[llvm] [LiveDebugValues] Avoid repeated hash lookups (NFC) (PR #108484)

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llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-debuginfo

Author: Kazu Hirata (kazutakahirata)

<details>
<summary>Changes</summary>



---
Full diff: https://github.com/llvm/llvm-project/pull/108484.diff


1 Files Affected:

- (modified) llvm/lib/CodeGen/LiveDebugValues/InstrRefBasedImpl.cpp (+3-5) 


``````````diff
diff --git a/llvm/lib/CodeGen/LiveDebugValues/InstrRefBasedImpl.cpp b/llvm/lib/CodeGen/LiveDebugValues/InstrRefBasedImpl.cpp
index a69dbbbbdab3cd..a73a3aa59403b3 100644
--- a/llvm/lib/CodeGen/LiveDebugValues/InstrRefBasedImpl.cpp
+++ b/llvm/lib/CodeGen/LiveDebugValues/InstrRefBasedImpl.cpp
@@ -2231,11 +2231,9 @@ void InstrRefBasedLDV::accumulateFragmentMap(MachineInstr &MI) {
   // If this is the first sighting of this variable, then we are guaranteed
   // there are currently no overlapping fragments either. Initialize the set
   // of seen fragments, record no overlaps for the current one, and return.
-  auto SeenIt = SeenFragments.find(MIVar.getVariable());
-  if (SeenIt == SeenFragments.end()) {
-    SmallSet<FragmentInfo, 4> OneFragment;
-    OneFragment.insert(ThisFragment);
-    SeenFragments.insert({MIVar.getVariable(), OneFragment});
+  auto [SeenIt, Inserted] = SeenFragments.try_emplace(MIVar.getVariable());
+  if (Inserted) {
+    SeenIt->second.insert(ThisFragment);
 
     OverlapFragments.insert({{MIVar.getVariable(), ThisFragment}, {}});
     return;

``````````

</details>


https://github.com/llvm/llvm-project/pull/108484