[cfe-dev] __is_trivially_copyable seems to be misbehaving

[Howard Hinnant via cfe-dev]

On May 27, 2016, at 3:17 PM, David Blaikie via cfe-dev <cfe-dev at lists.llvm.org> wrote:
> 
> Example:
> 
>   struct foo {
>     foo(foo &&) = default;
>     foo &operator=(foo &&) = default;
>   };
> 
>   static_assert(__is_trivially_copyable(foo), "this really shouldn't be true");
> 
> This static-assert succeeds, yet the code:
> 
>   void f(foo &x, foo &y) {
>     x = y;
>   }
> 
> fails.
> 
> This came up when someone on IRC tried to make a SmallVector of such things and LLVM's isPodLike trait said "yes, this thing is podlike" and tried to use std::copy to copy them around (& that was just luck that it failed - in other places it used memcpy to copy them around, which would've been silent badness). isPodLike is implemented in terms of __is_trivially_copyable, where available. (granted, it's implemented in terms of is_class where that's not available - so we don't have any code that /relies/ on the correctness of __is_trivially_copyable, only for optimization purposes)
> 
> Am I seeing that right?

http://stackoverflow.com/a/36164788/576911

Howard

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