[MemorySSA] Refactor removing multiple trivial phis [NFC].

[asbirlea]

Summary

Create a method to clean up multiple potentially trivial phis, since we will need this often.

[george.burgess.iv]

LGTM after two nits; thanks!

lib/Analysis/MemorySSAUpdater.cpp

358–360

nit: unsigned please, to match with the type of the RHS

360

nit: (parens) around InsertedPHIs[NewPhiIndex] are unnecessary; please remove

[asbirlea]

Address comments. Thank you for the review!

include/llvm/Analysis/MemorySSAUpdater.h

private:
   getPreviousDefFromEnd(BasicBlock *,
                         DenseMap<BasicBlock *, TrackingVH<MemoryAccess>> &);
   MemoryAccess *
   getPreviousDefRecursive(BasicBlock *,
                           DenseMap<BasicBlock *, TrackingVH<MemoryAccess>> &);
   MemoryAccess *recursePhi(MemoryAccess *Phi);
   template <class RangeType>
   MemoryAccess *tryRemoveTrivialPhi(MemoryPhi *Phi, RangeType &Operands);
+  void tryRemoveTrivialPhis(ArrayRef<WeakVH> UpdatedPHIs);
   void fixupDefs(const SmallVectorImpl<WeakVH> &);
   // Clone all uses and defs from BB to NewBB given a 1:1 map of all
   // instructions and blocks cloned, and a map of MemoryPhi : Definition
   // (MemoryAccess Phi or Def). VMap maps old instructions to cloned
   // instructions and old blocks to cloned blocks. MPhiMap, is created in the
   // caller of this private method, and maps existing MemoryPhis to new
   // definitions that new MemoryAccesses must point to. These definitions may
   // not necessarily be MemoryPhis themselves, they may be MemoryDefs. As such,

lib/Analysis/MemorySSAUpdater.cpp

while (!FixupList.empty()) {
     unsigned StartingPHISize = InsertedPHIs.size();
     fixupDefs(FixupList);
     FixupList.clear();
     // Put any new phis on the fixup list, and process them
     FixupList.append(InsertedPHIs.begin() + StartingPHISize, InsertedPHIs.end());
   }
 
   // Optimize potentially non-minimal phis added in this method.
-  for (unsigned Idx = NewPhiIndex; Idx < NewPhiIndexEnd; ++Idx) {
-    if (auto *MPhi = cast_or_null<MemoryPhi>(InsertedPHIs[Idx])) {
-      auto OperRange = MPhi->operands();
-      tryRemoveTrivialPhi(MPhi, OperRange);
-    }
-  }
+  unsigned NewPhiSize = NewPhiIndexEnd - NewPhiIndex;
+  if (NewPhiSize)
+    tryRemoveTrivialPhis(ArrayRef<WeakVH>(&InsertedPHIs[NewPhiIndex], NewPhiSize));
 
   // Now that all fixups are done, rename all uses if we are asked.
   if (RenameUses) {
     SmallPtrSet<BasicBlock *, 16> Visited;
     BasicBlock *StartBlock = MD->getBlock();
     // We are guaranteed there is a def in the block, because we just got it
     // handed to us in this function.
     MemoryAccess *FirstDef = &*MSSA->getWritableBlockDefs(StartBlock)->begin();
for (auto AB = Acc->begin(), AE = Acc->end(); AB != AE;) {
       MemoryAccess *MA = &*AB;
       ++AB;
       MSSA->removeFromLookups(MA);
       MSSA->removeFromLists(MA);
     }
   }
 }
 
+void MemorySSAUpdater::tryRemoveTrivialPhis(ArrayRef<WeakVH> UpdatedPHIs) {
+  for (auto &VH : UpdatedPHIs)
+    if (auto *MPhi = cast_or_null<MemoryPhi>(VH)) {
+      auto OperRange = MPhi->operands();
+      tryRemoveTrivialPhi(MPhi, OperRange);
+    }
+}
+
 MemoryAccess *MemorySSAUpdater::createMemoryAccessInBB(
     Instruction *I, MemoryAccess *Definition, const BasicBlock *BB,
     MemorySSA::InsertionPlace Point) {
   MemoryUseOrDef *NewAccess = MSSA->createDefinedAccess(I, Definition);
   MSSA->insertIntoListsForBlock(NewAccess, BB, Point);
   return NewAccess;
 }