[llvm] [GlobalISel] Fix store merging incorrectly classifying an unknown index expr as 0. (PR #90375)

[Thorsten Schütt via llvm-commits]

================
@@ -35,11 +35,29 @@ struct LegalityQuery;
 class MachineRegisterInfo;
 namespace GISelAddressing {
 /// Helper struct to store a base, index and offset that forms an address
-struct BaseIndexOffset {
+class BaseIndexOffset {
+private:
   Register BaseReg;
   Register IndexReg;
-  int64_t Offset = 0;
-  bool IsIndexSignExt = false;
+  std::optional<int64_t> Offset;
+
+public:
+  BaseIndexOffset() = default;
+  BaseIndexOffset(Register Base, Register Index, bool IsIndexSignExt)
----------------
tschuett wrote:

The constructor is unused and there is no member variable.

https://github.com/llvm/llvm-project/pull/90375