diff --git a/llvm/tools/llvm-exegesis/lib/BenchmarkRunner.h b/llvm/tools/llvm-exegesis/lib/BenchmarkRunner.h
--- a/llvm/tools/llvm-exegesis/lib/BenchmarkRunner.h
+++ b/llvm/tools/llvm-exegesis/lib/BenchmarkRunner.h
@@ -89,8 +89,15 @@
   public:
     virtual ~FunctionExecutor();
 
+    Expected<llvm::SmallVector<int64_t, 4>>
+    runAndSample(const char *Counters) const;
+
+  protected:
+    static void
+    accumulateCounterValues(const llvm::SmallVectorImpl<int64_t> &NewValues,
+                            llvm::SmallVectorImpl<int64_t> *Result);
     virtual Expected<llvm::SmallVector<int64_t, 4>>
-    runAndSample(const char *Counters) const = 0;
+    runWithCounter(StringRef CounterName) const = 0;
   };
 
 protected:
diff --git a/llvm/tools/llvm-exegesis/lib/BenchmarkRunner.cpp b/llvm/tools/llvm-exegesis/lib/BenchmarkRunner.cpp
--- a/llvm/tools/llvm-exegesis/lib/BenchmarkRunner.cpp
+++ b/llvm/tools/llvm-exegesis/lib/BenchmarkRunner.cpp
@@ -37,6 +37,34 @@
 
 BenchmarkRunner::~BenchmarkRunner() = default;
 
+void BenchmarkRunner::FunctionExecutor::accumulateCounterValues(
+    const llvm::SmallVectorImpl<int64_t> &NewValues,
+    llvm::SmallVectorImpl<int64_t> *Result) {
+  const size_t NumValues = std::max(NewValues.size(), Result->size());
+  if (NumValues > Result->size())
+    Result->resize(NumValues, 0);
+  for (size_t I = 0, End = NewValues.size(); I < End; ++I)
+    (*Result)[I] += NewValues[I];
+}
+
+Expected<llvm::SmallVector<int64_t, 4>>
+BenchmarkRunner::FunctionExecutor::runAndSample(const char *Counters) const {
+  // We sum counts when there are several counters for a single ProcRes
+  // (e.g. P23 on SandyBridge).
+  llvm::SmallVector<int64_t, 4> CounterValues;
+  SmallVector<StringRef, 2> CounterNames;
+  StringRef(Counters).split(CounterNames, '+');
+  for (auto &CounterName : CounterNames) {
+    CounterName = CounterName.trim();
+    Expected<SmallVector<int64_t, 4>> ValueOrError =
+        runWithCounter(CounterName);
+    if (!ValueOrError)
+      return ValueOrError.takeError();
+    accumulateCounterValues(ValueOrError.get(), &CounterValues);
+  }
+  return CounterValues;
+};
+
 namespace {
 class FunctionExecutorImpl : public BenchmarkRunner::FunctionExecutor {
 public:
@@ -58,67 +86,43 @@
   }
 
   Expected<llvm::SmallVector<int64_t, 4>>
-  runAndSample(const char *Counters) const override {
-    // We sum counts when there are several counters for a single ProcRes
-    // (e.g. P23 on SandyBridge).
-    llvm::SmallVector<int64_t, 4> CounterValues;
-    int Reserved = 0;
-    SmallVector<StringRef, 2> CounterNames;
-    StringRef(Counters).split(CounterNames, '+');
-    char *const ScratchPtr = Scratch->ptr();
+  runWithCounter(StringRef CounterName) const override {
     const ExegesisTarget &ET = State.getExegesisTarget();
-    for (auto &CounterName : CounterNames) {
-      CounterName = CounterName.trim();
-      auto CounterOrError = ET.createCounter(CounterName, State);
-
-      if (!CounterOrError)
-        return CounterOrError.takeError();
-
-      pfm::Counter *Counter = CounterOrError.get().get();
-      if (Reserved == 0) {
-        Reserved = Counter->numValues();
-        CounterValues.reserve(Reserved);
-      } else if (Reserved != Counter->numValues())
-        // It'd be wrong to accumulate vectors of different sizes.
-        return make_error<Failure>(
-            llvm::Twine("Inconsistent number of values for counter ")
-                .concat(CounterName)
-                .concat(std::to_string(Counter->numValues()))
-                .concat(" vs expected of ")
-                .concat(std::to_string(Reserved)));
-      Scratch->clear();
-      {
-        auto PS = ET.withSavedState();
-        CrashRecoveryContext CRC;
-        CrashRecoveryContext::Enable();
-        const bool Crashed = !CRC.RunSafely([this, Counter, ScratchPtr]() {
-          Counter->start();
-          this->Function(ScratchPtr);
-          Counter->stop();
-        });
-        CrashRecoveryContext::Disable();
-        PS.reset();
-        if (Crashed) {
-          std::string Msg = "snippet crashed while running";
+    char *const ScratchPtr = Scratch->ptr();
+    auto CounterOrError = ET.createCounter(CounterName, State);
+
+    if (!CounterOrError)
+      return CounterOrError.takeError();
+
+    pfm::Counter *Counter = CounterOrError.get().get();
+    Scratch->clear();
+    {
+      auto PS = ET.withSavedState();
+      CrashRecoveryContext CRC;
+      CrashRecoveryContext::Enable();
+      const bool Crashed = !CRC.RunSafely([this, Counter, ScratchPtr]() {
+        Counter->start();
+        this->Function(ScratchPtr);
+        Counter->stop();
+      });
+      CrashRecoveryContext::Disable();
+      PS.reset();
+      if (Crashed) {
+        std::string Msg = "snippet crashed while running";
 #ifdef LLVM_ON_UNIX
-          // See "Exit Status for Commands":
-          // https://pubs.opengroup.org/onlinepubs/9699919799/xrat/V4_xcu_chap02.html
-          constexpr const int kSigOffset = 128;
-          if (const char *const SigName = strsignal(CRC.RetCode - kSigOffset)) {
-            Msg += ": ";
-            Msg += SigName;
-          }
-#endif
-          return make_error<SnippetCrash>(std::move(Msg));
+        // See "Exit Status for Commands":
+        // https://pubs.opengroup.org/onlinepubs/9699919799/xrat/V4_xcu_chap02.html
+        constexpr const int kSigOffset = 128;
+        if (const char *const SigName = strsignal(CRC.RetCode - kSigOffset)) {
+          Msg += ": ";
+          Msg += SigName;
         }
+#endif
+        return make_error<SnippetCrash>(std::move(Msg));
       }
-
-      auto ValueOrError = Counter->readOrError(Function.getFunctionBytes());
-      if (!ValueOrError)
-        return ValueOrError.takeError();
-      accumulateCounterValues(ValueOrError.get(), &CounterValues);
     }
-    return CounterValues;
+
+    return Counter->readOrError(Function.getFunctionBytes());
   }
 
   const LLVMState &State;