Split getOpenFile into getOpenFile and getOpenFileSlice.

The main observation is that we never need both the filesize and the map size.
When mapping a slice of a file, it doesn't make sense to request a null
terminator and that would be the only case where the filesize would be used.

There are other cleanups that should be done in this area:

* A client should not have to pass the size (even an explicit -1) to say if
  it wants a null terminator or not, so we should probably swap the argument
  order.
* The default should be to not require a null terminator. Very few clients
  require this, but many end up asking for it just because it is the default.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@186984 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 10 insertions, 6 deletions

diff --git a/include/llvm/Support/MemoryBuffer.h b/include/llvm/Support/MemoryBuffer.h
index e443b68..9609e33 100644
--- a/include/llvm/Support/MemoryBuffer.h
+++ b/include/llvm/Support/MemoryBuffer.h
@@ -74,13 +74,17 @@ public:
                             int64_t FileSize = -1,
                             bool RequiresNullTerminator = true);
 
-  /// getOpenFile - Given an already-open file descriptor, read the file and
-  /// return a MemoryBuffer.
+  // Get a MemoryBuffer of part of a file. Since this is in the middle of a
+  // file, the buffer is not null terminated.
+  static error_code getOpenFileSlice(int FD, const char *Filename,
+                                     OwningPtr<MemoryBuffer> &Result,
+                                     uint64_t MapSize, int64_t Offset);
+
+  /// Given an already-open file descriptor, read the file and return a
+  /// MemoryBuffer.
   static error_code getOpenFile(int FD, const char *Filename,
-                                OwningPtr<MemoryBuffer> &result,
-                                uint64_t FileSize = -1,
-                                uint64_t MapSize = -1,
-                                int64_t Offset = 0,
+                                OwningPtr<MemoryBuffer> &Result,
+                                uint64_t FileSize,
                                 bool RequiresNullTerminator = true);
 
   /// getMemBuffer - Open the specified memory range as a MemoryBuffer.  Note