[Passes] Avoid repeated hash lookups (NFC) (#126404)

Author: kazutakahirata

llvm/include/llvm/Passes/DroppedVariableStats.h

@@ -96,9 +96,10 @@ class DroppedVariableStats {
     DenseSet<VarID> &DebugVariablesBeforeSet =
         DbgVariables.DebugVariablesBefore;
     DenseSet<VarID> &DebugVariablesAfterSet = DbgVariables.DebugVariablesAfter;
-    if (InlinedAts.back().find(FuncName) == InlinedAts.back().end())
+    auto It = InlinedAts.back().find(FuncName);
+    if (It == InlinedAts.back().end())
       return;
-    DenseMap<VarID, DILocation *> &InlinedAtsMap = InlinedAts.back()[FuncName];
+    DenseMap<VarID, DILocation *> &InlinedAtsMap = It->second;
     // Find an Instruction that shares the same scope as the dropped #dbg_value
     // or has a scope that is the child of the scope of the #dbg_value, and has
     // an inlinedAt equal to the inlinedAt of the #dbg_value or it's inlinedAt