allow SSAUpdater to be used for Swift

[bob.wilson]

Summary

The SSAUpdater is already implemented as a template so that we can reuse it for both IR-level and Machine-level updates. This simple change adds a new PhiItT typedef to the traits so that it can also be used for Swift's SIL representation, where phis are separate from other instructions.

[mehdi_amini]

lib/CodeGen/MachineSSAUpdater.cpp

252

The interface is somehow lying: PhiItT_end is not the end of the PHIs list.
(not that I have a great suggestion to solve that)

[aschwaighofer]

lib/CodeGen/MachineSSAUpdater.cpp

252

How about calling it PhiCandidateItT?

[dblaikie]

Could you add a unit test (with comments describing the use case) so this
isn't accidentally broken later?

Would it be possible to refactor the begin/end as ADL begin/end so they'd
work with range-based for? (Or I guess that doesn't work - iteration over
the basic block's phis is a separate range from iterating over the basic
block's instructions? (so there's no authoritative begin/end to provide))
Perhaps it could be refactored as a range type/functor/function instead?
(not sure if that's better)

[mehdi_amini]

lib/CodeGen/MachineSSAUpdater.cpp

252

At least it wouldn't be a lie :)

I wonder if it would be useful to have real Phi iterator in LLVM though?

[aschwaighofer]

I don't see a reasonable way to write a unit test without either creating a stub IR or making the typedef typename Traits::PhiItT public and then just testing the presence.

I think swift users will notice when this breaks and complain.

[bob.wilson]

Chandler came up with a much better solution for phi iterators in r303964.
I have proposed a similar change for machine-level IR in https://reviews.llvm.org/D41672
Abandoning this one.

include/llvm/Transforms/Utils/SSAUpdaterImpl.h

   typedef typename Traits::BlkT BlkT;
   typedef typename Traits::ValT ValT;
   typedef typename Traits::PhiT PhiT;
+  typedef typename Traits::PhiItT PhiItT;
 
   /// BBInfo - Per-basic block information used internally by SSAUpdaterImpl.
   /// The predecessors of each block are cached here since pred_iterator is

   /// FindExistingPHI - Look through the PHI nodes in a block to see if any of
   /// them match what is needed.
   void FindExistingPHI(BlkT *BB, BlockListTy *BlockList) {
-    for (typename BlkT::iterator BBI = BB->begin(), BBE = BB->end();
+    for (PhiItT BBI = Traits::PhiItT_begin(BB), BBE = Traits::PhiItT_end(BB);
          BBI != BBE; ++BBI) {
       PhiT *SomePHI = Traits::InstrIsPHI(&*BBI);
       if (!SomePHI)

lib/CodeGen/MachineSSAUpdater.cpp

   static BlkSucc_iterator BlkSucc_begin(BlkT *BB) { return BB->succ_begin(); }
   static BlkSucc_iterator BlkSucc_end(BlkT *BB) { return BB->succ_end(); }
 
+  /// Iterator over phis in a block.
+  typedef BlkT::iterator PhiItT;
+  static PhiItT PhiItT_begin(BlkT *BB) { return BB->begin(); }
+  static PhiItT PhiItT_end(BlkT *BB) { return BB->end(); }
+
   /// Iterator for PHI operands.
   class PHI_iterator {
   private:

lib/Transforms/Utils/SSAUpdater.cpp

   static BlkSucc_iterator BlkSucc_begin(BlkT *BB) { return succ_begin(BB); }
   static BlkSucc_iterator BlkSucc_end(BlkT *BB) { return succ_end(BB); }
 
+  /// Iterator over phis in a block.
+  typedef BlkT::iterator PhiItT;
+  static PhiItT PhiItT_begin(BlkT *BB) { return BB->begin(); }
+  static PhiItT PhiItT_end(BlkT *BB) { return BB->end(); }
+
   class PHI_iterator {
   private:
     PHINode *PHI;