Use BasicBlock Util SplitBlock interface to update DT

[davidxl]

Summary

This fixed a bug in CodeExtractor that is only exposed with the partial inliner improvement patch (thus no test yet)

[wmi]

LGTM.

lib/Transforms/Utils/CodeExtractor.cpp

221

nit: AfterPHIs can be moved closer to its use.

[davide]

LGTM

lib/Transforms/Utils/CodeExtractor.cpp

     // need to do anything special.
     if (NumPredsOutsideRegion <= 1) return;
   }
 
   // Otherwise, we need to split the header block into two pieces: one
   // containing PHI nodes merging values from outside of the region, and a
   // second that contains all of the code for the block and merges back any
   // incoming values from inside of the region.
-  BasicBlock::iterator AfterPHIs = Header->getFirstNonPHI()->getIterator();
-  BasicBlock *NewBB = Header->splitBasicBlock(AfterPHIs,
-                                              Header->getName()+".ce");
+  BasicBlock::iterator AfterPHIs;
+
+  BasicBlock *NewBB = llvm::SplitBlock(Header, Header->getFirstNonPHI(), DT);
 
   // We only want to code extract the second block now, and it becomes the new
   // header of the region.
   BasicBlock *OldPred = Header;
   Blocks.remove(OldPred);
   Blocks.insert(NewBB);
   Header = NewBB;
 
-  // Okay, update dominator sets. The blocks that dominate the new one are the
-  // blocks that dominate TIBB plus the new block itself.
-  if (DT)
-    DT->splitBlock(NewBB);
-
   // Okay, now we need to adjust the PHI nodes and any branches from within the
   // region to go to the new header block instead of the old header block.
   if (NumPredsFromRegion) {
     PHINode *PN = cast<PHINode>(OldPred->begin());
     // Loop over all of the predecessors of OldPred that are in the region,
     // changing them to branch to NewBB instead.
     for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i)
       if (Blocks.count(PN->getIncomingBlock(i))) {