As noted in https://bugs.llvm.org/show_bug.cgi?id=36651, the specialization for isPodLike<std::pair<...>> did not match the expectation of std::is_trivially_copyable which makes the memcpy optimization invalid.
This patch renames the llvm::isPodLike trait into llvm::is_trivially_copyable. Unfortunately std::is_trivially_copyable is not portable across compiler / STL versions. So a portable version is provided too.
Note that the following specialization were invalid:
- std::pair<T0, T1>
Tests have been added to assert that former specialization are respected by the standard usage of llvm::is_trivially_copyable, and that in debug build, and when a decent version of std::is_trivially_copyable is available, llvm::is_trivially_copyable is compared to std::is_trivially_copyable
As of this patch, llvm::Optional is no longer considered trivially copyable, even if T is. this is to be fixed in a later patch, as it has impact on a long-running bug (see r347004)
Note that GCC warns about this UB, but this got silented by https://reviews.llvm.org/D50296.