Index: include/llvm/CodeGen/SelectionDAGNodes.h
===================================================================
--- include/llvm/CodeGen/SelectionDAGNodes.h
+++ include/llvm/CodeGen/SelectionDAGNodes.h
@@ -66,6 +66,7 @@
 class SelectionDAG;
 class Type;
 class Value;
+class AtomicSDNode; //forward declare for type check
 
 void checkForCycles(const SDNode *N, const SelectionDAG *DAG = nullptr,
                     bool force = false);
@@ -1287,6 +1288,7 @@
     return Data;
   }
 
+  bool isAtomic() const { return isa<AtomicSDNode>(this); }
   bool isVolatile() const { return MemSDNodeBits.IsVolatile; }
   bool isNonTemporal() const { return MemSDNodeBits.IsNonTemporal; }
   bool isDereferenceable() const { return MemSDNodeBits.IsDereferenceable; }
Index: lib/CodeGen/MachineInstr.cpp
===================================================================
--- lib/CodeGen/MachineInstr.cpp
+++ lib/CodeGen/MachineInstr.cpp
@@ -1305,6 +1305,7 @@
 
   for (MachineMemOperand *MMO : memoperands()) {
     if (MMO->isVolatile()) return false;
+    if (MMO->isAtomic()) return false;
     if (MMO->isStore()) return false;
     if (MMO->isInvariant() && MMO->isDereferenceable())
       continue;
Index: lib/CodeGen/MachinePipeliner.cpp
===================================================================
--- lib/CodeGen/MachinePipeliner.cpp
+++ lib/CodeGen/MachinePipeliner.cpp
@@ -2766,7 +2766,8 @@
     return;
   SmallVector<MachineMemOperand *, 2> NewMMOs;
   for (MachineMemOperand *MMO : NewMI.memoperands()) {
-    if (MMO->isVolatile() || (MMO->isInvariant() && MMO->isDereferenceable()) ||
+    if (MMO->isVolatile() || MMO->isAtomic() ||
+        (MMO->isInvariant() && MMO->isDereferenceable()) ||
         (!MMO->getValue())) {
       NewMMOs.push_back(MMO);
       continue;
Index: lib/CodeGen/ScheduleDAGInstrs.cpp
===================================================================
--- lib/CodeGen/ScheduleDAGInstrs.cpp
+++ lib/CodeGen/ScheduleDAGInstrs.cpp
@@ -131,7 +131,7 @@
                                          const DataLayout &DL) {
   auto allMMOsOkay = [&]() {
     for (const MachineMemOperand *MMO : MI->memoperands()) {
-      if (MMO->isVolatile())
+      if (MMO->isVolatile() || MMO->isAtomic())
         return false;
 
       if (const PseudoSourceValue *PSV = MMO->getPseudoValue()) {
Index: lib/CodeGen/SelectionDAG/LegalizeVectorTypes.cpp
===================================================================
--- lib/CodeGen/SelectionDAG/LegalizeVectorTypes.cpp
+++ lib/CodeGen/SelectionDAG/LegalizeVectorTypes.cpp
@@ -4180,7 +4180,8 @@
 
   int LdWidth = LdVT.getSizeInBits();
   int WidthDiff = WidenWidth - LdWidth;
-  unsigned LdAlign = LD->isVolatile() ? 0 : Align; // Allow wider loads.
+  // Allow wider loads.
+  unsigned LdAlign = (LD->isVolatile() || LD->isAtomic()) ? 0 : Align;
 
   // Find the vector type that can load from.
   EVT NewVT = FindMemType(DAG, TLI, LdWidth, WidenVT, LdAlign, WidthDiff);
Index: lib/CodeGen/SelectionDAG/SelectionDAG.cpp
===================================================================
--- lib/CodeGen/SelectionDAG/SelectionDAG.cpp
+++ lib/CodeGen/SelectionDAG/SelectionDAG.cpp
@@ -8829,7 +8829,7 @@
 
   // Loads don't have side effects, look through them.
   if (LoadSDNode *Ld = dyn_cast<LoadSDNode>(*this)) {
-    if (!Ld->isVolatile())
+    if (!Ld->isVolatile() && !Ld->isAtomic())
       return Ld->getChain().reachesChainWithoutSideEffects(Dest, Depth-1);
   }
   return false;
@@ -8980,6 +8980,8 @@
                                                   int Dist) const {
   if (LD->isVolatile() || Base->isVolatile())
     return false;
+  if (LD->isAtomic() || Base->isAtomic())
+    return false;
   if (LD->isIndexed() || Base->isIndexed())
     return false;
   if (LD->getChain() != Base->getChain())
Index: lib/CodeGen/SelectionDAG/TargetLowering.cpp
===================================================================
--- lib/CodeGen/SelectionDAG/TargetLowering.cpp
+++ lib/CodeGen/SelectionDAG/TargetLowering.cpp
@@ -2379,7 +2379,7 @@
       LoadSDNode *Lod = cast<LoadSDNode>(N0.getOperand(0));
       APInt bestMask;
       unsigned bestWidth = 0, bestOffset = 0;
-      if (!Lod->isVolatile() && Lod->isUnindexed()) {
+      if (!Lod->isVolatile() && !Lod->isAtomic() && Lod->isUnindexed()) {
         unsigned origWidth = N0.getValueSizeInBits();
         unsigned maskWidth = origWidth;
         // We can narrow (e.g.) 16-bit extending loads on 32-bit target to