Revert r85667. LoopUnroll currently can't call utility functions which

auto-update the DominatorTree because it doesn't keep the DominatorTree
current while it works.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@85670 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 47 insertions, 1 deletions

diff --git a/lib/Transforms/Utils/LoopUnroll.cpp b/lib/Transforms/Utils/LoopUnroll.cpp
index 9b68df05b8..d68427afce 100644
--- a/lib/Transforms/Utils/LoopUnroll.cpp
+++ b/lib/Transforms/Utils/LoopUnroll.cpp
@@ -49,6 +49,52 @@ static inline void RemapInstruction(Instruction *I,
   }
 }
 
+/// FoldBlockIntoPredecessor - Folds a basic block into its predecessor if it
+/// only has one predecessor, and that predecessor only has one successor.
+/// The LoopInfo Analysis that is passed will be kept consistent.
+/// Returns the new combined block.
+static BasicBlock *FoldBlockIntoPredecessor(BasicBlock *BB, LoopInfo* LI) {
+  // Merge basic blocks into their predecessor if there is only one distinct
+  // pred, and if there is only one distinct successor of the predecessor, and
+  // if there are no PHI nodes.
+  BasicBlock *OnlyPred = BB->getSinglePredecessor();
+  if (!OnlyPred) return 0;
+
+  if (OnlyPred->getTerminator()->getNumSuccessors() != 1)
+    return 0;
+
+  DEBUG(errs() << "Merging: " << *BB << "into: " << *OnlyPred);
+
+  // Resolve any PHI nodes at the start of the block.  They are all
+  // guaranteed to have exactly one entry if they exist, unless there are
+  // multiple duplicate (but guaranteed to be equal) entries for the
+  // incoming edges.  This occurs when there are multiple edges from
+  // OnlyPred to OnlySucc.
+  FoldSingleEntryPHINodes(BB);
+
+  // Delete the unconditional branch from the predecessor...
+  OnlyPred->getInstList().pop_back();
+
+  // Move all definitions in the successor to the predecessor...
+  OnlyPred->getInstList().splice(OnlyPred->end(), BB->getInstList());
+
+  // Make all PHI nodes that referred to BB now refer to Pred as their
+  // source...
+  BB->replaceAllUsesWith(OnlyPred);
+
+  std::string OldName = BB->getName();
+
+  // Erase basic block from the function...
+  LI->removeBlock(BB);
+  BB->eraseFromParent();
+
+  // Inherit predecessor's name if it exists...
+  if (!OldName.empty() && !OnlyPred->hasName())
+    OnlyPred->setName(OldName);
+
+  return OnlyPred;
+}
+
 /// Unroll the given loop by Count. The loop must be in LCSSA form. Returns true
 /// if unrolling was succesful, or false if the loop was unmodified. Unrolling
 /// can only fail when the loop's latch block is not terminated by a conditional
@@ -287,7 +333,7 @@ bool llvm::UnrollLoop(Loop *L, unsigned Count, LoopInfo* LI, LPPassManager* LPM)
     } else {
       Term->setUnconditionalDest(Dest);
       // Merge adjacent basic blocks, if possible.
-      if (BasicBlock *Fold = MergeBlockIntoPredecessor(Dest, LI)) {
+      if (BasicBlock *Fold = FoldBlockIntoPredecessor(Dest, LI)) {
         std::replace(Latches.begin(), Latches.end(), Dest, Fold);
         std::replace(Headers.begin(), Headers.end(), Dest, Fold);
       }