[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:

> Blocks should not track both LiveInRegUnits and LiveIns. 

What I feel both is important! LiveIns maintains the list of exact physReg with laneBitmask (what is live to use) & LiveInRegUnits to utilize that info to precisely perform checks for isLiveIn like functions!


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