Revert "[LoopDeletion] Break backedge of loops when known not taken"

This reverts commit dd6bb367d19e3bf18353e40de54d35480999a930.

Multi-stage builders are showing an assertion failure w/LCSSA not being preserved on entry to IndVars.  Reason isn't clear, reverting while investigating.

1 files changed, 0 insertions, 31 deletions

diff --git a/llvm/lib/Transforms/Utils/LoopUtils.cpp b/llvm/lib/Transforms/Utils/LoopUtils.cpp
index 4f98995..96f1d42 100644
--- a/llvm/lib/Transforms/Utils/LoopUtils.cpp
+++ b/llvm/lib/Transforms/Utils/LoopUtils.cpp
@@ -756,37 +756,6 @@ void llvm::deleteDeadLoop(Loop *L, DominatorTree *DT, ScalarEvolution *SE,
   }
 }
 
-void llvm::breakLoopBackedge(Loop *L, DominatorTree &DT, ScalarEvolution &SE,
-                             LoopInfo &LI, MemorySSA *MSSA) {
-
-  auto *Latch = L->getLoopLatch();
-  assert(Latch);
-  auto *Header = L->getHeader();
-
-  SE.forgetLoop(L);
-
-  // Note: By splitting the backedge, and then explicitly making it unreachable
-  // we gracefully handle corner cases such as non-bottom tested loops and the
-  // like.  We also have the benefit of being able to reuse existing well tested
-  // code.  It might be worth special casing the common bottom tested case at
-  // some point to avoid code churn.
-
-  std::unique_ptr<MemorySSAUpdater> MSSAU;
-  if (MSSA)
-    MSSAU = std::make_unique<MemorySSAUpdater>(MSSA);
-
-  auto *BackedgeBB = SplitEdge(Latch, Header, &DT, &LI, MSSAU.get());
-
-  DomTreeUpdater DTU(&DT, DomTreeUpdater::UpdateStrategy::Eager);
-  (void)changeToUnreachable(BackedgeBB->getTerminator(), /*UseTrap*/false,
-                            /*PreserveLCSSA*/true, &DTU, MSSAU.get());
-
-  // Erase (and destroy) this loop instance.  Handles relinking sub-loops
-  // and blocks within the loop as needed.
-  LI.erase(L);
-}
-
-
 /// Checks if \p L has single exit through latch block except possibly
 /// "deoptimizing" exits. Returns branch instruction terminating the loop
 /// latch if above check is successful, nullptr otherwise.