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, 2 insertions, 0 deletions

diff --git a/llvm/unittests/CodeGen/MachineInstrTest.cpp b/llvm/unittests/CodeGen/MachineInstrTest.cpp
index 880e013b99f..2678a4589f9 100644
--- a/llvm/unittests/CodeGen/MachineInstrTest.cpp
+++ b/llvm/unittests/CodeGen/MachineInstrTest.cpp
@@ -272,4 +272,6 @@ TEST(MachineInstrPrintingTest, DebugLocPrinting) {
       StringRef(OS.str()).endswith("filename:1:5"));
 }
 
+static_assert(is_trivially_copyable<MCOperand>::value, "trivially copyable");
+
 } // end namespace