[Atomics][LoopIdiom] Recognize unordered atomic memcpy

Summary:
Expanding the loop idiom test for memcpy to also recognize
unordered atomic memcpy. The only difference for recognizing
an unordered atomic memcpy and instead of a normal memcpy is
that the loads and/or stores involved are unordered atomic operations.

Background:  http://lists.llvm.org/pipermail/llvm-dev/2017-May/112779.html

Patch by Daniel Neilson!

Reviewers: reames, anna, skatkov

Reviewed By: reames, anna

Subscribers: llvm-commits, mzolotukhin

Differential Revision: https://reviews.llvm.org/D33243

llvm-svn: 304806
diff --git a/llvm/lib/Target/X86/X86TargetTransformInfo.cpp b/llvm/lib/Target/X86/X86TargetTransformInfo.cpp
index fe94079..1d58ccc 100644
--- a/llvm/lib/Target/X86/X86TargetTransformInfo.cpp
+++ b/llvm/lib/Target/X86/X86TargetTransformInfo.cpp
@@ -1383,6 +1383,8 @@
   return BaseT::getCmpSelInstrCost(Opcode, ValTy, CondTy, I);
 }
 
+unsigned X86TTIImpl::getAtomicMemIntrinsicMaxElementSize() const { return 16; }
+
 int X86TTIImpl::getIntrinsicInstrCost(Intrinsic::ID IID, Type *RetTy,
                                       ArrayRef<Type *> Tys, FastMathFlags FMF,
                                       unsigned ScalarizationCostPassed) {