[llvm] GlobalISel lane masks merging (PR #73337)

[Matt Arsenault via llvm-commits]

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@@ -40,8 +40,8 @@ class MachineSSAUpdater {
   //typedef DenseMap<MachineBasicBlock*, Register> AvailableValsTy;
   void *AV = nullptr;
 
-  /// VRC - Register class of the current virtual register.
-  const TargetRegisterClass *VRC = nullptr;
+  /// RegAttrs - current virtual register, new registers copy its attributes.
+  Register RegAttrs;
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arsenm wrote:

One downside is a TargetRegisterClass is truly supposed to be constant. The register's attributes could change in the background 

https://github.com/llvm/llvm-project/pull/73337