[llvm] [WIP][CodeGen] Modifying MBB's liveins representation as into regUnits (PR #129847)

[Jay Foad via llvm-commits]

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@@ -174,8 +176,7 @@ class MachineBasicBlock
   std::optional<uint64_t> IrrLoopHeaderWeight;
 
   /// Keep track of the physical registers that are livein of the basicblock.
-  using LiveInVector = std::vector<RegisterMaskPair>;
-  LiveInVector LiveIns;
+  DenseSet<MCRegister> LiveIns;
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jayfoad wrote:

I'm not sure if it's a good idea to change from std::vector to DenseSet. The patch would be less invasive if you just changed it to `std:vector<MCRegister>`

You should at least benchmark it using http://llvm-compile-time-tracker.com/. You can do this by asking @nikic to add your fork of LLVM, and then any branches you create called "perf/*" will automatically get benchmarked.

https://github.com/llvm/llvm-project/pull/129847