[llvm] [AMDGPU] Fix machine verification failure from INIT_EXEC lowering (PR #98333)

[Matt Arsenault via llvm-commits]

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@@ -1717,7 +1719,7 @@ bool SIWholeQuadMode::runOnMachineFunction(MachineFunction &MF) {
   LIS->removeAllRegUnitsForPhysReg(AMDGPU::SCC);
 
   // If we performed any kills then recompute EXEC
-  if (!KillInstrs.empty())
+  if (!KillInstrs.empty() || !InitExecInstrs.empty())
     LIS->removeAllRegUnitsForPhysReg(AMDGPU::EXEC);
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arsenm wrote:

This shouldn't be necessary in the first place. Reserved registers, like exec, do not have liveness tracked 

https://github.com/llvm/llvm-project/pull/98333