Standardize {pred,succ,use,user}_empty()

The functions {pred,succ,use,user}_{begin,end} exist, but many users
have to check *_begin() with *_end() by hand to determine if the
BasicBlock or User is empty. Fix this with a standard *_empty(),
demonstrating a few usecases.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@225760 91177308-0d34-0410-b5e6-96231b3b80d8

include/llvm/IR/CFG.h

@@ -93,6 +93,9 @@ inline pred_iterator pred_end(BasicBlock *BB) { return pred_iterator(BB, true);}
 inline const_pred_iterator pred_end(const BasicBlock *BB) {
   return const_pred_iterator(BB, true);
 }
+inline bool pred_empty(const BasicBlock *BB) {
+  return pred_begin(BB) == pred_end(BB);
+}
 
 
 
@@ -257,6 +260,9 @@ inline succ_iterator succ_end(BasicBlock *BB) {
 inline succ_const_iterator succ_end(const BasicBlock *BB) {
   return succ_const_iterator(BB->getTerminator(), true);
 }
+inline bool succ_empty(const BasicBlock *BB) {
+  return succ_begin(BB) == succ_end(BB);
+}
 
 template <typename T, typename U> struct isPodLike<SuccIterator<T, U> > {
   static const bool value = isPodLike<T>::value;

include/llvm/IR/Value.h

@@ -286,6 +286,8 @@ public:
     return iterator_range<const_use_iterator>(use_begin(), use_end());
   }
 
+  bool               user_empty() const { return UseList == nullptr; }
+
   typedef user_iterator_impl<User>       user_iterator;
   typedef user_iterator_impl<const User> const_user_iterator;
   user_iterator       user_begin()       { return user_iterator(UseList); }

lib/Analysis/CFG.cpp

@@ -27,7 +27,7 @@ using namespace llvm;
 void llvm::FindFunctionBackedges(const Function &F,
      SmallVectorImpl<std::pair<const BasicBlock*,const BasicBlock*> > &Result) {
   const BasicBlock *BB = &F.getEntryBlock();
-  if (succ_begin(BB) == succ_end(BB))
+  if (succ_empty(BB))
     return;
 
   SmallPtrSet<const BasicBlock*, 8> Visited;

lib/IR/Verifier.cpp

@@ -1128,7 +1128,7 @@ void Verifier::visitFunction(const Function &F) {
 
     // Check the entry node
     const BasicBlock *Entry = &F.getEntryBlock();
-    Assert1(pred_begin(Entry) == pred_end(Entry),
+    Assert1(pred_empty(Entry),
             "Entry block to function must not have predecessors!", Entry);
 
     // The address of the entry block cannot be taken, unless it is dead.

lib/Transforms/IPO/PruneEH.cpp

@@ -200,7 +200,7 @@ bool PruneEH::SimplifyFunction(Function *F) {
         BB->getInstList().pop_back();
 
         // If the unwind block is now dead, nuke it.
-        if (pred_begin(UnwindBlock) == pred_end(UnwindBlock))
+        if (pred_empty(UnwindBlock))
           DeleteBasicBlock(UnwindBlock);  // Delete the new BB.
 
         ++NumRemoved;
@@ -234,7 +234,7 @@ bool PruneEH::SimplifyFunction(Function *F) {
 /// updating the callgraph to reflect any now-obsolete edges due to calls that
 /// exist in the BB.
 void PruneEH::DeleteBasicBlock(BasicBlock *BB) {
-  assert(pred_begin(BB) == pred_end(BB) && "BB is not dead!");
+  assert(pred_empty(BB) && "BB is not dead!");
   CallGraph &CG = getAnalysis<CallGraphWrapperPass>().getCallGraph();
 
   CallGraphNode *CGN = CG[BB->getParent()];

lib/Transforms/Scalar/JumpThreading.cpp

@@ -188,7 +188,7 @@ bool JumpThreading::runOnFunction(Function &F) {
 
       // If the block is trivially dead, zap it.  This eliminates the successor
       // edges which simplifies the CFG.
-      if (pred_begin(BB) == pred_end(BB) &&
+      if (pred_empty(BB) &&
           BB != &BB->getParent()->getEntryBlock()) {
         DEBUG(dbgs() << "  JT: Deleting dead block '" << BB->getName()
               << "' with terminator: " << *BB->getTerminator() << '\n');
@@ -662,7 +662,7 @@ static bool hasAddressTakenAndUsed(BasicBlock *BB) {
 bool JumpThreading::ProcessBlock(BasicBlock *BB) {
   // If the block is trivially dead, just return and let the caller nuke it.
   // This simplifies other transformations.
-  if (pred_begin(BB) == pred_end(BB) &&
+  if (pred_empty(BB) &&
       BB != &BB->getParent()->getEntryBlock())
     return false;
 

lib/Transforms/Scalar/Reg2Mem.cpp

@@ -73,7 +73,7 @@ bool RegToMem::runOnFunction(Function &F) {
 
   // Insert all new allocas into entry block.
   BasicBlock *BBEntry = &F.getEntryBlock();
-  assert(pred_begin(BBEntry) == pred_end(BBEntry) &&
+  assert(pred_empty(BBEntry) &&
          "Entry block to function must not have predecessors!");
 
   // Find first non-alloca instruction and create insertion point. This is

lib/Transforms/Utils/SimplifyCFG.cpp

@@ -3020,7 +3020,7 @@ bool SimplifyCFGOpt::SimplifyReturn(ReturnInst *RI, IRBuilder<> &Builder) {
     }
 
     // If we eliminated all predecessors of the block, delete the block now.
-    if (pred_begin(BB) == pred_end(BB))
+    if (pred_empty(BB))
       // We know there are no successors, so just nuke the block.
       BB->eraseFromParent();
 
@@ -3193,7 +3193,7 @@ bool SimplifyCFGOpt::SimplifyUnreachable(UnreachableInst *UI) {
   }
 
   // If this block is now dead, remove it.
-  if (pred_begin(BB) == pred_end(BB) &&
+  if (pred_empty(BB) &&
       BB != &BB->getParent()->getEntryBlock()) {
     // We know there are no successors, so just nuke the block.
     BB->eraseFromParent();
@@ -4587,7 +4587,7 @@ bool SimplifyCFGOpt::run(BasicBlock *BB) {
 
   // Remove basic blocks that have no predecessors (except the entry block)...
   // or that just have themself as a predecessor.  These are unreachable.
-  if ((pred_begin(BB) == pred_end(BB) &&
+  if ((pred_emtpy(BB) &&
        BB != &BB->getParent()->getEntryBlock()) ||
       BB->getSinglePredecessor() == BB) {
     DEBUG(dbgs() << "Removing BB: \n" << *BB);