[llvm-exegesis] Add debug option to print per-measurement values (#81219)

This patch adds a debug option to print per measurement latency and
validation counter values. This makes it easier to debug certain
transient issues that can be hard to spot just using the summary view at
the end.

I've hacked print statements into this part of the code base enough
times for debugging various things that I think it makes sense to be a
proper debug macro.

Author: boomanaiden154

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

@@ -193,55 +193,12 @@ template <> struct SequenceElementTraits<exegesis::BenchmarkMeasure> {
   static const bool flow = false;
 };
 
-const char *validationEventToString(exegesis::ValidationEvent VE) {
-  switch (VE) {
-  case exegesis::ValidationEvent::InstructionRetired:
-    return "instructions-retired";
-  case exegesis::ValidationEvent::L1DCacheLoadMiss:
-    return "l1d-cache-load-misses";
-  case exegesis::ValidationEvent::L1DCacheStoreMiss:
-    return "l1d-cache-store-misses";
-  case exegesis::ValidationEvent::L1ICacheLoadMiss:
-    return "l1i-cache-load-misses";
-  case exegesis::ValidationEvent::DataTLBLoadMiss:
-    return "data-tlb-load-misses";
-  case exegesis::ValidationEvent::DataTLBStoreMiss:
-    return "data-tlb-store-misses";
-  case exegesis::ValidationEvent::InstructionTLBLoadMiss:
-    return "instruction-tlb-load-misses";
-  case exegesis::ValidationEvent::BranchPredictionMiss:
-    return "branch-prediction-misses";
-  }
-  llvm_unreachable("Unhandled exegesis::ValidationEvent enum");
-}
-
-Expected<exegesis::ValidationEvent> stringToValidationEvent(StringRef Input) {
-  if (Input == "instructions-retired")
-    return exegesis::ValidationEvent::InstructionRetired;
-  else if (Input == "l1d-cache-load-misses")
-    return exegesis::ValidationEvent::L1DCacheLoadMiss;
-  else if (Input == "l1d-cache-store-misses")
-    return exegesis::ValidationEvent::L1DCacheStoreMiss;
-  else if (Input == "l1i-cache-load-misses")
-    return exegesis::ValidationEvent::L1ICacheLoadMiss;
-  else if (Input == "data-tlb-load-misses")
-    return exegesis::ValidationEvent::DataTLBLoadMiss;
-  else if (Input == "data-tlb-store-misses")
-    return exegesis::ValidationEvent::DataTLBStoreMiss;
-  else if (Input == "instruction-tlb-load-misses")
-    return exegesis::ValidationEvent::InstructionTLBLoadMiss;
-  else if (Input == "branch-prediction-misses")
-    return exegesis::ValidationEvent::BranchPredictionMiss;
-  else
-    return make_error<StringError>("Invalid validation event string",
-                                   errc::invalid_argument);
-}
-
 template <>
 struct CustomMappingTraits<std::map<exegesis::ValidationEvent, int64_t>> {
   static void inputOne(IO &Io, StringRef KeyStr,
                        std::map<exegesis::ValidationEvent, int64_t> &VI) {
-    Expected<exegesis::ValidationEvent> Key = stringToValidationEvent(KeyStr);
+    Expected<exegesis::ValidationEvent> Key =
+        exegesis::stringToValidationEvent(KeyStr);
     if (!Key) {
       Io.setError("Key is not a valid validation event");
       return;
@@ -251,7 +208,7 @@ struct CustomMappingTraits<std::map<exegesis::ValidationEvent, int64_t>> {
 
   static void output(IO &Io, std::map<exegesis::ValidationEvent, int64_t> &VI) {
     for (auto &IndividualVI : VI) {
-      Io.mapRequired(validationEventToString(IndividualVI.first),
+      Io.mapRequired(exegesis::validationEventToString(IndividualVI.first),
                      IndividualVI.second);
     }
   }
@@ -484,6 +441,49 @@ bool operator==(const BenchmarkMeasure &A, const BenchmarkMeasure &B) {
          std::tie(B.Key, B.PerInstructionValue, B.PerSnippetValue);
 }
 
+const char *validationEventToString(ValidationEvent VE) {
+  switch (VE) {
+  case exegesis::ValidationEvent::InstructionRetired:
+    return "instructions-retired";
+  case exegesis::ValidationEvent::L1DCacheLoadMiss:
+    return "l1d-cache-load-misses";
+  case exegesis::ValidationEvent::L1DCacheStoreMiss:
+    return "l1d-cache-store-misses";
+  case exegesis::ValidationEvent::L1ICacheLoadMiss:
+    return "l1i-cache-load-misses";
+  case exegesis::ValidationEvent::DataTLBLoadMiss:
+    return "data-tlb-load-misses";
+  case exegesis::ValidationEvent::DataTLBStoreMiss:
+    return "data-tlb-store-misses";
+  case exegesis::ValidationEvent::InstructionTLBLoadMiss:
+    return "instruction-tlb-load-misses";
+  case exegesis::ValidationEvent::BranchPredictionMiss:
+    return "branch-prediction-misses";
+  }
+  llvm_unreachable("Unhandled exegesis::ValidationEvent enum");
+}
+
+Expected<ValidationEvent> stringToValidationEvent(StringRef Input) {
+  if (Input == "instructions-retired")
+    return exegesis::ValidationEvent::InstructionRetired;
+  else if (Input == "l1d-cache-load-misses")
+    return exegesis::ValidationEvent::L1DCacheLoadMiss;
+  else if (Input == "l1d-cache-store-misses")
+    return exegesis::ValidationEvent::L1DCacheStoreMiss;
+  else if (Input == "l1i-cache-load-misses")
+    return exegesis::ValidationEvent::L1ICacheLoadMiss;
+  else if (Input == "data-tlb-load-misses")
+    return exegesis::ValidationEvent::DataTLBLoadMiss;
+  else if (Input == "data-tlb-store-misses")
+    return exegesis::ValidationEvent::DataTLBStoreMiss;
+  else if (Input == "instruction-tlb-load-misses")
+    return exegesis::ValidationEvent::InstructionTLBLoadMiss;
+  else if (Input == "branch-prediction-misses")
+    return exegesis::ValidationEvent::BranchPredictionMiss;
+  else
+    return make_error<StringError>("Invalid validation event string",
+                                   errc::invalid_argument);
+}
 
 } // namespace exegesis
 } // namespace llvm

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

@@ -43,6 +43,9 @@ enum ValidationEvent {
   BranchPredictionMiss
 };
 
+const char *validationEventToString(exegesis::ValidationEvent VE);
+Expected<ValidationEvent> stringToValidationEvent(StringRef Input);
+
 enum class BenchmarkPhaseSelectorE {
   PrepareSnippet,
   PrepareAndAssembleSnippet,

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

@@ -15,6 +15,8 @@
 #include <algorithm>
 #include <cmath>
 
+#define DEBUG_TYPE "exegesis-latency-benchmarkrunner"
+
 namespace llvm {
 namespace exegesis {
 
@@ -91,9 +93,11 @@ Expected<std::vector<BenchmarkMeasure>> LatencyBenchmarkRunner::runMeasurements(
     if (!ExpectedCounterValues)
       return ExpectedCounterValues.takeError();
     ValuesCount = ExpectedCounterValues.get().size();
-    if (ValuesCount == 1)
+    if (ValuesCount == 1) {
+      LLVM_DEBUG(dbgs() << "Latency value: " << ExpectedCounterValues.get()[0]
+                        << "\n");
       AccumulatedValues.push_back(ExpectedCounterValues.get()[0]);
-    else {
+    } else {
       // We'll keep the reading with lowest variance (ie., most stable)
       double Variance = computeVariance(*ExpectedCounterValues);
       if (MinVariance > Variance) {
@@ -102,8 +106,11 @@ Expected<std::vector<BenchmarkMeasure>> LatencyBenchmarkRunner::runMeasurements(
       }
     }
 
-    for (size_t I = 0; I < ValCounterValues.size(); ++I)
+    for (size_t I = 0; I < ValCounterValues.size(); ++I) {
+      LLVM_DEBUG(dbgs() << validationEventToString(ValidationCounters[I])
+                        << ": " << IterationValCounterValues[I] << "\n");
       ValCounterValues[I] += IterationValCounterValues[I];
+    }
   }
 
   std::map<ValidationEvent, int64_t> ValidationInfo;