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

[Benjamin Maxwell via llvm-commits]

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@@ -19994,6 +19994,38 @@ static bool checkTreeSizes(ArrayRef<std::pair<unsigned, unsigned>> Sizes,
   return Dev * 96 / (Mean * Mean) == 0;
 }
 
+namespace {
+
+/// A group of instructions that we'll try to bundle together using vector ops.
+/// They are ordered using the signed distance of their address operand to the
+/// address of this group's BaseInstr.
+struct RelatedStoreInsts {
+  RelatedStoreInsts(unsigned BaseInstrIdx) { reset(BaseInstrIdx); }
+  void reset(unsigned NewBaseInstr) {
+    BaseInstrIdx = NewBaseInstr;
+    Instrs.clear();
+    insertOrLookup(NewBaseInstr, 0);
+  }
+
+  /// Tries to insert \p InstrIdx as the instruction with a pointer distance of
+  /// \p PtrDist.
+  /// Does nothing if there is already an instruction with that \p PtrDist.
+  /// \returns The previously associated Instruction index, or std::nullopt
+  std::optional<unsigned> insertOrLookup(unsigned InstrIdx, int PtrDist) {
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MacDue wrote:

I think the value this function returns is the previous index (if it exists), not the current index (which is what the parameter would be at the time of calling). 

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