[MemorySSA] Make the Updater movable.

[asbirlea]

Summary

Make the MemorySSAUpdater movable.

[chandlerc]

include/llvm/Analysis/MemorySSAUpdater.h

76

You don't zero it out in the move constructor, why do it here? Do we do something in the destructor with it, if so it should be in both?

Also, if we do need this, s/0/nullptr/

[asbirlea]

Nope, don't need that.

[george.burgess.iv]

include/llvm/Analysis/MemorySSAUpdater.h

73

Can we = default;? I'd imagine the associated Small* data structures are really cheap to move/etc. if they're empty.

If not, that's sad, but OK, this works. :)

74

nit: please clang-format

[chandlerc]

include/llvm/Analysis/MemorySSAUpdater.h

73

We shouldn't need to write it at all if that worked....

I think the issue is the SmallSet of AssertingVH's?

[chandlerc]

include/llvm/Analysis/MemorySSAUpdater.h

73

This does raise the point that as-is, this is a very surprising move constructor.

I'd suggest moving all members somewhat pedantically to make it less surprising. And you might need to clear the actual AssertingVH container after that so that, not sure.

[asbirlea]

Dropping this, updater is movable, some mishap on my side.

include/llvm/Analysis/MemorySSAUpdater.h

private:
   /// MemoryPhis are created eagerly and sometimes get zapped shortly afterwards.
   SmallVector<WeakVH, 16> InsertedPHIs;
 
   SmallPtrSet<BasicBlock *, 8> VisitedBlocks;
   SmallSet<AssertingVH<MemoryPhi>, 8> NonOptPhis;
 
 public:
   MemorySSAUpdater(MemorySSA *MSSA) : MSSA(MSSA) {}
+  MemorySSAUpdater(MemorySSAUpdater &&MSSAU) : MSSA(MSSAU.MSSA) {}
+  MemorySSAUpdater& operator=(MemorySSAUpdater&& MSSAU) {
+    MSSA = MSSAU.MSSA;
+    return *this;
+  }
   /// Insert a definition into the MemorySSA IR.  RenameUses will rename any use
   /// below the new def block (and any inserted phis).  RenameUses should be set
   /// to true if the definition may cause new aliases for loads below it.  This
   /// is not the case for hoisting or sinking or other forms of code *movement*.
   /// It *is* the case for straight code insertion.
   /// For example:
   /// store a
   /// if (foo) { }