diff --git a/llvm/include/llvm/Transforms/Vectorize/SandboxVectorizer/DependencyGraph.h b/llvm/include/llvm/Transforms/Vectorize/SandboxVectorizer/DependencyGraph.h
index 134adc4b21ab1..5036dae1f0e27 100644
--- a/llvm/include/llvm/Transforms/Vectorize/SandboxVectorizer/DependencyGraph.h
+++ b/llvm/include/llvm/Transforms/Vectorize/SandboxVectorizer/DependencyGraph.h
@@ -154,6 +154,14 @@ class MemDGNode final : public DGNode {
 /// Convenience builders for a MemDGNode interval.
 class MemDGNodeIntervalBuilder {
 public:
+  /// Scans the instruction chain in \p Intvl top-down, returning the top-most
+  /// MemDGNode, or nullptr.
+  static MemDGNode *getTopMemDGNode(const Interval<Instruction> &Intvl,
+                                    const DependencyGraph &DAG);
+  /// Scans the instruction chain in \p Intvl bottom-up, returning the
+  /// bottom-most MemDGNode, or nullptr.
+  static MemDGNode *getBotMemDGNode(const Interval<Instruction> &Intvl,
+                                    const DependencyGraph &DAG);
   /// Given \p Instrs it finds their closest mem nodes in the interval and
   /// returns the corresponding mem range. Note: BotN (or its neighboring mem
   /// node) is included in the range.
diff --git a/llvm/lib/Transforms/Vectorize/SandboxVectorizer/DependencyGraph.cpp b/llvm/lib/Transforms/Vectorize/SandboxVectorizer/DependencyGraph.cpp
index 82f253d4c6323..c02eba167390d 100644
--- a/llvm/lib/Transforms/Vectorize/SandboxVectorizer/DependencyGraph.cpp
+++ b/llvm/lib/Transforms/Vectorize/SandboxVectorizer/DependencyGraph.cpp
@@ -32,23 +32,43 @@ void DGNode::dump() const {
 }
 #endif // NDEBUG
 
+MemDGNode *
+MemDGNodeIntervalBuilder::getTopMemDGNode(const Interval<Instruction> &Intvl,
+                                          const DependencyGraph &DAG) {
+  Instruction *I = Intvl.top();
+  Instruction *BeforeI = Intvl.bottom();
+  // Walk down the chain looking for a mem-dep candidate instruction.
+  while (!DGNode::isMemDepNodeCandidate(I) && I != BeforeI)
+    I = I->getNextNode();
+  if (!DGNode::isMemDepNodeCandidate(I))
+    return nullptr;
+  return cast<MemDGNode>(DAG.getNode(I));
+}
+
+MemDGNode *
+MemDGNodeIntervalBuilder::getBotMemDGNode(const Interval<Instruction> &Intvl,
+                                          const DependencyGraph &DAG) {
+  Instruction *I = Intvl.bottom();
+  Instruction *AfterI = Intvl.top();
+  // Walk up the chain looking for a mem-dep candidate instruction.
+  while (!DGNode::isMemDepNodeCandidate(I) && I != AfterI)
+    I = I->getPrevNode();
+  if (!DGNode::isMemDepNodeCandidate(I))
+    return nullptr;
+  return cast<MemDGNode>(DAG.getNode(I));
+}
+
 Interval<MemDGNode>
 MemDGNodeIntervalBuilder::make(const Interval<Instruction> &Instrs,
                                DependencyGraph &DAG) {
-  // If top or bottom instructions are not mem-dep candidate nodes we need to
-  // walk down/up the chain and find the mem-dep ones.
-  Instruction *MemTopI = Instrs.top();
-  Instruction *MemBotI = Instrs.bottom();
-  while (!DGNode::isMemDepNodeCandidate(MemTopI) && MemTopI != MemBotI)
-    MemTopI = MemTopI->getNextNode();
-  while (!DGNode::isMemDepNodeCandidate(MemBotI) && MemBotI != MemTopI)
-    MemBotI = MemBotI->getPrevNode();
+  auto *TopMemN = getTopMemDGNode(Instrs, DAG);
   // If we couldn't find a mem node in range TopN - BotN then it's empty.
-  if (!DGNode::isMemDepNodeCandidate(MemTopI))
+  if (TopMemN == nullptr)
     return {};
+  auto *BotMemN = getBotMemDGNode(Instrs, DAG);
+  assert(BotMemN != nullptr && "TopMemN should be null too!");
   // Now that we have the mem-dep nodes, create and return the range.
-  return Interval<MemDGNode>(cast<MemDGNode>(DAG.getNode(MemTopI)),
-                             cast<MemDGNode>(DAG.getNode(MemBotI)));
+  return Interval<MemDGNode>(TopMemN, BotMemN);
 }
 
 DependencyGraph::DependencyType
diff --git a/llvm/unittests/Transforms/Vectorize/SandboxVectorizer/DependencyGraphTest.cpp b/llvm/unittests/Transforms/Vectorize/SandboxVectorizer/DependencyGraphTest.cpp
index e2f16919a5cdd..b425e5a8ad214 100644
--- a/llvm/unittests/Transforms/Vectorize/SandboxVectorizer/DependencyGraphTest.cpp
+++ b/llvm/unittests/Transforms/Vectorize/SandboxVectorizer/DependencyGraphTest.cpp
@@ -305,6 +305,20 @@ define void @foo(ptr %ptr, i8 %v0, i8 %v1) {
   auto *S0N = cast<sandboxir::MemDGNode>(DAG.getNode(S0));
   auto *S1N = cast<sandboxir::MemDGNode>(DAG.getNode(S1));
 
+  // Check getTopMemDGNode().
+  using B = sandboxir::MemDGNodeIntervalBuilder;
+  using InstrInterval = sandboxir::Interval<sandboxir::Instruction>;
+  EXPECT_EQ(B::getTopMemDGNode(InstrInterval(S0, S0), DAG), S0N);
+  EXPECT_EQ(B::getTopMemDGNode(InstrInterval(S0, Ret), DAG), S0N);
+  EXPECT_EQ(B::getTopMemDGNode(InstrInterval(Add0, Add1), DAG), S0N);
+  EXPECT_EQ(B::getTopMemDGNode(InstrInterval(Add0, Add0), DAG), nullptr);
+
+  // Check getBotMemDGNode().
+  EXPECT_EQ(B::getBotMemDGNode(InstrInterval(S1, S1), DAG), S1N);
+  EXPECT_EQ(B::getBotMemDGNode(InstrInterval(Add0, S1), DAG), S1N);
+  EXPECT_EQ(B::getBotMemDGNode(InstrInterval(Add0, Ret), DAG), S1N);
+  EXPECT_EQ(B::getBotMemDGNode(InstrInterval(Ret, Ret), DAG), nullptr);
+
   // Check empty range.
   EXPECT_THAT(sandboxir::MemDGNodeIntervalBuilder::makeEmpty(),
               testing::ElementsAre());