[llvm] [SandboxIR] Adds BasicBlock and adds functionality to Function and Context (PR #97637)

[via llvm-commits]

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@@ -231,6 +283,8 @@ class Instruction : public sandboxir::User {
     return OS;
   }
 #endif
+  /// This is used by BasicBlcok::iterator.
+  virtual unsigned getNumOfIRInstrs() const = 0;
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vporpo wrote:

Yes, I think we could replace these with CRTPs later.

https://github.com/llvm/llvm-project/pull/97637