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

[Matt Arsenault via llvm-commits]

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@@ -895,3 +910,7 @@ void SILowerI1Copies::buildMergeLaneMasks(MachineBasicBlock &MBB,
         .addReg(CurMaskedReg ? CurMaskedReg : ExecReg);
   }
 }
+
+void Vreg1LoweringHelper::constrainIncomingRegisterTakenAsIs(Incoming &In) {
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arsenm wrote:

What's the point of this function? Don't really understand the name 

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