[PGO] make the number of records for each value site metada adjustable

[xur]

Summary

Add a parameter in annotateValueSite() to control the max number of records written
to the value profile meta data for each value site. The default is kept as the
current value of 3.

[davidxl]

need to add a unit test.

[xur]

I expanded an existing unit test to test the added feature. I hope this is ok.

[davidxl]

lgtm

include/llvm/ProfileData/InstrProf.h

 #define VALUE_PROF_KIND(Enumerator, Value) Enumerator = Value,
 #include "llvm/ProfileData/InstrProfData.inc"
 };
 
 struct InstrProfRecord;
 
 /// Get the value profile data for value site \p SiteIdx from \p InstrProfR
 /// and annotate the instruction \p Inst with the value profile meta data.
+/// Annotate up to \p MaxMDCount (default 3) number of records per value site.
 void annotateValueSite(Module &M, Instruction &Inst,
                        const InstrProfRecord &InstrProfR,
-                       InstrProfValueKind ValueKind, uint32_t SiteIndx);
+                       InstrProfValueKind ValueKind, uint32_t SiteIndx,
+                       uint32_t MaxMDCount = 3);
 /// Extract the value profile data from \p Inst which is annotated with
 /// value profile meta data. Return false if there is no value data annotated,
 /// otherwise  return true.
 bool getValueProfDataFromInst(const Instruction &Inst,
                               InstrProfValueKind ValueKind,
                               uint32_t MaxNumValueData,
                               InstrProfValueData ValueData[],
                               uint32_t &ActualNumValueData, uint64_t &TotalC);

lib/ProfileData/InstrProf.cpp

for (uint32_t K = 0; K < NumValueKinds; K++) {
     VR = NVR;
   }
   sys::swapByteOrder<uint32_t>(TotalSize);
   sys::swapByteOrder<uint32_t>(NumValueKinds);
 }
 
 void annotateValueSite(Module &M, Instruction &Inst,
                        const InstrProfRecord &InstrProfR,
-                       InstrProfValueKind ValueKind, uint32_t SiteIdx) {
+                       InstrProfValueKind ValueKind, uint32_t SiteIdx,
+                       uint32_t MaxMDCount) {
   uint32_t NV = InstrProfR.getNumValueDataForSite(ValueKind, SiteIdx);
 
   uint64_t Sum = 0;
   std::unique_ptr<InstrProfValueData[]> VD =
       InstrProfR.getValueForSite(ValueKind, SiteIdx, &Sum);
 
   LLVMContext &Ctx = M.getContext();
   MDBuilder MDHelper(Ctx);
   SmallVector<Metadata *, 3> Vals;
   // Tag
   Vals.push_back(MDHelper.createString("VP"));
   // Value Kind
   Vals.push_back(MDHelper.createConstant(
       ConstantInt::get(Type::getInt32Ty(Ctx), ValueKind)));
   // Total Count
   Vals.push_back(
       MDHelper.createConstant(ConstantInt::get(Type::getInt64Ty(Ctx), Sum)));
 
   // Value Profile Data
-  uint32_t MDCount = 3;
+  uint32_t MDCount = MaxMDCount;
   for (uint32_t I = 0; I < NV; ++I) {
     Vals.push_back(MDHelper.createConstant(
         ConstantInt::get(Type::getInt64Ty(Ctx), VD[I].Value)));
     Vals.push_back(MDHelper.createConstant(
         ConstantInt::get(Type::getInt64Ty(Ctx), VD[I].Count)));
     if (--MDCount == 0)
       break;
   }