[llvm-exegesis] Fix D80610.

[courbet]

Summary

Using a .data() member on a StringRef was discarding the StringRef
size, breaking llvm-exegesis on machines with counter sums (e.g.
Zen2).

[kadircet]

LGTM

[courbet]

Thanks

[oontvoo]

Thanks for the fix, Clement !
Sorry for the late response, this was a bit early in my timezone. :-)

llvm/tools/llvm-exegesis/lib/BenchmarkRunner.cpp

Expected<int64_t> runAndMeasure(const char *Counters) const override {
     // (e.g. P23 on SandyBridge).
     int64_t CounterValue = 0;
     SmallVector<StringRef, 2> CounterNames;
     StringRef(Counters).split(CounterNames, '+');
     char *const ScratchPtr = Scratch->ptr();
     for (auto &CounterName : CounterNames) {
       CounterName = CounterName.trim();
       auto CounterOrError =
-          State.getExegesisTarget().createCounter(CounterName.data(), State);
+          State.getExegesisTarget().createCounter(CounterName, State);
 
       if (!CounterOrError)
         return CounterOrError.takeError();
 
       pfm::Counter *Counter = CounterOrError.get().get();
       Scratch->clear();
       {
         CrashRecoveryContext CRC;

llvm/tools/llvm-exegesis/lib/Target.h

 
 class ExegesisTarget {
 public:
   explicit ExegesisTarget(ArrayRef<CpuAndPfmCounters> CpuPfmCounters)
       : CpuPfmCounters(CpuPfmCounters) {}
 
   // Targets can use this to create target-specific perf counters.
   virtual Expected<std::unique_ptr<pfm::Counter>>
-  createCounter(const char *CounterName, const LLVMState &State) const;
+  createCounter(StringRef CounterName, const LLVMState &State) const;
 
   // Targets can use this to add target-specific passes in assembleToStream();
   virtual void addTargetSpecificPasses(PassManagerBase &PM) const {}
 
   // Generates code to move a constant into a the given register.
   // Precondition: Value must fit into Reg.
   virtual std::vector<MCInst> setRegTo(const MCSubtargetInfo &STI, unsigned Reg,
                                        const APInt &Value) const = 0;

llvm/tools/llvm-exegesis/lib/Target.cpp

const ExegesisTarget *ExegesisTarget::lookup(Triple TT) {
   for (const ExegesisTarget *T = FirstTarget; T != nullptr; T = T->Next) {
     if (T->matchesArch(TT.getArch()))
       return T;
   }
   return nullptr;
 }
 
 Expected<std::unique_ptr<pfm::Counter>>
-ExegesisTarget::createCounter(const char *CounterName,
-                              const LLVMState &) const {
+ExegesisTarget::createCounter(StringRef CounterName, const LLVMState &) const {
   pfm::PerfEvent Event(CounterName);
   if (!Event.valid())
     return llvm::make_error<Failure>(
         llvm::Twine("Unable to create counter with name '")
             .concat(CounterName)
             .concat("'"));
 
   return std::make_unique<pfm::Counter>(std::move(Event));