diff --git a/llvm/lib/CodeGen/SelectionDAG/SelectionDAGAddressAnalysis.cpp b/llvm/lib/CodeGen/SelectionDAG/SelectionDAGAddressAnalysis.cpp
--- a/llvm/lib/CodeGen/SelectionDAG/SelectionDAGAddressAnalysis.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/SelectionDAGAddressAnalysis.cpp
@@ -7,6 +7,7 @@
 //===----------------------------------------------------------------------===//
 
 #include "llvm/CodeGen/SelectionDAGAddressAnalysis.h"
+#include "llvm/Analysis/MemoryLocation.h"
 #include "llvm/CodeGen/ISDOpcodes.h"
 #include "llvm/CodeGen/MachineFrameInfo.h"
 #include "llvm/CodeGen/MachineFunction.h"
@@ -96,6 +97,12 @@
   int64_t PtrDiff;
   if (NumBytes0.hasValue() && NumBytes1.hasValue() &&
       BasePtr0.equalBaseIndex(BasePtr1, DAG, PtrDiff)) {
+    // If the size of memory access is unknown, do not use it to analysis.
+    // One example of unknown size memory access is to load/store scalable
+    // vector objects on the stack.
+    if (*NumBytes0 == static_cast<int64_t>(MemoryLocation::UnknownSize) ||
+        *NumBytes1 == static_cast<int64_t>(MemoryLocation::UnknownSize))
+      return false;
     // BasePtr1 is PtrDiff away from BasePtr0. They alias if none of the
     // following situations arise:
     IsAlias = !(