[PBQP] Add begin and end to Vector (NFC)

This patch adds begin and end to Vector.

The new functions will allow us to use llvm::interleaved in operator<<
for example.

Author: kazutakahirata

llvm/include/llvm/CodeGen/PBQP/Math.h

@@ -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());
   }
 
   /// Return the length of the vector
@@ -80,15 +86,14 @@ class Vector {
   Vector& operator+=(const Vector &V) {
     assert(Length != 0 && Data && "Invalid vector");
     assert(Length == V.Length && "Vector length mismatch.");
-    std::transform(Data.get(), Data.get() + Length, V.Data.get(), Data.get(),
-                   std::plus<PBQPNum>());
+    std::transform(begin(), end(), V.begin(), begin(), std::plus<PBQPNum>());
     return *this;
   }
 
   /// Returns the index of the minimum value in this vector
   unsigned minIndex() const {
     assert(Length != 0 && Data && "Invalid vector");
-    return std::min_element(Data.get(), Data.get() + Length) - Data.get();
+    return llvm::min_element(*this) - begin();
   }
 
 private:
@@ -98,8 +103,8 @@ class Vector {
 
 /// Return a hash_value for the given vector.
 inline hash_code hash_value(const Vector &V) {
-  unsigned *VBegin = reinterpret_cast<unsigned*>(V.Data.get());
-  unsigned *VEnd = reinterpret_cast<unsigned*>(V.Data.get() + V.Length);
+  const unsigned *VBegin = reinterpret_cast<const unsigned *>(V.begin());
+  const unsigned *VEnd = reinterpret_cast<const unsigned *>(V.end());
   return hash_combine(V.Length, hash_combine_range(VBegin, VEnd));
 }