[NFC][GVNSink] Don't pretend that iteration is over instructions when it's actually over blocks

[nikic]

llvm/lib/Transforms/Scalar/GVNSink.cpp

787

Make this something like erase_if(Preds, [](BasicBlock *BB) { return BB->getTerminator()->getNumSuccessors() != 1; }?

[nikic]

LGTM

llvm/lib/Transforms/Scalar/GVNSink.cpp

else
       return 0;
   }
   if (Preds.size() < 2)
     return 0;
   llvm::sort(Preds);
 
   unsigned NumOrigPreds = Preds.size();
   // We can only sink instructions through unconditional branches.
-  for (auto I = Preds.begin(); I != Preds.end();) {
-    if ((*I)->getTerminator()->getNumSuccessors() != 1)
-      I = Preds.erase(I);
+  for (auto BB = Preds.begin(); BB != Preds.end();) {
+    if ((*BB)->getTerminator()->getNumSuccessors() != 1)
+      BB = Preds.erase(BB);
     else
-      ++I;
+      ++BB;
   }
 
   LockstepReverseIterator LRI(Preds);
   SmallVector<SinkingInstructionCandidate, 4> Candidates;
   unsigned InstNum = 0, MemoryInstNum = 0;
   ModelledPHISet NeededPHIs;
   SmallPtrSet<Value *, 4> PHIContents;
   analyzeInitialPHIs(BBEnd, NeededPHIs, PHIContents);
   unsigned NumOrigPHIs = NeededPHIs.size();