diff --git a/llvm/lib/Analysis/LoopNestAnalysis.cpp b/llvm/lib/Analysis/LoopNestAnalysis.cpp
--- a/llvm/lib/Analysis/LoopNestAnalysis.cpp
+++ b/llvm/lib/Analysis/LoopNestAnalysis.cpp
@@ -228,6 +228,28 @@
       InnerLoop.getExitingBlock() != InnerLoopLatch || !InnerLoopExit)
     return false;
 
+  // Returns whether the block `ExitBlock` contains at least one LCSSA Phi node.
+  auto ContainsLCSSAPhi = [](const BasicBlock &ExitBlock) {
+    return any_of(ExitBlock.phis(), [](const PHINode &PN) {
+      return PN.getNumIncomingValues() == 1;
+    });
+  };
+
+  // Returns whether the block `BB` qualifies for being an extra Phi block. The
+  // extra Phi block is the additional block inserted after the exit block of an
+  // "guarded" inner loop which contains "only" Phi nodes corresponding to the
+  // LCSSA Phi nodes in the exit block.
+  auto IsExtraPhiBlock = [&](const BasicBlock &BB) {
+    return BB.getFirstNonPHI() == BB.getTerminator() &&
+           all_of(BB.phis(), [&](const PHINode &PN) {
+             return all_of(PN.blocks(), [&](const BasicBlock *IncomingBlock) {
+               return IncomingBlock == InnerLoopExit ||
+                      IncomingBlock == OuterLoopHeader;
+             });
+           });
+  };
+
+  const BasicBlock *ExtraPhiBlock = nullptr;
   // Ensure the only branch that may exist between the loops is the inner loop
   // guard.
   if (OuterLoopHeader != InnerLoopPreHeader) {
@@ -237,6 +259,8 @@
     if (!BI || BI != InnerLoop.getLoopGuardBranch())
       return false;
 
+    bool InnerLoopExitContainsLCSSA = ContainsLCSSAPhi(*InnerLoopExit);
+
     // The successors of the inner loop guard should be the inner loop
     // preheader and the outer loop latch.
     for (const BasicBlock *Succ : BI->successors()) {
@@ -245,6 +269,20 @@
       if (Succ == OuterLoopLatch)
         continue;
 
+      // If `InnerLoopExit` contains LCSSA Phi instructions, additional block
+      // may be inserted before the `OuterLoopLatch` to which `BI` jumps. The
+      // loops are still considered perfectly nested if the extra block only
+      // contains Phi instructions from InnerLoopExit and OuterLoopHeader.
+      if (InnerLoopExitContainsLCSSA && IsExtraPhiBlock(*Succ) &&
+          Succ->getSingleSuccessor() == OuterLoopLatch) {
+        // Points to the extra block so that we can reference it later in the
+        // final check. We can also conclude that the inner loop is
+        // guarded and there exists LCSSA Phi node in the exit block later if we
+        // see a non-null `ExtraPhiBlock`.
+        ExtraPhiBlock = Succ;
+        continue;
+      }
+
       DEBUG_WITH_TYPE(VerboseDebug, {
         dbgs() << "Inner loop guard successor " << Succ->getName()
                << " doesn't lead to inner loop preheader or "
@@ -255,7 +293,9 @@
   }
 
   // Ensure the inner loop exit block leads to the outer loop latch.
-  if (InnerLoopExit->getSingleSuccessor() != OuterLoopLatch) {
+  const BasicBlock *SuccInner = InnerLoopExit->getSingleSuccessor();
+  if (!SuccInner ||
+      (SuccInner != OuterLoopLatch && SuccInner != ExtraPhiBlock)) {
     DEBUG_WITH_TYPE(
         VerboseDebug,
         dbgs() << "Inner loop exit block " << *InnerLoopExit
diff --git a/llvm/test/Analysis/LoopNestAnalysis/nests-with-lcssa.ll b/llvm/test/Analysis/LoopNestAnalysis/nests-with-lcssa.ll
new file mode 100644
--- /dev/null
+++ b/llvm/test/Analysis/LoopNestAnalysis/nests-with-lcssa.ll
@@ -0,0 +1,248 @@
+; RUN: opt -S -passes='print<loopnest>' < %s 2>&1 > /dev/null | FileCheck %s
+
+; int f(int N, int M) {
+;   int res = 0;
+;   for (int i = 0; i < N; ++i) {
+;     for (int j = 0; j < M; ++j) res += i * j;
+;   }
+;   return res;
+; }
+
+define i32 @f(i32 %N, i32 %M) #0 {
+; CHECK: IsPerfect=true, Depth=1, OutermostLoop: for.j, Loops: ( for.j )
+; CHECK: IsPerfect=true, Depth=2, OutermostLoop: for.i, Loops: ( for.i for.j )
+entry:
+  %cmp4 = icmp slt i32 0, %N
+  br i1 %cmp4, label %for.i.ph, label %for.i.end
+
+for.i.ph:                                         ; preds = %entry
+  br label %for.i
+
+for.i:                                            ; preds = %for.i.ph, %for.i.inc
+  %i.06 = phi i32 [ 0, %for.i.ph ], [ %inc5, %for.i.inc ]
+  %res.05 = phi i32 [ 0, %for.i.ph ], [ %res.1.lcssa, %for.i.inc ]
+  %cmp21 = icmp slt i32 0, %M
+  br i1 %cmp21, label %for.j.ph, label %for.j.end
+
+for.j.ph:                                         ; preds = %for.i
+  br label %for.j
+
+for.j:                                            ; preds = %for.j.ph, %for.j.inc
+  %j.03 = phi i32 [ 0, %for.j.ph ], [ %inc, %for.j.inc ]
+  %res.12 = phi i32 [ %res.05, %for.j.ph ], [ %add, %for.j.inc ]
+  %mul = mul nsw i32 %i.06, %j.03
+  %add = add nsw i32 %res.12, %mul
+  br label %for.j.inc
+
+for.j.inc:                                        ; preds = %for.j
+  %inc = add nsw i32 %j.03, 1
+  %cmp2 = icmp slt i32 %inc, %M
+  br i1 %cmp2, label %for.j, label %for.j.end_crit_edge
+
+for.j.end_crit_edge:                              ; preds = %for.j.inc
+  %split = phi i32 [ %add, %for.j.inc ]
+  br label %for.j.end
+
+for.j.end:                                        ; preds = %for.j.end_crit_edge, %for.i
+  %res.1.lcssa = phi i32 [ %split, %for.j.end_crit_edge ], [ %res.05, %for.i ]
+  br label %for.i.inc
+
+for.i.inc:                                        ; preds = %for.j.end
+  %inc5 = add nsw i32 %i.06, 1
+  %cmp = icmp slt i32 %inc5, %N
+  br i1 %cmp, label %for.i, label %for.i.end_crit_edge
+
+for.i.end_crit_edge:                              ; preds = %for.i.inc
+  %split7 = phi i32 [ %res.1.lcssa, %for.i.inc ]
+  br label %for.i.end
+
+for.i.end:                                        ; preds = %for.i.end_crit_edge, %entry
+  %res.0.lcssa = phi i32 [ %split7, %for.i.end_crit_edge ], [ 0, %entry ]
+  ret i32 %res.0.lcssa
+}
+
+; int g(int N, int M, int K) {
+;   int sum = 0, prod = 1;
+;   for (int i = 0; i < N; ++i) {
+;     for (int j = 0; j < M; ++j) {
+;       for (int k = 0; k < K; ++k) {
+;         sum += i * j * k;
+;       }
+;       prod *= (i + j);
+;     }
+;   }
+;   return sum + prod;
+; }
+define i32 @g(i32 %N, i32 %M, i32 %K) #0 {
+; CHECK: IsPerfect=true, Depth=1, OutermostLoop: for.k, Loops: ( for.k )
+; CHECK: IsPerfect=false, Depth=2, OutermostLoop: for.j, Loops: ( for.j for.k )
+; CHECK: IsPerfect=false, Depth=3, OutermostLoop: for.i, Loops: ( for.i for.j for.k )
+entry:
+  %cmp10 = icmp slt i32 0, %N
+  br i1 %cmp10, label %for.i.ph, label %for.i.end
+
+for.i.ph:                                         ; preds = %entry
+  br label %for.i
+
+for.i:                                            ; preds = %for.i.ph, %for.i.inc
+  %i.013 = phi i32 [ 0, %for.i.ph ], [ %inc14, %for.i.inc ]
+  %sum.012 = phi i32 [ 0, %for.i.ph ], [ %sum.1.lcssa, %for.i.inc ]
+  %prod.011 = phi i32 [ 1, %for.i.ph ], [ %prod.1.lcssa, %for.i.inc ]
+  %cmp24 = icmp slt i32 0, %M
+  br i1 %cmp24, label %for.j.ph, label %for.j.end
+
+for.j.ph:                                         ; preds = %for.i
+  br label %for.j
+
+for.j:                                            ; preds = %for.j.ph, %for.j.inc
+  %j.07 = phi i32 [ 0, %for.j.ph ], [ %inc11, %for.j.inc ]
+  %sum.16 = phi i32 [ %sum.012, %for.j.ph ], [ %sum.2.lcssa, %for.j.inc ]
+  %prod.15 = phi i32 [ %prod.011, %for.j.ph ], [ %mul9, %for.j.inc ]
+  %cmp51 = icmp slt i32 0, %K
+  br i1 %cmp51, label %for.k.ph, label %for.k.end
+
+for.k.ph:                                         ; preds = %for.j
+  br label %for.k
+
+for.k:                                            ; preds = %for.k.ph, %for.k.inc
+  %k.03 = phi i32 [ 0, %for.k.ph ], [ %inc, %for.k.inc ]
+  %sum.22 = phi i32 [ %sum.16, %for.k.ph ], [ %add, %for.k.inc ]
+  %mul = mul nsw i32 %i.013, %j.07
+  %mul7 = mul nsw i32 %mul, %k.03
+  %add = add nsw i32 %sum.22, %mul7
+  br label %for.k.inc
+
+for.k.inc:                                        ; preds = %for.k
+  %inc = add nsw i32 %k.03, 1
+  %cmp5 = icmp slt i32 %inc, %K
+  br i1 %cmp5, label %for.k, label %for.k.end_crit_edge
+
+for.k.end_crit_edge:                              ; preds = %for.k.inc
+  %split = phi i32 [ %add, %for.k.inc ]
+  br label %for.k.end
+
+for.k.end:                                        ; preds = %for.k.end_crit_edge, %for.j
+  %sum.2.lcssa = phi i32 [ %split, %for.k.end_crit_edge ], [ %sum.16, %for.j ]
+  %add8 = add nsw i32 %i.013, %j.07
+  %mul9 = mul nsw i32 %prod.15, %add8
+  br label %for.j.inc
+
+for.j.inc:                                        ; preds = %for.k.end
+  %inc11 = add nsw i32 %j.07, 1
+  %cmp2 = icmp slt i32 %inc11, %M
+  br i1 %cmp2, label %for.j, label %for.j.end_crit_edge
+
+for.j.end_crit_edge:                              ; preds = %for.j.inc
+  %split8 = phi i32 [ %mul9, %for.j.inc ]
+  %split9 = phi i32 [ %sum.2.lcssa, %for.j.inc ]
+  br label %for.j.end
+
+for.j.end:                                        ; preds = %for.j.end1crit_edge, %for.i
+  %prod.1.lcssa = phi i32 [ %split8, %for.j.end_crit_edge ], [ %prod.011, %for.i ]
+  %sum.1.lcssa = phi i32 [ %split9, %for.j.end_crit_edge ], [ %sum.012, %for.i ]
+  br label %for.i.inc
+
+for.i.inc:                                        ; preds = %for.j.end
+  %inc14 = add nsw i32 %i.013, 1
+  %cmp = icmp slt i32 %inc14, %N
+  br i1 %cmp, label %for.i, label %for.i.end_crit_edge
+
+for.i.end_crit_edge:                              ; preds = %for.i.inc
+  %split14 = phi i32 [ %prod.1.lcssa, %for.i.inc ]
+  %split15 = phi i32 [ %sum.1.lcssa, %for.i.inc ]
+  br label %for.i.end
+
+for.i.end:                                        ; preds = %for.i.end_crit_edge, %entry
+  %prod.0.lcssa = phi i32 [ %split14, %for.i.end_crit_edge ], [ 1, %entry ]
+  %sum.0.lcssa = phi i32 [ %split15, %for.i.end_crit_edge ], [ 0, %entry ]
+  %add16 = add nsw i32 %sum.0.lcssa, %prod.0.lcssa
+  ret i32 %add16
+}
+
+; int h(int N, int M, int K) {
+;   int sum = 0;
+;   for (int i = 0; i < N; ++i) {
+;     for (int j = 0; j < M; ++j) {
+;       for (int k = 0; k < K; ++k) {
+;         sum += i * j * k;
+;       }
+;     }
+;   }
+;   return sum;
+; }
+define i32 @h(i32 %N, i32 %M, i32 %K) #0 {
+; CHECK: IsPerfect=true, Depth=1, OutermostLoop: for.k, Loops: ( for.k )
+; CHECK: IsPerfect=true, Depth=2, OutermostLoop: for.j, Loops: ( for.j for.k )
+; CHECK: IsPerfect=true, Depth=3, OutermostLoop: for.i, Loops: ( for.i for.j for.k )
+entry:
+  %cmp8 = icmp slt i32 0, %N
+  br i1 %cmp8, label %for.i.ph, label %for.i.end
+
+for.i.ph:                                         ; preds = %entry
+  br label %for.i
+
+for.i:                                            ; preds = %for.i.ph, %for.i.inc
+  %i.010 = phi i32 [ 0, %for.i.ph ], [ %inc12, %for.i.inc ]
+  %sum.09 = phi i32 [ 0, %for.i.ph ], [ %sum.1.lcssa, %for.i.inc ]
+  %cmp24 = icmp slt i32 0, %M
+  br i1 %cmp24, label %for.j.ph, label %for.j.end
+
+for.j.ph:                                         ; preds = %for.i
+  br label %for.j
+
+for.j:                                            ; preds = %for.j.ph, %for.j.inc
+  %j.06 = phi i32 [ 0, %for.j.ph ], [ %inc9, %for.j.inc ]
+  %sum.15 = phi i32 [ %sum.09, %for.j.ph ], [ %sum.2.lcssa, %for.j.inc ]
+  %cmp51 = icmp slt i32 0, %K
+  br i1 %cmp51, label %for.k.ph, label %for.k.end
+
+for.k.ph:                                         ; preds = %for.j
+  br label %for.k
+
+for.k:                                            ; preds = %for.k.ph, %for.k.inc
+  %k.03 = phi i32 [ 0, %for.k.ph ], [ %inc, %for.k.inc ]
+  %sum.22 = phi i32 [ %sum.15, %for.k.ph ], [ %add, %for.k.inc ]
+  %mul = mul nsw i32 %i.010, %j.06
+  %mul7 = mul nsw i32 %mul, %k.03
+  %add = add nsw i32 %sum.22, %mul7
+  br label %for.k.inc
+
+for.k.inc:                                        ; preds = %for.k
+  %inc = add nsw i32 %k.03, 1
+  %cmp5 = icmp slt i32 %inc, %K
+  br i1 %cmp5, label %for.k, label %for.k.end_crit_edge
+
+for.k.end_crit_edge:                              ; preds = %for.k.inc
+  %split = phi i32 [ %add, %for.k.inc ]
+  br label %for.k.end
+
+for.k.end:                                        ; preds = %for.k.end_crit_edge, %for.j
+  %sum.2.lcssa = phi i32 [ %split, %for.k.end_crit_edge ], [ %sum.15, %for.j ]
+  br label %for.j.inc
+
+for.j.inc:                                        ; preds = %for.k.end
+  %inc9 = add nsw i32 %j.06, 1
+  %cmp2 = icmp slt i32 %inc9, %M
+  br i1 %cmp2, label %for.j, label %for.j.end_crit_edge
+
+for.j.end_crit_edge:                              ; preds = %for.j.inc
+  %split7 = phi i32 [ %sum.2.lcssa, %for.j.inc ]
+  br label %for.j.end
+
+for.j.end:                                        ; preds = %for.j.end_crit_edge, %for.i
+  %sum.1.lcssa = phi i32 [ %split7, %for.j.end_crit_edge ], [ %sum.09, %for.i ]
+  br label %for.i.inc
+
+for.i.inc:                                        ; preds = %for.j.end
+  %inc12 = add nsw i32 %i.010, 1
+  %cmp = icmp slt i32 %inc12, %N
+  br i1 %cmp, label %for.i, label %for.i.end_crit_edge
+
+for.i.end_crit_edge:                              ; preds = %for.i.inc
+  %split11 = phi i32 [ %sum.1.lcssa, %for.i.inc ]
+  br label %for.i.end
+
+for.i.end:                                        ; preds = %for.i.end_crit_edge, %entry
+  %sum.0.lcssa = phi i32 [ %split11, %for.i.end_crit_edge ], [ 0, %entry ]
+  ret i32 %sum.0.lcssa
+}