Index: llvm/include/llvm/CodeGen/MachineInstr.h
===================================================================
--- llvm/include/llvm/CodeGen/MachineInstr.h
+++ llvm/include/llvm/CodeGen/MachineInstr.h
@@ -106,6 +106,7 @@
                                         // known to be exact.
     NoFPExcept   = 1 << 14,             // Instruction does not raise
                                         // floatint-point exceptions.
+    NoMerge      = 1 << 15,             // Instruction should not be merged
   };
 
 private:
Index: llvm/include/llvm/CodeGen/SelectionDAG.h
===================================================================
--- llvm/include/llvm/CodeGen/SelectionDAG.h
+++ llvm/include/llvm/CodeGen/SelectionDAG.h
@@ -278,6 +278,7 @@
   struct CallSiteDbgInfo {
     CallSiteInfo CSInfo;
     MDNode *HeapAllocSite = nullptr;
+    bool NoMerge;
   };
 
   DenseMap<const SDNode *, CallSiteDbgInfo> SDCallSiteDbgInfo;
@@ -1911,6 +1912,17 @@
     return It->second.HeapAllocSite;
   }
 
+  void addNoMergeSiteInfo(const SDNode *Node, bool NoMerge) {
+    SDCallSiteDbgInfo[Node].NoMerge = NoMerge;
+  }
+
+  bool getNoMergeSiteInfo(const SDNode *Node) {
+    auto I = SDCallSiteDbgInfo.find(Node);
+    if (I == SDCallSiteDbgInfo.end())
+      return false;
+    return I->second.NoMerge;
+  }
+  
   /// Return the current function's default denormal handling kind for the given
   /// floating point type.
   DenormalMode getDenormalMode(EVT VT) const {
Index: llvm/include/llvm/CodeGen/TargetLowering.h
===================================================================
--- llvm/include/llvm/CodeGen/TargetLowering.h
+++ llvm/include/llvm/CodeGen/TargetLowering.h
@@ -3608,6 +3608,7 @@
     bool IsReturnValueUsed : 1;
     bool IsConvergent      : 1;
     bool IsPatchPoint      : 1;
+    bool NoMerge           : 1;
 
     // IsTailCall should be modified by implementations of
     // TargetLowering::LowerCall that perform tail call conversions.
@@ -3631,7 +3632,7 @@
     CallLoweringInfo(SelectionDAG &DAG)
         : RetSExt(false), RetZExt(false), IsVarArg(false), IsInReg(false),
           DoesNotReturn(false), IsReturnValueUsed(true), IsConvergent(false),
-          IsPatchPoint(false), DAG(DAG) {}
+          IsPatchPoint(false), NoMerge(false), DAG(DAG) {}
 
     CallLoweringInfo &setDebugLoc(const SDLoc &dl) {
       DL = dl;
@@ -3680,6 +3681,7 @@
       IsReturnValueUsed = !Call.use_empty();
       RetSExt = Call.hasRetAttr(Attribute::SExt);
       RetZExt = Call.hasRetAttr(Attribute::ZExt);
+      NoMerge = Call.hasFnAttr(Attribute::NoMerge);
 
       Callee = Target;
 
Index: llvm/lib/CodeGen/BranchFolding.cpp
===================================================================
--- llvm/lib/CodeGen/BranchFolding.cpp
+++ llvm/lib/CodeGen/BranchFolding.cpp
@@ -355,6 +355,9 @@
         MBBI1->isInlineAsm()) {
       break;
     }
+    if (MBBI1->getFlag(MachineInstr::NoMerge) || 
+        MBBI2->getFlag(MachineInstr::NoMerge))
+      break;
     ++TailLen;
     I1 = MBBI1;
     I2 = MBBI2;
Index: llvm/lib/CodeGen/MIRPrinter.cpp
===================================================================
--- llvm/lib/CodeGen/MIRPrinter.cpp
+++ llvm/lib/CodeGen/MIRPrinter.cpp
@@ -778,6 +778,8 @@
     OS << "exact ";
   if (MI.getFlag(MachineInstr::NoFPExcept))
     OS << "nofpexcept ";
+  if (MI.getFlag(MachineInstr::NoMerge))
+    OS << "nomerge ";
 
   OS << TII->getName(MI.getOpcode());
   if (I < E)
Index: llvm/lib/CodeGen/MachineInstr.cpp
===================================================================
--- llvm/lib/CodeGen/MachineInstr.cpp
+++ llvm/lib/CodeGen/MachineInstr.cpp
@@ -1595,6 +1595,8 @@
     OS << "exact ";
   if (getFlag(MachineInstr::NoFPExcept))
     OS << "nofpexcept ";
+  if (getFlag(MachineInstr::NoMerge))
+    OS << "nomerge ";
 
   // Print the opcode name.
   if (TII)
Index: llvm/lib/CodeGen/SelectionDAG/ScheduleDAGSDNodes.cpp
===================================================================
--- llvm/lib/CodeGen/SelectionDAG/ScheduleDAGSDNodes.cpp
+++ llvm/lib/CodeGen/SelectionDAG/ScheduleDAGSDNodes.cpp
@@ -871,6 +871,10 @@
         DAG->getTarget().Options.EmitCallSiteInfo)
       MF.addCallArgsForwardingRegs(MI, DAG->getSDCallSiteInfo(Node));
 
+    if (DAG->getNoMergeSiteInfo(Node)) {
+      MI->setFlag(MachineInstr::MIFlag::NoMerge);
+    }
+
     return MI;
   };
 
Index: llvm/lib/Target/X86/X86ISelLowering.cpp
===================================================================
--- llvm/lib/Target/X86/X86ISelLowering.cpp
+++ llvm/lib/Target/X86/X86ISelLowering.cpp
@@ -4269,6 +4269,8 @@
     Chain = DAG.getNode(X86ISD::NT_CALL, dl, NodeTys, Ops);
   } else {
     Chain = DAG.getNode(X86ISD::CALL, dl, NodeTys, Ops);
+    // set nomerge.
+    DAG.addNoMergeSiteInfo(Chain.getNode(), CLI.NoMerge);
   }
   InFlag = Chain.getValue(1);
   DAG.addCallSiteInfo(Chain.getNode(), std::move(CSInfo));