r243948 - [UB] Another place where we were trying to put string data into

[Chandler Carruth]

Author: chandlerc
Date: Mon Aug  3 22:53:00 2015
New Revision: 243948

URL: http://llvm.org/viewvc/llvm-project?rev=243948&view=rev
Log:
[UB] Another place where we were trying to put string data into
a BumpPtrAllocator. This at least now handles the case where there is no
concatentation without calling memcpy on a null pointer. It might be
interesting to handle the case where everything is empty without
round-tripping through the allocator, but it wasn't clear to me if the
pointer returned is significant in any way, so I've left it in
a conservatively more-correct state.

Again, found with UBSan.

Modified:
    cfe/trunk/lib/CodeGen/CGDebugInfo.h

Modified: cfe/trunk/lib/CodeGen/CGDebugInfo.h
URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/lib/CodeGen/CGDebugInfo.h?rev=243948&r1=243947&r2=243948&view=diff
==============================================================================
--- cfe/trunk/lib/CodeGen/CGDebugInfo.h (original)
+++ cfe/trunk/lib/CodeGen/CGDebugInfo.h Mon Aug  3 22:53:00 2015
@@ -485,8 +485,10 @@ private:
   /// are concatenated.
   StringRef internString(StringRef A, StringRef B = StringRef()) {
     char *Data = DebugInfoNames.Allocate<char>(A.size() + B.size());
-    std::memcpy(Data, A.data(), A.size());
-    std::memcpy(Data + A.size(), B.data(), B.size());
+    if (!A.empty())
+      std::memcpy(Data, A.data(), A.size());
+    if (!B.empty())
+      std::memcpy(Data + A.size(), B.data(), B.size());
     return StringRef(Data, A.size() + B.size());
   }
 };