Avoid usage of char16_t as MSVC "14" doesn't appear to support it

Fixes the MSVC "14" build.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@221932 91177308-0d34-0410-b5e6-96231b3b80d8
Move calls to push_back out of readAbbreviated(Literal|Field).

These functions always return a single value and not all callers want to
push them into a SmallVector.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@221934 91177308-0d34-0410-b5e6-96231b3b80d8
[x86] Add some tests for specific patterns of lane-flips combined with
in-lane shuffles that aren't always handled well by the current vector
shuffle lowering.

No functionality change yet, that will follow in a subsequent commit.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@221938 91177308-0d34-0410-b5e6-96231b3b80d8
Revert "[GVN] Perform Scalar PRE on gep indices that feed loads before doing Load PRE."

This reverts commit r221924.  It appears the commit was a bit premature and is causing
bot failures that need further investigation.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@221939 91177308-0d34-0410-b5e6-96231b3b80d8
Use nullptr instead of NULL for variadic sentinels

Windows defines NULL to 0, which when used as an argument to a variadic
function, is not a null pointer constant. As a result, Clang's
-Wsentinel fires on this code. Using '0' would be wrong on most 64-bit
platforms, but both MSVC and Clang make it work on Windows. Sidestep the
issue with nullptr.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@221940 91177308-0d34-0410-b5e6-96231b3b80d8