[llvm-exegesis] Fix SNB counter definition and handling.

[courbet]

Summary

SNB is the only one that has P23 as a single proc res.

[lebedev.ri]

Thanks, that fixed PR39470!

tools/llvm-exegesis/lib/BenchmarkRunner.cpp

FunctionExecutorImpl(const LLVMState &State,
         Scratch(Scratch) {}
 
 private:
   llvm::Expected<int64_t> runAndMeasure(const char *Counters) const override {
     // We sum counts when there are several counters for a single ProcRes
     // (e.g. P23 on SandyBridge).
     int64_t CounterValue = 0;
     llvm::SmallVector<llvm::StringRef, 2> CounterNames;
-    llvm::StringRef(Counters).split(CounterNames, ',');
+    llvm::StringRef(Counters).split(CounterNames, '+');
     char *const ScratchPtr = Scratch->ptr();
-    for (const auto &CounterName : CounterNames) {
+    for (auto &CounterName : CounterNames) {
+      CounterName = CounterName.trim();
       pfm::PerfEvent PerfEvent(CounterName);
       if (!PerfEvent.valid())
         llvm::report_fatal_error(
-            llvm::Twine("invalid perf event ").concat(Counters));
+            llvm::Twine("invalid perf event '").concat(CounterName).concat("'"));
       pfm::Counter Counter(PerfEvent);
       Scratch->clear();
       {
         llvm::CrashRecoveryContext CRC;
         llvm::CrashRecoveryContext::Enable();
         const bool Crashed = !CRC.RunSafely([this, &Counter, ScratchPtr]() {
           Counter.start();
           this->Function(ScratchPtr);