[Support] Add WritableMemoryBuffer::getNewMemBuffer

Summary:
The idea is that it would replace
(non-Writable)MemoryBuffer::getNewMemBuffer, which is quite useless
unless you const_cast its contents to write to it (which all (both)
callers of this function were doing). This patch also fixes one of the usages in
COFFWriter. After fixing the other usage in clang, I plan to delete the old
function.

Reviewers: dblaikie, Bigcheese

Subscribers: llvm-commits

Differential Revision: https://reviews.llvm.org/D41540

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@322094 91177308-0d34-0410-b5e6-96231b3b80d8

include/llvm/Support/MemoryBuffer.h

@@ -117,9 +117,8 @@ class MemoryBuffer {
   static std::unique_ptr<MemoryBuffer>
   getMemBufferCopy(StringRef InputData, const Twine &BufferName = "");
 
-  /// Allocate a new zero-initialized MemoryBuffer of the specified size. Note
-  /// that the caller need not initialize the memory allocated by this method.
-  /// The memory is owned by the MemoryBuffer object.
+  // TODO: Remove after all callers are switched to
+  // WritableMemoryBuffer::getNewMemBuffer
   static std::unique_ptr<MemoryBuffer>
   getNewMemBuffer(size_t Size, StringRef BufferName = "");
 
@@ -196,6 +195,12 @@ class WritableMemoryBuffer : public MemoryBuffer {
   static std::unique_ptr<WritableMemoryBuffer>
   getNewUninitMemBuffer(size_t Size, const Twine &BufferName = "");
 
+  /// Allocate a new zero-initialized MemoryBuffer of the specified size. Note
+  /// that the caller need not initialize the memory allocated by this method.
+  /// The memory is owned by the MemoryBuffer object.
+  static std::unique_ptr<WritableMemoryBuffer>
+  getNewMemBuffer(size_t Size, const Twine &BufferName = "");
+
 private:
   // Hide these base class factory function so one can't write
   //   WritableMemoryBuffer::getXXX()
@@ -204,7 +209,6 @@ class WritableMemoryBuffer : public MemoryBuffer {
   using MemoryBuffer::getFileOrSTDIN;
   using MemoryBuffer::getMemBuffer;
   using MemoryBuffer::getMemBufferCopy;
-  using MemoryBuffer::getNewMemBuffer;
   using MemoryBuffer::getOpenFile;
   using MemoryBuffer::getOpenFileSlice;
   using MemoryBuffer::getSTDIN;

lib/Object/WindowsResource.cpp

@@ -334,7 +334,7 @@ class WindowsResourceCOFFWriter {
   void writeDirectoryTree();
   void writeDirectoryStringTable();
   void writeFirstSectionRelocations();
-  std::unique_ptr<MemoryBuffer> OutputBuffer;
+  std::unique_ptr<WritableMemoryBuffer> OutputBuffer;
   char *BufferStart;
   uint64_t CurrentOffset = 0;
   COFF::MachineTypes MachineType;
@@ -360,7 +360,7 @@ WindowsResourceCOFFWriter::WindowsResourceCOFFWriter(
       Data(Parser.getData()), StringTable(Parser.getStringTable()) {
   performFileLayout();
 
-  OutputBuffer = MemoryBuffer::getNewMemBuffer(FileSize);
+  OutputBuffer = WritableMemoryBuffer::getNewMemBuffer(FileSize);
 }
 
 void WindowsResourceCOFFWriter::performFileLayout() {
@@ -425,7 +425,7 @@ static std::time_t getTime() {
 }
 
 std::unique_ptr<MemoryBuffer> WindowsResourceCOFFWriter::write() {
-  BufferStart = const_cast<char *>(OutputBuffer->getBufferStart());
+  BufferStart = OutputBuffer->getBufferStart();
 
   writeCOFFHeader();
   writeFirstSectionHeader();

lib/Support/MemoryBuffer.cpp

@@ -141,11 +141,7 @@ MemoryBuffer::getMemBufferCopy(StringRef InputData, const Twine &BufferName) {
 
 std::unique_ptr<MemoryBuffer>
 MemoryBuffer::getNewMemBuffer(size_t Size, StringRef BufferName) {
-  auto SB = WritableMemoryBuffer::getNewUninitMemBuffer(Size, BufferName);
-  if (!SB)
-    return nullptr;
-  memset(SB->getBufferStart(), 0, Size);
-  return std::move(SB);
+  return WritableMemoryBuffer::getNewMemBuffer(Size, BufferName);
 }
 
 ErrorOr<std::unique_ptr<MemoryBuffer>>
@@ -306,6 +302,15 @@ WritableMemoryBuffer::getNewUninitMemBuffer(size_t Size, const Twine &BufferName
   return std::unique_ptr<WritableMemoryBuffer>(Ret);
 }
 
+std::unique_ptr<WritableMemoryBuffer>
+WritableMemoryBuffer::getNewMemBuffer(size_t Size, const Twine &BufferName) {
+  auto SB = WritableMemoryBuffer::getNewUninitMemBuffer(Size, BufferName);
+  if (!SB)
+    return nullptr;
+  memset(SB->getBufferStart(), 0, Size);
+  return SB;
+}
+
 static bool shouldUseMmap(int FD,
                           size_t FileSize,
                           size_t MapSize,

unittests/Support/MemoryBufferTest.cpp

@@ -116,13 +116,13 @@ TEST_F(MemoryBufferTest, make_new) {
   EXPECT_TRUE(nullptr != Two.get());
 
   // 0-initialized buffer with no name
-  OwningBuffer Three(MemoryBuffer::getNewMemBuffer(321, data));
+  OwningBuffer Three(WritableMemoryBuffer::getNewMemBuffer(321, data));
   EXPECT_TRUE(nullptr != Three.get());
   for (size_t i = 0; i < 321; ++i)
     EXPECT_EQ(0, Three->getBufferStart()[0]);
 
   // 0-initialized buffer with name
-  OwningBuffer Four(MemoryBuffer::getNewMemBuffer(123, "zeros"));
+  OwningBuffer Four(WritableMemoryBuffer::getNewMemBuffer(123, "zeros"));
   EXPECT_TRUE(nullptr != Four.get());
   for (size_t i = 0; i < 123; ++i)
     EXPECT_EQ(0, Four->getBufferStart()[0]);