[Transforms] Use llvm::pred_size and llvm::predecessors (NFC)

Author: kazutakahirata

llvm/lib/Transforms/Scalar/JumpThreading.cpp

@@ -1431,16 +1431,14 @@ bool JumpThreadingPass::simplifyPartiallyRedundantLoad(LoadInst *LoadI) {
   array_pod_sort(AvailablePreds.begin(), AvailablePreds.end());
 
   // Create a PHI node at the start of the block for the PRE'd load value.
-  pred_iterator PB = pred_begin(LoadBB), PE = pred_end(LoadBB);
-  PHINode *PN = PHINode::Create(LoadI->getType(), std::distance(PB, PE), "");
+  PHINode *PN = PHINode::Create(LoadI->getType(), pred_size(LoadBB), "");
   PN->insertBefore(LoadBB->begin());
   PN->takeName(LoadI);
   PN->setDebugLoc(LoadI->getDebugLoc());
 
   // Insert new entries into the PHI for each predecessor.  A single block may
   // have multiple entries here.
-  for (pred_iterator PI = PB; PI != PE; ++PI) {
-    BasicBlock *P = *PI;
+  for (BasicBlock *P : predecessors(LoadBB)) {
     AvailablePredsTy::iterator I =
         llvm::lower_bound(AvailablePreds, std::make_pair(P, (Value *)nullptr));