diff --git a/llvm/lib/Analysis/ScalarEvolution.cpp b/llvm/lib/Analysis/ScalarEvolution.cpp
index 51cffac808768..2fdfe243e2dc5 100644
--- a/llvm/lib/Analysis/ScalarEvolution.cpp
+++ b/llvm/lib/Analysis/ScalarEvolution.cpp
@@ -597,11 +597,14 @@ void SCEVUnknown::allUsesReplacedWith(Value *New) {
 ///
 /// Since we do not continue running this routine on expression trees once we
 /// have seen unequal values, there is no need to track them in the cache.
-static int
+static std::optional<int>
 CompareValueComplexity(EquivalenceClasses<const Value *> &EqCacheValue,
                        const LoopInfo *const LI, Value *LV, Value *RV,
                        unsigned Depth) {
-  if (Depth > MaxValueCompareDepth || EqCacheValue.isEquivalent(LV, RV))
+  if (Depth > MaxValueCompareDepth)
+    return std::nullopt;
+
+  if (EqCacheValue.isEquivalent(LV, RV))
     return 0;
 
   // Order pointer values after integer values. This helps SCEVExpander form
@@ -660,7 +663,7 @@ CompareValueComplexity(EquivalenceClasses<const Value *> &EqCacheValue,
       return (int)LNumOps - (int)RNumOps;
 
     for (unsigned Idx : seq(LNumOps)) {
-      int Result =
+      std::optional<int> Result =
           CompareValueComplexity(EqCacheValue, LI, LInst->getOperand(Idx),
                                  RInst->getOperand(Idx), Depth + 1);
       if (Result != 0)
@@ -705,8 +708,8 @@ CompareSCEVComplexity(EquivalenceClasses<const SCEV *> &EqCacheSCEV,
     const SCEVUnknown *LU = cast<SCEVUnknown>(LHS);
     const SCEVUnknown *RU = cast<SCEVUnknown>(RHS);
 
-    int X = CompareValueComplexity(EqCacheValue, LI, LU->getValue(),
-                                   RU->getValue(), Depth + 1);
+    std::optional<int> X = CompareValueComplexity(
+        EqCacheValue, LI, LU->getValue(), RU->getValue(), Depth + 1);
     if (X == 0)
       EqCacheSCEV.unionSets(LHS, RHS);
     return X;
diff --git a/llvm/unittests/Analysis/ScalarEvolutionTest.cpp b/llvm/unittests/Analysis/ScalarEvolutionTest.cpp
index a6a5ffda3cb70..76e6095636305 100644
--- a/llvm/unittests/Analysis/ScalarEvolutionTest.cpp
+++ b/llvm/unittests/Analysis/ScalarEvolutionTest.cpp
@@ -1625,4 +1625,40 @@ TEST_F(ScalarEvolutionsTest, ForgetValueWithOverflowInst) {
   });
 }
 
+TEST_F(ScalarEvolutionsTest, ComplexityComparatorIsStrictWeakOrdering) {
+  // Regression test for a case where caching of equivalent values caused the
+  // comparator to get inconsistent.
+  LLVMContext C;
+  SMDiagnostic Err;
+  std::unique_ptr<Module> M = parseAssemblyString(R"(
+    define i32 @foo(i32 %arg0) {
+      %1 = add i32 %arg0, 1
+      %2 = add i32 %arg0, 1
+      %3 = xor i32 %2, %1
+      %4 = add i32 %3, %2
+      %5 = add i32 %arg0, 1
+      %6 = xor i32 %5, %arg0
+      %7 = add i32 %arg0, %6
+      %8 = add i32 %5, %7
+      %9 = xor i32 %8, %7
+      %10 = add i32 %9, %8
+      %11 = xor i32 %10, %9
+      %12 = add i32 %11, %10
+      %13 = xor i32 %12, %11
+      %14 = add i32 %12, %13
+      %15 = add i32 %14, %4
+      ret i32 %15
+    })",
+                                                  Err, C);
+
+  ASSERT_TRUE(M && "Could not parse module?");
+  ASSERT_TRUE(!verifyModule(*M) && "Must have been well formed!");
+
+  runWithSE(*M, "foo", [](Function &F, LoopInfo &LI, ScalarEvolution &SE) {
+    // When _LIBCPP_HARDENING_MODE == _LIBCPP_HARDENING_MODE_DEBUG, this will
+    // crash if the comparator has the specific caching bug.
+    SE.getSCEV(F.getEntryBlock().getTerminator()->getOperand(0));
+  });
+}
+
 }  // end namespace llvm
diff --git a/polly/test/ScopInfo/invariant_load_zext_parameter-2.ll b/polly/test/ScopInfo/invariant_load_zext_parameter-2.ll
index a6108320d5608..4389fb8b8d033 100644
--- a/polly/test/ScopInfo/invariant_load_zext_parameter-2.ll
+++ b/polly/test/ScopInfo/invariant_load_zext_parameter-2.ll
@@ -25,8 +25,8 @@
 ; CHECK: p0: ((sext i32 %tmp6 to i64) * %p1)
 ; CHECK: p1: ((sext i32 %tmp3 to i64) * (sext i32 %tmp8 to i64) * (%p0 + %p1) * %p3)
 ; CHECK: p2: ((sext i32 %tmp3 to i64) * (%p0 + %p1))
-; CHECK: p3: ((sext i32 %tmp5 to i64) * %p0)
-; CHECK: p4: ((sext i32 %tmp7 to i64) * %p2)
+; CHECK: p3: ((sext i32 %tmp7 to i64) * %p2)
+; CHECK: p4: ((sext i32 %tmp5 to i64) * %p0)
 ;
 target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"