[SimplifyCFG] Use getSingleSuccessor() to simplify some code

[craig.topper]

Summary

Rather than acquiring the TerminatorInst and asking how many successors it has and comparing to 1 this patch just uses getSingleSuccessor() which should be equivalent.

[davide]

Is this just a cleanup or is there any particular reason why you're doing this? I don't find it much more readable, FWIW.

[craig.topper]

It was just cleanup. I was looking at the code and noticed that it was using getSinglePredecessor, but was taking a longer way to get the single successor.

lib/Transforms/Utils/SimplifyCFG.cpp

bool SimplifyCFGOpt::SimplifyCondBranch(BranchInst *BI, IRBuilder<> &Builder) {
   // can hoist it up to the branching block.
   if (BI->getSuccessor(0)->getSinglePredecessor()) {
     if (BI->getSuccessor(1)->getSinglePredecessor()) {
       if (HoistThenElseCodeToIf(BI, TTI))
         return SimplifyCFG(BB, TTI, BonusInstThreshold, AC) | true;
     } else {
       // If Successor #1 has multiple preds, we may be able to conditionally
       // execute Successor #0 if it branches to Successor #1.
-      TerminatorInst *Succ0TI = BI->getSuccessor(0)->getTerminator();
-      if (Succ0TI->getNumSuccessors() == 1 &&
-          Succ0TI->getSuccessor(0) == BI->getSuccessor(1))
+      if (BI->getSuccessor(0)->getSingleSuccessor() == BI->getSuccessor(1))
         if (SpeculativelyExecuteBB(BI, BI->getSuccessor(0), TTI))
           return SimplifyCFG(BB, TTI, BonusInstThreshold, AC) | true;
     }
   } else if (BI->getSuccessor(1)->getSinglePredecessor()) {
     // If Successor #0 has multiple preds, we may be able to conditionally
     // execute Successor #1 if it branches to Successor #0.
-    TerminatorInst *Succ1TI = BI->getSuccessor(1)->getTerminator();
-    if (Succ1TI->getNumSuccessors() == 1 &&
-        Succ1TI->getSuccessor(0) == BI->getSuccessor(0))
+    if (BI->getSuccessor(1)->getSingleSuccessor() == BI->getSuccessor(0))
       if (SpeculativelyExecuteBB(BI, BI->getSuccessor(1), TTI))
         return SimplifyCFG(BB, TTI, BonusInstThreshold, AC) | true;
   }
 
   // If this is a branch on a phi node in the current block, thread control
   // through this block if any PHI node entries are constants.
   if (PHINode *PN = dyn_cast<PHINode>(BI->getCondition()))
     if (PN->getParent() == BI->getParent())