[llvm] Fix non-determinism in debuginfo (PR #68332)

[Orlando Cazalet-Hyams via llvm-commits]

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@@ -314,6 +317,27 @@ class AssignmentTrackingPass : public PassInfoMixin<AssignmentTrackingPass> {
 
 /// Return true if assignment tracking is enabled for module \p M.
 bool isAssignmentTrackingEnabled(const Module &M);
+
+template <> struct DenseMapInfo<at::VarRecord> {
+  static inline at::VarRecord getEmptyKey() {
+    return at::VarRecord{DenseMapInfo<DILocalVariable *>::getEmptyKey(),
+                         DenseMapInfo<DILocation *>::getEmptyKey()};
+  }
+
+  static inline at::VarRecord getTombstoneKey() {
+    return at::VarRecord{DenseMapInfo<DILocalVariable *>::getTombstoneKey(),
+                         DenseMapInfo<DILocation *>::getTombstoneKey()};
+  }
+
+  static unsigned getHashValue(const at::VarRecord &Var) {
+    return hash_combine(Var.Var, Var.DL);
+  }
+
+  static bool isEqual(const at::VarRecord &A, const at::VarRecord &B) {
+    return A == B;
+  }
+};
+
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OCHyams wrote:

We could throw away `VarRecord` and use `std::pair` instead to avoid adding this boilerplate (keeping the VarRecord comment next to a `using VarRecord = std::pair<...>` perhaps). I think a case can be made for both approaches, so I'm happy to stick with the path of least resistance.

Please could you move this `struct DenseMapInfo` next to `VarRecord` so that it's easier to notice that it needs updating if a field is added to `VarRecord`.

https://github.com/llvm/llvm-project/pull/68332