[llvm-profgen] Warn for empty LBR of hybrid sample instead of error

[wlei]

Summary

Warn for the missing LBR sample case instead of error, it should allow processing the remaining samples.

[wenlei]

Wondering why we would have such cases?

[wlei]

In D115841#3196483, @wenlei wrote:

Wondering why we would have such cases?

ok..It turned out I used the incomplete input, the last sample is truncated like:

106db8f0
cf481a1
cf47ec7
106c0fc7
106c0cbb
106c0c3c
cf444df
cf458e9
ceef560
ceecfb8
ceea6ae
cee7ced
cef70ad
cf2b

The complete sample in the service won't have the case. so seems we don't need this.

[wenlei]

In D115841#3196500, @wlei wrote:

In D115841#3196483, @wenlei wrote:

Wondering why we would have such cases?

ok..It turned out I used the incomplete input, the last sample is truncated like:

106db8f0
cf481a1
cf47ec7
106c0fc7
106c0cbb
106c0c3c
cf444df
cf458e9
ceef560
ceecfb8
ceea6ae
cee7ced
cef70ad
cf2b

The complete sample in the service won't have the case. so seems we don't need this.

Ok, then it probably makes more sense to treat it as error still.

[wlei]

In D115841#3196542, @wenlei wrote:

In D115841#3196500, @wlei wrote:

In D115841#3196483, @wenlei wrote:

Wondering why we would have such cases?

ok..It turned out I used the incomplete input, the last sample is truncated like:

106db8f0
cf481a1
cf47ec7
106c0fc7
106c0cbb
106c0c3c
cf444df
cf458e9
ceef560
ceecfb8
ceea6ae
cee7ced
cef70ad
cf2b

The complete sample in the service won't have the case. so seems we don't need this.

Ok, then it probably makes more sense to treat it as error still.

Sounds good, abandoning it.

llvm/tools/llvm-profgen/PerfReader.h

protected:
   StringRef PerfTraceFile;
 
   ContextSampleCounterMap SampleCounters;
   bool ProfileIsCSFlat = false;
 
   uint64_t NumTotalSample = 0;
   uint64_t NumLeafExternalFrame = 0;
   uint64_t NumLeadingOutgoingLBR = 0;
+  uint64_t NumEmptyLBRSample = 0;
 };
 
 // Read perf script to parse the events and samples.
 class PerfScriptReader : public PerfReaderBase {
 public:
   PerfScriptReader(ProfiledBinary *B, StringRef PerfTrace)
       : PerfReaderBase(B, PerfTrace){};
 

llvm/tools/llvm-profgen/PerfReader.cpp

if (extractLBRStack(TraceIt, Sample->LBRStack)) {
         // ranges
         Sample->CallStack.front() = Sample->LBRStack[0].Target;
       }
       // Record samples by aggregation
       AggregatedSamples[Hashable<PerfSample>(Sample)] += Count;
     }
   } else {
     // LBR sample is encoded in single line after stack sample
-    exitWithError("'Hybrid perf sample is corrupted, No LBR sample line");
+    NumEmptyLBRSample++;
   }
 }
 
 void PerfScriptReader::writeUnsymbolizedProfile(StringRef Filename) {
   std::error_code EC;
   raw_fd_ostream OS(Filename, EC, llvm::sys::fs::OF_TextWithCRLF);
   if (EC)
     exitWithError(EC, Filename);
emitWarningSummary(UnmatchedRange, TotalRangeNum,
                      "of profiled ranges do not belong to any functions.");
   emitWarningSummary(RangeCrossFunc, TotalRangeNum,
                      "of profiled ranges do cross function boundaries.");
 }
 
 void PerfScriptReader::parsePerfTraces() {
   // Parse perf traces and do aggregation.
   parseAndAggregateTrace();
 
+  emitWarningSummary(NumEmptyLBRSample, NumTotalSample,
+                     "of hybrid samples have call stack sample but no LBR sample");
   emitWarningSummary(NumLeafExternalFrame, NumTotalSample,
                      "of samples have leaf external frame in call stack.");
   emitWarningSummary(NumLeadingOutgoingLBR, NumTotalSample,
                      "of samples have leading external LBR.");
 
   // Generate unsymbolized profile.
   warnTruncatedStack();
   warnInvalidRange();