[llvm-profgen] Truncate the context with zero probe ID

[wlei]

Summary

Due to the debug info merging, there may have some contexts with zero probe id, we should truncate the context to avoid misleading pre-inliner.

[wlei]

Updating D114284: [llvm-profgen] Truncate the context with zero probe ID

[wlei]

Updating D114284: [llvm-profgen] Truncate the context with zero probe ID

[hoy]

lgtm, thanks.

llvm/tools/llvm-profgen/ProfiledBinary.h

459

nit: // clear the current context for an unknown probe

[wlei]

Updating D114284: [llvm-profgen] Truncate the context with zero probe ID

[wenlei]

llvm/tools/llvm-profgen/ProfileGenerator.cpp

775

Before this fix, when CalleeContextId only has one frame, what did we get for CallerProfile? A dummy root profile with empty name?

[wlei]

fix lint

llvm/tools/llvm-profgen/ProfileGenerator.cpp

775

Before this fix, CalleeContextId is guaranteed to have >1 frame, see there is a check if (InlinerDesc != nullptr) to make sure the callee always has the inliner which means we only infer caller's count for inlining.

llvm/tools/llvm-profgen/ProfileGenerator.cpp

for (auto PI : ProbeCounter) {
     // zero count probes of the frame later.
     FrameSamples[Probe->getInlineTreeNode()].insert(&FunctionProfile);
     FunctionProfile.addBodySamplesForProbe(Probe->getIndex(), Count);
     FunctionProfile.addTotalSamples(Count);
     if (Probe->isEntry()) {
       FunctionProfile.addHeadSamples(Count);
       // Look up for the caller's function profile
       const auto *InlinerDesc = Binary->getInlinerDescForProbe(Probe);
-      if (InlinerDesc != nullptr) {
+      SampleContextFrames CalleeContextId =
+          FunctionProfile.getContext().getContextFrames();
+      if (InlinerDesc != nullptr && CalleeContextId.size() > 1) {
         // Since the context id will be compressed, we have to use callee's
         // context id to infer caller's context id to ensure they share the
         // same context prefix.
-        SampleContextFrames CalleeContextId =
-            FunctionProfile.getContext().getContextFrames();
         SampleContextFrameVector CallerContextId;
         SampleContextFrame &&CallerLeafFrameLoc =
             getCallerContext(CalleeContextId, CallerContextId);
         uint64_t CallerIndex = CallerLeafFrameLoc.Location.LineOffset;
         assert(CallerIndex &&
                "Inferred caller's location index shouldn't be zero!");
         FunctionSamples &CallerProfile =
             getFunctionProfileForContext(CallerContextId);
         CallerProfile.setFunctionHash(InlinerDesc->FuncHash);
         CallerProfile.addBodySamples(CallerIndex, 0, Count);
         CallerProfile.addTotalSamples(Count);
         CallerProfile.addCalledTargetSamples(
             CallerIndex, 0, FunctionProfile.getContext().getName(), Count);
       }
     }

llvm/tools/llvm-profgen/ProfiledBinary.h

public:
   }
 
   void getInlineContextForProbe(const MCDecodedPseudoProbe *Probe,
                                 SampleContextFrameVector &InlineContextStack,
                                 bool IncludeLeaf = false) const {
     SmallVector<MCPseduoProbeFrameLocation, 16> ProbeInlineContext;
     ProbeDecoder.getInlineContextForProbe(Probe, ProbeInlineContext,
                                           IncludeLeaf);
-    for (auto &Callsite : ProbeInlineContext) {
+    for (uint32_t I = 0; I < ProbeInlineContext.size(); I++) {
+      auto &Callsite = ProbeInlineContext[I];
+      // Ignore the context if the probe of the callsite is zero.
+      if(Callsite.second == 0 && I != ProbeInlineContext.size() - 1) {
+        InlineContextStack.clear();
+        continue;
+      }
       InlineContextStack.emplace_back(Callsite.first,
                                       LineLocation(Callsite.second, 0));
     }
   }
   const AddressProbesMap &getAddress2ProbesMap() const {
     return ProbeDecoder.getAddress2ProbesMap();
   }
   const MCPseudoProbeFuncDesc *getFuncDescForGUID(uint64_t GUID) {