Add an AllocationOrder class that can iterate over the allocatable physical
registers for a given virtual register.

Reserved registers are filtered from the allocation order, and any valid hint is
returned as the first suggestion.

For target dependent hints, a number of arcane target hooks are invoked.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@121497 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/CodeGen/VirtRegMap.h b/lib/CodeGen/VirtRegMap.h
index 0bf52be..2fe27ce 100644
--- a/lib/CodeGen/VirtRegMap.h
+++ b/lib/CodeGen/VirtRegMap.h
@@ -156,10 +156,13 @@
     }
 
     MachineFunction &getMachineFunction() const {
-      assert(MF && "getMachineFunction called before runOnMAchineFunction");
+      assert(MF && "getMachineFunction called before runOnMachineFunction");
       return *MF;
     }
 
+    MachineRegisterInfo &getRegInfo() const { return *MRI; }
+    const TargetRegisterInfo &getTargetRegInfo() const { return *TRI; }
+
     void grow();
 
     /// @brief returns true if the specified virtual register is