[CloneFunction] Preserve DT in DuplicateInstructionsInSplitBetween.

[fhahn]

Summary

DuplicateInstructionsInSplitBetween can preserve the DT by passing
through DT to SplitEdge.

[brzycki]

I'm not a reviewer, but it LGTM. You might want to ask @kuhar to review too.

[junbuml]

+1

[fhahn]

Just passing in DT here is the easy way to update the dominator tree. But we should start switching to deferred dominators (or a more generic update object) at some point.

include/llvm/Transforms/Utils/Cloning.h

 /// from BB between its beginning and the StopAt instruction into the split
 /// block. Phi nodes are not duplicated, but their uses are handled correctly:
 /// we replace them with the uses of corresponding Phi inputs. ValueMapping
 /// is used to map the original instructions from BB to their newly-created
 /// copies. Returns the split block.
 BasicBlock *
 DuplicateInstructionsInSplitBetween(BasicBlock *BB, BasicBlock *PredBB,
                                     Instruction *StopAt,
-                                    ValueToValueMapTy &ValueMapping);
+                                    ValueToValueMapTy &ValueMapping,
+                                    DominatorTree *DT = nullptr);
 } // end namespace llvm
 
 #endif // LLVM_TRANSFORMS_UTILS_CLONING_H

lib/Transforms/Utils/CloneFunction.cpp

Loop *llvm::cloneLoopWithPreheader(BasicBlock *Before, BasicBlock *LoopDomBB,
   return NewLoop;
 }
 
 /// \brief Duplicate non-Phi instructions from the beginning of block up to
 /// StopAt instruction into a split block between BB and its predecessor.
 BasicBlock *
 llvm::DuplicateInstructionsInSplitBetween(BasicBlock *BB, BasicBlock *PredBB,
                                           Instruction *StopAt,
-                                          ValueToValueMapTy &ValueMapping) {
+                                          ValueToValueMapTy &ValueMapping,
+                                          DominatorTree *DT) {
   // We are going to have to map operands from the original BB block to the new
   // copy of the block 'NewBB'.  If there are PHI nodes in BB, evaluate them to
   // account for entry from PredBB.
   BasicBlock::iterator BI = BB->begin();
   for (; PHINode *PN = dyn_cast<PHINode>(BI); ++BI)
     ValueMapping[PN] = PN->getIncomingValueForBlock(PredBB);
 
-  BasicBlock *NewBB = SplitEdge(PredBB, BB);
+  BasicBlock *NewBB = SplitEdge(PredBB, BB, DT);
   NewBB->setName(PredBB->getName() + ".split");
   Instruction *NewTerm = NewBB->getTerminator();
 
   // Clone the non-phi instructions of BB into NewBB, keeping track of the
   // mapping and using it to remap operands in the cloned instructions.
   // Stop once we see the terminator too. This covers the case where BB's
   // terminator gets replaced and StopAt == BB's terminator.
   for (; StopAt != &*BI && BB->getTerminator() != &*BI; ++BI) {