[LSV] Use make_range, and reformat a DEBUG message. NFC

[jlebar]

Summary

The DEBUG message was hard to read because two Values were being printed
on the same line with only the delimiter "aliases". This change makes
us print each Value on its own line.

[asbirlea]

lib/Transforms/Vectorize/LoadStoreVectorizer.cpp

482

I'd like to have some indentation for all lines following this, it looks easier to follow that this is a single message.
I find the previous message clearer (explicitly adding "aliases"), but I guess having the instruction and pointer on different lines is also ok with some indentation.
This is more a personal preference, so leaving it up to you.

[jlebar]

Add indentation.

lib/Transforms/Vectorize/LoadStoreVectorizer.cpp

482

The way I've been reading it is looking for lines that start with "LSV". It's not great, but it sort of works.

I just remembered, the reason I did this with no indentation is to match the "LSV: Stores to vectorize:" message. This one calls V->dump(), and we can't directly add indentation to that. I suppose we could do dbgs() << " " << *V << "\n", though...

In practice the instructions will almost always have indentation because we (apparently) carry the indentation from the original ir. But it would be nice to be able to indent the strings in this message, so I went ahead and added the indentation everywhere.

lib/Transforms/Vectorize/LoadStoreVectorizer.cpp

 
 unsigned Vectorizer::getVectorizablePrefixEndIdx(ArrayRef<Value *> Chain,
                                                  BasicBlock::iterator From,
                                                  BasicBlock::iterator To) {
   SmallVector<std::pair<Value *, unsigned>, 16> MemoryInstrs;
   SmallVector<std::pair<Value *, unsigned>, 16> ChainInstrs;
 
   unsigned InstrIdx = 0;
-  for (auto I = From; I != To; ++I, ++InstrIdx) {
+  for (Instruction &I : make_range(From, To)) {
+    ++InstrIdx;
     if (isa<LoadInst>(I) || isa<StoreInst>(I)) {
-      if (!is_contained(Chain, &*I))
-        MemoryInstrs.push_back({&*I, InstrIdx});
+      if (!is_contained(Chain, &I))
+        MemoryInstrs.push_back({&I, InstrIdx});
       else
-        ChainInstrs.push_back({&*I, InstrIdx});
-    } else if (I->mayHaveSideEffects()) {
-      DEBUG(dbgs() << "LSV: Found side-effecting operation: " << *I << '\n');
+        ChainInstrs.push_back({&I, InstrIdx});
+    } else if (I.mayHaveSideEffects()) {
+      DEBUG(dbgs() << "LSV: Found side-effecting operation: " << I << '\n');
       return 0;
     }
   }
 
   assert(Chain.size() == ChainInstrs.size() &&
          "All instructions in the Chain must exist in [From, To).");
 
   unsigned ChainIdx = 0;
for (auto EntryMem : MemoryInstrs) {
       Instruction *M0 = cast<Instruction>(MemInstrValue);
       Instruction *M1 = cast<Instruction>(ChainInstrValue);
 
       if (!AA.isNoAlias(MemoryLocation::get(M0), MemoryLocation::get(M1))) {
         DEBUG({
           Value *Ptr0 = getPointerOperand(M0);
           Value *Ptr1 = getPointerOperand(M1);
 
-          dbgs() << "LSV: Found alias.\n"
-                    "        Aliasing instruction and pointer:\n"
-                 << *MemInstrValue << " aliases " << *Ptr0 << '\n'
-                 << "        Aliased instruction and pointer:\n"
-                 << *ChainInstrValue << " aliases " << *Ptr1 << '\n';
+          dbgs() << "LSV: Found alias:\n"
+                    "  Aliasing instruction and pointer:\n"
+                 << "  " << *MemInstrValue << '\n'
+                 << "  " << *Ptr0 << '\n'
+                 << "  Aliased instruction and pointer:\n"
+                 << "  " << *ChainInstrValue << '\n'
+                 << "  " << *Ptr1 << '\n';
         });
 
         return ChainIdx;
       }
     }
     ChainIdx++;
   }
   return Chain.size();
DEBUG(dbgs() << "LSV: Vector factor is too big."
                     " Creating two separate arrays.\n");
     return vectorizeStoreChain(Chain.slice(0, VF), InstructionsProcessed) |
            vectorizeStoreChain(Chain.slice(VF), InstructionsProcessed);
   }
 
   DEBUG({
     dbgs() << "LSV: Stores to vectorize:\n";
     for (Value *V : Chain)
-      V->dump();
+      dbgs() << "  " << *V << "\n";
   });
 
   // We won't try again to vectorize the elements of the chain, regardless of
   // whether we succeed below.
   InstructionsProcessed->insert(Chain.begin(), Chain.end());
 
   // Check alignment restrictions.
   unsigned Alignment = getAlignment(S0);