Support: Add operator== for MemoryBufferRef and split out MemoryBufferRef.h

As preparation for changing `LineIterator` to work with `MemoryBufferRef`:

- Add an `operator==` that uses buffer pointer identity to ensure two buffers
  are equivalent.
- Split out `MemoryBufferRef.h`, to avoid polluting `LineIterator.h` includers
  with everything from `MemoryBuffer.h`. This also means moving the
  `MemoryBuffer` constructor to a source file.

Differential Revision: https://reviews.llvm.org/D89279

include/llvm/Support/MemoryBuffer.h

@@ -19,14 +19,12 @@
 #include "llvm/ADT/Twine.h"
 #include "llvm/Support/CBindingWrapping.h"
 #include "llvm/Support/ErrorOr.h"
+#include "llvm/Support/MemoryBufferRef.h"
 #include <cstddef>
 #include <cstdint>
 #include <memory>
 
 namespace llvm {
-
-class MemoryBufferRef;
-
 namespace sys {
 namespace fs {
 // Duplicated from FileSystem.h to avoid a dependency.
@@ -260,26 +258,6 @@ private:
   using MemoryBuffer::getSTDIN;
 };
 
-class MemoryBufferRef {
-  StringRef Buffer;
-  StringRef Identifier;
-
-public:
-  MemoryBufferRef() = default;
-  MemoryBufferRef(const MemoryBuffer& Buffer)
-      : Buffer(Buffer.getBuffer()), Identifier(Buffer.getBufferIdentifier()) {}
-  MemoryBufferRef(StringRef Buffer, StringRef Identifier)
-      : Buffer(Buffer), Identifier(Identifier) {}
-
-  StringRef getBuffer() const { return Buffer; }
-
-  StringRef getBufferIdentifier() const { return Identifier; }
-
-  const char *getBufferStart() const { return Buffer.begin(); }
-  const char *getBufferEnd() const { return Buffer.end(); }
-  size_t getBufferSize() const { return Buffer.size(); }
-};
-
 // Create wrappers for C Binding types (see CBindingWrapping.h).
 DEFINE_SIMPLE_CONVERSION_FUNCTIONS(MemoryBuffer, LLVMMemoryBufferRef)
 

include/llvm/Support/MemoryBufferRef.h

@@ -0,0 +1,56 @@
+//===- MemoryBufferRef.h - Memory Buffer Reference --------------*- C++ -*-===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+//
+//  This file defines the MemoryBuffer interface.
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_SUPPORT_MEMORYBUFFERREF_H
+#define LLVM_SUPPORT_MEMORYBUFFERREF_H
+
+#include "llvm/ADT/StringRef.h"
+
+namespace llvm {
+
+class MemoryBuffer;
+
+class MemoryBufferRef {
+  StringRef Buffer;
+  StringRef Identifier;
+
+public:
+  MemoryBufferRef() = default;
+  MemoryBufferRef(const MemoryBuffer &Buffer);
+  MemoryBufferRef(StringRef Buffer, StringRef Identifier)
+      : Buffer(Buffer), Identifier(Identifier) {}
+
+  StringRef getBuffer() const { return Buffer; }
+  StringRef getBufferIdentifier() const { return Identifier; }
+
+  const char *getBufferStart() const { return Buffer.begin(); }
+  const char *getBufferEnd() const { return Buffer.end(); }
+  size_t getBufferSize() const { return Buffer.size(); }
+
+  /// Check pointer identity (not value) of identifier and data.
+  friend bool operator==(const MemoryBufferRef &LHS,
+                         const MemoryBufferRef &RHS) {
+    return LHS.Buffer.begin() == RHS.Buffer.begin() &&
+           LHS.Buffer.end() == RHS.Buffer.end() &&
+           LHS.Identifier.begin() == RHS.Identifier.begin() &&
+           LHS.Identifier.end() == RHS.Identifier.end();
+  }
+
+  friend bool operator!=(const MemoryBufferRef &LHS,
+                         const MemoryBufferRef &RHS) {
+    return !(LHS == RHS);
+  }
+};
+
+} // namespace llvm
+
+#endif // LLVM_SUPPORT_MEMORYBUFFERREF_H

lib/Support/CMakeLists.txt

@@ -142,6 +142,7 @@ add_llvm_component_library(LLVMSupport
   MathExtras.cpp
   MemAlloc.cpp
   MemoryBuffer.cpp
+  MemoryBufferRef.cpp
   MD5.cpp
   NativeFormatting.cpp
   OptimizedStructLayout.cpp

lib/Support/MemoryBufferRef.cpp

@@ -0,0 +1,19 @@
+//===- MemoryBufferRef.cpp - Memory Buffer Reference ----------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+//
+//  This file implements the MemoryBufferRef interface.
+//
+//===----------------------------------------------------------------------===//
+
+#include "llvm/Support/MemoryBufferRef.h"
+#include "llvm/Support/MemoryBuffer.h"
+
+using namespace llvm;
+
+MemoryBufferRef::MemoryBufferRef(const MemoryBuffer &Buffer)
+    : Buffer(Buffer.getBuffer()), Identifier(Buffer.getBufferIdentifier()) {}

unittests/Support/CMakeLists.txt

@@ -50,6 +50,7 @@ add_llvm_unittest(SupportTests
   MD5Test.cpp
   ManagedStatic.cpp
   MathExtrasTest.cpp
+  MemoryBufferRefTest.cpp
   MemoryBufferTest.cpp
   MemoryTest.cpp
   NativeFormatTests.cpp

unittests/Support/MemoryBufferRefTest.cpp

@@ -0,0 +1,51 @@
+//===- MemoryBufferRefTest.cpp - MemoryBufferRef tests --------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+//
+// This file implements unit tests for the MemoryBufferRef support class.
+//
+//===----------------------------------------------------------------------===//
+
+#include "llvm/Support/MemoryBufferRef.h"
+#include "llvm/Support/MemoryBuffer.h"
+#include "gtest/gtest.h"
+
+using namespace llvm;
+
+namespace {
+
+TEST(MemoryBufferRefTest, construct) {
+  std::unique_ptr<MemoryBuffer> MB(MemoryBuffer::getMemBuffer("data", "id"));
+  MemoryBufferRef MBR(*MB);
+
+  EXPECT_EQ(MB->getBufferStart(), MBR.getBufferStart());
+  EXPECT_EQ(MB->getBufferIdentifier(), MBR.getBufferIdentifier());
+}
+
+TEST(MemoryBufferRefTest, compareEquals) {
+  std::string Data = "data";
+  std::unique_ptr<MemoryBuffer> MB(MemoryBuffer::getMemBuffer(Data, "id"));
+  MemoryBufferRef Ref(*MB);
+  MemoryBufferRef Empty;
+  MemoryBufferRef NoIdentifier(MB->getBuffer(), "");
+  MemoryBufferRef NoData("", MB->getBufferIdentifier());
+  MemoryBufferRef Same(MB->getBuffer(), MB->getBufferIdentifier());
+
+  EXPECT_NE(Empty, Ref);
+  EXPECT_NE(NoIdentifier, Ref);
+  EXPECT_NE(NoData, Ref);
+  EXPECT_EQ(Same, Ref);
+
+  // Confirm NE when content matches but pointer identity does not.
+  std::unique_ptr<MemoryBuffer> Copy(
+      MemoryBuffer::getMemBufferCopy(Data, "id"));
+  MemoryBufferRef CopyRef(*Copy);
+  EXPECT_EQ(Ref.getBuffer(), CopyRef.getBuffer());
+  EXPECT_NE(Ref, CopyRef);
+}
+
+} // end namespace

unittests/Support/MemoryBufferTest.cpp

@@ -265,14 +265,6 @@ TEST_F(MemoryBufferTest, getOpenFileReopened) {
   testGetOpenFileSlice(true);
 }
 
-TEST_F(MemoryBufferTest, reference) {
-  OwningBuffer MB(MemoryBuffer::getMemBuffer(data));
-  MemoryBufferRef MBR(*MB);
-
-  EXPECT_EQ(MB->getBufferStart(), MBR.getBufferStart());
-  EXPECT_EQ(MB->getBufferIdentifier(), MBR.getBufferIdentifier());
-}
-
 TEST_F(MemoryBufferTest, slice) {
   // Create a file that is six pages long with different data on each page.
   int FD;