Index: include/llvm/IR/IntrinsicsX86.td
===================================================================
--- include/llvm/IR/IntrinsicsX86.td
+++ include/llvm/IR/IntrinsicsX86.td
@@ -8709,3 +8709,14 @@
   def int_x86_sha256msg2 : GCCBuiltin<"__builtin_ia32_sha256msg2">,
       Intrinsic<[llvm_v4i32_ty], [llvm_v4i32_ty, llvm_v4i32_ty], [IntrNoMem]>;
 }
+
+//===----------------------------------------------------------------------===//
+// Thread synchronization ops with timer.
+let TargetPrefix = "x86" in {
+  def int_x86_monitorx
+      : GCCBuiltin<"__builtin_ia32_monitorx">,
+        Intrinsic<[], [ llvm_ptr_ty, llvm_i32_ty, llvm_i32_ty ], []>;
+  def int_x86_mwaitx
+      : GCCBuiltin<"__builtin_ia32_mwaitx">,
+        Intrinsic<[], [ llvm_i32_ty, llvm_i32_ty, llvm_i32_ty ], []>;
+}
Index: lib/Support/Host.cpp
===================================================================
--- lib/Support/Host.cpp
+++ lib/Support/Host.cpp
@@ -252,6 +252,7 @@
   GetX86CpuIDAndInfo(0x80000001, &EAX, &EBX, &ECX, &EDX);
   bool Em64T = (EDX >> 29) & 0x1;
   bool HasTBM = (ECX >> 21) & 0x1;
+  bool HasMWAITX = (ECX >> 29) & 0x1;
 
   if (memcmp(text.c, "GenuineIntel", 12) == 0) {
     switch (Family) {
@@ -802,6 +803,7 @@
   Features["xop"]    = HasExtLeaf1 && ((ECX >> 11) & 1) && HasAVXSave;
   Features["fma4"]   = HasExtLeaf1 && ((ECX >> 16) & 1) && HasAVXSave;
   Features["tbm"]    = HasExtLeaf1 && ((ECX >> 21) & 1);
+  Features["mwaitx"] = HasExtLeaf1 && ((ECX >> 29) & 1);
 
   bool HasLeaf7 = MaxLevel >= 7 &&
                   !GetX86CpuIDAndInfoEx(0x7, 0x0, &EAX, &EBX, &ECX, &EDX);
Index: lib/Target/X86/X86.td
===================================================================
--- lib/Target/X86/X86.td
+++ lib/Target/X86/X86.td
@@ -198,6 +198,8 @@
                                       "Support RDSEED instruction">;
 def FeatureLAHFSAHF : SubtargetFeature<"sahf", "HasLAHFSAHF", "true",
                                        "Support LAHF and SAHF instructions">;
+def FeatureMWAITX  : SubtargetFeature<"mwaitx", "HasMWAITX", "true",
+                                      "Enable MONITORX/MWAITX timer functionality">;
 def FeatureMPX     : SubtargetFeature<"mpx", "HasMPX", "true",
                                       "Support MPX instructions">;
 def FeatureLEAForSP : SubtargetFeature<"lea-sp", "UseLeaForSP", "true",
@@ -728,7 +730,8 @@
   FeatureFMA,
   FeatureXSAVEOPT,
   FeatureFSGSBase,
-  FeatureLAHFSAHF
+  FeatureLAHFSAHF,
+  FeatureMWAITX
 ]>;
 
 def : Proc<"geode",           [FeatureX87, FeatureSlowUAMem16, Feature3DNowA]>;
Index: lib/Target/X86/X86ISelLowering.cpp
===================================================================
--- lib/Target/X86/X86ISelLowering.cpp
+++ lib/Target/X86/X86ISelLowering.cpp
@@ -22221,7 +22221,8 @@
 }
 
 static MachineBasicBlock *emitMonitor(MachineInstr *MI, MachineBasicBlock *BB,
-                                      const X86Subtarget &Subtarget) {
+                                      const X86Subtarget &Subtarget,
+                                      unsigned Opc) {
   DebugLoc dl = MI->getDebugLoc();
   const TargetInstrInfo *TII = Subtarget.getInstrInfo();
   // Address into RAX/EAX, other two args into ECX, EDX.
@@ -22238,7 +22239,7 @@
     .addReg(MI->getOperand(ValOps+1).getReg());
 
   // The instruction doesn't actually take any operands though.
-  BuildMI(*BB, MI, dl, TII->get(X86::MONITORrrr));
+  BuildMI(*BB, MI, dl, TII->get(Opc));
 
   MI->eraseFromParent(); // The pseudo is gone now.
   return BB;
@@ -23739,7 +23740,9 @@
 
   // Thread synchronization.
   case X86::MONITOR:
-    return emitMonitor(MI, BB, Subtarget);
+    return emitMonitor(MI, BB, Subtarget, X86::MONITORrrr);
+  case X86::MONITORX:
+    return emitMonitor(MI, BB, Subtarget, X86::MONITORXrrr);
   // PKU feature
   case X86::WRPKRU:
     return emitWRPKRU(MI, BB, Subtarget);
Index: lib/Target/X86/X86InstrInfo.td
===================================================================
--- lib/Target/X86/X86InstrInfo.td
+++ lib/Target/X86/X86InstrInfo.td
@@ -847,6 +847,7 @@
 def HasRDSEED    : Predicate<"Subtarget->hasRDSEED()">;
 def HasPrefetchW : Predicate<"Subtarget->hasPRFCHW()">;
 def HasLAHFSAHF  : Predicate<"Subtarget->hasLAHFSAHF()">;
+def HasMWAITX    : Predicate<"Subtarget->hasMWAITX()">;
 def FPStackf32   : Predicate<"!Subtarget->hasSSE1()">;
 def FPStackf64   : Predicate<"!Subtarget->hasSSE2()">;
 def HasMPX       : Predicate<"Subtarget->hasMPX()">;
@@ -2401,22 +2402,34 @@
 //===----------------------------------------------------------------------===//
 // MONITORX/MWAITX Instructions
 //
-let SchedRW = [WriteSystem] in {
-let Uses = [EAX, ECX, EDX] in
-def MONITORXrrr : I<0x01, MRM_FA, (outs), (ins), "monitorx", [],
-                    IIC_SSE_MONITOR>, TB;
-let Uses = [ECX, EAX, EBX] in
-def MWAITXrr   : I<0x01, MRM_FB, (outs), (ins), "mwaitx", [], IIC_SSE_MWAIT>,
-                 TB;
+let SchedRW = [ WriteSystem ] in {
+  let usesCustomInserter = 1 in {
+    def MONITORX : PseudoI<(outs), (ins i32mem:$src1, GR32:$src2, GR32:$src3),
+                           [(int_x86_monitorx addr:$src1, GR32:$src2, GR32:$src3)]>,
+                   Requires<[ HasMWAITX ]>;
+  }
+
+  let Uses = [ EAX, ECX, EDX ] in {
+    def MONITORXrrr : I<0x01, MRM_FA, (outs), (ins), "monitorx", [], IIC_SSE_MONITORX>,
+                      TB, Requires<[ HasMWAITX ]>;
+  }
+
+  let Uses = [ ECX, EAX, EBX ] in {
+    def MWAITXrrr : I<0x01, MRM_FB, (outs), (ins), "mwaitx", 
+                    [(int_x86_mwaitx ECX, EAX, EBX)], IIC_SSE_MWAITX>,
+                    TB, Requires<[ HasMWAITX ]>;
+  }
 } // SchedRW
 
-def : InstAlias<"mwaitx\t{%eax, %ecx, %ebx|ebx, ecx, eax}", (MWAITXrr)>, Requires<[Not64BitMode]>;
-def : InstAlias<"mwaitx\t{%rax, %rcx, %rbx|rbx, rcx, rax}", (MWAITXrr)>, Requires<[In64BitMode]>;
+def : InstAlias<"mwaitx\t{%eax, %ecx, %ebx|ebx, ecx, eax}", (MWAITXrrr)>,
+      Requires<[ Not64BitMode ]>;
+def : InstAlias<"mwaitx\t{%rax, %rcx, %rbx|rbx, rcx, rax}", (MWAITXrrr)>,
+      Requires<[ In64BitMode ]>;
 
 def : InstAlias<"monitorx\t{%eax, %ecx, %edx|edx, ecx, eax}", (MONITORXrrr)>,
-      Requires<[Not64BitMode]>;
+      Requires<[ Not64BitMode ]>;
 def : InstAlias<"monitorx\t{%rax, %rcx, %rdx|rdx, rcx, rax}", (MONITORXrrr)>,
-      Requires<[In64BitMode]>;
+      Requires<[ In64BitMode ]>;
 
 //===----------------------------------------------------------------------===//
 // CLZERO Instruction
Index: lib/Target/X86/X86InstrSSE.td
===================================================================
--- lib/Target/X86/X86InstrSSE.td
+++ lib/Target/X86/X86InstrSSE.td
@@ -5849,6 +5849,7 @@
 let Uses = [EAX, ECX, EDX] in
 def MONITORrrr : I<0x01, MRM_C8, (outs), (ins), "monitor", [], IIC_SSE_MONITOR>,
                  TB, Requires<[HasSSE3]>;
+
 let Uses = [ECX, EAX] in
 def MWAITrr   : I<0x01, MRM_C9, (outs), (ins), "mwait",
                 [(int_x86_sse3_mwait ECX, EAX)], IIC_SSE_MWAIT>,
Index: lib/Target/X86/X86Schedule.td
===================================================================
--- lib/Target/X86/X86Schedule.td
+++ lib/Target/X86/X86Schedule.td
@@ -364,6 +364,8 @@
 def IIC_SSE_PALIGNRM : InstrItinClass;
 def IIC_SSE_MWAIT : InstrItinClass;
 def IIC_SSE_MONITOR : InstrItinClass;
+def IIC_SSE_MWAITX : InstrItinClass;
+def IIC_SSE_MONITORX : InstrItinClass;
 
 def IIC_SSE_PREFETCH : InstrItinClass;
 def IIC_SSE_PAUSE : InstrItinClass;
Index: lib/Target/X86/X86Subtarget.h
===================================================================
--- lib/Target/X86/X86Subtarget.h
+++ lib/Target/X86/X86Subtarget.h
@@ -164,6 +164,9 @@
   /// Processor has LAHF/SAHF instructions.
   bool HasLAHFSAHF;
 
+  /// Processor has MONITORX/MWAITX instructions.
+  bool HasMWAITX;
+
   /// Processor has Prefetch with intent to Write instruction
   bool HasPFPREFETCHWT1;
 
@@ -421,6 +424,7 @@
   bool hasPRFCHW() const { return HasPRFCHW; }
   bool hasRDSEED() const { return HasRDSEED; }
   bool hasLAHFSAHF() const { return HasLAHFSAHF; }
+  bool hasMWAITX() const { return HasMWAITX; }
   bool isBTMemSlow() const { return IsBTMemSlow; }
   bool isSHLDSlow() const { return IsSHLDSlow; }
   bool isUnalignedMem16Slow() const { return IsUAMem16Slow; }
Index: lib/Target/X86/X86Subtarget.cpp
===================================================================
--- lib/Target/X86/X86Subtarget.cpp
+++ lib/Target/X86/X86Subtarget.cpp
@@ -314,6 +314,7 @@
   HasPRFCHW = false;
   HasRDSEED = false;
   HasLAHFSAHF = false;
+  HasMWAITX = false;
   HasMPX = false;
   IsBTMemSlow = false;
   IsSHLDSlow = false;
Index: test/CodeGen/X86/mwaitx.ll
===================================================================
--- test/CodeGen/X86/mwaitx.ll
+++ test/CodeGen/X86/mwaitx.ll
@@ -0,0 +1,36 @@
+; RUN: llc < %s -mtriple=x86_64-linux -mattr=+mwaitx | FileCheck %s
+; RUN: llc < %s -mtriple=x86_64-win32 -mattr=+mwaitx | FileCheck %s -check-prefix=WIN64
+
+; CHECK-LABEL: foo:
+; CHECK: leaq    (%rdi), %rax
+; CHECK-NEXT: movl    %esi, %ecx
+; CHECK-NEXT: monitorx
+; WIN64-LABEL: foo:
+; WIN64:      leaq    (%rcx), %rax
+; WIN64-NEXT: movl    %edx, %ecx
+; WIN64-NEXT: movl    %r8d, %edx
+; WIN64-NEXT: monitorx
+define void @foo(i8* %P, i32 %E, i32 %H) nounwind {
+entry:
+  tail call void @llvm.x86.monitorx(i8* %P, i32 %E, i32 %H)
+  ret void
+}
+
+declare void @llvm.x86.monitorx(i8*, i32, i32) nounwind
+
+; CHECK-LABEL: bar:
+; CHECK: movl    %edi, %ecx
+; CHECK-NEXT: movl    %esi, %eax
+; CHECK-NEXT: movl    %edx, %ebx
+; CHECK-NEXT: mwaitx
+; WIN64-LABEL: bar:
+; WIN64:      movl    %edx, %eax
+; WIN64:      movl    %r8d, %ebx
+; WIN64-NEXT: mwaitx
+define void @bar(i32 %E, i32 %H, i32 %C) nounwind {
+entry:
+  tail call void @llvm.x86.mwaitx(i32 %E, i32 %H, i32 %C)
+  ret void
+}
+
+declare void @llvm.x86.mwaitx(i32, i32, i32) nounwind
Index: test/MC/Disassembler/X86/simple-tests.txt
===================================================================
--- test/MC/Disassembler/X86/simple-tests.txt
+++ test/MC/Disassembler/X86/simple-tests.txt
@@ -51,6 +51,12 @@
 # CHECK: rdtscp
 0x0f 0x01 0xf9
 
+# CHECK: monitorx 
+0x0f 0x01 0xfa
+
+# CHECK: mwaitx 
+0x0f 0x01 0xfb
+
 # CHECK: vmxon
 0xf3 0x0f 0xc7 0x30
 
Index: test/MC/Disassembler/X86/x86-32.txt
===================================================================
--- test/MC/Disassembler/X86/x86-32.txt
+++ test/MC/Disassembler/X86/x86-32.txt
@@ -90,6 +90,12 @@
 # CHECK: rdtscp
 0x0f 0x01 0xf9
 
+# CHECK: monitorx
+0x0f 0x01 0xfa
+
+# CHECK: mwaitx
+0x0f 0x01 0xfb
+
 # CHECK: vmxon
 0xf3 0x0f 0xc7 0x30