Index: clang/lib/CodeGen/TargetInfo.cpp
===================================================================
--- clang/lib/CodeGen/TargetInfo.cpp
+++ clang/lib/CodeGen/TargetInfo.cpp
@@ -486,12 +486,13 @@
   return Ctx.getOrInsertSyncScopeID(""); /* default sync scope */
 }
 
-static bool isEmptyRecord(ASTContext &Context, QualType T, bool AllowArrays);
+static bool isEmptyRecord(ASTContext &Context, QualType T, bool AllowArrays,
+                          bool AllowNoUniqueAddr = false);
 
 /// isEmptyField - Return true iff a the field is "empty", that is it
 /// is an unnamed bit-field or an (array of) empty record(s).
 static bool isEmptyField(ASTContext &Context, const FieldDecl *FD,
-                         bool AllowArrays) {
+                         bool AllowArrays, bool AllowNoUniqueAddr = false) {
   if (FD->isUnnamedBitfield())
     return true;
 
@@ -514,16 +515,23 @@
   //
   // FIXME: We should use a predicate for whether this behavior is true in the
   // current ABI.
-  if (isa<CXXRecordDecl>(RT->getDecl()))
+  //
+  // The exception to the above rule are fields marked with the
+  // [[no_unique_address]] attribute (since C++20).  Those do count
+  // as empty according to the Itanium ABI.  This property is currently
+  // only respected if the AllowNoUniqueAddr parameter is true.
+  if (isa<CXXRecordDecl>(RT->getDecl()) &&
+      !(AllowNoUniqueAddr && FD->hasAttr<NoUniqueAddressAttr>()))
     return false;
 
-  return isEmptyRecord(Context, FT, AllowArrays);
+  return isEmptyRecord(Context, FT, AllowArrays, AllowNoUniqueAddr);
 }
 
 /// isEmptyRecord - Return true iff a structure contains only empty
 /// fields. Note that a structure with a flexible array member is not
 /// considered empty.
-static bool isEmptyRecord(ASTContext &Context, QualType T, bool AllowArrays) {
+static bool isEmptyRecord(ASTContext &Context, QualType T, bool AllowArrays,
+                          bool AllowNoUniqueAddr) {
   const RecordType *RT = T->getAs<RecordType>();
   if (!RT)
     return false;
@@ -534,11 +542,11 @@
   // If this is a C++ record, check the bases first.
   if (const CXXRecordDecl *CXXRD = dyn_cast<CXXRecordDecl>(RD))
     for (const auto &I : CXXRD->bases())
-      if (!isEmptyRecord(Context, I.getType(), true))
+      if (!isEmptyRecord(Context, I.getType(), true, AllowNoUniqueAddr))
         return false;
 
   for (const auto *I : RD->fields())
-    if (!isEmptyField(Context, I, AllowArrays))
+    if (!isEmptyField(Context, I, AllowArrays, AllowNoUniqueAddr))
       return false;
   return true;
 }
@@ -7220,7 +7228,7 @@
         QualType Base = I.getType();
 
         // Empty bases don't affect things either way.
-        if (isEmptyRecord(getContext(), Base, true))
+        if (isEmptyRecord(getContext(), Base, true, true))
           continue;
 
         if (!Found.isNull())
@@ -7230,12 +7238,17 @@
 
     // Check the fields.
     for (const auto *FD : RD->fields()) {
-      // For compatibility with GCC, ignore empty bitfields in C++ mode.
+      // For compatibility with GCC, ignore empty bitfields in C++ mode,
+      // and empty C++ classes marked with the no_unique_address attribute.
       // Unlike isSingleElementStruct(), empty structure and array fields
       // do count.  So do anonymous bitfields that aren't zero-sized.
-      if (getContext().getLangOpts().CPlusPlus &&
-          FD->isZeroLengthBitField(getContext()))
-        continue;
+      if (getContext().getLangOpts().CPlusPlus) {
+        if (FD->isZeroLengthBitField(getContext()))
+          continue;
+        if (FD->hasAttr<NoUniqueAddressAttr>() &&
+            isEmptyRecord(getContext(), FD->getType(), true, true))
+          continue;
+      }
 
       // Unlike isSingleElementStruct(), arrays do not count.
       // Nested structures still do though.
Index: clang/test/CodeGen/systemz-abi.cpp
===================================================================
--- clang/test/CodeGen/systemz-abi.cpp
+++ clang/test/CodeGen/systemz-abi.cpp
@@ -23,3 +23,28 @@
 // CHECK-LABEL: define void @_Z18pass_agg_float_cpp13agg_float_cpp(%struct.agg_float_cpp* noalias sret align 4 %{{.*}}, float %{{.*}})
 // SOFT-FLOAT-LABEL:  define void @_Z18pass_agg_float_cpp13agg_float_cpp(%struct.agg_float_cpp* noalias sret align 4 %{{.*}}, i32 %{{.*}})
 
+
+// A field member of empty class type in C++ makes the record nonhomogeneous,
+// unless it is marked as [[no_unique_address]];
+struct empty { };
+struct agg_nofloat_empty { float a; empty dummy; };
+struct agg_nofloat_empty pass_agg_nofloat_empty(struct agg_nofloat_empty arg) { return arg; }
+// CHECK-LABEL: define void @_Z22pass_agg_nofloat_empty17agg_nofloat_empty(%struct.agg_nofloat_empty* noalias sret align 4 %{{.*}}, i64 %{{.*}})
+// SOFT-FLOAT-LABEL:  define void @_Z22pass_agg_nofloat_empty17agg_nofloat_empty(%struct.agg_nofloat_empty* noalias sret align 4 %{{.*}}, i64 %{{.*}})
+struct agg_float_empty { float a; [[no_unique_address]] empty dummy; };
+struct agg_float_empty pass_agg_float_empty(struct agg_float_empty arg) { return arg; }
+// CHECK-LABEL: define void @_Z20pass_agg_float_empty15agg_float_empty(%struct.agg_float_empty* noalias sret align 4 %{{.*}}, float %{{.*}})
+// SOFT-FLOAT-LABEL:  define void @_Z20pass_agg_float_empty15agg_float_empty(%struct.agg_float_empty* noalias sret align 4 %{{.*}}, i32 %{{.*}})
+
+// And likewise for members of base classes.
+struct noemptybase { empty dummy; };
+struct agg_nofloat_emptybase : noemptybase { float a; };
+struct agg_nofloat_emptybase pass_agg_nofloat_emptybase(struct agg_nofloat_emptybase arg) { return arg; }
+// CHECK-LABEL: define void @_Z26pass_agg_nofloat_emptybase21agg_nofloat_emptybase(%struct.agg_nofloat_emptybase* noalias sret align 4 %{{.*}}, i64 %{{.*}})
+// SOFT-FLOAT-LABEL:  define void @_Z26pass_agg_nofloat_emptybase21agg_nofloat_emptybase(%struct.agg_nofloat_emptybase* noalias sret align 4 %{{.*}}, i64 %{{.*}})
+struct emptybase { [[no_unique_address]] empty dummy; };
+struct agg_float_emptybase : emptybase { float a; };
+struct agg_float_emptybase pass_agg_float_emptybase(struct agg_float_emptybase arg) { return arg; }
+// CHECK-LABEL: define void @_Z24pass_agg_float_emptybase19agg_float_emptybase(%struct.agg_float_emptybase* noalias sret align 4 %{{.*}}, float %{{.*}})
+// SOFT-FLOAT-LABEL:  define void @_Z24pass_agg_float_emptybase19agg_float_emptybase(%struct.agg_float_emptybase* noalias sret align 4 %{{.*}}, i32 %{{.*}})
+