[llvm] [AMDGPU][CodeGen] Utilized MBB's liveIn check in SILowerSGPRSpills (PR #129848)

[Vikash Gupta via llvm-commits]

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@@ -177,6 +179,10 @@ class MachineBasicBlock
   using LiveInVector = std::vector<RegisterMaskPair>;
   LiveInVector LiveIns;
 
+  /// Keeps track of live register units for those physical registers which
+  /// are livein of the basicblock.
+  BitVector LiveInRegUnits;
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vg0204 wrote:

> I think you should decouple these issues. In this PR, just use the MCRegAliasIterator at the use point to get it functional. Fixing the APIs is for later

Can you bit more specific...

https://github.com/llvm/llvm-project/pull/129848