[llvm] r300213 - [APSInt] Add a static_assert to ensure APSInt is packed well with APInt after r300171.

[Reid Kleckner via llvm-commits]

MSVC does not pack data into base class tail padding, so this static_assert
fails everywhere on Windows. If we want to do this optimization portably,
we need to use the ugly SubclassData pattern that Value uses.

On Thu, Apr 13, 2017 at 9:34 AM, Craig Topper via llvm-commits <
llvm-commits at lists.llvm.org> wrote:

> Author: ctopper
> Date: Thu Apr 13 11:34:49 2017
> New Revision: 300213
>
> URL: http://llvm.org/viewvc/llvm-project?rev=300213&view=rev
> Log:
> [APSInt] Add a static_assert to ensure APSInt is packed well with APInt
> after r300171.
>
> Modified:
>     llvm/trunk/include/llvm/ADT/APSInt.h
>
> Modified: llvm/trunk/include/llvm/ADT/APSInt.h
> URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/include/
> llvm/ADT/APSInt.h?rev=300213&r1=300212&r2=300213&view=diff
> ============================================================
> ==================
> --- llvm/trunk/include/llvm/ADT/APSInt.h (original)
> +++ llvm/trunk/include/llvm/ADT/APSInt.h Thu Apr 13 11:34:49 2017
> @@ -24,7 +24,9 @@ class LLVM_NODISCARD APSInt : public API
>
>  public:
>    /// Default constructor that creates an uninitialized APInt.
> -  explicit APSInt() : IsUnsigned(false) {}
> +  explicit APSInt() : IsUnsigned(false) {
> +    static_assert(sizeof(*this) == 16, "APSInt fields poorly packed");
> +  }
>
>    /// APSInt ctor - Create an APSInt with the specified width, default to
>    /// unsigned.
>
>
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