Index: lib/Target/X86/AsmParser/X86AsmParser.cpp
===================================================================
--- lib/Target/X86/AsmParser/X86AsmParser.cpp
+++ lib/Target/X86/AsmParser/X86AsmParser.cpp
@@ -1515,7 +1515,8 @@
     Name == "lock" || Name == "rep" ||
     Name == "repe" || Name == "repz" ||
     Name == "repne" || Name == "repnz" ||
-    Name == "rex64" || Name == "data16";
+    Name == "rex64" || Name == "data16" ||
+    Name == "xacquire" || Name == "xrelease";
 
 
   // This does the actual operand parsing.  Don't parse any more if we have a
Index: lib/Target/X86/InstPrinter/X86ATTInstPrinter.cpp
===================================================================
--- lib/Target/X86/InstPrinter/X86ATTInstPrinter.cpp
+++ lib/Target/X86/InstPrinter/X86ATTInstPrinter.cpp
@@ -47,6 +47,16 @@
   if (TSFlags & X86II::LOCK)
     OS << "\tlock\n";
 
+  if (TSFlags & X86II::XACQUIRE) {
+    assert(!(TSFlags & X86II::XRELEASE) && "unknown HLE prefix hints!");
+    OS << "\txacquire\n";
+  }
+
+  if (TSFlags & X86II::XRELEASE) {
+    assert(!(TSFlags & X86II::XACQUIRE) && "unknown HLE prefix hints!");
+    OS << "\txrelease\n";
+  }
+
   // Try to print any aliases first.
   if (!printAliasInstr(MI, OS))
     printInstruction(MI, OS);
Index: lib/Target/X86/InstPrinter/X86IntelInstPrinter.cpp
===================================================================
--- lib/Target/X86/InstPrinter/X86IntelInstPrinter.cpp
+++ lib/Target/X86/InstPrinter/X86IntelInstPrinter.cpp
@@ -39,6 +39,16 @@
   if (TSFlags & X86II::LOCK)
     OS << "\tlock\n";
 
+  if (TSFlags & X86II::XACQUIRE) {
+    assert(!(TSFlags & X86II::XRELEASE) && "unknown HLE prefix hints!");
+    OS << "\txacquire\n";
+  }
+
+  if (TSFlags & X86II::XRELEASE) {
+    assert(!(TSFlags & X86II::XACQUIRE) && "unknown HLE prefix hints!");
+    OS << "\txrelease\n";
+  }
+
   printInstruction(MI, OS);
 
   // Next always print the annotation.
Index: lib/Target/X86/MCTargetDesc/X86BaseInfo.h
===================================================================
--- lib/Target/X86/MCTargetDesc/X86BaseInfo.h
+++ lib/Target/X86/MCTargetDesc/X86BaseInfo.h
@@ -415,9 +415,19 @@
     LOCKShift = FPTypeShift + 3,
     LOCK = 1 << LOCKShift,
 
+    // TSX/HLE prefix
+    TSXShift = LOCKShift + 1,
+    TSXMask  = 3 << TSXShift,
+
+    // XACQUIRE - Specifies that this instruction has XACQUIRE HLE prefix hint
+    XACQUIRE = 1 << TSXShift,
+
+    // XRELEASE - Specifies that this instruction has XRELEASE HLE prefix hint
+    XRELEASE = 2 << TSXShift,
+
     // Segment override prefixes. Currently we just need ability to address
     // stuff in gs and fs segments.
-    SegOvrShift = LOCKShift + 1,
+    SegOvrShift = TSXShift + 2,
     SegOvrMask  = 3 << SegOvrShift,
     FS          = 1 << SegOvrShift,
     GS          = 2 << SegOvrShift,
Index: lib/Target/X86/MCTargetDesc/X86MCCodeEmitter.cpp
===================================================================
--- lib/Target/X86/MCTargetDesc/X86MCCodeEmitter.cpp
+++ lib/Target/X86/MCTargetDesc/X86MCCodeEmitter.cpp
@@ -851,6 +851,16 @@
   if (TSFlags & X86II::LOCK)
     EmitByte(0xF0, CurByte, OS);
 
+  if (TSFlags & X86II::XACQUIRE) {
+    assert(!(TSFlags & X86II::XRELEASE) && "unknown HLE prefix hints!");
+    EmitByte(0xF2, CurByte, OS);
+  }
+
+  if (TSFlags & X86II::XRELEASE) {
+    assert(!(TSFlags & X86II::XACQUIRE) && "unknown HLE prefix hints!");
+    EmitByte(0xF3, CurByte, OS);
+  }
+
   // Emit segment override opcode prefix as needed.
   EmitSegmentOverridePrefix(TSFlags, CurByte, MemOperand, MI, OS);
 
Index: lib/Target/X86/X86InstrFormats.td
===================================================================
--- lib/Target/X86/X86InstrFormats.td
+++ lib/Target/X86/X86InstrFormats.td
@@ -99,6 +99,8 @@
 class AdSize { bit hasAdSizePrefix = 1; }
 class REX_W  { bit hasREX_WPrefix = 1; }
 class LOCK   { bit hasLockPrefix = 1; }
+class XACQ   { bit hasXAcquire = 1; }
+class XREL   { bit hasXRelease = 1; }
 class SegFS  { bits<2> SegOvrBits = 1; }
 class SegGS  { bits<2> SegOvrBits = 2; }
 class TB     { bits<5> Prefix = 1; }
@@ -163,6 +165,8 @@
   bit hasREX_WPrefix  = 0;  // Does this inst require the REX.W prefix?
   FPFormat FPForm = NotFP;  // What flavor of FP instruction is this?
   bit hasLockPrefix = 0;    // Does this inst have a 0xF0 prefix?
+  bit hasXAcquire = 0;      // Does this instruction require an XACQUIRE prefix?
+  bit hasXRelease = 0;      // Does this instruction require an XRELEASE prefix?
   bits<2> SegOvrBits = 0;   // Segment override prefix.
   Domain ExeDomain = d;
   bit hasVEXPrefix = 0;     // Does this inst require a VEX prefix?
@@ -187,19 +191,21 @@
   let TSFlags{16-14} = ImmT.Value;
   let TSFlags{19-17} = FPForm.Value;
   let TSFlags{20}    = hasLockPrefix;
-  let TSFlags{22-21} = SegOvrBits;
-  let TSFlags{24-23} = ExeDomain.Value;
-  let TSFlags{32-25} = Opcode;
-  let TSFlags{33}    = hasVEXPrefix;
-  let TSFlags{34}    = hasVEX_WPrefix;
-  let TSFlags{35}    = hasVEX_4VPrefix;
-  let TSFlags{36}    = hasVEX_4VOp3Prefix;
-  let TSFlags{37}    = hasVEX_i8ImmReg;
-  let TSFlags{38}    = hasVEX_L;
-  let TSFlags{39}    = ignoresVEX_L;
-  let TSFlags{40}    = has3DNow0F0FOpcode;
-  let TSFlags{41}    = hasMemOp4Prefix;
-  let TSFlags{42}    = hasXOP_Prefix;
+  let TSFlags{21}    = hasXAcquire;
+  let TSFlags{22}    = hasXRelease;
+  let TSFlags{24-23} = SegOvrBits;
+  let TSFlags{26-25} = ExeDomain.Value;
+  let TSFlags{34-27} = Opcode;
+  let TSFlags{35}    = hasVEXPrefix;
+  let TSFlags{36}    = hasVEX_WPrefix;
+  let TSFlags{37}    = hasVEX_4VPrefix;
+  let TSFlags{38}    = hasVEX_4VOp3Prefix;
+  let TSFlags{39}    = hasVEX_i8ImmReg;
+  let TSFlags{40}    = hasVEX_L;
+  let TSFlags{41}    = ignoresVEX_L;
+  let TSFlags{42}    = has3DNow0F0FOpcode;
+  let TSFlags{43}    = hasMemOp4Prefix;
+  let TSFlags{44}    = hasXOP_Prefix;
 }
 
 class PseudoI<dag oops, dag iops, list<dag> pattern>
Index: lib/Target/X86/X86InstrInfo.td
===================================================================
--- lib/Target/X86/X86InstrInfo.td
+++ lib/Target/X86/X86InstrInfo.td
@@ -1460,6 +1460,10 @@
 def REPNE_PREFIX : I<0xF2, RawFrm, (outs),  (ins), "repne", []>;
 }
 
+// HLE hint prefix
+def : MnemonicAlias<"xacquire", "repne">;
+def : MnemonicAlias<"xrelease", "rep">;
+
 
 // String manipulation instructions
 def LODSB : I<0xAC, RawFrm, (outs), (ins), "lodsb", [], IIC_LODS>;
Index: test/MC/X86/x86_64-hle-encoding.s
===================================================================
--- /dev/null
+++ test/MC/X86/x86_64-hle-encoding.s
@@ -0,0 +1,25 @@
+// RUN: llvm-mc -triple x86_64-unknown-unknown --show-encoding %s | FileCheck %s
+
+// CHECK: lock
+// CHECK: encoding: [0xf0]
+// CHECK: repne
+// CHECK: encoding: [0xf2]
+	lock xacquire xaddq %rax, sym(%rip)
+
+// CHECK: repne
+// CHECK: encoding: [0xf2]
+// CHECK: lock
+// CHECK: encoding: [0xf0]
+	xacquire lock xaddq %rax, sym(%rip)
+
+// CHECK: lock
+// CHECK: encoding: [0xf0]
+// CHECK: rep
+// CHECK: encoding: [0xf3]
+	lock xrelease xaddq %rax, sym(%rip)
+
+// CHECK: rep
+// CHECK: encoding: [0xf3]
+// CHECK: lock
+// CHECK: encoding: [0xf0]
+	xrelease lock xaddq %rax, sym(%rip)