[llvm] [SelectionDAG] Avoid repeated hash lookups (NFC) (PR #128999)

[Craig Topper via llvm-commits]

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@@ -343,9 +343,10 @@ void FunctionLoweringInfo::set(const Function &fn, MachineFunction &mf,
     for (auto &KV : EHInfo.UnwindDestToSrcs) {
       const auto *Dest = cast<const BasicBlock *>(KV.first);
       MachineBasicBlock *DestMBB = getMBB(Dest);
-      UnwindDestToSrcs[DestMBB] = SmallPtrSet<BBOrMBB, 4>();
+      auto &Srcs = UnwindDestToSrcs[DestMBB];
+      Srcs = SmallPtrSet<BBOrMBB, 4>();
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topperc wrote:

Is `DestMBB` ever already in the map or was it always default constructed on the line before?

https://github.com/llvm/llvm-project/pull/128999