[llvm] r243932 - [UB] Fix another place where we would pass a null pointer to memcpy.

[Chandler Carruth]

Should probably pull this into the release as it fixes something that could
miscompile in the future with a new host compiler.

On Mon, Aug 3, 2015 at 5:56 PM Chandler Carruth <chandlerc at gmail.com> wrote:

> Author: chandlerc
> Date: Mon Aug  3 19:53:01 2015
> New Revision: 243932
>
> URL: http://llvm.org/viewvc/llvm-project?rev=243932&view=rev
> Log:
> [UB] Fix another place where we would pass a null pointer to memcpy.
>
> This too was found by UBSan. Down to 35 failures for me.
>
> Modified:
>     llvm/trunk/include/llvm/ADT/StringMap.h
>
> Modified: llvm/trunk/include/llvm/ADT/StringMap.h
> URL:
> http://llvm.org/viewvc/llvm-project/llvm/trunk/include/llvm/ADT/StringMap.h?rev=243932&r1=243931&r2=243932&view=diff
>
> ==============================================================================
> --- llvm/trunk/include/llvm/ADT/StringMap.h (original)
> +++ llvm/trunk/include/llvm/ADT/StringMap.h Mon Aug  3 19:53:01 2015
> @@ -158,7 +158,8 @@ public:
>
>      // Copy the string information.
>      char *StrBuffer = const_cast<char*>(NewItem->getKeyData());
> -    memcpy(StrBuffer, Key.data(), KeyLength);
> +    if (KeyLength > 0)
> +      memcpy(StrBuffer, Key.data(), KeyLength);
>      StrBuffer[KeyLength] = 0;  // Null terminate for convenience of
> clients.
>      return NewItem;
>    }
>
>
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