[llvm] [PBQP] Add begin and end to Vector (NFC) (PR #136454)

[Kazu Hirata via llvm-commits]

================
@@ -48,12 +48,18 @@ class Vector {
     V.Length = 0;
   }
 
+  // Iterator-based access.
+  const PBQPNum *begin() const { return Data.get(); }
+  const PBQPNum *end() const { return Data.get() + Length; }
+  PBQPNum *begin() { return Data.get(); }
+  PBQPNum *end() { return Data.get() + Length; }
+
   /// Comparison operator.
   bool operator==(const Vector &V) const {
     assert(Length != 0 && Data && "Invalid vector");
     if (Length != V.Length)
       return false;
-    return std::equal(Data.get(), Data.get() + Length, V.Data.get());
+    return std::equal(begin(), end(), V.begin());
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kazutakahirata wrote:

Yes, the variant of `std::equal` that takes four arguments is exposed via `llvm::equal`.  That variant compares the size with `std::distance`, so I should be able to remove the `Length` comparison above.  Thanks!

https://github.com/llvm/llvm-project/pull/136454