diff --git a/src/coreclr/jit/gentree.cpp b/src/coreclr/jit/gentree.cpp
index 027bc375cf076c..ac418fac0b11fa 100644
--- a/src/coreclr/jit/gentree.cpp
+++ b/src/coreclr/jit/gentree.cpp
@@ -5145,6 +5145,11 @@ unsigned Compiler::gtSetEvalOrder(GenTree* tree)
                             costSz = 12;
                             break;
 
+                        case NI_System_Runtime_CompilerServices_RuntimeHelpers_IsKnownConstant:
+                            costEx = 1;
+                            costSz = 1;
+                            break;
+
                         case NI_System_Math_Abs:
                             costEx = 5;
                             costSz = 15;
diff --git a/src/coreclr/jit/lower.cpp b/src/coreclr/jit/lower.cpp
index decaed31eeb836..b67f7fc28bc109 100644
--- a/src/coreclr/jit/lower.cpp
+++ b/src/coreclr/jit/lower.cpp
@@ -583,11 +583,9 @@ GenTree* Lowering::LowerNode(GenTree* node)
             ContainCheckLclHeap(node->AsOp());
             break;
 
-#ifdef TARGET_XARCH
         case GT_INTRINSIC:
-            ContainCheckIntrinsic(node->AsOp());
+            LowerIntrinsic(node->AsIntrinsic());
             break;
-#endif // TARGET_XARCH
 
 #ifdef FEATURE_HW_INTRINSICS
         case GT_HWINTRINSIC:
@@ -7786,6 +7784,27 @@ void Lowering::TransformUnusedIndirection(GenTreeIndir* ind, Compiler* comp, Bas
     }
 }
 
+//------------------------------------------------------------------------
+// LowerIntrinsic: a common logic to lower INTRINSIC.
+//
+// Arguments:
+//    node - the INTRINSIC node we are lowering.
+//
+void Lowering::LowerIntrinsic(GenTreeIntrinsic* node)
+{
+    if (node->gtIntrinsicName == NI_System_Runtime_CompilerServices_RuntimeHelpers_IsKnownConstant)
+    {
+        // IsKnownConstant is expected to be folded in Importer/Morph/VN+ConstantProp
+        // This path is just in case if VN+ConstantProp didn't fold them for some reason (or e.g. they were disabled)
+        node->gtGetOp1()->SetUnusedValue();
+        node->BashToConst(0);
+        return;
+    }
+#ifdef TARGET_XARCH
+    ContainCheckIntrinsic(node->AsOp());
+#endif
+}
+
 //------------------------------------------------------------------------
 // LowerBlockStoreCommon: a common logic to lower STORE_OBJ/BLK/DYN_BLK.
 //
diff --git a/src/coreclr/jit/lower.h b/src/coreclr/jit/lower.h
index 6937d2e3c0430f..cd7efe3319d3bf 100644
--- a/src/coreclr/jit/lower.h
+++ b/src/coreclr/jit/lower.h
@@ -312,6 +312,7 @@ class Lowering final : public Phase
     bool LowerUnsignedDivOrMod(GenTreeOp* divMod);
     GenTree* LowerConstIntDivOrMod(GenTree* node);
     GenTree* LowerSignedDivOrMod(GenTree* node);
+    void LowerIntrinsic(GenTreeIntrinsic* node);
     void LowerBlockStore(GenTreeBlk* blkNode);
     void LowerBlockStoreCommon(GenTreeBlk* blkNode);
     void ContainBlockStoreAddress(GenTreeBlk* blkNode, unsigned size, GenTree* addr, GenTree* addrParent);
diff --git a/src/coreclr/jit/morph.cpp b/src/coreclr/jit/morph.cpp
index 64006e890d8595..a585338d8bc392 100644
--- a/src/coreclr/jit/morph.cpp
+++ b/src/coreclr/jit/morph.cpp
@@ -10010,8 +10010,8 @@ GenTree* Compiler::fgMorphSmpOp(GenTree* tree, MorphAddrContext* mac, bool* optA
             if (tree->AsIntrinsic()->gtIntrinsicName ==
                 NI_System_Runtime_CompilerServices_RuntimeHelpers_IsKnownConstant)
             {
-                // Should be expanded by the time it reaches CSE phase
-                assert(!optValnumCSE_phase);
+                // Should be expanded in importer for MinOpts
+                assert(opts.OptimizationEnabled());
 
                 JITDUMP("\nExpanding RuntimeHelpers.IsKnownConstant to ");
                 if (op1->OperIsConst() || gtIsTypeof(op1))
@@ -10023,22 +10023,8 @@ GenTree* Compiler::fgMorphSmpOp(GenTree* tree, MorphAddrContext* mac, bool* optA
                 }
                 else
                 {
-                    GenTree* op1SideEffects = nullptr;
-                    gtExtractSideEffList(op1, &op1SideEffects, GTF_ALL_EFFECT);
-                    if (op1SideEffects != nullptr)
-                    {
-                        DEBUG_DESTROY_NODE(tree);
-                        // Keep side-effects of op1
-                        tree = gtNewOperNode(GT_COMMA, TYP_INT, op1SideEffects, gtNewIconNode(0));
-                        JITDUMP("false with side effects:\n")
-                        DISPTREE(tree);
-                    }
-                    else
-                    {
-                        JITDUMP("false\n");
-                        DEBUG_DESTROY_NODE(tree, op1);
-                        tree = gtNewIconNode(0);
-                    }
+                    // Leave it for VN/ConstantProp (or Lowering)
+                    return tree;
                 }
                 INDEBUG(tree->gtDebugFlags |= GTF_DEBUG_NODE_MORPHED);
                 return tree;
diff --git a/src/coreclr/jit/valuenum.cpp b/src/coreclr/jit/valuenum.cpp
index 1c9e7460285ed8..7c7be1e7c85162 100644
--- a/src/coreclr/jit/valuenum.cpp
+++ b/src/coreclr/jit/valuenum.cpp
@@ -11047,6 +11047,12 @@ void Compiler::fgValueNumberIntrinsic(GenTree* tree)
             intrinsic->gtVNPair = vnStore->VNPWithExc(newVNP, excSet);
         }
     }
+    else if (intrinsic->gtIntrinsicName == NI_System_Runtime_CompilerServices_RuntimeHelpers_IsKnownConstant)
+    {
+        ValueNum isCnsVNL   = vnStore->VNForIntCon(vnStore->IsVNConstant(arg0VNP.GetLiberal()) ? 1 : 0);
+        ValueNum isCnsVNC   = vnStore->VNForIntCon(vnStore->IsVNConstant(arg0VNP.GetConservative()) ? 1 : 0);
+        intrinsic->gtVNPair = vnStore->VNPWithExc(ValueNumPair(isCnsVNL, isCnsVNC), arg0VNPx);
+    }
     else
     {
         assert(intrinsic->gtIntrinsicName == NI_System_Object_GetType);