[ProfileData] Avoid repeated hash lookups (NFC) (llvm#110619)

Author: kazutakahirata

llvm/lib/ProfileData/Coverage/CoverageMapping.cpp

@@ -49,13 +49,10 @@ using namespace coverage;
 #define DEBUG_TYPE "coverage-mapping"
 
 Counter CounterExpressionBuilder::get(const CounterExpression &E) {
-  auto It = ExpressionIndices.find(E);
-  if (It != ExpressionIndices.end())
-    return Counter::getExpression(It->second);
-  unsigned I = Expressions.size();
-  Expressions.push_back(E);
-  ExpressionIndices[E] = I;
-  return Counter::getExpression(I);
+  auto [It, Inserted] = ExpressionIndices.try_emplace(E, Expressions.size());
+  if (Inserted)
+    Expressions.push_back(E);
+  return Counter::getExpression(It->second);
 }
 
 void CounterExpressionBuilder::extractTerms(Counter C, int Factor,