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

[Arthur Eubanks via llvm-commits]

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@@ -205,6 +210,53 @@ class Constant : public sandboxir::User {
 #endif
 };
 
+/// The BasicBlock::iterator.
+class BBIterator {
+public:
+  using difference_type = std::ptrdiff_t;
+  using value_type = Instruction;
+  using pointer = value_type *;
+  using reference = value_type &;
+  using iterator_category = std::bidirectional_iterator_tag;
+
+private:
+  llvm::BasicBlock *BB;
+  llvm::BasicBlock::iterator It;
+  Context *Ctx;
+  pointer getI(llvm::BasicBlock::iterator It) const;
+
+public:
+  BBIterator() : BB(nullptr), Ctx(nullptr) {}
+  BBIterator(llvm::BasicBlock *BB, llvm::BasicBlock::iterator It, Context *Ctx)
+      : BB(BB), It(It), Ctx(Ctx) {}
+  reference operator*() const { return *getI(It); }
+  BBIterator &operator++();
+  BBIterator operator++(int) {
+    auto Copy = *this;
+    ++*this;
+    return Copy;
+  }
+  BBIterator &operator--();
+  BBIterator operator--(int) {
+    auto Copy = *this;
+    --*this;
+    return Copy;
+  }
+  bool operator==(const BBIterator &Other) const {
+    assert(Ctx == Other.Ctx && "BBIterators in different context!");
+    return It == Other.It;
+  }
+  bool operator!=(const BBIterator &Other) const { return !(*this == Other); }
+  /// \Returns true if the internal iterator is at the beginning of the IR BB.
+  /// NOTE: This is meant to be used internally, during the construction of a
+  /// SBBB, during which SBBB->begin() fails due to the missing mapping of
+  /// BB->begin() to SandboxIR.
+  bool atBegin() const;
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aeubanks wrote:

can you remove the declaration if it's unused?

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