[BOLT] Add itrace aggregation for AUX data (#70426)

If you have a perf.data with Arm ETM data the only way to use perf2bolt
with Branch Aggregation is to first run `perf inject --itrace=l64i1us -o
perf-brstack.data` and then pass the new perf-brstack.data into
perf2bolt. perf2bolt then runs `perf script -F pid,ip,brstack` to
produce the brstacks.

This PR adds `--itrace` arg to perf2bolt to enable Itrace Aggregation.
It takes a string which is what is passed to the `perf script -F
pid,ip,brstack --itrace={0}`. This command produces the brstacks without
having to run perf inject and creating a new perf.data file.

Author: jonathandavies-arm

bolt/lib/Profile/DataAggregator.cpp

@@ -46,6 +46,11 @@ static cl::opt<bool>
                      cl::desc("aggregate basic samples (without LBR info)"),
                      cl::cat(AggregatorCategory));
 
+static cl::opt<std::string>
+    ITraceAggregation("itrace",
+                      cl::desc("Generate LBR info with perf itrace argument"),
+                      cl::cat(AggregatorCategory));
+
 static cl::opt<bool>
 FilterMemProfile("filter-mem-profile",
   cl::desc("if processing a memory profile, filter out stack or heap accesses "
@@ -163,16 +168,23 @@ void DataAggregator::start() {
 
   findPerfExecutable();
 
-  if (opts::BasicAggregation)
+  if (opts::BasicAggregation) {
     launchPerfProcess("events without LBR",
                       MainEventsPPI,
                       "script -F pid,event,ip",
                       /*Wait = */false);
-  else
+  } else if (!opts::ITraceAggregation.empty()) {
+    std::string ItracePerfScriptArgs = llvm::formatv(
+        "script -F pid,ip,brstack --itrace={0}", opts::ITraceAggregation);
+    launchPerfProcess("branch events with itrace", MainEventsPPI,
+                      ItracePerfScriptArgs.c_str(),
+                      /*Wait = */ false);
+  } else {
     launchPerfProcess("branch events",
                       MainEventsPPI,
                       "script -F pid,ip,brstack",
                       /*Wait = */false);
+  }
 
   // Note: we launch script for mem events regardless of the option, as the
   //       command fails fairly fast if mem events were not collected.