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, 8 insertions, 0 deletions

diff --git a/llvm/unittests/ADT/PointerIntPairTest.cpp b/llvm/unittests/ADT/PointerIntPairTest.cpp
index 95e280330a7..6b3a4c055c9 100644
--- a/llvm/unittests/ADT/PointerIntPairTest.cpp
+++ b/llvm/unittests/ADT/PointerIntPairTest.cpp
@@ -61,6 +61,9 @@ TEST(PointerIntPairTest, GetSet) {
   Pair2.setPointerAndInt(&s, E::Case3);
   EXPECT_EQ(&s, Pair2.getPointer());
   EXPECT_EQ(E::Case3, Pair2.getInt());
+
+  static_assert(is_trivially_copyable<PointerIntPair<S *, 2, E>>::value,
+                "trivially copyable");
 }
 
 TEST(PointerIntPairTest, DefaultInitialize) {
@@ -96,6 +99,11 @@ TEST(PointerIntPairTest, ManyUnusedBits) {
 
   EXPECT_EQ(FixnumPointerTraits::NumLowBitsAvailable - 1,
             PointerLikeTypeTraits<decltype(pair)>::NumLowBitsAvailable);
+
+  static_assert(
+      is_trivially_copyable<
+          PointerIntPair<Fixnum31, 1, bool, FixnumPointerTraits>>::value,
+      "trivially copyable");
 }
 
 } // end anonymous namespace