Replace llvm::isPodLike<...> by llvm::is_trivially_copyable<...>

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>
    llvm::Optional<T>

Tests have been added to assert that former specialization are respected by the
standard usage of llvm::is_trivially_copyable, and that 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.

Differential Revision: https://reviews.llvm.org/D54472

llvm-svn: 351701

1 files changed, 1 insertions, 1 deletions

diff --git a/llvm/docs/ProgrammersManual.rst b/llvm/docs/ProgrammersManual.rst
index 0903a22fc3e..7faba112ffe 100644
--- a/llvm/docs/ProgrammersManual.rst
+++ b/llvm/docs/ProgrammersManual.rst
@@ -1456,7 +1456,7 @@ SmallVector has grown a few other minor advantages over std::vector, causing
 #. std::vector is exception-safe, and some implementations have pessimizations
    that copy elements when SmallVector would move them.
 
-#. SmallVector understands ``isPodLike<Type>`` and uses realloc aggressively.
+#. SmallVector understands ``llvm::is_trivially_copyable<Type>`` and uses realloc aggressively.
 
 #. Many LLVM APIs take a SmallVectorImpl as an out parameter (see the note
    below).