[llvm] 3a063d6 - [LoopNest]: Analysis to discover properties of a loop nest.

Whitney Tsang via llvm-commits llvm-commits at lists.llvm.org
Tue Mar 3 05:25:42 PST 2020


Author: Whitney Tsang
Date: 2020-03-03T13:25:28Z
New Revision: 3a063d68e3c97136d10a2e770f389e6c13c3b317

URL: https://github.com/llvm/llvm-project/commit/3a063d68e3c97136d10a2e770f389e6c13c3b317
DIFF: https://github.com/llvm/llvm-project/commit/3a063d68e3c97136d10a2e770f389e6c13c3b317.diff

LOG: [LoopNest]: Analysis to discover properties of a loop nest.

Summary: This patch adds an analysis pass to collect loop nests and
summarize properties of the nest (e.g the nest depth, whether the nest
is perfect, what's the innermost loop, etc...).

The motivation for this patch was discussed at the latest meeting of the
LLVM loop group (https://ibm.box.com/v/llvm-loop-nest-analysis) where we
discussed
the unimodular loop transformation framework ( “A Loop Transformation
Theory and an Algorithm to Maximize Parallelism”, Michael E. Wolf and
Monica S. Lam, IEEE TPDS, October 1991). The unimodular framework
provides a convenient way to unify legality checking and code generation
for several loop nest transformations (e.g. loop reversal, loop
interchange, loop skewing) and their compositions. Given that the
unimodular framework is applicable to perfect loop nests this is one
property of interest we expose in this analysis. Several other utility
functions are also provided. In the future other properties of interest
can be added in a centralized place.
Authored By: etiotto
Reviewer: Meinersbur, bmahjour, kbarton, Whitney, dmgreen, fhahn,
reames, hfinkel, jdoerfert, ppc-slack
Reviewed By: Meinersbur
Subscribers: bryanpkc, ppc-slack, mgorny, hiraditya, llvm-commits
Tag: LLVM
Differential Revision: https://reviews.llvm.org/D68789

Added: 
    llvm/include/llvm/Analysis/LoopNestAnalysis.h
    llvm/lib/Analysis/LoopNestAnalysis.cpp
    llvm/test/Analysis/LoopNestAnalysis/imperfectnest.ll
    llvm/test/Analysis/LoopNestAnalysis/infinite.ll
    llvm/test/Analysis/LoopNestAnalysis/perfectnest.ll
    llvm/unittests/Analysis/LoopNestTest.cpp

Modified: 
    llvm/lib/Analysis/CMakeLists.txt
    llvm/lib/Passes/PassBuilder.cpp
    llvm/lib/Passes/PassRegistry.def
    llvm/unittests/Analysis/CMakeLists.txt

Removed: 
    


################################################################################
diff  --git a/llvm/include/llvm/Analysis/LoopNestAnalysis.h b/llvm/include/llvm/Analysis/LoopNestAnalysis.h
new file mode 100644
index 000000000000..5b2ec3a26536
--- /dev/null
+++ b/llvm/include/llvm/Analysis/LoopNestAnalysis.h
@@ -0,0 +1,162 @@
+//===- llvm/Analysis/LoopNestAnalysis.h -------------------------*- C++ -*-===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+///
+/// \file
+/// This file defines the interface for the loop nest analysis.
+///
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_ANALYSIS_LOOPNESTANALYSIS_H
+#define LLVM_ANALYSIS_LOOPNESTANALYSIS_H
+
+#include "llvm/Analysis/LoopPass.h"
+#include "llvm/Analysis/ScalarEvolution.h"
+#include "llvm/Transforms/Scalar/LoopPassManager.h"
+
+namespace llvm {
+
+using LoopVectorTy = SmallVector<Loop *, 8>;
+
+/// This class represents a loop nest and can be used to query its properties.
+class LoopNest {
+public:
+  /// Construct a loop nest rooted by loop \p Root.
+  LoopNest(Loop &Root, ScalarEvolution &SE);
+
+  LoopNest() = delete;
+  LoopNest &operator=(const LoopNest &) = delete;
+
+  /// Construct a LoopNest object.
+  static std::unique_ptr<LoopNest> getLoopNest(Loop &Root, ScalarEvolution &SE);
+
+  /// Return true if the given loops \p OuterLoop and \p InnerLoop are
+  /// perfectly nested with respect to each other, and false otherwise.
+  /// Example:
+  /// \code
+  ///   for(i)
+  ///     for(j)
+  ///       for(k)
+  /// \endcode
+  /// arePerfectlyNested(loop_i, loop_j, SE) would return true.
+  /// arePerfectlyNested(loop_j, loop_k, SE) would return true.
+  /// arePerfectlyNested(loop_i, loop_k, SE) would return false.
+  static bool arePerfectlyNested(const Loop &OuterLoop, const Loop &InnerLoop,
+                                 ScalarEvolution &SE);
+
+  /// Return the maximum nesting depth of the loop nest rooted by loop \p Root.
+  /// For example given the loop nest:
+  /// \code
+  ///   for(i)     // loop at level 1 and Root of the nest
+  ///     for(j)   // loop at level 2
+  ///       <code>
+  ///       for(k) // loop at level 3
+  /// \endcode
+  /// getMaxPerfectDepth(Loop_i) would return 2.
+  static unsigned getMaxPerfectDepth(const Loop &Root, ScalarEvolution &SE);
+
+  /// Return the outermost loop in the loop nest.
+  Loop &getOutermostLoop() const { return *Loops.front(); }
+
+  /// Return the innermost loop in the loop nest if the nest has only one
+  /// innermost loop, and a nullptr otherwise.
+  /// Note: the innermost loop returned is not necessarily perfectly nested.
+  Loop *getInnermostLoop() const {
+    if (Loops.size() == 1)
+      return Loops.back();
+
+    // The loops in the 'Loops' vector have been collected in breadth first
+    // order, therefore if the last 2 loops in it have the same nesting depth
+    // there isn't a unique innermost loop in the nest.
+    Loop *LastLoop = Loops.back();
+    auto SecondLastLoopIter = ++Loops.rbegin();
+    return (LastLoop->getLoopDepth() == (*SecondLastLoopIter)->getLoopDepth())
+               ? nullptr
+               : LastLoop;
+  }
+
+  /// Return the loop at the given \p Index.
+  Loop *getLoop(unsigned Index) const {
+    assert(Index < Loops.size() && "Index is out of bounds");
+    return Loops[Index];
+  }
+
+  /// Return the number of loops in the nest.
+  size_t getNumLoops() const { return Loops.size(); }
+
+  /// Get the loops in the nest.
+  ArrayRef<Loop *> getLoops() const { return Loops; }
+
+  /// Retrieve a vector of perfect loop nests contained in the current loop
+  /// nest. For example, given the following  nest containing 4 loops, this
+  /// member function would return {{L1,L2},{L3,L4}}.
+  /// \code
+  ///   for(i) // L1
+  ///     for(j) // L2
+  ///       <code>
+  ///       for(k) // L3
+  ///         for(l) // L4
+  /// \endcode
+  SmallVector<LoopVectorTy, 4> getPerfectLoops(ScalarEvolution &SE) const;
+
+  /// Return the loop nest depth (i.e. the loop depth of the 'deepest' loop)
+  /// For example given the loop nest:
+  /// \code
+  ///   for(i)      // loop at level 1 and Root of the nest
+  ///     for(j1)   // loop at level 2
+  ///       for(k)  // loop at level 3
+  ///     for(j2)   // loop at level 2
+  /// \endcode
+  /// getNestDepth() would return 3.
+  unsigned getNestDepth() const {
+    int NestDepth =
+        Loops.back()->getLoopDepth() - Loops.front()->getLoopDepth() + 1;
+    assert(NestDepth > 0 && "Expecting NestDepth to be at least 1");
+    return NestDepth;
+  }
+
+  /// Return the maximum perfect nesting depth.
+  unsigned getMaxPerfectDepth() const { return MaxPerfectDepth; }
+
+  /// Return true if all loops in the loop nest are in simplify form.
+  bool areAllLoopsSimplifyForm() const {
+    return llvm::all_of(Loops,
+                        [](const Loop *L) { return L->isLoopSimplifyForm(); });
+  }
+
+protected:
+  const unsigned MaxPerfectDepth; // maximum perfect nesting depth level.
+  LoopVectorTy Loops; // the loops in the nest (in breadth first order).
+};
+
+raw_ostream &operator<<(raw_ostream &, const LoopNest &);
+
+/// This analysis provides information for a loop nest. The analysis runs on
+/// demand and can be initiated via AM.getResult<LoopNestAnalysis>.
+class LoopNestAnalysis : public AnalysisInfoMixin<LoopNestAnalysis> {
+  friend AnalysisInfoMixin<LoopNestAnalysis>;
+  static AnalysisKey Key;
+
+public:
+  using Result = LoopNest;
+  Result run(Loop &L, LoopAnalysisManager &AM, LoopStandardAnalysisResults &AR);
+};
+
+/// Printer pass for the \c LoopNest results.
+class LoopNestPrinterPass : public PassInfoMixin<LoopNestPrinterPass> {
+  raw_ostream &OS;
+
+public:
+  explicit LoopNestPrinterPass(raw_ostream &OS) : OS(OS) {}
+
+  PreservedAnalyses run(Loop &L, LoopAnalysisManager &AM,
+                        LoopStandardAnalysisResults &AR, LPMUpdater &U);
+};
+
+} // namespace llvm
+
+#endif // LLVM_ANALYSIS_LOOPNESTANALYSIS_H

diff  --git a/llvm/lib/Analysis/CMakeLists.txt b/llvm/lib/Analysis/CMakeLists.txt
index 34140e18677d..969049f90782 100644
--- a/llvm/lib/Analysis/CMakeLists.txt
+++ b/llvm/lib/Analysis/CMakeLists.txt
@@ -53,6 +53,7 @@ add_llvm_component_library(LLVMAnalysis
   LoopAccessAnalysis.cpp
   LoopAnalysisManager.cpp
   LoopCacheAnalysis.cpp
+  LoopNestAnalysis.cpp
   LoopUnrollAnalyzer.cpp
   LoopInfo.cpp
   LoopPass.cpp

diff  --git a/llvm/lib/Analysis/LoopNestAnalysis.cpp b/llvm/lib/Analysis/LoopNestAnalysis.cpp
new file mode 100644
index 000000000000..61e53de93151
--- /dev/null
+++ b/llvm/lib/Analysis/LoopNestAnalysis.cpp
@@ -0,0 +1,296 @@
+//===- LoopNestAnalysis.cpp - Loop Nest Analysis --------------------------==//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+///
+/// \file
+/// The implementation for the loop nest analysis.
+///
+//===----------------------------------------------------------------------===//
+
+#include "llvm/Analysis/LoopNestAnalysis.h"
+#include "llvm/ADT/BreadthFirstIterator.h"
+#include "llvm/ADT/Statistic.h"
+#include "llvm/Analysis/PostDominators.h"
+#include "llvm/Analysis/ValueTracking.h"
+
+using namespace llvm;
+
+#define DEBUG_TYPE "loopnest"
+#ifndef NDEBUG
+static const char *VerboseDebug = DEBUG_TYPE "-verbose";
+#endif
+
+/// Determine whether the loops structure violates basic requirements for
+/// perfect nesting:
+///  - the inner loop should be the outer loop's only child
+///  - the outer loop header should 'flow' into the inner loop preheader
+///    or jump around the inner loop to the outer loop latch
+///  - if the inner loop latch exits the inner loop, it should 'flow' into
+///    the outer loop latch.
+/// Returns true if the loop structure satisfies the basic requirements and
+/// false otherwise.
+static bool checkLoopsStructure(const Loop &OuterLoop, const Loop &InnerLoop,
+                                ScalarEvolution &SE);
+
+//===----------------------------------------------------------------------===//
+// LoopNest implementation
+//
+
+LoopNest::LoopNest(Loop &Root, ScalarEvolution &SE)
+    : MaxPerfectDepth(getMaxPerfectDepth(Root, SE)) {
+  for (Loop *L : breadth_first(&Root))
+    Loops.push_back(L);
+}
+
+std::unique_ptr<LoopNest> LoopNest::getLoopNest(Loop &Root,
+                                                ScalarEvolution &SE) {
+  return std::make_unique<LoopNest>(Root, SE);
+}
+
+bool LoopNest::arePerfectlyNested(const Loop &OuterLoop, const Loop &InnerLoop,
+                                  ScalarEvolution &SE) {
+  assert(!OuterLoop.getSubLoops().empty() && "Outer loop should have subloops");
+  assert(InnerLoop.getParentLoop() && "Inner loop should have a parent");
+  LLVM_DEBUG(dbgs() << "Checking whether loop '" << OuterLoop.getName()
+                    << "' and '" << InnerLoop.getName()
+                    << "' are perfectly nested.\n");
+
+  // Determine whether the loops structure satisfies the following requirements:
+  //  - the inner loop should be the outer loop's only child
+  //  - the outer loop header should 'flow' into the inner loop preheader
+  //    or jump around the inner loop to the outer loop latch
+  //  - if the inner loop latch exits the inner loop, it should 'flow' into
+  //    the outer loop latch.
+  if (!checkLoopsStructure(OuterLoop, InnerLoop, SE)) {
+    LLVM_DEBUG(dbgs() << "Not perfectly nested: invalid loop structure.\n");
+    return false;
+  }
+
+  // Bail out if we cannot retrieve the outer loop bounds.
+  auto OuterLoopLB = OuterLoop.getBounds(SE);
+  if (OuterLoopLB == None) {
+    LLVM_DEBUG(dbgs() << "Cannot compute loop bounds of OuterLoop: "
+                      << OuterLoop << "\n";);
+    return false;
+  }
+
+  // Identify the outer loop latch comparison instruction.
+  const BasicBlock *Latch = OuterLoop.getLoopLatch();
+  assert(Latch && "Expecting a valid loop latch");
+  const BranchInst *BI = dyn_cast<BranchInst>(Latch->getTerminator());
+  assert(BI && BI->isConditional() &&
+         "Expecting loop latch terminator to be a branch instruction");
+
+  const CmpInst *OuterLoopLatchCmp = dyn_cast<CmpInst>(BI->getCondition());
+  DEBUG_WITH_TYPE(
+      VerboseDebug, if (OuterLoopLatchCmp) {
+        dbgs() << "Outer loop latch compare instruction: " << *OuterLoopLatchCmp
+               << "\n";
+      });
+
+  // Identify the inner loop guard instruction.
+  BranchInst *InnerGuard = InnerLoop.getLoopGuardBranch();
+  const CmpInst *InnerLoopGuardCmp =
+      (InnerGuard) ? dyn_cast<CmpInst>(InnerGuard->getCondition()) : nullptr;
+
+  DEBUG_WITH_TYPE(
+      VerboseDebug, if (InnerLoopGuardCmp) {
+        dbgs() << "Inner loop guard compare instruction: " << *InnerLoopGuardCmp
+               << "\n";
+      });
+
+  // Determine whether instructions in a basic block are one of:
+  //  - the inner loop guard comparison
+  //  - the outer loop latch comparison
+  //  - the outer loop induction variable increment
+  //  - a phi node, a cast or a branch
+  auto containsOnlySafeInstructions = [&](const BasicBlock &BB) {
+    return llvm::all_of(BB, [&](const Instruction &I) {
+      bool isAllowed = isSafeToSpeculativelyExecute(&I) || isa<PHINode>(I) ||
+                       isa<BranchInst>(I);
+      if (!isAllowed) {
+        DEBUG_WITH_TYPE(VerboseDebug, {
+          dbgs() << "Instruction: " << I << "\nin basic block: " << BB
+                 << " is considered unsafe.\n";
+        });
+        return false;
+      }
+
+      // The only binary instruction allowed is the outer loop step instruction,
+      // the only comparison instructions allowed are the inner loop guard
+      // compare instruction and the outer loop latch compare instruction.
+      if ((isa<BinaryOperator>(I) && &I != &OuterLoopLB->getStepInst()) ||
+          (isa<CmpInst>(I) && &I != OuterLoopLatchCmp &&
+           &I != InnerLoopGuardCmp)) {
+        DEBUG_WITH_TYPE(VerboseDebug, {
+          dbgs() << "Instruction: " << I << "\nin basic block:" << BB
+                 << "is unsafe.\n";
+        });
+        return false;
+      }
+      return true;
+    });
+  };
+
+  // Check the code surrounding the inner loop for instructions that are deemed
+  // unsafe.
+  const BasicBlock *OuterLoopHeader = OuterLoop.getHeader();
+  const BasicBlock *OuterLoopLatch = OuterLoop.getLoopLatch();
+  const BasicBlock *InnerLoopPreHeader = InnerLoop.getLoopPreheader();
+
+  if (!containsOnlySafeInstructions(*OuterLoopHeader) ||
+      !containsOnlySafeInstructions(*OuterLoopLatch) ||
+      (InnerLoopPreHeader != OuterLoopHeader &&
+       !containsOnlySafeInstructions(*InnerLoopPreHeader)) ||
+      !containsOnlySafeInstructions(*InnerLoop.getExitBlock())) {
+    LLVM_DEBUG(dbgs() << "Not perfectly nested: code surrounding inner loop is "
+                         "unsafe\n";);
+    return false;
+  }
+
+  LLVM_DEBUG(dbgs() << "Loop '" << OuterLoop.getName() << "' and '"
+                    << InnerLoop.getName() << "' are perfectly nested.\n");
+
+  return true;
+}
+
+SmallVector<LoopVectorTy, 4>
+LoopNest::getPerfectLoops(ScalarEvolution &SE) const {
+  SmallVector<LoopVectorTy, 4> LV;
+  LoopVectorTy PerfectNest;
+
+  for (Loop *L : depth_first(const_cast<Loop *>(Loops.front()))) {
+    if (PerfectNest.empty())
+      PerfectNest.push_back(L);
+
+    auto &SubLoops = L->getSubLoops();
+    if (SubLoops.size() == 1 && arePerfectlyNested(*L, *SubLoops.front(), SE)) {
+      PerfectNest.push_back(SubLoops.front());
+    } else {
+      LV.push_back(PerfectNest);
+      PerfectNest.clear();
+    }
+  }
+
+  return LV;
+}
+
+unsigned LoopNest::getMaxPerfectDepth(const Loop &Root, ScalarEvolution &SE) {
+  LLVM_DEBUG(dbgs() << "Get maximum perfect depth of loop nest rooted by loop '"
+                    << Root.getName() << "'\n");
+
+  const Loop *CurrentLoop = &Root;
+  const auto *SubLoops = &CurrentLoop->getSubLoops();
+  unsigned CurrentDepth = 1;
+
+  while (SubLoops->size() == 1) {
+    const Loop *InnerLoop = SubLoops->front();
+    if (!arePerfectlyNested(*CurrentLoop, *InnerLoop, SE)) {
+      LLVM_DEBUG({
+        dbgs() << "Not a perfect nest: loop '" << CurrentLoop->getName()
+               << "' is not perfectly nested with loop '"
+               << InnerLoop->getName() << "'\n";
+      });
+      break;
+    }
+
+    CurrentLoop = InnerLoop;
+    SubLoops = &CurrentLoop->getSubLoops();
+    ++CurrentDepth;
+  }
+
+  return CurrentDepth;
+}
+
+static bool checkLoopsStructure(const Loop &OuterLoop, const Loop &InnerLoop,
+                                ScalarEvolution &SE) {
+  // The inner loop must be the only outer loop's child.
+  if ((OuterLoop.getSubLoops().size() != 1) ||
+      (InnerLoop.getParentLoop() != &OuterLoop))
+    return false;
+
+  // We expect loops in normal form which have a preheader, header, latch...
+  if (!OuterLoop.isLoopSimplifyForm() || !InnerLoop.isLoopSimplifyForm())
+    return false;
+
+  const BasicBlock *OuterLoopHeader = OuterLoop.getHeader();
+  const BasicBlock *OuterLoopLatch = OuterLoop.getLoopLatch();
+  const BasicBlock *InnerLoopPreHeader = InnerLoop.getLoopPreheader();
+  const BasicBlock *InnerLoopLatch = InnerLoop.getLoopLatch();
+  const BasicBlock *InnerLoopExit = InnerLoop.getExitBlock();
+
+  // We expect rotated loops. The inner loop should have a single exit block.
+  if (OuterLoop.getExitingBlock() != OuterLoopLatch ||
+      InnerLoop.getExitingBlock() != InnerLoopLatch || !InnerLoopExit)
+    return false;
+
+  // Ensure the only branch that may exist between the loops is the inner loop
+  // guard.
+  if (OuterLoopHeader != InnerLoopPreHeader) {
+    const BranchInst *BI =
+        dyn_cast<BranchInst>(OuterLoopHeader->getTerminator());
+
+    if (!BI || BI != InnerLoop.getLoopGuardBranch())
+      return false;
+
+    // The successors of the inner loop guard should be the inner loop
+    // preheader and the outer loop latch.
+    for (const BasicBlock *Succ : BI->successors()) {
+      if (Succ == InnerLoopPreHeader)
+        continue;
+      if (Succ == OuterLoopLatch)
+        continue;
+
+      DEBUG_WITH_TYPE(VerboseDebug, {
+        dbgs() << "Inner loop guard successor " << Succ->getName()
+               << " doesn't lead to inner loop preheader or "
+                  "outer loop latch.\n";
+      });
+      return false;
+    }
+  }
+
+  // Ensure the inner loop exit block leads to the outer loop latch.
+  if (InnerLoopExit->getSingleSuccessor() != OuterLoopLatch) {
+    DEBUG_WITH_TYPE(
+        VerboseDebug,
+        dbgs() << "Inner loop exit block " << *InnerLoopExit
+               << " does not directly lead to the outer loop latch.\n";);
+    return false;
+  }
+
+  return true;
+}
+
+raw_ostream &llvm::operator<<(raw_ostream &OS, const LoopNest &LN) {
+  OS << "IsPerfect=";
+  if (LN.getMaxPerfectDepth() == LN.getNestDepth())
+    OS << "true";
+  else
+    OS << "false";
+  OS << ", Depth=" << LN.getNestDepth();
+  OS << ", OutermostLoop: " << LN.getOutermostLoop().getName();
+  OS << ", Loops: ( ";
+  for (const Loop *L : LN.getLoops())
+    OS << L->getName() << " ";
+  OS << ")";
+
+  return OS;
+}
+
+//===----------------------------------------------------------------------===//
+// LoopNestPrinterPass implementation
+//
+
+PreservedAnalyses LoopNestPrinterPass::run(Loop &L, LoopAnalysisManager &AM,
+                                           LoopStandardAnalysisResults &AR,
+                                           LPMUpdater &U) {
+  if (auto LN = LoopNest::getLoopNest(L, AR.SE))
+    OS << *LN << "\n";
+
+  return PreservedAnalyses::all();
+}

diff  --git a/llvm/lib/Passes/PassBuilder.cpp b/llvm/lib/Passes/PassBuilder.cpp
index 446d349500ba..e0ef37a9562b 100644
--- a/llvm/lib/Passes/PassBuilder.cpp
+++ b/llvm/lib/Passes/PassBuilder.cpp
@@ -38,6 +38,7 @@
 #include "llvm/Analysis/LoopAccessAnalysis.h"
 #include "llvm/Analysis/LoopCacheAnalysis.h"
 #include "llvm/Analysis/LoopInfo.h"
+#include "llvm/Analysis/LoopNestAnalysis.h"
 #include "llvm/Analysis/MemoryDependenceAnalysis.h"
 #include "llvm/Analysis/MemorySSA.h"
 #include "llvm/Analysis/ModuleSummaryAnalysis.h"

diff  --git a/llvm/lib/Passes/PassRegistry.def b/llvm/lib/Passes/PassRegistry.def
index 12f4f85548f3..056e8833ab83 100644
--- a/llvm/lib/Passes/PassRegistry.def
+++ b/llvm/lib/Passes/PassRegistry.def
@@ -325,6 +325,7 @@ LOOP_PASS("unroll-full", LoopFullUnrollPass())
 LOOP_PASS("print-access-info", LoopAccessInfoPrinterPass(dbgs()))
 LOOP_PASS("print<ddg>", DDGAnalysisPrinterPass(dbgs()))
 LOOP_PASS("print<ivusers>", IVUsersPrinterPass(dbgs()))
+LOOP_PASS("print<loopnest>", LoopNestPrinterPass(dbgs()))
 LOOP_PASS("print<loop-cache-cost>", LoopCachePrinterPass(dbgs()))
 LOOP_PASS("loop-predication", LoopPredicationPass())
 LOOP_PASS("guard-widening", GuardWideningPass())

diff  --git a/llvm/test/Analysis/LoopNestAnalysis/imperfectnest.ll b/llvm/test/Analysis/LoopNestAnalysis/imperfectnest.ll
new file mode 100644
index 000000000000..4c8066ec5877
--- /dev/null
+++ b/llvm/test/Analysis/LoopNestAnalysis/imperfectnest.ll
@@ -0,0 +1,493 @@
+; RUN: opt < %s -passes='print<loopnest>' -disable-output 2>&1 | FileCheck %s
+
+; Test an imperfect 2-dim loop nest of the form:
+;   for (int i = 0; i < nx; ++i) {
+;     x[i] = i;
+;     for (int j = 0; j < ny; ++j)
+;       y[j][i] = x[i] + j;
+;   }
+
+define void @imperf_nest_1(i32 signext %nx, i32 signext %ny) {
+; CHECK-LABEL: IsPerfect=false, Depth=2, OutermostLoop: imperf_nest_1_loop_i, Loops: ( imperf_nest_1_loop_i imperf_nest_1_loop_j )
+entry:
+  %0 = zext i32 %ny to i64
+  %1 = zext i32 %nx to i64
+  %2 = mul nuw i64 %0, %1
+  %vla = alloca double, i64 %2, align 8
+  %3 = zext i32 %ny to i64
+  %vla1 = alloca double, i64 %3, align 8
+  br label %imperf_nest_1_loop_i
+
+imperf_nest_1_loop_i:
+  %i2.0 = phi i32 [ 0, %entry ], [ %inc16, %for.inc15 ]
+  %cmp = icmp slt i32 %i2.0, %nx
+  br i1 %cmp, label %for.body, label %for.end17
+
+for.body:
+  %conv = sitofp i32 %i2.0 to double
+  %idxprom = sext i32 %i2.0 to i64
+  %arrayidx = getelementptr inbounds double, double* %vla1, i64 %idxprom
+  store double %conv, double* %arrayidx, align 8
+  br label %imperf_nest_1_loop_j
+
+imperf_nest_1_loop_j:
+  %j3.0 = phi i32 [ 0, %for.body ], [ %inc, %for.inc ]
+  %cmp5 = icmp slt i32 %j3.0, %ny
+  br i1 %cmp5, label %for.body7, label %for.end
+
+for.body7:
+  %idxprom8 = sext i32 %i2.0 to i64
+  %arrayidx9 = getelementptr inbounds double, double* %vla1, i64 %idxprom8
+  %4 = load double, double* %arrayidx9, align 8
+  %conv10 = sitofp i32 %j3.0 to double
+  %add = fadd double %4, %conv10
+  %idxprom11 = sext i32 %j3.0 to i64
+  %5 = mul nsw i64 %idxprom11, %1
+  %arrayidx12 = getelementptr inbounds double, double* %vla, i64 %5
+  %idxprom13 = sext i32 %i2.0 to i64
+  %arrayidx14 = getelementptr inbounds double, double* %arrayidx12, i64 %idxprom13
+  store double %add, double* %arrayidx14, align 8
+  br label %for.inc
+
+for.inc:
+  %inc = add nsw i32 %j3.0, 1
+  br label %imperf_nest_1_loop_j
+
+for.end:
+  br label %for.inc15
+
+for.inc15:
+  %inc16 = add nsw i32 %i2.0, 1
+  br label %imperf_nest_1_loop_i
+
+for.end17:
+  ret void
+}
+
+; Test an imperfect 2-dim loop nest of the form:
+;   for (int i = 0; i < nx; ++i) {
+;     for (int j = 0; j < ny; ++j)
+;       y[j][i] = x[i] + j;
+;     y[0][i] += i;
+;   }
+
+define void @imperf_nest_2(i32 signext %nx, i32 signext %ny) {
+; CHECK-LABEL: IsPerfect=false, Depth=2, OutermostLoop: imperf_nest_2_loop_i, Loops: ( imperf_nest_2_loop_i imperf_nest_2_loop_j )
+entry:
+  %0 = zext i32 %ny to i64
+  %1 = zext i32 %nx to i64
+  %2 = mul nuw i64 %0, %1
+  %vla = alloca double, i64 %2, align 8
+  %3 = zext i32 %ny to i64
+  %vla1 = alloca double, i64 %3, align 8
+  br label %imperf_nest_2_loop_i
+
+imperf_nest_2_loop_i:
+  %i2.0 = phi i32 [ 0, %entry ], [ %inc17, %for.inc16 ]
+  %cmp = icmp slt i32 %i2.0, %nx
+  br i1 %cmp, label %for.body, label %for.end18
+ 
+for.body:
+  br label %imperf_nest_2_loop_j
+
+imperf_nest_2_loop_j:
+  %j3.0 = phi i32 [ 0, %for.body ], [ %inc, %for.inc ]
+  %cmp5 = icmp slt i32 %j3.0, %ny
+  br i1 %cmp5, label %for.body6, label %for.end
+
+for.body6:
+  %idxprom = sext i32 %i2.0 to i64
+  %arrayidx = getelementptr inbounds double, double* %vla1, i64 %idxprom
+  %4 = load double, double* %arrayidx, align 8
+  %conv = sitofp i32 %j3.0 to double
+  %add = fadd double %4, %conv
+  %idxprom7 = sext i32 %j3.0 to i64
+  %5 = mul nsw i64 %idxprom7, %1
+  %arrayidx8 = getelementptr inbounds double, double* %vla, i64 %5
+  %idxprom9 = sext i32 %i2.0 to i64
+  %arrayidx10 = getelementptr inbounds double, double* %arrayidx8, i64 %idxprom9
+  store double %add, double* %arrayidx10, align 8
+  br label %for.inc
+
+for.inc:
+  %inc = add nsw i32 %j3.0, 1
+  br label %imperf_nest_2_loop_j
+
+for.end:
+  %conv11 = sitofp i32 %i2.0 to double
+  %6 = mul nsw i64 0, %1
+  %arrayidx12 = getelementptr inbounds double, double* %vla, i64 %6
+  %idxprom13 = sext i32 %i2.0 to i64
+  %arrayidx14 = getelementptr inbounds double, double* %arrayidx12, i64 %idxprom13
+  %7 = load double, double* %arrayidx14, align 8
+  %add15 = fadd double %7, %conv11
+  store double %add15, double* %arrayidx14, align 8
+  br label %for.inc16
+
+for.inc16:
+  %inc17 = add nsw i32 %i2.0, 1
+  br label %imperf_nest_2_loop_i
+
+for.end18:
+  ret void
+}
+
+; Test an imperfect 2-dim loop nest of the form:
+;   for (i = 0; i < nx; ++i) {
+;     for (j = 0; j < ny-nk; ++j)
+;       y[i][j] = x[i] + j;
+;     for (j = ny-nk; j < ny; ++j)
+;       y[i][j] = x[i] - j;
+;   }
+
+define void @imperf_nest_3(i32 signext %nx, i32 signext %ny, i32 signext %nk) {
+; CHECK-LABEL: IsPerfect=false, Depth=2, OutermostLoop: imperf_nest_3_loop_i, Loops: ( imperf_nest_3_loop_i imperf_nest_3_loop_j imperf_nest_3_loop_k )
+entry:
+  %0 = zext i32 %nx to i64
+  %1 = zext i32 %ny to i64
+  %2 = mul nuw i64 %0, %1
+  %vla = alloca double, i64 %2, align 8
+  %3 = zext i32 %ny to i64
+  %vla1 = alloca double, i64 %3, align 8
+  br label %imperf_nest_3_loop_i
+
+imperf_nest_3_loop_i:                                         ; preds = %for.inc25, %entry
+  %i.0 = phi i32 [ 0, %entry ], [ %inc26, %for.inc25 ]
+  %cmp = icmp slt i32 %i.0, %nx
+  br i1 %cmp, label %for.body, label %for.end27
+
+for.body:                                         ; preds = %for.cond
+  br label %imperf_nest_3_loop_j
+
+imperf_nest_3_loop_j:                                        ; preds = %for.inc, %for.body
+  %j.0 = phi i32 [ 0, %for.body ], [ %inc, %for.inc ]
+  %sub = sub nsw i32 %ny, %nk
+  %cmp3 = icmp slt i32 %j.0, %sub
+  br i1 %cmp3, label %for.body4, label %for.end
+
+for.body4:                                        ; preds = %imperf_nest_3_loop_j
+  %idxprom = sext i32 %i.0 to i64
+  %arrayidx = getelementptr inbounds double, double* %vla1, i64 %idxprom
+  %4 = load double, double* %arrayidx, align 8
+  %conv = sitofp i32 %j.0 to double
+  %add = fadd double %4, %conv
+  %idxprom5 = sext i32 %i.0 to i64
+  %5 = mul nsw i64 %idxprom5, %1
+  %arrayidx6 = getelementptr inbounds double, double* %vla, i64 %5
+  %idxprom7 = sext i32 %j.0 to i64
+  %arrayidx8 = getelementptr inbounds double, double* %arrayidx6, i64 %idxprom7
+  store double %add, double* %arrayidx8, align 8
+  br label %for.inc
+
+for.inc:                                          ; preds = %for.body4
+  %inc = add nsw i32 %j.0, 1
+  br label %imperf_nest_3_loop_j
+
+for.end:                                          ; preds = %imperf_nest_3_loop_j
+  %sub9 = sub nsw i32 %ny, %nk
+  br label %imperf_nest_3_loop_k
+
+imperf_nest_3_loop_k:                                       ; preds = %for.inc22, %for.end
+  %j.1 = phi i32 [ %sub9, %for.end ], [ %inc23, %for.inc22 ]
+  %cmp11 = icmp slt i32 %j.1, %ny
+  br i1 %cmp11, label %for.body13, label %for.end24
+
+for.body13:                                       ; preds = %imperf_nest_3_loop_k
+  %idxprom14 = sext i32 %i.0 to i64
+  %arrayidx15 = getelementptr inbounds double, double* %vla1, i64 %idxprom14
+  %6 = load double, double* %arrayidx15, align 8
+  %conv16 = sitofp i32 %j.1 to double
+  %sub17 = fsub double %6, %conv16
+  %idxprom18 = sext i32 %i.0 to i64
+  %7 = mul nsw i64 %idxprom18, %1
+  %arrayidx19 = getelementptr inbounds double, double* %vla, i64 %7
+  %idxprom20 = sext i32 %j.1 to i64
+  %arrayidx21 = getelementptr inbounds double, double* %arrayidx19, i64 %idxprom20
+  store double %sub17, double* %arrayidx21, align 8
+  br label %for.inc22
+
+for.inc22:                                        ; preds = %for.body13
+  %inc23 = add nsw i32 %j.1, 1
+  br label %imperf_nest_3_loop_k
+
+for.end24:                                        ; preds = %imperf_nest_3_loop_k
+  br label %for.inc25
+
+for.inc25:                                        ; preds = %for.end24
+  %inc26 = add nsw i32 %i.0, 1
+  br label %imperf_nest_3_loop_i
+
+for.end27:                                        ; preds = %for.cond
+  ret void
+}
+
+; Test an imperfect loop nest of the form:
+;   for (i = 0; i < nx; ++i) {
+;     for (j = 0; j < ny-nk; ++j)
+;       for (k = 0; k < nk; ++k)
+;         y[i][j][k] = x[i+j] + k;
+;     for (j = ny-nk; j < ny; ++j)
+;       y[i][j][0] = x[i] - j;
+;   }
+
+define void @imperf_nest_4(i32 signext %nx, i32 signext %ny, i32 signext %nk) {
+; CHECK-LABEL: IsPerfect=false, Depth=2, OutermostLoop: imperf_nest_4_loop_j, Loops: ( imperf_nest_4_loop_j imperf_nest_4_loop_k )
+; CHECK-LABEL: IsPerfect=false, Depth=3, OutermostLoop: imperf_nest_4_loop_i, Loops: ( imperf_nest_4_loop_i imperf_nest_4_loop_j imperf_nest_4_loop_j2 imperf_nest_4_loop_k )
+entry:
+  %0 = zext i32 %nx to i64
+  %1 = zext i32 %ny to i64
+  %2 = zext i32 %nk to i64
+  %3 = mul nuw i64 %0, %1
+  %4 = mul nuw i64 %3, %2
+  %vla = alloca double, i64 %4, align 8
+  %5 = zext i32 %ny to i64
+  %vla1 = alloca double, i64 %5, align 8
+  %cmp5 = icmp slt i32 0, %nx
+  br i1 %cmp5, label %imperf_nest_4_loop_i.lr.ph, label %for.end37
+
+imperf_nest_4_loop_i.lr.ph:
+  br label %imperf_nest_4_loop_i
+
+imperf_nest_4_loop_i:
+  %i.0 = phi i32 [ 0, %imperf_nest_4_loop_i.lr.ph ], [ %inc36, %for.inc35 ]
+  %sub2 = sub nsw i32 %ny, %nk
+  %cmp33 = icmp slt i32 0, %sub2
+  br i1 %cmp33, label %imperf_nest_4_loop_j.lr.ph, label %for.end17
+
+imperf_nest_4_loop_j.lr.ph:
+  br label %imperf_nest_4_loop_j
+
+imperf_nest_4_loop_j:
+  %j.0 = phi i32 [ 0, %imperf_nest_4_loop_j.lr.ph ], [ %inc16, %for.inc15 ]
+  %cmp61 = icmp slt i32 0, %nk
+  br i1 %cmp61, label %imperf_nest_4_loop_k.lr.ph, label %for.end
+
+imperf_nest_4_loop_k.lr.ph:
+  br label %imperf_nest_4_loop_k
+
+imperf_nest_4_loop_k:
+  %k.0 = phi i32 [ 0, %imperf_nest_4_loop_k.lr.ph ], [ %inc, %for.inc ]
+  %add = add nsw i32 %i.0, %j.0
+  %idxprom = sext i32 %add to i64
+  %arrayidx = getelementptr inbounds double, double* %vla1, i64 %idxprom
+  %6 = load double, double* %arrayidx, align 8
+  %conv = sitofp i32 %k.0 to double
+  %add8 = fadd double %6, %conv
+  %idxprom9 = sext i32 %i.0 to i64
+  %7 = mul nuw i64 %1, %2
+  %8 = mul nsw i64 %idxprom9, %7
+  %arrayidx10 = getelementptr inbounds double, double* %vla, i64 %8
+  %idxprom11 = sext i32 %j.0 to i64
+  %9 = mul nsw i64 %idxprom11, %2
+  %arrayidx12 = getelementptr inbounds double, double* %arrayidx10, i64 %9
+  %idxprom13 = sext i32 %k.0 to i64
+  %arrayidx14 = getelementptr inbounds double, double* %arrayidx12, i64 %idxprom13
+  store double %add8, double* %arrayidx14, align 8
+  br label %for.inc
+
+for.inc:
+  %inc = add nsw i32 %k.0, 1
+  %cmp6 = icmp slt i32 %inc, %nk
+  br i1 %cmp6, label %imperf_nest_4_loop_k, label %for.cond5.for.end_crit_edge
+
+for.cond5.for.end_crit_edge:
+  br label %for.end
+
+for.end:
+  br label %for.inc15
+
+for.inc15:
+  %inc16 = add nsw i32 %j.0, 1
+  %sub = sub nsw i32 %ny, %nk
+  %cmp3 = icmp slt i32 %inc16, %sub
+  br i1 %cmp3, label %imperf_nest_4_loop_j, label %for.cond2.for.end17_crit_edge
+
+for.cond2.for.end17_crit_edge:
+  br label %for.end17
+
+for.end17:
+  %sub18 = sub nsw i32 %ny, %nk
+  %cmp204 = icmp slt i32 %sub18, %ny
+  br i1 %cmp204, label %imperf_nest_4_loop_j2.lr.ph, label %for.end34
+
+imperf_nest_4_loop_j2.lr.ph:
+  br label %imperf_nest_4_loop_j2
+
+imperf_nest_4_loop_j2:
+  %j.1 = phi i32 [ %sub18, %imperf_nest_4_loop_j2.lr.ph ], [ %inc33, %for.inc32 ]
+  %idxprom23 = sext i32 %i.0 to i64
+  %arrayidx24 = getelementptr inbounds double, double* %vla1, i64 %idxprom23
+  %10 = load double, double* %arrayidx24, align 8
+  %conv25 = sitofp i32 %j.1 to double
+  %sub26 = fsub double %10, %conv25
+  %idxprom27 = sext i32 %i.0 to i64
+  %idxprom29 = sext i32 %j.1 to i64
+  %11 = mul nsw i64 %idxprom29, %2
+  %12 = mul nuw i64 %1, %2
+  %13 = mul nsw i64 %idxprom27, %12
+  %arrayidx28 = getelementptr inbounds double, double* %vla, i64 %13
+  %arrayidx30 = getelementptr inbounds double, double* %arrayidx28, i64 %11
+  %arrayidx31 = getelementptr inbounds double, double* %arrayidx30, i64 0
+  store double %sub26, double* %arrayidx31, align 8
+  br label %for.inc32
+
+for.inc32:
+  %inc33 = add nsw i32 %j.1, 1
+  %cmp20 = icmp slt i32 %inc33, %ny
+  br i1 %cmp20, label %imperf_nest_4_loop_j2, label %for.cond19.for.end34_crit_edge
+
+for.cond19.for.end34_crit_edge:
+  br label %for.end34
+
+for.end34:                   
+  br label %for.inc35
+
+for.inc35:                   
+  %inc36 = add nsw i32 %i.0, 1
+  %cmp = icmp slt i32 %inc36, %nx
+  br i1 %cmp, label %imperf_nest_4_loop_i, label %for.cond.for.end37_crit_edge
+
+for.cond.for.end37_crit_edge:
+  br label %for.end37
+
+for.end37:
+  ret void
+}
+
+; Test an imperfect loop nest of the form:
+;   for (int i = 0; i < nx; ++i)
+;     if (i > 5) {
+;       for (int j = 0; j < ny; ++j)
+;         y[j][i] = x[i][j] + j;
+;     }
+
+define void @imperf_nest_5(i32** %y, i32** %x, i32 signext %nx, i32 signext %ny) {
+; CHECK-LABEL: IsPerfect=false, Depth=2, OutermostLoop: imperf_nest_5_loop_i, Loops: ( imperf_nest_5_loop_i imperf_nest_5_loop_j )
+entry:
+  %cmp2 = icmp slt i32 0, %nx
+  br i1 %cmp2, label %imperf_nest_5_loop_i.lr.ph, label %for.end13
+
+imperf_nest_5_loop_i.lr.ph:
+  br label %imperf_nest_5_loop_i
+
+imperf_nest_5_loop_i:      
+  %i.0 = phi i32 [ 0, %imperf_nest_5_loop_i.lr.ph ], [ %inc12, %for.inc11 ]
+  %cmp1 = icmp sgt i32 %i.0, 5
+  br i1 %cmp1, label %if.then, label %if.end
+
+if.then:         
+  %cmp31 = icmp slt i32 0, %ny
+  br i1 %cmp31, label %imperf_nest_5_loop_j.lr.ph, label %for.end
+
+imperf_nest_5_loop_j.lr.ph:
+  br label %imperf_nest_5_loop_j
+
+imperf_nest_5_loop_j:      
+  %j.0 = phi i32 [ 0, %imperf_nest_5_loop_j.lr.ph ], [ %inc, %for.inc ]
+  %idxprom = sext i32 %i.0 to i64
+  %arrayidx = getelementptr inbounds i32*, i32** %x, i64 %idxprom
+  %0 = load i32*, i32** %arrayidx, align 8
+  %idxprom5 = sext i32 %j.0 to i64
+  %arrayidx6 = getelementptr inbounds i32, i32* %0, i64 %idxprom5
+  %1 = load i32, i32* %arrayidx6, align 4
+  %add = add nsw i32 %1, %j.0
+  %idxprom7 = sext i32 %j.0 to i64
+  %arrayidx8 = getelementptr inbounds i32*, i32** %y, i64 %idxprom7
+  %2 = load i32*, i32** %arrayidx8, align 8
+  %idxprom9 = sext i32 %i.0 to i64
+  %arrayidx10 = getelementptr inbounds i32, i32* %2, i64 %idxprom9
+  store i32 %add, i32* %arrayidx10, align 4
+  br label %for.inc
+
+for.inc:
+  %inc = add nsw i32 %j.0, 1
+  %cmp3 = icmp slt i32 %inc, %ny
+  br i1 %cmp3, label %imperf_nest_5_loop_j, label %for.cond2.for.end_crit_edge
+
+for.cond2.for.end_crit_edge:
+  br label %for.end
+
+for.end:                    
+  br label %if.end
+
+if.end:                     
+  br label %for.inc11
+
+for.inc11:                  
+  %inc12 = add nsw i32 %i.0, 1
+  %cmp = icmp slt i32 %inc12, %nx
+  br i1 %cmp, label %imperf_nest_5_loop_i, label %for.cond.for.end13_crit_edge
+
+for.cond.for.end13_crit_edge:
+  br label %for.end13
+
+for.end13:                   
+  ret void
+}
+
+; Test an imperfect loop nest of the form:
+;   for (int i = 0; i < nx; ++i)
+;     if (i > 5) { // user branch
+;       for (int j = 1; j <= 5; j+=2)
+;         y[j][i] = x[i][j] + j;
+;     }
+
+define void @imperf_nest_6(i32** %y, i32** %x, i32 signext %nx, i32 signext %ny) {
+;    CHECK-LABEL: IsPerfect=false, Depth=2, OutermostLoop: imperf_nest_6_loop_i, Loops: ( imperf_nest_6_loop_i imperf_nest_6_loop_j )
+entry:
+  %cmp2 = icmp slt i32 0, %nx
+  br i1 %cmp2, label %imperf_nest_6_loop_i.lr.ph, label %for.end13
+
+imperf_nest_6_loop_i.lr.ph:
+  br label %imperf_nest_6_loop_i
+
+imperf_nest_6_loop_i:      
+  %i.0 = phi i32 [ 0, %imperf_nest_6_loop_i.lr.ph ], [ %inc12, %for.inc11 ]
+  %cmp1 = icmp sgt i32 %i.0, 5
+  br i1 %cmp1, label %imperf_nest_6_loop_j.lr.ph, label %if.end
+
+imperf_nest_6_loop_j.lr.ph:
+  br label %imperf_nest_6_loop_j
+
+imperf_nest_6_loop_j:      
+  %j.0 = phi i32 [ 1, %imperf_nest_6_loop_j.lr.ph ], [ %inc, %for.inc ]
+  %idxprom = sext i32 %i.0 to i64
+  %arrayidx = getelementptr inbounds i32*, i32** %x, i64 %idxprom
+  %0 = load i32*, i32** %arrayidx, align 8
+  %idxprom5 = sext i32 %j.0 to i64
+  %arrayidx6 = getelementptr inbounds i32, i32* %0, i64 %idxprom5
+  %1 = load i32, i32* %arrayidx6, align 4
+  %add = add nsw i32 %1, %j.0
+  %idxprom7 = sext i32 %j.0 to i64
+  %arrayidx8 = getelementptr inbounds i32*, i32** %y, i64 %idxprom7
+  %2 = load i32*, i32** %arrayidx8, align 8
+  %idxprom9 = sext i32 %i.0 to i64
+  %arrayidx10 = getelementptr inbounds i32, i32* %2, i64 %idxprom9
+  store i32 %add, i32* %arrayidx10, align 4
+  br label %for.inc
+
+for.inc:
+  %inc = add nsw i32 %j.0, 2
+  %cmp3 = icmp sle i32 %inc, 5
+  br i1 %cmp3, label %imperf_nest_6_loop_j, label %for.cond2.for.end_crit_edge
+
+for.cond2.for.end_crit_edge:
+  br label %for.end
+
+for.end:                    
+  br label %if.end
+
+if.end:                     
+  br label %for.inc11
+
+for.inc11:                  
+  %inc12 = add nsw i32 %i.0, 1
+  %cmp = icmp slt i32 %inc12, %nx
+  br i1 %cmp, label %imperf_nest_6_loop_i, label %for.cond.for.end13_crit_edge
+
+for.cond.for.end13_crit_edge:
+  br label %for.end13
+
+for.end13:                   
+  ret void
+}

diff  --git a/llvm/test/Analysis/LoopNestAnalysis/infinite.ll b/llvm/test/Analysis/LoopNestAnalysis/infinite.ll
new file mode 100644
index 000000000000..7a6cf21584ff
--- /dev/null
+++ b/llvm/test/Analysis/LoopNestAnalysis/infinite.ll
@@ -0,0 +1,35 @@
+; RUN: opt < %s -passes='print<loopnest>' -disable-output 2>&1 | FileCheck %s
+
+; Test that the loop nest analysis is able to analyze an infinite loop in a loop nest.
+define void @test1(i32** %A, i1 %cond) {
+; CHECK-LABEL: IsPerfect=true, Depth=1, OutermostLoop: for.inner, Loops: ( for.inner )
+; CHECK-LABEL: IsPerfect=false, Depth=2, OutermostLoop: for.outer, Loops: ( for.outer for.inner )
+; CHECK-LABEL: IsPerfect=true, Depth=1, OutermostLoop: for.infinite, Loops: ( for.infinite )
+entry:
+  br label %for.outer
+
+for.outer:
+  %i = phi i64 [ 0, %entry ], [ %inc_i, %for.outer.latch ]
+  br i1 %cond, label %for.inner, label %for.infinite
+
+for.inner:
+  %j = phi i64 [ 0, %for.outer ], [ %inc_j, %for.inner ]
+  %arrayidx_i = getelementptr inbounds i32*, i32** %A, i64 %i
+  %0 = load i32*, i32** %arrayidx_i, align 8
+  %arrayidx_j = getelementptr inbounds i32, i32* %0, i64 %j
+  store i32 0, i32* %arrayidx_j, align 4
+  %inc_j = add nsw i64 %j, 1
+  %cmp_j = icmp slt i64 %inc_j, 100
+  br i1 %cmp_j, label %for.inner, label %for.outer.latch
+
+for.infinite:
+  br label %for.infinite
+
+for.outer.latch:
+  %inc_i = add nsw i64 %i, 1
+  %cmp_i = icmp slt i64 %inc_i, 100
+  br i1 %cmp_i, label %for.outer, label %for.end
+
+for.end:
+  ret void
+}

diff  --git a/llvm/test/Analysis/LoopNestAnalysis/perfectnest.ll b/llvm/test/Analysis/LoopNestAnalysis/perfectnest.ll
new file mode 100644
index 000000000000..b7b3b7a7c93e
--- /dev/null
+++ b/llvm/test/Analysis/LoopNestAnalysis/perfectnest.ll
@@ -0,0 +1,275 @@
+; RUN: opt < %s -passes='print<loopnest>' -disable-output 2>&1 | FileCheck %s
+
+; Test a perfect 2-dim loop nest of the form:
+;   for(i=0; i<nx; ++i)
+;     for(j=0; j<nx; ++j)
+;       y[i][j] = x[i][j];
+
+define void @perf_nest_2D_1(i32** %y, i32** %x, i64 signext %nx, i64 signext %ny) {
+; CHECK-LABEL: IsPerfect=true, Depth=1, OutermostLoop: perf_nest_2D_1_loop_j, Loops: ( perf_nest_2D_1_loop_j )
+; CHECK-LABEL: IsPerfect=true, Depth=2, OutermostLoop: perf_nest_2D_1_loop_i, Loops: ( perf_nest_2D_1_loop_i perf_nest_2D_1_loop_j )
+entry:
+  br label %perf_nest_2D_1_loop_i
+
+perf_nest_2D_1_loop_i:
+  %i = phi i64 [ 0, %entry ], [ %inc13, %inc_i ]
+  %cmp21 = icmp slt i64 0, %ny
+  br i1 %cmp21, label %perf_nest_2D_1_loop_j, label %inc_i
+
+perf_nest_2D_1_loop_j:
+  %j = phi i64 [ 0, %perf_nest_2D_1_loop_i ], [ %inc, %inc_j ]
+  %arrayidx = getelementptr inbounds i32*, i32** %x, i64 %j
+  %0 = load i32*, i32** %arrayidx, align 8
+  %arrayidx6 = getelementptr inbounds i32, i32* %0, i64 %j
+  %1 = load i32, i32* %arrayidx6, align 4
+  %arrayidx8 = getelementptr inbounds i32*, i32** %y, i64 %j
+  %2 = load i32*, i32** %arrayidx8, align 8
+  %arrayidx11 = getelementptr inbounds i32, i32* %2, i64 %i
+  store i32 %1, i32* %arrayidx11, align 4
+  br label %inc_j
+
+inc_j:
+  %inc = add nsw i64 %j, 1
+  %cmp2 = icmp slt i64 %inc, %ny
+  br i1 %cmp2, label %perf_nest_2D_1_loop_j, label %inc_i
+
+inc_i:
+  %inc13 = add nsw i64 %i, 1
+  %cmp = icmp slt i64 %inc13, %nx
+  br i1 %cmp, label %perf_nest_2D_1_loop_i, label %perf_nest_2D_1_loop_i_end
+
+perf_nest_2D_1_loop_i_end:
+  ret void
+}
+
+; Test a perfect 2-dim loop nest of the form:
+;   for (i=0; i<100; ++i)
+;     for (j=0; j<100; ++j)
+;       y[i][j] = x[i][j];
+define void @perf_nest_2D_2(i32** %y, i32** %x) {
+; CHECK-LABEL: IsPerfect=true, Depth=1, OutermostLoop: perf_nest_2D_2_loop_j, Loops: ( perf_nest_2D_2_loop_j )
+; CHECK-LABEL: IsPerfect=true, Depth=2, OutermostLoop: perf_nest_2D_2_loop_i, Loops: ( perf_nest_2D_2_loop_i perf_nest_2D_2_loop_j )
+entry:
+  br label %perf_nest_2D_2_loop_i
+
+perf_nest_2D_2_loop_i:
+  %i = phi i64 [ 0, %entry ], [ %inc13, %inc_i ]
+  br label %perf_nest_2D_2_loop_j
+
+perf_nest_2D_2_loop_j:
+  %j = phi i64 [ 0, %perf_nest_2D_2_loop_i ], [ %inc, %inc_j ]
+  %arrayidx = getelementptr inbounds i32*, i32** %x, i64 %j
+  %0 = load i32*, i32** %arrayidx, align 8
+  %arrayidx6 = getelementptr inbounds i32, i32* %0, i64 %j
+  %1 = load i32, i32* %arrayidx6, align 4
+  %arrayidx8 = getelementptr inbounds i32*, i32** %y, i64 %j
+  %2 = load i32*, i32** %arrayidx8, align 8
+  %arrayidx11 = getelementptr inbounds i32, i32* %2, i64 %i
+  store i32 %1, i32* %arrayidx11, align 4
+  br label %inc_j
+
+inc_j:
+  %inc = add nsw i64 %j, 1
+  %cmp2 = icmp slt i64 %inc, 100
+  br i1 %cmp2, label %perf_nest_2D_2_loop_j, label %loop_j_end
+
+loop_j_end:
+  br label %inc_i
+
+inc_i:
+  %inc13 = add nsw i64 %i, 1
+  %cmp = icmp slt i64 %inc13, 100
+  br i1 %cmp, label %perf_nest_2D_2_loop_i, label %perf_nest_2D_2_loop_i_end
+
+perf_nest_2D_2_loop_i_end:
+  ret void
+}
+
+; Test a perfect 3-dim loop nest of the form:
+;   for (i=0; i<nx; ++i)
+;     for (j=0; j<ny; ++j)
+;       for (k=0; j<nk; ++k)
+;          y[j][j][k] = x[i][j][k];
+;
+
+define void @perf_nest_3D_1(i32*** %y, i32*** %x, i32 signext %nx, i32 signext %ny, i32 signext %nk) {
+; CHECK-LABEL: IsPerfect=true, Depth=1, OutermostLoop: perf_nest_3D_1_loop_k, Loops: ( perf_nest_3D_1_loop_k )
+; CHECK-NEXT: IsPerfect=true, Depth=2, OutermostLoop: perf_nest_3D_1_loop_j, Loops: ( perf_nest_3D_1_loop_j perf_nest_3D_1_loop_k )
+; CHECK-NEXT: IsPerfect=true, Depth=3, OutermostLoop: perf_nest_3D_1_loop_i, Loops: ( perf_nest_3D_1_loop_i perf_nest_3D_1_loop_j perf_nest_3D_1_loop_k )
+entry:
+  br label %perf_nest_3D_1_loop_i
+
+perf_nest_3D_1_loop_i:
+  %i = phi i32 [ 0, %entry ], [ %inci, %for.inci ]
+  %cmp21 = icmp slt i32 0, %ny
+  br i1 %cmp21, label %perf_nest_3D_1_loop_j, label %for.inci
+
+perf_nest_3D_1_loop_j:
+  %j = phi i32 [ 0, %perf_nest_3D_1_loop_i ], [ %incj, %for.incj ]
+  %cmp22 = icmp slt i32 0, %nk
+  br i1 %cmp22, label %perf_nest_3D_1_loop_k, label %for.incj
+
+perf_nest_3D_1_loop_k:
+  %k = phi i32 [ 0, %perf_nest_3D_1_loop_j ], [ %inck, %for.inck ]
+  %idxprom = sext i32 %i to i64
+  %arrayidx = getelementptr inbounds i32**, i32*** %x, i64 %idxprom
+  %0 = load i32**, i32*** %arrayidx, align 8
+  %idxprom7 = sext i32 %j to i64
+  %arrayidx8 = getelementptr inbounds i32*, i32** %0, i64 %idxprom7
+  %1 = load i32*, i32** %arrayidx8, align 8
+  %idxprom9 = sext i32 %k to i64
+  %arrayidx10 = getelementptr inbounds i32, i32* %1, i64 %idxprom9
+  %2 = load i32, i32* %arrayidx10, align 4
+  %idxprom11 = sext i32 %j to i64
+  %arrayidx12 = getelementptr inbounds i32**, i32*** %y, i64 %idxprom11
+  %3 = load i32**, i32*** %arrayidx12, align 8
+  %idxprom13 = sext i32 %j to i64
+  %arrayidx14 = getelementptr inbounds i32*, i32** %3, i64 %idxprom13
+  %4 = load i32*, i32** %arrayidx14, align 8
+  %idxprom15 = sext i32 %k to i64
+  %arrayidx16 = getelementptr inbounds i32, i32* %4, i64 %idxprom15
+  store i32 %2, i32* %arrayidx16, align 4
+  br label %for.inck
+
+for.inck:
+  %inck = add nsw i32 %k, 1
+  %cmp5 = icmp slt i32 %inck, %nk
+  br i1 %cmp5, label %perf_nest_3D_1_loop_k, label %for.incj
+
+for.incj:
+  %incj = add nsw i32 %j, 1
+  %cmp2 = icmp slt i32 %incj, %ny
+  br i1 %cmp2, label %perf_nest_3D_1_loop_j, label %for.inci
+
+for.inci:
+  %inci = add nsw i32 %i, 1
+  %cmp = icmp slt i32 %inci, %nx
+  br i1 %cmp, label %perf_nest_3D_1_loop_i, label %perf_nest_3D_1_loop_i_end
+
+perf_nest_3D_1_loop_i_end:
+  ret void
+}
+
+; Test a perfect 3-dim loop nest of the form:
+;   for (i=0; i<100; ++i)
+;     for (j=0; j<100; ++j)
+;       for (k=0; j<100; ++k)
+;          y[j][j][k] = x[i][j][k];
+;
+
+define void @perf_nest_3D_2(i32*** %y, i32*** %x) {
+; CHECK-LABEL: IsPerfect=true, Depth=1, OutermostLoop: perf_nest_3D_2_loop_k, Loops: ( perf_nest_3D_2_loop_k )
+; CHECK-NEXT: IsPerfect=true, Depth=2, OutermostLoop: perf_nest_3D_2_loop_j, Loops: ( perf_nest_3D_2_loop_j perf_nest_3D_2_loop_k )
+; CHECK-NEXT: IsPerfect=true, Depth=3, OutermostLoop: perf_nest_3D_2_loop_i, Loops: ( perf_nest_3D_2_loop_i perf_nest_3D_2_loop_j perf_nest_3D_2_loop_k )
+entry:
+  br label %perf_nest_3D_2_loop_i
+
+perf_nest_3D_2_loop_i:
+  %i = phi i32 [ 0, %entry ], [ %inci, %for.inci ]
+  br label %perf_nest_3D_2_loop_j
+
+perf_nest_3D_2_loop_j:
+  %j = phi i32 [ 0, %perf_nest_3D_2_loop_i ], [ %incj, %for.incj ]
+  br label %perf_nest_3D_2_loop_k
+
+perf_nest_3D_2_loop_k:
+  %k = phi i32 [ 0, %perf_nest_3D_2_loop_j ], [ %inck, %for.inck ]
+  %idxprom = sext i32 %i to i64
+  %arrayidx = getelementptr inbounds i32**, i32*** %x, i64 %idxprom
+  %0 = load i32**, i32*** %arrayidx, align 8
+  %idxprom7 = sext i32 %j to i64
+  %arrayidx8 = getelementptr inbounds i32*, i32** %0, i64 %idxprom7
+  %1 = load i32*, i32** %arrayidx8, align 8
+  %idxprom9 = sext i32 %k to i64
+  %arrayidx10 = getelementptr inbounds i32, i32* %1, i64 %idxprom9
+  %2 = load i32, i32* %arrayidx10, align 4
+  %idxprom11 = sext i32 %j to i64
+  %arrayidx12 = getelementptr inbounds i32**, i32*** %y, i64 %idxprom11
+  %3 = load i32**, i32*** %arrayidx12, align 8
+  %idxprom13 = sext i32 %j to i64
+  %arrayidx14 = getelementptr inbounds i32*, i32** %3, i64 %idxprom13
+  %4 = load i32*, i32** %arrayidx14, align 8
+  %idxprom15 = sext i32 %k to i64
+  %arrayidx16 = getelementptr inbounds i32, i32* %4, i64 %idxprom15
+  store i32 %2, i32* %arrayidx16, align 4
+  br label %for.inck
+
+for.inck:
+  %inck = add nsw i32 %k, 1
+  %cmp5 = icmp slt i32 %inck, 100
+  br i1 %cmp5, label %perf_nest_3D_2_loop_k, label %loop_k_end
+
+loop_k_end:
+  br label %for.incj
+
+for.incj:
+  %incj = add nsw i32 %j, 1
+  %cmp2 = icmp slt i32 %incj, 100
+  br i1 %cmp2, label %perf_nest_3D_2_loop_j, label %loop_j_end
+
+loop_j_end:
+  br label %for.inci
+
+for.inci:
+  %inci = add nsw i32 %i, 1
+  %cmp = icmp slt i32 %inci, 100
+  br i1 %cmp, label %perf_nest_3D_2_loop_i, label %perf_nest_3D_2_loop_i_end
+
+perf_nest_3D_2_loop_i_end:
+  ret void
+}
+
+; Test a perfect loop nest with a live out reduction:
+;   for (i = 0; i<ni; ++i)
+;     if (0<nj) { // guard branch for the j-loop
+;       for (j=0; j<nj; j+=1)
+;         x+=(i+j);
+;     }
+;   return x;
+
+define signext i32 @perf_nest_live_out(i32 signext %x, i32 signext %ni, i32 signext %nj) {
+; CHECK-LABEL: IsPerfect=true, Depth=1, OutermostLoop: perf_nest_live_out_loop_j, Loops: ( perf_nest_live_out_loop_j )
+; CHECK-LABEL: IsPerfect=true, Depth=2, OutermostLoop: perf_nest_live_out_loop_i, Loops: ( perf_nest_live_out_loop_i perf_nest_live_out_loop_j )
+entry:
+  %cmp4 = icmp slt i32 0, %ni
+  br i1 %cmp4, label %perf_nest_live_out_loop_i.lr.ph, label %for.end7
+
+perf_nest_live_out_loop_i.lr.ph:
+  br label %perf_nest_live_out_loop_i
+
+perf_nest_live_out_loop_i:
+  %x.addr.06 = phi i32 [ %x, %perf_nest_live_out_loop_i.lr.ph ], [ %x.addr.1.lcssa, %for.inc5 ]
+  %i.05 = phi i32 [ 0, %perf_nest_live_out_loop_i.lr.ph ], [ %inc6, %for.inc5 ]
+  %cmp21 = icmp slt i32 0, %nj
+  br i1 %cmp21, label %perf_nest_live_out_loop_j.lr.ph, label %for.inc5
+
+perf_nest_live_out_loop_j.lr.ph:
+  br label %perf_nest_live_out_loop_j
+
+perf_nest_live_out_loop_j:
+  %x.addr.13 = phi i32 [ %x.addr.06, %perf_nest_live_out_loop_j.lr.ph ], [ %add4, %perf_nest_live_out_loop_j ]
+  %j.02 = phi i32 [ 0, %perf_nest_live_out_loop_j.lr.ph ], [ %inc, %perf_nest_live_out_loop_j ]
+  %add = add nsw i32 %i.05, %j.02
+  %add4 = add nsw i32 %x.addr.13, %add
+  %inc = add nsw i32 %j.02, 1
+  %cmp2 = icmp slt i32 %inc, %nj
+  br i1 %cmp2, label %perf_nest_live_out_loop_j, label %for.cond1.for.inc5_crit_edge
+
+for.cond1.for.inc5_crit_edge:
+  %split = phi i32 [ %add4, %perf_nest_live_out_loop_j ]
+  br label %for.inc5
+
+for.inc5:
+  %x.addr.1.lcssa = phi i32 [ %split, %for.cond1.for.inc5_crit_edge ], [ %x.addr.06, %perf_nest_live_out_loop_i ]
+  %inc6 = add nsw i32 %i.05, 1
+  %cmp = icmp slt i32 %inc6, %ni
+  br i1 %cmp, label %perf_nest_live_out_loop_i, label %for.cond.for.end7_crit_edge
+
+for.cond.for.end7_crit_edge:
+  %split7 = phi i32 [ %x.addr.1.lcssa, %for.inc5 ]
+  br label %for.end7
+
+for.end7:
+  %x.addr.0.lcssa = phi i32 [ %split7, %for.cond.for.end7_crit_edge ], [ %x, %entry ]
+  ret i32 %x.addr.0.lcssa
+}

diff  --git a/llvm/unittests/Analysis/CMakeLists.txt b/llvm/unittests/Analysis/CMakeLists.txt
index d66dd39c6013..6fabd940a74a 100644
--- a/llvm/unittests/Analysis/CMakeLists.txt
+++ b/llvm/unittests/Analysis/CMakeLists.txt
@@ -23,6 +23,7 @@ add_llvm_unittest(AnalysisTests
   LazyCallGraphTest.cpp
   LoadsTest.cpp
   LoopInfoTest.cpp
+  LoopNestTest.cpp
   MemoryBuiltinsTest.cpp
   MemorySSATest.cpp
   OrderedInstructionsTest.cpp

diff  --git a/llvm/unittests/Analysis/LoopNestTest.cpp b/llvm/unittests/Analysis/LoopNestTest.cpp
new file mode 100644
index 000000000000..4e31b1f2e904
--- /dev/null
+++ b/llvm/unittests/Analysis/LoopNestTest.cpp
@@ -0,0 +1,194 @@
+//===- LoopNestTest.cpp - LoopNestAnalysis unit tests ---------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#include "llvm/Analysis/LoopNestAnalysis.h"
+#include "llvm/Analysis/ScalarEvolution.h"
+#include "llvm/Analysis/TargetLibraryInfo.h"
+#include "llvm/AsmParser/Parser.h"
+#include "llvm/IR/Dominators.h"
+#include "llvm/Support/SourceMgr.h"
+#include "gtest/gtest.h"
+
+using namespace llvm;
+
+/// Build the loop nest analysis for a loop nest and run the given test \p Test.
+static void runTest(
+    Module &M, StringRef FuncName,
+    function_ref<void(Function &F, LoopInfo &LI, ScalarEvolution &SE)> Test) {
+  auto *F = M.getFunction(FuncName);
+  ASSERT_NE(F, nullptr) << "Could not find " << FuncName;
+
+  TargetLibraryInfoImpl TLII;
+  TargetLibraryInfo TLI(TLII);
+  AssumptionCache AC(*F);
+  DominatorTree DT(*F);
+  LoopInfo LI(DT);
+  ScalarEvolution SE(*F, TLI, AC, DT, LI);
+
+  Test(*F, LI, SE);
+}
+
+static std::unique_ptr<Module> makeLLVMModule(LLVMContext &Context,
+                                              const char *ModuleStr) {
+  SMDiagnostic Err;
+  return parseAssemblyString(ModuleStr, Err, Context);
+}
+
+TEST(LoopNestTest, PerfectLoopNest) {
+  const char *ModuleStr =
+    "target datalayout = \"e-m:o-i64:64-f80:128-n8:16:32:64-S128\"\n"
+    "define void @foo(i64 signext %nx, i64 signext %ny) {\n"
+    "entry:\n"
+    "  br label %for.outer\n"
+    "for.outer:\n"
+    "  %i = phi i64 [ 0, %entry ], [ %inc13, %for.outer.latch ]\n"
+    "  %cmp21 = icmp slt i64 0, %ny\n"
+    "  br i1 %cmp21, label %for.inner.preheader, label %for.outer.latch\n"
+    "for.inner.preheader:\n"
+    "  br label %for.inner\n"
+    "for.inner:\n"
+    "  %j = phi i64 [ 0, %for.inner.preheader ], [ %inc, %for.inner.latch ]\n"
+    "  br label %for.inner.latch\n"
+    "for.inner.latch:\n"
+    "  %inc = add nsw i64 %j, 1\n"
+    "  %cmp2 = icmp slt i64 %inc, %ny\n"
+    "  br i1 %cmp2, label %for.inner, label %for.inner.exit\n"
+    "for.inner.exit:\n"
+    "  br label %for.outer.latch\n"
+    "for.outer.latch:\n"
+    "  %inc13 = add nsw i64 %i, 1\n"
+    "  %cmp = icmp slt i64 %inc13, %nx\n"
+    "  br i1 %cmp, label %for.outer, label %for.outer.exit\n"
+    "for.outer.exit:\n"
+    "  br label %for.end\n"
+    "for.end:\n"
+    "  ret void\n"
+    "}\n";
+
+  LLVMContext Context;
+  std::unique_ptr<Module> M = makeLLVMModule(Context, ModuleStr);
+
+  runTest(*M, "foo", [&](Function &F, LoopInfo &LI, ScalarEvolution &SE) {
+    Function::iterator FI = F.begin();
+    // Skip the first basic block (entry), get to the outer loop header.
+    BasicBlock *Header = &*(++FI);
+    assert(Header->getName() == "for.outer");
+    Loop *L = LI.getLoopFor(Header);
+    EXPECT_NE(L, nullptr);
+
+    LoopNest LN(*L, SE);
+    EXPECT_TRUE(LN.areAllLoopsSimplifyForm());
+
+    // Ensure that we can identify the outermost loop in the nest.
+    const Loop &OL = LN.getOutermostLoop();
+    EXPECT_EQ(OL.getName(), "for.outer");
+
+    // Ensure that we can identify the innermost loop in the nest.
+    const Loop *IL = LN.getInnermostLoop();
+    EXPECT_NE(IL, nullptr);
+    EXPECT_EQ(IL->getName(), "for.inner");
+
+    // Ensure the loop nest is recognized as having 2 loops.
+    const ArrayRef<Loop*> Loops = LN.getLoops();
+    EXPECT_EQ(Loops.size(), 2ull);
+
+    // Ensure the loop nest is recognized as perfect in its entirety.
+    const SmallVector<LoopVectorTy, 4> &PLV = LN.getPerfectLoops(SE);
+    EXPECT_EQ(PLV.size(), 1ull);
+    EXPECT_EQ(PLV.front().size(), 2ull);
+
+    // Ensure the nest depth and perfect nest depth are computed correctly.
+    EXPECT_EQ(LN.getNestDepth(), 2u);
+    EXPECT_EQ(LN.getMaxPerfectDepth(), 2u);
+  });
+}
+
+TEST(LoopNestTest, ImperfectLoopNest) {
+  const char *ModuleStr =
+      "target datalayout = \"e-m:o-i64:64-f80:128-n8:16:32:64-S128\"\n"
+      "define void @foo(i32 signext %nx, i32 signext %ny, i32 signext %nk) {\n"
+      "entry:\n"
+      "  br label %loop.i\n"
+      "loop.i:\n"
+      "  %i = phi i32 [ 0, %entry ], [ %inci, %for.inci ]\n"
+      "  %cmp21 = icmp slt i32 0, %ny\n"
+      "  br i1 %cmp21, label %loop.j.preheader, label %for.inci\n"
+      "loop.j.preheader:\n"
+      "  br label %loop.j\n"
+      "loop.j:\n"
+      "  %j = phi i32 [ %incj, %for.incj ], [ 0, %loop.j.preheader ]\n"
+      "  %cmp22 = icmp slt i32 0, %nk\n"
+      "  br i1 %cmp22, label %loop.k.preheader, label %for.incj\n"
+      "loop.k.preheader:\n"
+      "  call void @bar()\n"
+      "  br label %loop.k\n"
+      "loop.k:\n"
+      "  %k = phi i32 [ %inck, %for.inck ], [ 0, %loop.k.preheader ]\n"
+      "  br label %for.inck\n"
+      "for.inck:\n"
+      "  %inck = add nsw i32 %k, 1\n"
+      "  %cmp5 = icmp slt i32 %inck, %nk\n"
+      "  br i1 %cmp5, label %loop.k, label %for.incj.loopexit\n"
+      "for.incj.loopexit:\n"
+      "  br label %for.incj\n"
+      "for.incj:\n"
+      "  %incj = add nsw i32 %j, 1\n"
+      "  %cmp2 = icmp slt i32 %incj, %ny\n"
+      "  br i1 %cmp2, label %loop.j, label %for.inci.loopexit\n"
+      "for.inci.loopexit:\n"
+      "  br label %for.inci\n"
+      "for.inci:\n"
+      "  %inci = add nsw i32 %i, 1\n"
+      "  %cmp = icmp slt i32 %inci, %nx\n"
+      "  br i1 %cmp, label %loop.i, label %loop.i.end\n"
+      "loop.i.end:\n"
+      "  ret void\n"
+      "}\n"
+      "declare void @bar()\n";
+
+  LLVMContext Context;
+  std::unique_ptr<Module> M = makeLLVMModule(Context, ModuleStr);
+
+  runTest(*M, "foo", [&](Function &F, LoopInfo &LI, ScalarEvolution &SE) {
+    Function::iterator FI = F.begin();
+    // Skip the first basic block (entry), get to the outermost loop header.
+    BasicBlock *Header = &*(++FI);
+    assert(Header->getName() == "loop.i");
+    Loop *L = LI.getLoopFor(Header);
+    EXPECT_NE(L, nullptr);
+
+    LoopNest LN(*L, SE);
+    EXPECT_TRUE(LN.areAllLoopsSimplifyForm());
+
+    dbgs() << "LN: " << LN << "\n";
+
+    // Ensure that we can identify the outermost loop in the nest.
+    const Loop &OL = LN.getOutermostLoop();
+    EXPECT_EQ(OL.getName(), "loop.i");
+
+    // Ensure that we can identify the innermost loop in the nest.
+    const Loop *IL = LN.getInnermostLoop();
+    EXPECT_NE(IL, nullptr);
+    EXPECT_EQ(IL->getName(), "loop.k");
+
+    // Ensure the loop nest is recognized as having 3 loops.
+    const ArrayRef<Loop*> Loops = LN.getLoops();
+    EXPECT_EQ(Loops.size(), 3ull);
+
+    // Ensure the loop nest is recognized as having 2 separate perfect loops groups.
+    const SmallVector<LoopVectorTy, 4> &PLV = LN.getPerfectLoops(SE);
+    EXPECT_EQ(PLV.size(), 2ull);
+    EXPECT_EQ(PLV.front().size(), 2ull);
+    EXPECT_EQ(PLV.back().size(), 1ull);
+
+    // Ensure the nest depth and perfect nest depth are computed correctly.
+    EXPECT_EQ(LN.getNestDepth(), 3u);
+    EXPECT_EQ(LN.getMaxPerfectDepth(), 2u);
+  });
+}
+


        


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