diff --git a/llvm/include/llvm/Support/LowLevelTypeImpl.h b/llvm/include/llvm/Support/LowLevelTypeImpl.h
--- a/llvm/include/llvm/Support/LowLevelTypeImpl.h
+++ b/llvm/include/llvm/Support/LowLevelTypeImpl.h
@@ -47,6 +47,13 @@
                /*AddressSpace=*/0};
   }
 
+  /// Get a low-level opaque type, defined as a scalar of zero size
+  static LLT opaque() {
+    return LLT{/*isPointer=*/false, /*isVector=*/false,
+               ElementCount::getFixed(0), 0,
+               /*AddressSpace=*/0};
+  }
+
   /// Get a low-level pointer in the given address space.
   static LLT pointer(unsigned AddressSpace, unsigned SizeInBits) {
     assert(SizeInBits > 0 && "invalid pointer size");
@@ -116,12 +123,18 @@
 
   bool isValid() const { return RawData != 0; }
 
-  bool isScalar() const { return isValid() && !IsPointer && !IsVector; }
+  bool isScalar() const {
+    return isValid() && !IsPointer && !IsVector && getScalarSizeInBits() != 0;
+  }
 
   bool isPointer() const { return isValid() && IsPointer && !IsVector; }
 
   bool isVector() const { return isValid() && IsVector; }
 
+  bool isOpaque() const {
+    return isValid() && !IsPointer && !IsVector && getScalarSizeInBits() == 0;
+  }
+
   /// Returns the number of elements in a vector LLT. Must only be called on
   /// vector types.
   uint16_t getNumElements() const {
diff --git a/llvm/lib/CodeGen/MachineOperand.cpp b/llvm/lib/CodeGen/MachineOperand.cpp
--- a/llvm/lib/CodeGen/MachineOperand.cpp
+++ b/llvm/lib/CodeGen/MachineOperand.cpp
@@ -1048,9 +1048,12 @@
                                      const MDNode *Ranges, SyncScope::ID SSID,
                                      AtomicOrdering Ordering,
                                      AtomicOrdering FailureOrdering)
-    : MachineMemOperand(ptrinfo, f,
-                        s == ~UINT64_C(0) ? LLT() : LLT::scalar(8 * s), a,
-                        AAInfo, Ranges, SSID, Ordering, FailureOrdering) {}
+    : MachineMemOperand(
+          ptrinfo, f,
+          s == ~UINT64_C(0)
+              ? LLT()
+              : (s == UINT64_C(0) ? LLT::opaque() : LLT::scalar(8 * s)),
+          a, AAInfo, Ranges, SSID, Ordering, FailureOrdering) {}
 
 /// Profile - Gather unique data for the object.
 ///
diff --git a/llvm/lib/Support/LowLevelType.cpp b/llvm/lib/Support/LowLevelType.cpp
--- a/llvm/lib/Support/LowLevelType.cpp
+++ b/llvm/lib/Support/LowLevelType.cpp
@@ -23,9 +23,12 @@
   } else if (VT.isValid()) {
     // Aggregates are no different from real scalars as far as GlobalISel is
     // concerned.
-    assert(VT.getSizeInBits().isNonZero() && "invalid zero-sized type");
-    init(/*IsPointer=*/false, /*IsVector=*/false, ElementCount::getFixed(0),
-         VT.getSizeInBits(), /*AddressSpace=*/0);
+    if (VT.getSizeInBits().isNonZero())
+      init(/*IsPointer=*/false, /*IsVector=*/false, ElementCount::getFixed(0),
+           VT.getSizeInBits(), /*AddressSpace=*/0);
+    else
+      init(/*IsPointer=*/false, /*IsVector=*/false, ElementCount::getFixed(0),
+           VT.getSizeInBits(), /*AddressSpace=*/0);
   } else {
     IsPointer = false;
     IsVector = false;
@@ -39,6 +42,8 @@
     OS << getElementCount() << " x " << getElementType() << ">";
   } else if (isPointer())
     OS << "p" << getAddressSpace();
+  else if (isOpaque())
+    OS << "<opaque>";
   else if (isValid()) {
     assert(isScalar() && "unexpected type");
     OS << "s" << getScalarSizeInBits();