[PGO] Comment how function pointers for indirect calls are mapped to …

…function names

Summary:
Hopefully this will make it easier for the next person to figure all
this out...

Reviewers: bogner, davidxl

Subscribers: llvm-commits

Differential Revision: http://reviews.llvm.org/D18490

llvm-svn: 264612

compiler-rt/lib/profile/InstrProfData.inc

@@ -73,6 +73,8 @@ INSTR_PROF_DATA(const uint64_t, llvm::Type::getInt64Ty(Ctx), FuncHash, \
 INSTR_PROF_DATA(const IntPtrT, llvm::Type::getInt64PtrTy(Ctx), CounterPtr, \
                 ConstantExpr::getBitCast(CounterPtr, \
                 llvm::Type::getInt64PtrTy(Ctx)))
+// This is used to map function pointers for the indirect call targets to
+// function name hashes during the conversion from raw to merged profile data.
 INSTR_PROF_DATA(const IntPtrT, llvm::Type::getInt8PtrTy(Ctx), FunctionPointer, \
                 FunctionAddr)
 INSTR_PROF_DATA(IntPtrT, llvm::Type::getInt8PtrTy(Ctx), Values, \