Index: lib/Target/Sparc/LeonFeatures.td
===================================================================
--- lib/Target/Sparc/LeonFeatures.td
+++ lib/Target/Sparc/LeonFeatures.td
@@ -58,3 +58,7 @@
   "true",
   "LEON erratum fix: Fix FDIVS/FDIVD/FSQRTS/FSQRTD instructions with NOPs and floating-point store" 
 >;
+
+def LeonCycleCounter
+  : SubtargetFeature<"leoncyclecounter", "HasLeonCycleCounter", "true",
+                     "Use the Leon cycle counter register">;
Index: lib/Target/Sparc/Sparc.td
===================================================================
--- lib/Target/Sparc/Sparc.td
+++ lib/Target/Sparc/Sparc.td
@@ -159,7 +159,7 @@
 // LEON 4 FT (GR740) 
 // TO DO: Place-holder: Processor specific features will be added *very* soon here.
 def : Processor<"gr740", LEON4Itineraries, 
-                [FeatureLeon, UMACSMACSupport, LeonCASA]>;
+                [FeatureLeon, UMACSMACSupport, LeonCASA, LeonCycleCounter]>;
 
 //===----------------------------------------------------------------------===//
 // Declare the target which we are implementing
Index: lib/Target/Sparc/SparcISelLowering.cpp
===================================================================
--- lib/Target/Sparc/SparcISelLowering.cpp
+++ lib/Target/Sparc/SparcISelLowering.cpp
@@ -1841,6 +1841,9 @@
     setOperationAction(ISD::FMUL, MVT::f32, Promote);
   }
 
+  if (Subtarget->hasLeonCycleCounter())
+    setOperationAction(ISD::READCYCLECOUNTER, MVT::i64, Custom);
+
   setOperationAction(ISD::INTRINSIC_WO_CHAIN, MVT::Other, Custom);
 
   setMinFunctionAlignment(2);
@@ -3587,7 +3590,16 @@
                                   getLibcallName(libCall),
                                   1));
     return;
-
+  case ISD::READCYCLECOUNTER: {
+    assert(Subtarget->hasLeonCycleCounter());
+    SDValue Lo = DAG.getCopyFromReg(N->getOperand(0), dl, SP::ASR23, MVT::i32);
+    SDValue Hi = DAG.getCopyFromReg(Lo, dl, SP::G0, MVT::i32);
+    SDValue Ops[] = { Lo, Hi };
+    SDValue Pair = DAG.getNode(ISD::BUILD_PAIR, dl, MVT::i64, Ops);
+    Results.push_back(Pair);
+    Results.push_back(N->getOperand(0));
+    return;
+  }
   case ISD::SINT_TO_FP:
   case ISD::UINT_TO_FP:
     // Custom lower only if it involves f128 or i64.
Index: lib/Target/Sparc/SparcRegisterInfo.cpp
===================================================================
--- lib/Target/Sparc/SparcRegisterInfo.cpp
+++ lib/Target/Sparc/SparcRegisterInfo.cpp
@@ -95,6 +95,9 @@
     }
   }
 
+  if (Subtarget.hasLeonCycleCounter())
+    Reserved.set(SP::ASR23);
+
   return Reserved;
 }
 
Index: lib/Target/Sparc/SparcSubtarget.h
===================================================================
--- lib/Target/Sparc/SparcSubtarget.h
+++ lib/Target/Sparc/SparcSubtarget.h
@@ -50,6 +50,7 @@
   bool InsertNOPLoad;
   bool FixAllFDIVSQRT;
   bool DetectRoundChange;
+  bool HasLeonCycleCounter;
 
   SparcInstrInfo InstrInfo;
   SparcTargetLowering TLInfo;
@@ -95,6 +96,7 @@
   bool insertNOPLoad() const { return InsertNOPLoad; }
   bool fixAllFDIVSQRT() const { return FixAllFDIVSQRT; }
   bool detectRoundChange() const { return DetectRoundChange; }
+  bool hasLeonCycleCounter() const { return HasLeonCycleCounter; }
 
   /// ParseSubtargetFeatures - Parses features string setting specified
   /// subtarget options.  Definition of function is auto generated by tblgen.
Index: lib/Target/Sparc/SparcSubtarget.cpp
===================================================================
--- lib/Target/Sparc/SparcSubtarget.cpp
+++ lib/Target/Sparc/SparcSubtarget.cpp
@@ -47,6 +47,7 @@
   InsertNOPLoad = false;
   FixAllFDIVSQRT = false;
   DetectRoundChange = false;
+  HasLeonCycleCounter = false;
 
   // Determine default and user specified characteristics
   std::string CPUName = CPU;
Index: test/CodeGen/SPARC/readcycle.ll
===================================================================
--- /dev/null
+++ test/CodeGen/SPARC/readcycle.ll
@@ -0,0 +1,11 @@
+; RUN: llc < %s -march=sparc -mcpu=gr740 -verify-machineinstrs | FileCheck %s
+; CHECK: rd %asr23, %o1
+; CHECK: mov %g0, %o0
+
+define i64 @test() {
+entry:
+  %0 = call i64 @llvm.readcyclecounter()
+  ret i64 %0
+}
+
+declare i64 @llvm.readcyclecounter()