[perf2bolt] Accept - as a valid misprediction symbol

Summary:
As reported in GH-28 `perf` can produce `-` symbol for misprediction bit
if the bit is not supported by the kernel/HW. In this case we can ignore
the bit.

(cherry picked from commit 0a4ad831e49388ccc49ae15ecdb51c58b6eaafff)

bolt/src/DataAggregator.cpp

@@ -653,13 +653,19 @@ ErrorOr<LBREntry> DataAggregator::parseLBREntry() {
     return EC;
   StringRef MispredStr = MispredStrRes.get();
   if (MispredStr.size() != 1 ||
-      (MispredStr[0] != 'P' && MispredStr[0] != 'M')) {
+      (MispredStr[0] != 'P' && MispredStr[0] != 'M' && MispredStr[0] != '-')) {
     reportError("expected single char for mispred bit");
     Diag << "Found: " << MispredStr << "\n";
     return make_error_code(llvm::errc::io_error);
   }
   Res.Mispred = MispredStr[0] == 'M';
 
+  static bool MispredWarning = true;;
+  if (MispredStr[0] == '-' && MispredWarning) {
+    errs() << "PERF2BOLT-WARNING: misprediction bit is missing in profile\n";
+    MispredWarning = false;
+  }
+
   auto Rest = parseString(FieldSeparator, true);
   if (std::error_code EC = Rest.getError())
     return EC;

bolt/src/DataReader.cpp

@@ -268,7 +268,7 @@ DataReader::readPerfData(StringRef Path, raw_ostream &Diag) {
 }
 
 void DataReader::reportError(StringRef ErrorMsg) {
-  Diag << "Error reading bolt data input file: line " << Line << ", column "
+  Diag << "Error reading BOLT data input file: line " << Line << ", column "
        << Col << ": " << ErrorMsg << '\n';
 }