[llvm] [CodeGen] Use RegisterClassInfo for remaining allocation-order users (PR #216510)

[Matt Arsenault via llvm-commits]

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@@ -804,6 +795,7 @@ bool RegAllocPBQP::runOnMachineFunction(MachineFunction &MF) {
       createInlineSpiller({LIS, LiveStks, MDT, MBFI}, MF, VRM, DefaultVRAI));
 
   MF.getRegInfo().freezeReservedRegs();
+  RCI.runOnMachineFunction(MF);
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arsenm wrote:

This should by handled by the pass manager. But I suspect this is unnecessary, and the prior freezeReserveRegs call is also unnecessary. Do the other RAs have this call now? I recall cleaning up unnecessary freezeReservedRegs calls, and PBQP likely got forgotten in that 

https://github.com/llvm/llvm-project/pull/216510