This reverts commit r306272.

Revert "[MBP] do not rotate loop if it creates extra branch"

It breaks the sanitizer build bots. Need to fix this.

llvm-svn: 306276

1 files changed, 0 insertions, 29 deletions

diff --git a/llvm/lib/CodeGen/MachineBlockPlacement.cpp b/llvm/lib/CodeGen/MachineBlockPlacement.cpp
index c8f8dda0c2d..2d4b95974cc 100644
--- a/llvm/lib/CodeGen/MachineBlockPlacement.cpp
+++ b/llvm/lib/CodeGen/MachineBlockPlacement.cpp
@@ -1944,35 +1944,6 @@ void MachineBlockPlacement::rotateLoop(BlockChain &LoopChain,
   if (ExitIt == LoopChain.end())
     return;
 
-  // Rotating a loop exit to the bottom when there is a fallthrough to top
-  // trades the entry fallthrough for an exit fallthrough.
-  // If there is no bottom->top edge, but the chosen exit block does have
-  // a fallthrough, we break that fallthrough for nothing in return.
-
-  // Let's consider an example. We have a built chain of basic blocks
-  // B1, B2, ..., Bn, where Bk is a ExitingBB - chosen exit block.
-  // By doing a rotation we get
-  // Bk+1, ..., Bn, B1, ..., Bk
-  // Break of fallthrough to B1 is compensated by a fallthrough from Bk.
-  // If we had a fallthrough Bk -> Bk+1 it is broken now.
-  // It might be compensated by fallthrough Bn -> B1.
-  // So we have a condition to avoid creation of extra branch by loop rotation.
-  // All below must be true to avoid loop rotation:
-  //   If there is a fallthrough to top (B1)
-  //   There was fallthrough from chosen exit block (Bk) to next one (Bk+1)
-  //   There is no fallthrough from bottom (Bn) to top (B1).
-  // Please note that there is no exit fallthrough from Bn because we checked it
-  // above.
-  if (ViableTopFallthrough) {
-    MachineBasicBlock *NextBlockInChain = *std::next(ExitIt);
-    MachineBasicBlock *Bottom = *std::prev(LoopChain.end());
-    if (NextBlockInChain->isPredecessor(ExitingBB))
-      if (!Top->isPredecessor(Bottom))
-        return;
-  }
-
-  DEBUG(dbgs() << "Rotating loop to put exit " << getBlockName(ExitingBB)
-               << " at bottom\n");
   std::rotate(LoopChain.begin(), std::next(ExitIt), LoopChain.end());
 }