diff --git a/llvm/unittests/Support/KnownBitsTest.cpp b/llvm/unittests/Support/KnownBitsTest.cpp
index 51e780c42af27..84882550117d8 100644
--- a/llvm/unittests/Support/KnownBitsTest.cpp
+++ b/llvm/unittests/Support/KnownBitsTest.cpp
@@ -77,7 +77,8 @@ static void testUnaryOpExhaustive(StringRef Name, UnaryBitsFn BitsFn,
 
 static void testBinaryOpExhaustive(StringRef Name, BinaryBitsFn BitsFn,
                                    BinaryIntFn IntFn,
-                                   bool CheckOptimality = true) {
+                                   bool CheckOptimality = true,
+                                   bool RefinePoisonToZero = false) {
   for (unsigned Bits : {1, 4}) {
     ForeachKnownBits(Bits, [&](const KnownBits &Known1) {
       ForeachKnownBits(Bits, [&](const KnownBits &Known2) {
@@ -99,6 +100,12 @@ static void testBinaryOpExhaustive(StringRef Name, BinaryBitsFn BitsFn,
           EXPECT_TRUE(checkResult(Name, Exact, Computed, {Known1, Known2},
                                   CheckOptimality));
         }
+        // In some cases we choose to return zero if the result is always
+        // poison.
+        if (RefinePoisonToZero && Exact.hasConflict() &&
+            !Known1.hasConflict() && !Known2.hasConflict()) {
+          EXPECT_TRUE(Computed.isZero());
+        }
       });
     });
   }
@@ -313,7 +320,7 @@ TEST(KnownBitsTest, BinaryExhaustive) {
   testBinaryOpExhaustive(
       "udiv exact",
       [](const KnownBits &Known1, const KnownBits &Known2) {
-        return KnownBits::udiv(Known1, Known2, /*Exact*/ true);
+        return KnownBits::udiv(Known1, Known2, /*Exact=*/true);
       },
       [](const APInt &N1, const APInt &N2) -> std::optional<APInt> {
         if (N2.isZero() || !N1.urem(N2).isZero())
@@ -335,7 +342,7 @@ TEST(KnownBitsTest, BinaryExhaustive) {
   testBinaryOpExhaustive(
       "sdiv exact",
       [](const KnownBits &Known1, const KnownBits &Known2) {
-        return KnownBits::sdiv(Known1, Known2, /*Exact*/ true);
+        return KnownBits::sdiv(Known1, Known2, /*Exact=*/true);
       },
       [](const APInt &N1, const APInt &N2) -> std::optional<APInt> {
         if (N2.isZero() || (N1.isMinSignedValue() && N2.isAllOnes()) ||
@@ -394,11 +401,11 @@ TEST(KnownBitsTest, BinaryExhaustive) {
           return std::nullopt;
         return N1.shl(N2);
       },
-      /*CheckOptimality=*/true);
+      /*CheckOptimality=*/true, /*RefinePoisonToZero=*/true);
   testBinaryOpExhaustive(
       "ushl_ov",
       [](const KnownBits &Known1, const KnownBits &Known2) {
-        return KnownBits::shl(Known1, Known2, /* NUW */ true);
+        return KnownBits::shl(Known1, Known2, /*NUW=*/true);
       },
       [](const APInt &N1, const APInt &N2) -> std::optional<APInt> {
         bool Overflow;
@@ -407,11 +414,11 @@ TEST(KnownBitsTest, BinaryExhaustive) {
           return std::nullopt;
         return Res;
       },
-      /*CheckOptimality=*/true);
+      /*CheckOptimality=*/true, /*RefinePoisonToZero=*/true);
   testBinaryOpExhaustive(
       "shl nsw",
       [](const KnownBits &Known1, const KnownBits &Known2) {
-        return KnownBits::shl(Known1, Known2, /* NUW */ false, /* NSW */ true);
+        return KnownBits::shl(Known1, Known2, /*NUW=*/false, /*NSW=*/true);
       },
       [](const APInt &N1, const APInt &N2) -> std::optional<APInt> {
         bool Overflow;
@@ -420,11 +427,11 @@ TEST(KnownBitsTest, BinaryExhaustive) {
           return std::nullopt;
         return Res;
       },
-      /*CheckOptimality=*/true);
+      /*CheckOptimality=*/true, /*RefinePoisonToZero=*/true);
   testBinaryOpExhaustive(
       "shl nuw",
       [](const KnownBits &Known1, const KnownBits &Known2) {
-        return KnownBits::shl(Known1, Known2, /* NUW */ true, /* NSW */ true);
+        return KnownBits::shl(Known1, Known2, /*NUW=*/true, /*NSW=*/true);
       },
       [](const APInt &N1, const APInt &N2) -> std::optional<APInt> {
         bool OverflowUnsigned, OverflowSigned;
@@ -434,7 +441,7 @@ TEST(KnownBitsTest, BinaryExhaustive) {
           return std::nullopt;
         return Res;
       },
-      /*CheckOptimality=*/true);
+      /*CheckOptimality=*/true, /*RefinePoisonToZero=*/true);
 
   testBinaryOpExhaustive(
       "lshr",
@@ -446,7 +453,7 @@ TEST(KnownBitsTest, BinaryExhaustive) {
           return std::nullopt;
         return N1.lshr(N2);
       },
-      /*CheckOptimality=*/true);
+      /*CheckOptimality=*/true, /*RefinePoisonToZero=*/true);
   testBinaryOpExhaustive(
       "lshr exact",
       [](const KnownBits &Known1, const KnownBits &Known2) {
@@ -460,7 +467,7 @@ TEST(KnownBitsTest, BinaryExhaustive) {
           return std::nullopt;
         return N1.lshr(N2);
       },
-      /*CheckOptimality=*/true);
+      /*CheckOptimality=*/true, /*RefinePoisonToZero=*/true);
   testBinaryOpExhaustive(
       "ashr",
       [](const KnownBits &Known1, const KnownBits &Known2) {
@@ -471,7 +478,7 @@ TEST(KnownBitsTest, BinaryExhaustive) {
           return std::nullopt;
         return N1.ashr(N2);
       },
-      /*CheckOptimality=*/true);
+      /*CheckOptimality=*/true, /*RefinePoisonToZero=*/true);
   testBinaryOpExhaustive(
       "ashr exact",
       [](const KnownBits &Known1, const KnownBits &Known2) {
@@ -485,7 +492,7 @@ TEST(KnownBitsTest, BinaryExhaustive) {
           return std::nullopt;
         return N1.ashr(N2);
       },
-      /*CheckOptimality=*/true);
+      /*CheckOptimality=*/true, /*RefinePoisonToZero=*/true);
   testBinaryOpExhaustive(
       "mul",
       [](const KnownBits &Known1, const KnownBits &Known2) {
@@ -538,7 +545,7 @@ TEST(KnownBitsTest, UnaryExhaustive) {
   testUnaryOpExhaustive(
       "mul self",
       [](const KnownBits &Known) {
-        return KnownBits::mul(Known, Known, /*SelfMultiply*/ true);
+        return KnownBits::mul(Known, Known, /*SelfMultiply=*/true);
       },
       [](const APInt &N) { return N * N; }, /*CheckOptimality=*/false);
 }
@@ -709,8 +716,8 @@ TEST(KnownBitsTest, SExtOrTrunc) {
   const unsigned NarrowerSize = 4;
   const unsigned BaseSize = 6;
   const unsigned WiderSize = 8;
-  APInt NegativeFitsNarrower(BaseSize, -4, /*isSigned*/ true);
-  APInt NegativeDoesntFitNarrower(BaseSize, -28, /*isSigned*/ true);
+  APInt NegativeFitsNarrower(BaseSize, -4, /*isSigned=*/true);
+  APInt NegativeDoesntFitNarrower(BaseSize, -28, /*isSigned=*/true);
   APInt PositiveFitsNarrower(BaseSize, 14);
   APInt PositiveDoesntFitNarrower(BaseSize, 36);
   auto InitKnownBits = [&](KnownBits &Res, const APInt &Input) {