[llvm] [SLP] Use named structs in vectorizeStores() (NFC) (PR #132781)

[Gaëtan Bossu via llvm-commits]

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@@ -884,6 +884,42 @@ class InstructionsState {
   static InstructionsState invalid() { return {nullptr, nullptr}; }
 };
 
+/// A reference to a ld/st instruction and the distance of its address to a base
+/// pointer.
+struct MemInstAndPtrDist {
+  MemInstAndPtrDist(unsigned InstrIdx, int DistToBasePtr)
+      : InstrIdx(InstrIdx), DistToBasePtr(DistToBasePtr) {}
+  unsigned InstrIdx;
+  int DistToBasePtr;
+};
+struct PtrDistCompare {
+  bool operator()(const MemInstAndPtrDist &Op1,
+                  const MemInstAndPtrDist &Op2) const {
+    return Op1.DistToBasePtr < Op2.DistToBasePtr;
+  }
+};
+
+/// A group of memory instructions that we'll try to bundle together using
+/// vector ops. They are ordered using their signed distance to the address of
+/// this group's BaseInstr.
+struct RelatedMemInsts {
+  RelatedMemInsts(unsigned BaseInstrIdx) { reset(BaseInstrIdx); }
+  void reset(unsigned NewBaseInstr) {
+    BaseInstrIdx = NewBaseInstr;
+    Instrs.clear();
+    Instrs.emplace(NewBaseInstr, 0);
+  }
+
+  // TODO: This should probably just be an std::map
----------------
gbossu wrote:

I understand that in IR there can be multiple stores with the same distance. But in the implementation, `std::set<..., PtrDistCompare>` will make sure that there is only one store with a given distance. ([see example](https://godbolt.org/z/bGed7nnnM)) I assumed this is on purpose, because the data structure is re-arranged every time a "duplicate pointer" is found.

https://github.com/llvm/llvm-project/pull/132781