[SimplifyCFG] Use BB::instructionsWithoutDebug to skip DbgInfo (NFC).

[fhahn]

Summary

This patch updates some code responsible the skip debug info to use
BasicBlock::instructionsWithoutDebug. I think this makes things slightly
simpler and more direct.

[hans]

Seems reasonable to me.

lib/Transforms/Utils/SimplifyCFG.cpp

static Value *isSafeToSpeculateStore(Instruction *I, BasicBlock *BrBB,
   // Volatile or atomic.
   if (!StoreToHoist->isSimple())
     return nullptr;
 
   Value *StorePtr = StoreToHoist->getPointerOperand();
 
   // Look for a store to the same pointer in BrBB.
   unsigned MaxNumInstToLookAt = 9;
-  for (Instruction &CurI : reverse(*BrBB)) {
+  for (Instruction &CurI : reverse(BrBB->instructionsWithoutDebug())) {
     if (!MaxNumInstToLookAt)
       break;
-    // Skip debug info.
-    if (isa<DbgInfoIntrinsic>(CurI))
-      continue;
     --MaxNumInstToLookAt;
 
     // Could be calling an instruction that affects memory like free().
     if (CurI.mayHaveSideEffects() && !isa<StoreInst>(CurI))
       return nullptr;
 
     if (auto *SI = dyn_cast<StoreInst>(&CurI)) {
       // Found the previous store make sure it stores to the same location.
for (Instruction *I : SpeculatedDbgIntrinsics)
     I->eraseFromParent();
 
   ++NumSpeculations;
   return true;
 }
 
 /// Return true if we can thread a branch across this block.
 static bool BlockIsSimpleEnoughToThreadThrough(BasicBlock *BB) {
-  BranchInst *BI = cast<BranchInst>(BB->getTerminator());
   unsigned Size = 0;
 
-  for (BasicBlock::iterator BBI = BB->begin(); &*BBI != BI; ++BBI) {
-    if (isa<DbgInfoIntrinsic>(BBI))
-      continue;
+  for (Instruction &I : BB->instructionsWithoutDebug()) {
     if (Size > 10)
       return false; // Don't clone large BB's.
     ++Size;
 
     // We can only support instructions that do not define values that are
     // live outside of the current basic block.
-    for (User *U : BBI->users()) {
+    for (User *U : I.users()) {
       Instruction *UI = cast<Instruction>(U);
       if (UI->getParent() != BB || isa<PHINode>(UI))
         return false;
     }
 
     // Looks ok, continue checking.
   }
 
static bool mergeConditionalStoreToAddress(BasicBlock *PTB, BasicBlock *PFB,
   // confidence that by optimizing we'll allow P and/or Q to be if-converted.
   auto IsWorthwhile = [&](BasicBlock *BB) {
     if (!BB)
       return true;
     // Heuristic: if the block can be if-converted/phi-folded and the
     // instructions inside are all cheap (arithmetic/GEPs), it's worthwhile to
     // thread this store.
     unsigned N = 0;
-    for (auto &I : *BB) {
+    for (auto &I : BB->instructionsWithoutDebug()) {
       // Cheap instructions viable for folding.
       if (isa<BinaryOperator>(I) || isa<GetElementPtrInst>(I) ||
           isa<StoreInst>(I))
         ++N;
       // Free instructions.
-      else if (isa<TerminatorInst>(I) || isa<DbgInfoIntrinsic>(I) ||
-               IsaBitcastOfPointerType(I))
+      else if (isa<TerminatorInst>(I) || IsaBitcastOfPointerType(I))
         continue;
       else
         return false;
     }
     // The store we want to merge is counted in N, so add 1 to make sure
     // we're counting the instructions that would be left.
     return N <= (PHINodeFoldingThreshold + 1);
   };
static bool SimplifyCondBranchToCondBranch(BranchInst *PBI, BranchInst *BI,
   // address, remove the stores from the conditionals and create a conditional
   // merged store at the end.
   if (MergeCondStores && mergeConditionalStores(PBI, BI, DL))
     return true;
 
   // If this is a conditional branch in an empty block, and if any
   // predecessors are a conditional branch to one of our destinations,
   // fold the conditions into logical ops and one cond br.
-  BasicBlock::iterator BBI = BB->begin();
+
   // Ignore dbg intrinsics.
-  while (isa<DbgInfoIntrinsic>(BBI))
-    ++BBI;
-  if (&*BBI != BI)
+  if (&*BB->instructionsWithoutDebug().begin() != BI)
     return false;
 
   int PBIOp, BIOp;
   if (PBI->getSuccessor(0) == BI->getSuccessor(0)) {
     PBIOp = 0;
     BIOp = 0;
   } else if (PBI->getSuccessor(0) == BI->getSuccessor(1)) {
     PBIOp = 0;
GetCaseResults(SwitchInst *SI, ConstantInt *CaseVal, BasicBlock *CaseDest,
                const DataLayout &DL, const TargetTransformInfo &TTI) {
   // The block from which we enter the common destination.
   BasicBlock *Pred = SI->getParent();
 
   // If CaseDest is empty except for some side-effect free instructions through
   // which we can constant-propagate the CaseVal, continue to its successor.
   SmallDenseMap<Value *, Constant *> ConstantPool;
   ConstantPool.insert(std::make_pair(SI->getCondition(), CaseVal));
-  for (BasicBlock::iterator I = CaseDest->begin(), E = CaseDest->end(); I != E;
-       ++I) {
-    if (TerminatorInst *T = dyn_cast<TerminatorInst>(I)) {
+  for (Instruction &I :CaseDest->instructionsWithoutDebug()) {
+    if (TerminatorInst *T = dyn_cast<TerminatorInst>(&I)) {
       // If the terminator is a simple branch, continue to the next block.
       if (T->getNumSuccessors() != 1 || T->isExceptional())
         return false;
       Pred = CaseDest;
       CaseDest = T->getSuccessor(0);
-    } else if (isa<DbgInfoIntrinsic>(I)) {
-      // Skip debug intrinsic.
-      continue;
-    } else if (Constant *C = ConstantFold(&*I, DL, ConstantPool)) {
+    } else if (Constant *C = ConstantFold(&I, DL, ConstantPool)) {
       // Instruction is side-effect free and constant.
 
       // If the instruction has uses outside this block or a phi node slot for
       // the block, it is not safe to bypass the instruction since it would then
       // no longer dominate all its uses.
-      for (auto &Use : I->uses()) {
+      for (auto &Use : I.uses()) {
         User *User = Use.getUser();
         if (Instruction *I = dyn_cast<Instruction>(User))
           if (I->getParent() == CaseDest)
             continue;
         if (PHINode *Phi = dyn_cast<PHINode>(User))
           if (Phi->getIncomingBlock(Use) == CaseDest)
             continue;
         return false;
       }
 
-      ConstantPool.insert(std::make_pair(&*I, C));
+      ConstantPool.insert(std::make_pair(&I, C));
     } else {
       break;
     }
   }
 
   // If we did not have a CommonDest before, use the current one.
   if (!*CommonDest)
     *CommonDest = CaseDest;
if (isValueEqualityComparison(SI)) {
 
     Value *Cond = SI->getCondition();
     if (SelectInst *Select = dyn_cast<SelectInst>(Cond))
       if (SimplifySwitchOnSelect(SI, Select))
         return simplifyCFG(BB, TTI, Options) | true;
 
     // If the block only contains the switch, see if we can fold the block
     // away into any preds.
-    BasicBlock::iterator BBI = BB->begin();
-    // Ignore dbg intrinsics.
-    while (isa<DbgInfoIntrinsic>(BBI))
-      ++BBI;
-    if (SI == &*BBI)
+    if (SI == &*BB->instructionsWithoutDebug().begin())
       if (FoldValueComparisonIntoPredecessors(SI, Builder))
         return simplifyCFG(BB, TTI, Options) | true;
   }
 
   // Try to transform the switch into an icmp and a branch.
   if (TurnSwitchRangeIntoICmp(SI, Builder))
     return simplifyCFG(BB, TTI, Options) | true;
 
if (isValueEqualityComparison(BI)) {
     // see if that predecessor totally determines the outcome of this
     // switch.
     if (BasicBlock *OnlyPred = BB->getSinglePredecessor())
       if (SimplifyEqualityComparisonWithOnlyPredecessor(BI, OnlyPred, Builder))
         return simplifyCFG(BB, TTI, Options) | true;
 
     // This block must be empty, except for the setcond inst, if it exists.
     // Ignore dbg intrinsics.
-    BasicBlock::iterator I = BB->begin();
-    // Ignore dbg intrinsics.
-    while (isa<DbgInfoIntrinsic>(I))
-      ++I;
+    auto I = BB->instructionsWithoutDebug().begin();
     if (&*I == BI) {
       if (FoldValueComparisonIntoPredecessors(BI, Builder))
         return simplifyCFG(BB, TTI, Options) | true;
     } else if (&*I == cast<Instruction>(BI->getCondition())) {
       ++I;
-      // Ignore dbg intrinsics.
-      while (isa<DbgInfoIntrinsic>(I))
-        ++I;
       if (&*I == BI && FoldValueComparisonIntoPredecessors(BI, Builder))
         return simplifyCFG(BB, TTI, Options) | true;
     }
   }
 
   // Try to turn "br (X == 0 | X == 1), T, F" into a switch instruction.
   if (SimplifyBranchOnICmpChain(BI, Builder, DL))
     return true;