[llvm] r292575 - BitVector: Fix undefined behaviour

[Matthias Braun via llvm-commits]

Sure, committed r292817 for that.

> On Jan 23, 2017, at 9:47 AM, David Blaikie via llvm-commits <llvm-commits at lists.llvm.org> wrote:
> 
> I realize it's UB, so not exactly testable - but a unit test that exercises this (& that, say, asan would have failed on without the fix) would be good.
> 
> On Thu, Jan 19, 2017 at 8:34 PM Matthias Braun via llvm-commits <llvm-commits at lists.llvm.org <mailto:llvm-commits at lists.llvm.org>> wrote:
> Author: matze
> Date: Thu Jan 19 22:23:08 2017
> New Revision: 292575
> 
> URL: http://llvm.org/viewvc/llvm-project?rev=292575&view=rev <http://llvm.org/viewvc/llvm-project?rev=292575&view=rev>
> Log:
> BitVector: Fix undefined behaviour
> 
> Calling reset() on an empty BitVector would call memset with a nullptr
> argument which is undefined behaviour.
> 
> This should fix the sanitizer bot.
> 
> Modified:
>     llvm/trunk/include/llvm/ADT/BitVector.h
> 
> Modified: llvm/trunk/include/llvm/ADT/BitVector.h
> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/include/llvm/ADT/BitVector.h?rev=292575&r1=292574&r2=292575&view=diff <http://llvm.org/viewvc/llvm-project/llvm/trunk/include/llvm/ADT/BitVector.h?rev=292575&r1=292574&r2=292575&view=diff>
> ==============================================================================
> --- llvm/trunk/include/llvm/ADT/BitVector.h (original)
> +++ llvm/trunk/include/llvm/ADT/BitVector.h Thu Jan 19 22:23:08 2017
> @@ -539,7 +539,8 @@ private:
>    }
> 
>    void init_words(BitWord *B, unsigned NumWords, bool t) {
> -    memset(B, 0 - (int)t, NumWords*sizeof(BitWord));
> +    if (NumWords > 0)
> +      memset(B, 0 - (int)t, NumWords*sizeof(BitWord));
>    }
> 
>    template<bool AddBits, bool InvertMask>
> 
> 
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