Make it possible to add the MIR Canonicalizer pass in a pipeline

[aditya_nandakumar]

Summary

Allow the pass to be added in a pipeline (for debugging purposes).
Alternatively we can separate the MIRCanonicalizer pass into a header, and not need to add the ID here.

[plotfi]

Any way to test this, or should this just go in as is? If not, LGTM as this is a pretty small change.

[aditya_nandakumar]

I don't think there's a way to test this - this needs to be added to a pipeline.

[aditya_nandakumar]

551acdbf93

llvm/include/llvm/CodeGen/Passes.h

/// MachineDominanaceFrontier - This pass is a machine dominators analysis pass.
 
   /// Creates a pass to print GC metadata.
   ///
   FunctionPass *createGCInfoPrinter(raw_ostream &OS);
 
   /// MachineCSE - This pass performs global CSE on machine instructions.
   extern char &MachineCSEID;
 
+  /// MIRCanonicalizer - This pass canonicalizes MIR by renaming vregs
+  /// according to the semantics of the instruction as well as hoists
+  /// code.
+  extern char &MIRCanonicalizerID;
+
   /// ImplicitNullChecks - This pass folds null pointer checks into nearby
   /// memory operations.
   extern char &ImplicitNullChecksID;
 
   /// This pass performs loop invariant code motion on machine instructions.
   extern char &MachineLICMID;
 
   /// This pass performs loop invariant code motion on machine instructions.