[ORC] Add specialized SPSSerializationTraits for ArrayRef<char>.

Deserializing from an SPSSequence<char> to an an ArrayRef<char> will point the
ArrayRef<char> at the input buffer.

llvm/include/llvm/ExecutionEngine/Orc/Shared/SimplePackedSerialization.h

@@ -296,6 +296,31 @@ public:
   static constexpr bool available = true;
 };
 
+/// Specialized SPSSequence<char> -> ArrayRef<char> serialization.
+///
+/// On deserialize, points directly into the input buffer.
+template <> class SPSSerializationTraits<SPSSequence<char>, ArrayRef<char>> {
+public:
+  static size_t size(const ArrayRef<char> &A) {
+    return SPSArgList<uint64_t>::size(static_cast<uint64_t>(A.size())) +
+           A.size();
+  }
+
+  static bool serialize(SPSOutputBuffer &OB, const ArrayRef<char> &A) {
+    if (!SPSArgList<uint64_t>::serialize(OB, static_cast<uint64_t>(A.size())))
+      return false;
+    return OB.write(A.data(), A.size());
+  }
+
+  static bool deserialize(SPSInputBuffer &IB, ArrayRef<char> &A) {
+    uint64_t Size;
+    if (!SPSArgList<uint64_t>::deserialize(IB, Size))
+      return false;
+    A = {IB.data(), Size};
+    return IB.skip(Size);
+  }
+};
+
 /// 'Trivial' sequence serialization: Sequence is serialized as a uint64_t size
 /// followed by a for-earch loop over the elements of the sequence to serialize
 /// each of them.

llvm/unittests/ExecutionEngine/Orc/SimplePackedSerializationTest.cpp

@@ -168,3 +168,23 @@ TEST(SimplePackedSerialization, StringMap) {
   StringMap<int32_t> M({{"A", 1}, {"B", 2}});
   spsSerializationRoundTrip<SPSSequence<SPSTuple<SPSString, int32_t>>>(M);
 }
+
+TEST(SimplePackedSerializationTest, ArrayRef) {
+  constexpr unsigned BufferSize = 6 + 8; // "hello\0" + sizeof(uint64_t)
+  ArrayRef<char> HelloOut = "hello";
+  char Buffer[BufferSize];
+  memset(Buffer, 0, BufferSize);
+
+  SPSOutputBuffer OB(Buffer, BufferSize);
+  EXPECT_TRUE(SPSArgList<SPSSequence<char>>::serialize(OB, HelloOut));
+
+  ArrayRef<char> HelloIn;
+  SPSInputBuffer IB(Buffer, BufferSize);
+  EXPECT_TRUE(SPSArgList<SPSSequence<char>>::deserialize(IB, HelloIn));
+
+  // Output should be copied to buffer.
+  EXPECT_NE(HelloOut.data(), Buffer);
+
+  // Input should reference buffer.
+  EXPECT_LT(HelloIn.data() - Buffer, BufferSize);
+}