Revert r168630, r168631, and r168633 as these are causing nightly test failures.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@168751 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/CodeGen/RegAllocBase.cpp b/lib/CodeGen/RegAllocBase.cpp
index 2b598e3..993dbc7 100644
--- a/lib/CodeGen/RegAllocBase.cpp
+++ b/lib/CodeGen/RegAllocBase.cpp
@@ -58,6 +58,7 @@
   VRM = &vrm;
   LIS = &lis;
   Matrix = &mat;
+  MRI->freezeReservedRegs(vrm.getMachineFunction());
   RegClassInfo.runOnMachineFunction(vrm.getMachineFunction());
 }