[PATCH] D32212: Create some helpers for generating bit masks

[Zachary Turner via llvm-commits]

We can just use a static_cast to get rid of the warning.  MathExtras.h
already has such a thing to silence this exact warning:

  // Replace "-Value" by "1+~Value" in the following commented code to avoid
  // MSVC warning C4146
  //    return (A | B) & -(A | B);
  return (A | B) & (1 + ~(A | B));


On Wed, Apr 19, 2017 at 9:26 AM Adrian McCarthy via Phabricator <
reviews at reviews.llvm.org> wrote:

> amccarth added inline comments.
>
>
> ================
> Comment at: llvm/trunk/include/llvm/Support/MathExtras.h:207
> +  assert(N <= Bits && "Invalid bit index");
> +  return -T(N != 0) & (T(-1) >> (Bits - N));
> +}
> ----------------
> Be aware that this can lead to compiler warnings, at least in MSVC, if T
> is an unsigned type:
>
>  [[ https://msdn.microsoft.com/en-us/library/4kh09110.aspx |  C4146:
> unary minus operator applied to unsigned type, result still unsigned ]]
>
> Depending on the specific details, this can be a level 2 or level 3
> warning.  I'm surprised the tests aren't triggering it.  We must disable
> this warning somewhere.
>
>
>
>
> Repository:
>   rL LLVM
>
> https://reviews.llvm.org/D32212
>
>
>
>
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