[llvm] 1131738 - Support: Avoid using SmallVector::set_size() in MemoryBuffer

[Duncan P. N. Exon Smith via llvm-commits]

Author: Duncan P. N. Exon Smith
Date: 2021-12-09T18:44:40-08:00
New Revision: 1131738698c49b194be278da3a2a21a7eaa915a9

URL: https://github.com/llvm/llvm-project/commit/1131738698c49b194be278da3a2a21a7eaa915a9
DIFF: https://github.com/llvm/llvm-project/commit/1131738698c49b194be278da3a2a21a7eaa915a9.diff

LOG: Support: Avoid using SmallVector::set_size() in MemoryBuffer

Update getMemoryBufferForStream() to use `resize_for_overwrite()` and
`truncate()` instead of `reserve()` and `set_size()`.

Differential Revision: https://reviews.llvm.org/D115384

Added: 
    

Modified: 
    llvm/lib/Support/MemoryBuffer.cpp

Removed: 
    


################################################################################
diff  --git a/llvm/lib/Support/MemoryBuffer.cpp b/llvm/lib/Support/MemoryBuffer.cpp
index bcf13d828a5df..d3fa3c6f065de 100644
--- a/llvm/lib/Support/MemoryBuffer.cpp
+++ b/llvm/lib/Support/MemoryBuffer.cpp
@@ -227,17 +227,20 @@ static ErrorOr<std::unique_ptr<WritableMemoryBuffer>>
 getMemoryBufferForStream(sys::fs::file_t FD, const Twine &BufferName) {
   const ssize_t ChunkSize = 4096*4;
   SmallString<ChunkSize> Buffer;
+
   // Read into Buffer until we hit EOF.
+  size_t Size = Buffer.size();
   for (;;) {
-    Buffer.reserve(Buffer.size() + ChunkSize);
+    Buffer.resize_for_overwrite(Size + ChunkSize);
     Expected<size_t> ReadBytes = sys::fs::readNativeFile(
-        FD, makeMutableArrayRef(Buffer.end(), ChunkSize));
+        FD, makeMutableArrayRef(Buffer.begin() + Size, ChunkSize));
     if (!ReadBytes)
       return errorToErrorCode(ReadBytes.takeError());
     if (*ReadBytes == 0)
       break;
-    Buffer.set_size(Buffer.size() + *ReadBytes);
+    Size += *ReadBytes;
   }
+  Buffer.truncate(Size);
 
   return getMemBufferCopyImpl(Buffer, BufferName);
 }