diff --git a/llvm/include/llvm/Transforms/Utils/LoopUtils.h b/llvm/include/llvm/Transforms/Utils/LoopUtils.h
--- a/llvm/include/llvm/Transforms/Utils/LoopUtils.h
+++ b/llvm/include/llvm/Transforms/Utils/LoopUtils.h
@@ -179,6 +179,12 @@
 void deleteDeadLoop(Loop *L, DominatorTree *DT, ScalarEvolution *SE,
                     LoopInfo *LI, MemorySSA *MSSA = nullptr);
 
+/// Remove the backedge of the specified loop.  Handles loop nests and general
+/// loop structures subject to the precondition that the loop has no parent
+/// loop and has a single latch block.  Preserves all listed analyses.
+void breakLoopBackedge(Loop *L, DominatorTree &DT, ScalarEvolution &SE,
+                       LoopInfo &LI, MemorySSA *MSSA);
+
 /// Try to promote memory values to scalars by sinking stores out of
 /// the loop and moving loads to before the loop.  We do this by looping over
 /// the stores in the loop, looking for stores to Must pointers which are
diff --git a/llvm/lib/Transforms/Scalar/LoopDeletion.cpp b/llvm/lib/Transforms/Scalar/LoopDeletion.cpp
--- a/llvm/lib/Transforms/Scalar/LoopDeletion.cpp
+++ b/llvm/lib/Transforms/Scalar/LoopDeletion.cpp
@@ -26,6 +26,7 @@
 #include "llvm/Transforms/Scalar.h"
 #include "llvm/Transforms/Scalar/LoopPassManager.h"
 #include "llvm/Transforms/Utils/LoopUtils.h"
+
 using namespace llvm;
 
 #define DEBUG_TYPE "loop-delete"
@@ -38,6 +39,14 @@
   Deleted,
 };
 
+static LoopDeletionResult merge(LoopDeletionResult A, LoopDeletionResult B) {
+  if (A == LoopDeletionResult::Deleted || B == LoopDeletionResult::Deleted)
+    return LoopDeletionResult::Deleted;
+  if (A == LoopDeletionResult::Modified || B == LoopDeletionResult::Modified)
+    return LoopDeletionResult::Modified;
+  return LoopDeletionResult::Unmodified;
+}
+
 /// Determines if a loop is dead.
 ///
 /// This assumes that we've already checked for unique exit and exiting blocks,
@@ -126,6 +135,34 @@
   return true;
 }
 
+/// If we can prove the backedge is untaken, remove it.  This destroys the
+/// loop, but leaves the (now trivially loop invariant) control flow and
+/// side effects (if any) in place.
+static LoopDeletionResult
+breakBackedgeIfNotTaken(Loop *L, DominatorTree &DT, ScalarEvolution &SE,
+                        LoopInfo &LI, MemorySSA *MSSA,
+                        OptimizationRemarkEmitter &ORE) {
+  assert(L->isLCSSAForm(DT) && "Expected LCSSA!");
+
+  if (!L->getLoopLatch())
+    return LoopDeletionResult::Unmodified;
+
+  auto *BTC = SE.getBackedgeTakenCount(L);
+  if (!BTC->isZero())
+    return LoopDeletionResult::Unmodified;
+
+  // For non-outermost loops, the tricky case is that we can drop blocks
+  // out of both inner and outer loops at the same time.  This results in
+  // new exiting block for the outer loop appearing, and possibly needing
+  // an lcssa phi inserted.  (See loop_nest_lcssa test case in zero-btc.ll)
+  // TODO: We can handle a bunch of cases here without much work, revisit.
+  if (!L->isOutermost())
+    return LoopDeletionResult::Unmodified;
+
+  breakLoopBackedge(L, DT, SE, LI, MSSA);
+  return LoopDeletionResult::Deleted;
+}
+
 /// Remove a loop if it is dead.
 ///
 /// A loop is considered dead either if it does not impact the observable
@@ -236,6 +273,14 @@
   // but ORE cannot be preserved (see comment before the pass definition).
   OptimizationRemarkEmitter ORE(L.getHeader()->getParent());
   auto Result = deleteLoopIfDead(&L, AR.DT, AR.SE, AR.LI, AR.MSSA, ORE);
+
+  // If we can prove the backedge isn't taken, just break it and be done.  This
+  // leaves the loop structure in place which means it can handle dispatching
+  // to the right exit based on whatever loop invariant structure remains.
+  if (Result != LoopDeletionResult::Deleted)
+    Result = merge(Result, breakBackedgeIfNotTaken(&L, AR.DT, AR.SE, AR.LI,
+                                                   AR.MSSA, ORE));
+
   if (Result == LoopDeletionResult::Unmodified)
     return PreservedAnalyses::all();
 
@@ -295,6 +340,12 @@
 
   LoopDeletionResult Result = deleteLoopIfDead(L, DT, SE, LI, MSSA, ORE);
 
+  // If we can prove the backedge isn't taken, just break it and be done.  This
+  // leaves the loop structure in place which means it can handle dispatching
+  // to the right exit based on whatever loop invariant structure remains.
+  if (Result != LoopDeletionResult::Deleted)
+    Result = merge(Result, breakBackedgeIfNotTaken(L, DT, SE, LI, MSSA, ORE));
+
   if (Result == LoopDeletionResult::Deleted)
     LPM.markLoopAsDeleted(*L);
 
diff --git a/llvm/lib/Transforms/Utils/LoopUtils.cpp b/llvm/lib/Transforms/Utils/LoopUtils.cpp
--- a/llvm/lib/Transforms/Utils/LoopUtils.cpp
+++ b/llvm/lib/Transforms/Utils/LoopUtils.cpp
@@ -762,6 +762,38 @@
   }
 }
 
+void llvm::breakLoopBackedge(Loop *L, DominatorTree &DT, ScalarEvolution &SE,
+                             LoopInfo &LI, MemorySSA *MSSA) {
+
+  assert(L->isOutermost() && "Can't yet preserve LCSSA for this case");
+  auto *Latch = L->getLoopLatch();
+  assert(Latch && "multiple latches not yet supported");
+  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.
diff --git a/llvm/test/Transforms/IndVarSimplify/exit_value_test2.ll b/llvm/test/Transforms/IndVarSimplify/exit_value_test2.ll
--- a/llvm/test/Transforms/IndVarSimplify/exit_value_test2.ll
+++ b/llvm/test/Transforms/IndVarSimplify/exit_value_test2.ll
@@ -89,8 +89,10 @@
 ; CHECK-NEXT:  entry:
 ; CHECK-NEXT:    br label [[LOOP:%.*]]
 ; CHECK:       loop:
-; CHECK-NEXT:    [[UNKNOWN_NEXT:%.*]] = load volatile i32, i32* [[UNKNOWN_MEM:%.*]]
-; CHECK-NEXT:    br i1 false, label [[LOOP]], label [[LEAVE:%.*]]
+; CHECK-NEXT:    [[UNKNOWN_NEXT:%.*]] = load volatile i32, i32* [[UNKNOWN_MEM:%.*]], align 4
+; CHECK-NEXT:    br i1 false, label [[LOOP_LOOP_CRIT_EDGE:%.*]], label [[LEAVE:%.*]]
+; CHECK:       loop.loop_crit_edge:
+; CHECK-NEXT:    unreachable
 ; CHECK:       leave:
 ; CHECK-NEXT:    ret i32 [[UNKNOWN_INIT:%.*]]
 ;
diff --git a/llvm/test/Transforms/LoopDeletion/update-scev.ll b/llvm/test/Transforms/LoopDeletion/update-scev.ll
--- a/llvm/test/Transforms/LoopDeletion/update-scev.ll
+++ b/llvm/test/Transforms/LoopDeletion/update-scev.ll
@@ -44,7 +44,8 @@
   %conv10 = zext i1 %cmp9 to i32
   %and = and i32 %conv10, %g.138
   %inc = add i32 %h.039, 1
-  br i1 undef, label %for.inc11, label %for.body6
+  %exit = icmp eq i32 %inc, 20000
+  br i1 %exit, label %for.inc11, label %for.body6
 
 for.inc11:                                        ; preds = %for.body6
   %and.lcssa = phi i32 [ %and, %for.body6 ]
diff --git a/llvm/test/Transforms/LoopDeletion/zero-btc.ll b/llvm/test/Transforms/LoopDeletion/zero-btc.ll
--- a/llvm/test/Transforms/LoopDeletion/zero-btc.ll
+++ b/llvm/test/Transforms/LoopDeletion/zero-btc.ll
@@ -9,7 +9,9 @@
 ; CHECK-NEXT:    br label [[LOOP:%.*]]
 ; CHECK:       loop:
 ; CHECK-NEXT:    store i32 0, i32* @G, align 4
-; CHECK-NEXT:    br i1 false, label [[LOOP]], label [[EXIT:%.*]]
+; CHECK-NEXT:    br i1 false, label [[LOOP_LOOP_CRIT_EDGE:%.*]], label [[EXIT:%.*]]
+; CHECK:       loop.loop_crit_edge:
+; CHECK-NEXT:    unreachable
 ; CHECK:       exit:
 ; CHECK-NEXT:    ret void
 ;
@@ -30,11 +32,13 @@
 ; CHECK-NEXT:  entry:
 ; CHECK-NEXT:    br label [[LOOP:%.*]]
 ; CHECK:       loop:
-; CHECK-NEXT:    [[IV:%.*]] = phi i32 [ 0, [[ENTRY:%.*]] ], [ [[IV_INC:%.*]], [[LOOP]] ]
+; CHECK-NEXT:    [[IV:%.*]] = phi i32 [ 0, [[ENTRY:%.*]] ]
 ; CHECK-NEXT:    store i32 0, i32* @G, align 4
-; CHECK-NEXT:    [[IV_INC]] = add i32 [[IV]], 1
+; CHECK-NEXT:    [[IV_INC:%.*]] = add i32 [[IV]], 1
 ; CHECK-NEXT:    [[BE_TAKEN:%.*]] = icmp ne i32 [[IV_INC]], 1
-; CHECK-NEXT:    br i1 [[BE_TAKEN]], label [[LOOP]], label [[EXIT:%.*]]
+; CHECK-NEXT:    br i1 [[BE_TAKEN]], label [[LOOP_LOOP_CRIT_EDGE:%.*]], label [[EXIT:%.*]]
+; CHECK:       loop.loop_crit_edge:
+; CHECK-NEXT:    unreachable
 ; CHECK:       exit:
 ; CHECK-NEXT:    ret void
 ;
@@ -57,13 +61,15 @@
 ; CHECK-NEXT:  entry:
 ; CHECK-NEXT:    br label [[LOOP:%.*]]
 ; CHECK:       loop:
-; CHECK-NEXT:    [[IV:%.*]] = phi i32 [ 0, [[ENTRY:%.*]] ], [ [[IV_INC:%.*]], [[LATCH:%.*]] ]
+; CHECK-NEXT:    [[IV:%.*]] = phi i32 [ 0, [[ENTRY:%.*]] ]
 ; CHECK-NEXT:    store i32 0, i32* @G, align 4
-; CHECK-NEXT:    [[IV_INC]] = add i32 [[IV]], 1
+; CHECK-NEXT:    [[IV_INC:%.*]] = add i32 [[IV]], 1
 ; CHECK-NEXT:    [[BE_TAKEN:%.*]] = icmp ne i32 [[IV_INC]], 1
-; CHECK-NEXT:    br i1 [[BE_TAKEN]], label [[LATCH]], label [[EXIT:%.*]]
+; CHECK-NEXT:    br i1 [[BE_TAKEN]], label [[LATCH:%.*]], label [[EXIT:%.*]]
 ; CHECK:       latch:
-; CHECK-NEXT:    br label [[LOOP]]
+; CHECK-NEXT:    br label [[LATCH_SPLIT:%.*]]
+; CHECK:       latch.split:
+; CHECK-NEXT:    unreachable
 ; CHECK:       exit:
 ; CHECK-NEXT:    ret void
 ;
@@ -88,15 +94,17 @@
 ; CHECK-NEXT:  entry:
 ; CHECK-NEXT:    br label [[LOOP:%.*]]
 ; CHECK:       loop:
-; CHECK-NEXT:    [[IV:%.*]] = phi i32 [ 0, [[ENTRY:%.*]] ], [ [[IV_INC:%.*]], [[LATCH:%.*]] ]
+; CHECK-NEXT:    [[IV:%.*]] = phi i32 [ 0, [[ENTRY:%.*]] ]
 ; CHECK-NEXT:    store i32 0, i32* @G, align 4
-; CHECK-NEXT:    [[IV_INC]] = add i32 [[IV]], 1
+; CHECK-NEXT:    [[IV_INC:%.*]] = add i32 [[IV]], 1
 ; CHECK-NEXT:    [[BE_TAKEN:%.*]] = icmp ne i32 [[IV_INC]], 1
-; CHECK-NEXT:    br i1 [[BE_TAKEN]], label [[LATCH]], label [[EXIT:%.*]]
+; CHECK-NEXT:    br i1 [[BE_TAKEN]], label [[LATCH:%.*]], label [[EXIT:%.*]]
 ; CHECK:       latch:
 ; CHECK-NEXT:    store i32 1, i32* @G, align 4
 ; CHECK-NEXT:    [[COND2:%.*]] = icmp ult i32 [[IV_INC]], 30
-; CHECK-NEXT:    br i1 [[COND2]], label [[LOOP]], label [[EXIT]]
+; CHECK-NEXT:    br i1 [[COND2]], label [[LATCH_LOOP_CRIT_EDGE:%.*]], label [[EXIT]]
+; CHECK:       latch.loop_crit_edge:
+; CHECK-NEXT:    unreachable
 ; CHECK:       exit:
 ; CHECK-NEXT:    ret void
 ;
@@ -127,7 +135,9 @@
 ; CHECK-NEXT:    br i1 true, label [[LATCH:%.*]], label [[EXIT:%.*]]
 ; CHECK:       latch:
 ; CHECK-NEXT:    store i32 1, i32* @G, align 4
-; CHECK-NEXT:    br i1 false, label [[LOOP]], label [[EXIT]]
+; CHECK-NEXT:    br i1 false, label [[LATCH_LOOP_CRIT_EDGE:%.*]], label [[EXIT]]
+; CHECK:       latch.loop_crit_edge:
+; CHECK-NEXT:    unreachable
 ; CHECK:       exit:
 ; CHECK-NEXT:    ret void
 ;
@@ -218,7 +228,9 @@
 ; CHECK-NEXT:    br i1 true, label [[LATCH:%.*]], label [[EXIT1:%.*]]
 ; CHECK:       latch:
 ; CHECK-NEXT:    store i32 1, i32* @G, align 4
-; CHECK-NEXT:    br i1 false, label [[LOOP]], label [[EXIT2:%.*]]
+; CHECK-NEXT:    br i1 false, label [[LATCH_LOOP_CRIT_EDGE:%.*]], label [[EXIT2:%.*]]
+; CHECK:       latch.loop_crit_edge:
+; CHECK-NEXT:    unreachable
 ; CHECK:       exit1:
 ; CHECK-NEXT:    ret void
 ; CHECK:       exit2:
@@ -254,7 +266,9 @@
 ; CHECK-NEXT:    [[CND:%.*]] = icmp ult i32 [[IV_INC]], 200
 ; CHECK-NEXT:    br i1 [[CND]], label [[INNER]], label [[LATCH:%.*]]
 ; CHECK:       latch:
-; CHECK-NEXT:    br i1 false, label [[LOOP]], label [[EXIT:%.*]]
+; CHECK-NEXT:    br i1 false, label [[LATCH_LOOP_CRIT_EDGE:%.*]], label [[EXIT:%.*]]
+; CHECK:       latch.loop_crit_edge:
+; CHECK-NEXT:    unreachable
 ; CHECK:       exit:
 ; CHECK-NEXT:    ret void
 ;
@@ -317,3 +331,45 @@
 exit:
   ret void
 }
+
+; Key point is that inner_latch drops out of the outer loop when
+; the inner loop is deleted, and thus the lcssa phi needs to be
+; in the inner_latch block to preserve LCSSA.  We either have to
+; insert the LCSSA phi, or not break the inner backedge.
+define void @loop_nest_lcssa() {
+; CHECK-LABEL: @loop_nest_lcssa(
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    [[TMP0:%.*]] = add i32 1, 2
+; CHECK-NEXT:    br label [[OUTER_HEADER:%.*]]
+; CHECK:       outer_header:
+; CHECK-NEXT:    br label [[INNER_HEADER:%.*]]
+; CHECK:       inner_header:
+; CHECK-NEXT:    br i1 false, label [[INNER_LATCH:%.*]], label [[OUTER_LATCH:%.*]]
+; CHECK:       inner_latch:
+; CHECK-NEXT:    br i1 false, label [[INNER_HEADER]], label [[LOOPEXIT:%.*]]
+; CHECK:       outer_latch:
+; CHECK-NEXT:    br label [[OUTER_HEADER]]
+; CHECK:       loopexit:
+; CHECK-NEXT:    [[DOTLCSSA32:%.*]] = phi i32 [ [[TMP0]], [[INNER_LATCH]] ]
+; CHECK-NEXT:    unreachable
+;
+entry:
+  br label %outer_header
+
+outer_header:
+  %0 = add i32 1, 2
+  br label %inner_header
+
+inner_header:
+  br i1 false, label %inner_latch, label %outer_latch
+
+inner_latch:
+  br i1 false, label %inner_header, label %loopexit
+
+outer_latch:
+  br label %outer_header
+
+loopexit:
+  %.lcssa32 = phi i32 [ %0, %inner_latch ]
+  unreachable
+}