore intrinsics (PR #122882)

[Simon Pilgrim via llvm-commits]

================
@@ -1469,6 +1469,13 @@ class BasicTTIImplBase : public TargetTransformInfoImplCRTPBase<T> {
                                        true, CostKind);
   }
 
+  InstructionCost getExpandCompressMemoryOpCost(
+      unsigned Opcode, Type *DataTy, bool VariableMask, Align Alignment,
+      TTI::TargetCostKind CostKind, const Instruction *I = nullptr) {
+    return getCommonMaskedMemoryOpCost(Opcode, DataTy, Alignment, VariableMask,
+                                       true, CostKind);
----------------
RKSimon wrote:

`/*IsGatherScatter=*/true` - add a comment explaining that we treat it as gather/scatter so people don't think its a typo.

https://github.com/llvm/llvm-project/pull/122882