[Passes] Avoid repeated hash lookups (NFC) (#110790)

Author: kazutakahirata

llvm/lib/Passes/StandardInstrumentations.cpp

@@ -2040,13 +2040,14 @@ DotCfgDiff::DotCfgDiff(StringRef Title, const FuncDataT<DCData> &Before,
     StringRef Colour = E.second;
 
     // Look for an edge from Source to Sink
-    if (EdgeLabels.count(SourceSink) == 0)
-      EdgeLabels.insert({SourceSink, colourize(Value.str(), Colour)});
+    auto [It, Inserted] = EdgeLabels.try_emplace(SourceSink);
+    if (Inserted)
+      It->getValue() = colourize(Value.str(), Colour);
     else {
-      StringRef V = EdgeLabels.find(SourceSink)->getValue();
+      StringRef V = It->getValue();
       std::string NV = colourize(V.str() + " " + Value.str(), Colour);
       Colour = CommonColour;
-      EdgeLabels[SourceSink] = NV;
+      It->getValue() = NV;
     }
     SourceNode.addEdge(SinkNode, Value, Colour);
   }