[MemorySSA] Stop tracking def-or-use blocks.

[bryant]

Summary

Unused because we no longer prune phi nodes.

llvm/trunk/lib/Analysis/MemorySSA.cpp

LiveOnEntryDef = make_unique<MemoryDef>(F.getContext(), nullptr, nullptr,
                                           &StartingPoint, NextID++);
   DenseMap<const BasicBlock *, unsigned int> BBNumbers;
   unsigned NextBBNum = 0;
 
   // We maintain lists of memory accesses per-block, trading memory for time. We
   // could just look up the memory access for every possible instruction in the
   // stream.
   SmallPtrSet<BasicBlock *, 32> DefiningBlocks;
-  SmallPtrSet<BasicBlock *, 32> DefUseBlocks;
   // Go through each block, figure out where defs occur, and chain together all
   // the accesses.
   for (BasicBlock &B : F) {
     BBNumbers[&B] = NextBBNum++;
     bool InsertIntoDef = false;
     AccessList *Accesses = nullptr;
     DefsList *Defs = nullptr;
     for (Instruction &I : B) {
       MemoryUseOrDef *MUD = createNewAccess(&I);
       if (!MUD)
         continue;
 
       if (!Accesses)
         Accesses = getOrCreateAccessList(&B);
       Accesses->push_back(MUD);
       if (isa<MemoryDef>(MUD)) {
         InsertIntoDef = true;
         if (!Defs)
           Defs = getOrCreateDefsList(&B);
         Defs->push_back(*MUD);
       }
     }
     if (InsertIntoDef)
       DefiningBlocks.insert(&B);
-    if (Accesses)
-      DefUseBlocks.insert(&B);
   }
   placePHINodes(DefiningBlocks, BBNumbers);
 
   // Now do regular SSA renaming on the MemoryDef/MemoryUse. Visited will get
   // filled in with all blocks.
   SmallPtrSet<BasicBlock *, 16> Visited;
   renamePass(DT->getRootNode(), LiveOnEntryDef.get(), Visited);