[PATCH] D50967: [Preamble] Fix an undefined behavior when checking an empty preamble can be reused.

[Haojian Wu via Phabricator via cfe-commits]

hokein created this revision.
hokein added a reviewer: ilya-biryukov.

Passing nullptr to memcmp is UB.


Repository:
  rC Clang

https://reviews.llvm.org/D50967

Files:
  lib/Frontend/PrecompiledPreamble.cpp


Index: lib/Frontend/PrecompiledPreamble.cpp
===================================================================
--- lib/Frontend/PrecompiledPreamble.cpp
+++ lib/Frontend/PrecompiledPreamble.cpp
@@ -416,6 +416,9 @@
       Bounds.Size <= MainFileBuffer->getBufferSize() &&
       "Buffer is too large. Bounds were calculated from a different buffer?");
 
+  if (Bounds.Size == 0)
+    return PreambleBytes.size() == Bounds.Size;
+
   auto PreambleInvocation = std::make_shared<CompilerInvocation>(Invocation);
   PreprocessorOptions &PreprocessorOpts =
       PreambleInvocation->getPreprocessorOpts();


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