[Sparc] Add support for the cycle counter available in GR740

[dcederman]

Summary

The GR740 provides an up cycle counter in the registers ASR22 and ASR23. As these registers can not be read together atomically we only use the value of ASR23 for llvm.readcyclecounter(). The ASR23 register holds the 32 LSBs of the up-counter.

[jyknight]

I suppose if it was useful, you could use a loop to read both halves of the counter safely, e.g. upper=ASR22; loop: lower=ASR23; newupper=ASR22; if (newupper != upper) { upper = newupper; goto loop; }}.

But I have no idea if that would be useful, so this seems fine.

[dcederman]

Reserved register ASR23 to avoid error stating that register ASR23 is "an undefined physical register". Not sure if this is the correct solution, so putting this up for review again.

[jyknight]

I wonder if we perhaps shouldn't've modeled the ASR registers as registers at all (other than Y -- it's "special"). That seems to be what other targets do with their MSRs. Not sure if it really matters...

Anyways, having it be marked reserved seems correct. It may be simpler to just always mark ASR1-31 as reserved, though?

[dcederman]

Reserving registers ASR1-ASR31

[jyknight]

LGTM.

It's possibly only theoretical at the moment, since I don't know if anything both supports this and is little endian, but --
On a little endian system, will the registers be swapped; that is, would ASR22 hold the 32 LSB instead of ASR23?

[dcederman]

In D48638#1213699, @jyknight wrote:

LGTM.

It's possibly only theoretical at the moment, since I don't know if anything both supports this and is little endian, but --
On a little endian system, will the registers be swapped; that is, would ASR22 hold the 32 LSB instead of ASR23?

We are not aware of any little endian system that supports this at the moment, but as the registers cannot be read together as a 64-bit value we do not think there is a reason to swap the registers for little endian systems.

lib/Target/Sparc/LeonFeatures.td

 >;
 
 def FixAllFDIVSQRT : SubtargetFeature<
   "fixallfdivsqrt",
   "FixAllFDIVSQRT",
   "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">;

lib/Target/Sparc/Sparc.td

 
 // LEON 4 FT generic
 def : Processor<"leon4", LEON4Itineraries,
                 [FeatureLeon, UMACSMACSupport, LeonCASA]>;
 
 // 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
 //===----------------------------------------------------------------------===//
 
 def SparcAsmWriter : AsmWriter {
   string AsmWriterClassName  = "InstPrinter";
   int PassSubtarget = 1;

lib/Target/Sparc/SparcISelLowering.cpp

if (Subtarget->fixAllFDIVSQRT()) {
     setOperationAction(ISD::FDIV, MVT::f32, Promote);
     setOperationAction(ISD::FSQRT, MVT::f32, Promote);
   }
 
   if (Subtarget->hasNoFMULS()) {
     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);
 
   computeRegisterProperties(Subtarget->getRegisterInfo());
 }
 
 bool SparcTargetLowering::useSoftFloat() const {
libCall = ((N->getOpcode() == ISD::FP_TO_SINT)
                ? RTLIB::FPTOSINT_F128_I64
                : RTLIB::FPTOUINT_F128_I64);
 
     Results.push_back(LowerF128Op(SDValue(N, 0),
                                   DAG,
                                   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.
     if (N->getValueType(0) != MVT::f128
         || N->getOperand(0).getValueType() != MVT::i64)
       return;
 
     libCall = ((N->getOpcode() == ISD::SINT_TO_FP)

lib/Target/Sparc/SparcSubtarget.h

class SparcSubtarget : public SparcGenSubtargetInfo {
   bool HasNoFMULS;
 
   // LEON features
   bool HasUmacSmac;
   bool HasLeonCasa;
   bool InsertNOPLoad;
   bool FixAllFDIVSQRT;
   bool DetectRoundChange;
+  bool HasLeonCycleCounter;
 
   SparcInstrInfo InstrInfo;
   SparcTargetLowering TLInfo;
   SelectionDAGTargetInfo TSInfo;
   SparcFrameLowering FrameLowering;
 
 public:
   SparcSubtarget(const Triple &TT, const std::string &CPU,
public:
   bool hasNoFMULS() const { return HasNoFMULS; }
 
   // Leon options
   bool hasUmacSmac() const { return HasUmacSmac; }
   bool hasLeonCasa() const { return HasLeonCasa; }
   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.
   void ParseSubtargetFeatures(StringRef CPU, StringRef FS);
   SparcSubtarget &initializeSubtargetDependencies(StringRef CPU, StringRef FS);
 
   bool is64Bit() const { return Is64Bit; }
 

lib/Target/Sparc/SparcSubtarget.cpp

SparcSubtarget &SparcSubtarget::initializeSubtargetDependencies(StringRef CPU,
   HasNoFMULS = false;
 
   // Leon features
   HasLeonCasa = false;
   HasUmacSmac = false;
   InsertNOPLoad = false;
   FixAllFDIVSQRT = false;
   DetectRoundChange = false;
+  HasLeonCycleCounter = false;
 
   // Determine default and user specified characteristics
   std::string CPUName = CPU;
   if (CPUName.empty())
     CPUName = (Is64Bit) ? "v9" : "v8";
 
   // Parse features string.
   ParseSubtargetFeatures(CPUName, FS);

test/CodeGen/SPARC/readcycle.ll

+; RUN: llc < %s -march=sparc -mcpu=gr740 | 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()