[llvm] [CodeGen] Avoid repeated hash lookups (NFC) (PR #131495)

[Kazu Hirata via llvm-commits]

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@@ -123,10 +123,13 @@ bool applyDebugifyMetadataToMachineFunction(MachineModuleInfo &MMI,
 
       // Find a suitable local variable for the DBG_VALUE.
       unsigned Line = MI.getDebugLoc().getLine();
-      if (!Line2Var.count(Line))
+      auto It = Line2Var.find(Line);
+      if (It == Line2Var.end()) {
         Line = EarliestDVI ? EarliestDVI->getDebugLoc().getLine()
                            : EarliestDVR->getDebugLoc().getLine();
-      DILocalVariable *LocalVar = Line2Var[Line];
+        It = Line2Var.try_emplace(Line).first;
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kazutakahirata wrote:

@nikic Thank you for pointing this out!  Yes, we can indeed use `find` here.  Just in case, I've put `assert` here.

https://github.com/llvm/llvm-project/pull/131495