[llvm-profgen] Fix perf script parsing issues

[wlei]

Summary

Fix two perf script parsing issues:

1. Redirect the error message to a new file. (the error message mixed in the perfscript could screw up the MMAP event line and cause a parsing failure)

2. Changed the MMap parsing error message to warning since the perfscript can still be parsed using the preferred address as base address.

[wenlei]

lgtm, thanks.

llvm/tools/llvm-profgen/PerfReader.cpp

PerfInputFile PerfScriptReader::convertPerfDataToTrace(
   StringRef PerfData = File.InputFile;
   // Run perf script to retrieve PIDs matching binary we're interested in.
   auto PerfExecutable = sys::Process::FindInEnvPath("PATH", "perf");
   if (!PerfExecutable) {
     exitWithError("Perf not found.");
   }
   std::string PerfPath = *PerfExecutable;
   std::string PerfTraceFile = PerfData.str() + ".script.tmp";
+  std::string ErrorFile = PerfData.str() + ".script.err.tmp";
   StringRef ScriptMMapArgs[] = {PerfPath, "script",   "--show-mmap-events",
                                 "-F",     "comm,pid", "-i",
                                 PerfData};
-  Optional<StringRef> Redirects[] = {llvm::None,                // Stdin
-                                     StringRef(PerfTraceFile),  // Stdout
-                                     StringRef(PerfTraceFile)}; // Stderr
+  Optional<StringRef> Redirects[] = {llvm::None,               // Stdin
+                                     StringRef(PerfTraceFile), // Stdout
+                                     StringRef(ErrorFile)};    // Stderr
   sys::ExecuteAndWait(PerfPath, ScriptMMapArgs, llvm::None, Redirects);
 
   // Collect the PIDs
   TraceStream TraceIt(PerfTraceFile);
   std::string PIDs;
   std::unordered_set<uint32_t> PIDSet;
   while (!TraceIt.isAtEoF()) {
     MMapEvent MMap;
enum EventIndex {
     PAGE_OFFSET = 4,
     BINARY_PATH = 5
   };
 
   Regex RegMmap2(Pattern);
   SmallVector<StringRef, 6> Fields;
   bool R = RegMmap2.match(Line, &Fields);
   if (!R) {
-    std::string ErrorMsg = "Cannot parse mmap event: " + Line.str() + " \n";
-    exitWithError(ErrorMsg);
+    std::string WarningMsg = "Cannot parse mmap event: " + Line.str() + " \n";
+    WithColor::warning() << WarningMsg;
   }
   Fields[PID].getAsInteger(10, MMap.PID);
   Fields[MMAPPED_ADDRESS].getAsInteger(0, MMap.Address);
   Fields[MMAPPED_SIZE].getAsInteger(0, MMap.Size);
   Fields[PAGE_OFFSET].getAsInteger(0, MMap.Offset);
   MMap.BinaryPath = Fields[BINARY_PATH];
   if (ShowMmapEvents) {
     outs() << "Mmap: Binary " << MMap.BinaryPath << " loaded at "