r340403 - [Preamble] Fix an undefined behavior when checking an empty preamble can be reused.

[Haojian Wu via cfe-commits]

Author: hokein
Date: Wed Aug 22 05:34:04 2018
New Revision: 340403

URL: http://llvm.org/viewvc/llvm-project?rev=340403&view=rev
Log:
[Preamble] Fix an undefined behavior when checking an empty preamble can be reused.

Summary: Passing nullptr to memcmp is UB.

Reviewers: ilya-biryukov

Reviewed By: ilya-biryukov

Subscribers: cfe-commits

Differential Revision: https://reviews.llvm.org/D50967

Modified:
    cfe/trunk/lib/Frontend/PrecompiledPreamble.cpp

Modified: cfe/trunk/lib/Frontend/PrecompiledPreamble.cpp
URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/lib/Frontend/PrecompiledPreamble.cpp?rev=340403&r1=340402&r2=340403&view=diff
==============================================================================
--- cfe/trunk/lib/Frontend/PrecompiledPreamble.cpp (original)
+++ cfe/trunk/lib/Frontend/PrecompiledPreamble.cpp Wed Aug 22 05:34:04 2018
@@ -426,8 +426,8 @@ bool PrecompiledPreamble::CanReuse(const
   // new main file.
   if (PreambleBytes.size() != Bounds.Size ||
       PreambleEndsAtStartOfLine != Bounds.PreambleEndsAtStartOfLine ||
-      memcmp(PreambleBytes.data(), MainFileBuffer->getBufferStart(),
-             Bounds.Size) != 0)
+      !std::equal(PreambleBytes.begin(), PreambleBytes.end(),
+                  MainFileBuffer->getBuffer().begin()))
     return false;
   // The preamble has not changed. We may be able to re-use the precompiled
   // preamble.