diff --git a/clang/include/clang/Basic/AddressSpaces.h b/clang/include/clang/Basic/AddressSpaces.h
--- a/clang/include/clang/Basic/AddressSpaces.h
+++ b/clang/include/clang/Basic/AddressSpaces.h
@@ -56,6 +56,9 @@
   ptr32_uptr,
   ptr64,
 
+  // HLSL specific address spaces.
+  hlsl_groupshared,
+
   // This denotes the count of language-specific address spaces and also
   // the offset added to the target-specific address spaces, which are usually
   // specified by address space attributes __attribute__(address_space(n))).
diff --git a/clang/include/clang/Basic/Attr.td b/clang/include/clang/Basic/Attr.td
--- a/clang/include/clang/Basic/Attr.td
+++ b/clang/include/clang/Basic/Attr.td
@@ -4041,6 +4041,11 @@
   let Documentation = [InternalOnly];
 }
 
+def HLSLGroupSharedAddressSpace : TypeAttr {
+  let Spellings = [Keyword<"groupshared">, Clang<"groupshared">];
+  let Documentation = [HLSLGroupSharedAddressSpaceDocs];
+}
+
 def RandomizeLayout : InheritableAttr {
   let Spellings = [GCC<"randomize_layout">];
   let Subjects = SubjectList<[Record]>;
diff --git a/clang/include/clang/Basic/AttrDocs.td b/clang/include/clang/Basic/AttrDocs.td
--- a/clang/include/clang/Basic/AttrDocs.td
+++ b/clang/include/clang/Basic/AttrDocs.td
@@ -6618,6 +6618,24 @@
   }];
 }
 
+def HLSLGroupSharedAddressSpaceDocs : Documentation {
+  let Category = DocCatVariable;
+  let Content = [{
+HLSL enables threads of a compute shader to exchange values via shared memory.
+HLSL provides barrier primitives such as GroupMemoryBarrierWithGroupSync,
+and so on to ensure the correct ordering of reads and writes to shared memory
+in the shader and to avoid data races.
+Here's an example to declare a groupshared variable.
+.. code-block:: c++
+
+  groupshared GSData data[5*5*1];
+
+
+
+The full documentation is available here: https://learn.microsoft.com/en-us/windows/win32/direct3dhlsl/dx-graphics-hlsl-variable-syntax#group-shared
+  }];
+}
+
 def AnnotateTypeDocs : Documentation {
   let Category = DocCatType;
   let Heading = "annotate_type";
diff --git a/clang/include/clang/Basic/DiagnosticSemaKinds.td b/clang/include/clang/Basic/DiagnosticSemaKinds.td
--- a/clang/include/clang/Basic/DiagnosticSemaKinds.td
+++ b/clang/include/clang/Basic/DiagnosticSemaKinds.td
@@ -11700,7 +11700,8 @@
 
 def err_hlsl_operator_unsupported : Error<
   "the '%select{&|*|->}0' operator is unsupported in HLSL">;
-
+def err_hlsl_attribute_address_function_return_type : Error<
+  "function return type may not be qualified with an address space">;
 // Layout randomization diagnostics.
 def err_non_designated_init_used : Error<
   "a randomized struct can only be initialized with a designated initializer">;
diff --git a/clang/include/clang/Basic/TokenKinds.def b/clang/include/clang/Basic/TokenKinds.def
--- a/clang/include/clang/Basic/TokenKinds.def
+++ b/clang/include/clang/Basic/TokenKinds.def
@@ -611,6 +611,7 @@
 // HLSL keywords.
 KEYWORD(cbuffer                     , KEYHLSL)
 KEYWORD(tbuffer                     , KEYHLSL)
+KEYWORD(groupshared                 , KEYHLSL)
 
 // OpenMP Type Traits
 UNARY_EXPR_OR_TYPE_TRAIT(__builtin_omp_required_simd_align, OpenMPRequiredSimdAlign, KEYALL)
diff --git a/clang/include/clang/Parse/Parser.h b/clang/include/clang/Parse/Parser.h
--- a/clang/include/clang/Parse/Parser.h
+++ b/clang/include/clang/Parse/Parser.h
@@ -2932,6 +2932,7 @@
   void ParseOpenCLQualifiers(ParsedAttributes &Attrs);
   void ParseNullabilityTypeSpecifiers(ParsedAttributes &attrs);
   void ParseCUDAFunctionAttributes(ParsedAttributes &attrs);
+  void ParseHLSLQualifiers(ParsedAttributes &Attrs);
 
   VersionTuple ParseVersionTuple(SourceRange &Range);
   void ParseAvailabilityAttribute(IdentifierInfo &Availability,
diff --git a/clang/include/clang/Sema/ParsedAttr.h b/clang/include/clang/Sema/ParsedAttr.h
--- a/clang/include/clang/Sema/ParsedAttr.h
+++ b/clang/include/clang/Sema/ParsedAttr.h
@@ -712,6 +712,17 @@
     }
   }
 
+  /// If this is an HLSL address space attribute, returns its representation
+  /// in LangAS, otherwise returns default address space.
+  LangAS asHLSLLangAS() const {
+    switch (getParsedKind()) {
+    case ParsedAttr::AT_HLSLGroupSharedAddressSpace:
+      return LangAS::hlsl_groupshared;
+    default:
+      return LangAS::Default;
+    }
+  }
+
   AttributeCommonInfo::Kind getKind() const {
     return AttributeCommonInfo::Kind(Info.AttrKind);
   }
diff --git a/clang/lib/AST/ASTContext.cpp b/clang/lib/AST/ASTContext.cpp
--- a/clang/lib/AST/ASTContext.cpp
+++ b/clang/lib/AST/ASTContext.cpp
@@ -949,7 +949,8 @@
         0,  // sycl_private
         10, // ptr32_sptr
         11, // ptr32_uptr
-        12  // ptr64
+        12, // ptr64
+        13, // hlsl_groupshared
     };
     return &FakeAddrSpaceMap;
   } else {
diff --git a/clang/lib/AST/TypePrinter.cpp b/clang/lib/AST/TypePrinter.cpp
--- a/clang/lib/AST/TypePrinter.cpp
+++ b/clang/lib/AST/TypePrinter.cpp
@@ -1727,6 +1727,7 @@
   case attr::OpenCLLocalAddressSpace:
   case attr::OpenCLConstantAddressSpace:
   case attr::OpenCLGenericAddressSpace:
+  case attr::HLSLGroupSharedAddressSpace:
     // FIXME: Update printAttributedBefore to print these once we generate
     // AttributedType nodes for them.
     break;
@@ -2222,6 +2223,8 @@
     return "__uptr __ptr32";
   case LangAS::ptr64:
     return "__ptr64";
+  case LangAS::hlsl_groupshared:
+    return "groupshared";
   default:
     return std::to_string(toTargetAddressSpace(AS));
   }
diff --git a/clang/lib/Basic/Targets/AMDGPU.cpp b/clang/lib/Basic/Targets/AMDGPU.cpp
--- a/clang/lib/Basic/Targets/AMDGPU.cpp
+++ b/clang/lib/Basic/Targets/AMDGPU.cpp
@@ -55,7 +55,8 @@
     Private,  // sycl_private
     Generic,  // ptr32_sptr
     Generic,  // ptr32_uptr
-    Generic   // ptr64
+    Generic,  // ptr64
+    Generic,  // hlsl_gourpshared
 };
 
 const LangASMap AMDGPUTargetInfo::AMDGPUDefIsPrivMap = {
@@ -71,14 +72,15 @@
     Constant, // cuda_constant
     Local,    // cuda_shared
     // SYCL address space values for this map are dummy
-    Generic,  // sycl_global
-    Generic,  // sycl_global_device
-    Generic,  // sycl_global_host
-    Generic,  // sycl_local
-    Generic,  // sycl_private
-    Generic,  // ptr32_sptr
-    Generic,  // ptr32_uptr
-    Generic   // ptr64
+    Generic, // sycl_global
+    Generic, // sycl_global_device
+    Generic, // sycl_global_host
+    Generic, // sycl_local
+    Generic, // sycl_private
+    Generic, // ptr32_sptr
+    Generic, // ptr32_uptr
+    Generic, // ptr64
+    Generic, // hlsl_gourpshared
 
 };
 } // namespace targets
diff --git a/clang/lib/Basic/Targets/DirectX.h b/clang/lib/Basic/Targets/DirectX.h
--- a/clang/lib/Basic/Targets/DirectX.h
+++ b/clang/lib/Basic/Targets/DirectX.h
@@ -40,7 +40,8 @@
     0, // sycl_private
     0, // ptr32_sptr
     0, // ptr32_uptr
-    0  // ptr64
+    0, // ptr64
+    3, // hlsl_gourpshared
 };
 
 class LLVM_LIBRARY_VISIBILITY DirectXTargetInfo : public TargetInfo {
diff --git a/clang/lib/Basic/Targets/NVPTX.h b/clang/lib/Basic/Targets/NVPTX.h
--- a/clang/lib/Basic/Targets/NVPTX.h
+++ b/clang/lib/Basic/Targets/NVPTX.h
@@ -42,7 +42,8 @@
     0, // sycl_private
     0, // ptr32_sptr
     0, // ptr32_uptr
-    0  // ptr64
+    0, // ptr64
+    0, // hlsl_gourpshared
 };
 
 /// The DWARF address class. Taken from
diff --git a/clang/lib/Basic/Targets/SPIR.h b/clang/lib/Basic/Targets/SPIR.h
--- a/clang/lib/Basic/Targets/SPIR.h
+++ b/clang/lib/Basic/Targets/SPIR.h
@@ -42,7 +42,8 @@
     0, // sycl_private
     0, // ptr32_sptr
     0, // ptr32_uptr
-    0  // ptr64
+    0, // ptr64
+    0, // hlsl_gourpshared
 };
 
 // Used by both the SPIR and SPIR-V targets.
@@ -71,7 +72,8 @@
     0, // sycl_private
     0, // ptr32_sptr
     0, // ptr32_uptr
-    0  // ptr64
+    0, // ptr64
+    0, // hlsl_gourpshared
 };
 
 // Base class for SPIR and SPIR-V target info.
diff --git a/clang/lib/Basic/Targets/TCE.h b/clang/lib/Basic/Targets/TCE.h
--- a/clang/lib/Basic/Targets/TCE.h
+++ b/clang/lib/Basic/Targets/TCE.h
@@ -50,6 +50,7 @@
     0, // ptr32_sptr
     0, // ptr32_uptr
     0, // ptr64
+    0, // hlsl_gourpshared
 };
 
 class LLVM_LIBRARY_VISIBILITY TCETargetInfo : public TargetInfo {
diff --git a/clang/lib/Basic/Targets/X86.h b/clang/lib/Basic/Targets/X86.h
--- a/clang/lib/Basic/Targets/X86.h
+++ b/clang/lib/Basic/Targets/X86.h
@@ -43,7 +43,8 @@
     0,   // sycl_private
     270, // ptr32_sptr
     271, // ptr32_uptr
-    272  // ptr64
+    272, // ptr64
+    0,   // hlsl_gourpshared
 };
 
 // X86 target abstract base class; x86-32 and x86-64 are very close, so
diff --git a/clang/lib/Parse/ParseDecl.cpp b/clang/lib/Parse/ParseDecl.cpp
--- a/clang/lib/Parse/ParseDecl.cpp
+++ b/clang/lib/Parse/ParseDecl.cpp
@@ -914,6 +914,13 @@
                ParsedAttr::AS_Keyword);
 }
 
+void Parser::ParseHLSLQualifiers(ParsedAttributes &Attrs) {
+  IdentifierInfo *AttrName = Tok.getIdentifierInfo();
+  SourceLocation AttrNameLoc = Tok.getLocation();
+  Attrs.addNew(AttrName, AttrNameLoc, nullptr, AttrNameLoc, nullptr, 0,
+               ParsedAttr::AS_Keyword);
+}
+
 void Parser::ParseNullabilityTypeSpecifiers(ParsedAttributes &attrs) {
   // Treat these like attributes, even though they're type specifiers.
   while (true) {
@@ -4329,6 +4336,10 @@
       ParseOpenCLQualifiers(DS.getAttributes());
       break;
 
+    case tok::kw_groupshared:
+      ParseHLSLQualifiers(DS.getAttributes());
+      break;
+
     case tok::less:
       // GCC ObjC supports types like "<SomeProtocol>" as a synonym for
       // "id<SomeProtocol>".  This is hopelessly old fashioned and dangerous,
@@ -5352,6 +5363,8 @@
   case tok::kw___read_only:
   case tok::kw___read_write:
   case tok::kw___write_only:
+
+  case tok::kw_groupshared:
     return true;
 
   case tok::kw_private:
@@ -5592,6 +5605,7 @@
 #define GENERIC_IMAGE_TYPE(ImgType, Id) case tok::kw_##ImgType##_t:
 #include "clang/Basic/OpenCLImageTypes.def"
 
+  case tok::kw_groupshared:
     return true;
 
   case tok::kw_private:
@@ -5819,6 +5833,10 @@
       ParseOpenCLQualifiers(DS.getAttributes());
       break;
 
+    case tok::kw_groupshared:
+      ParseHLSLQualifiers(DS.getAttributes());
+      break;
+
     case tok::kw___unaligned:
       isInvalid = DS.SetTypeQual(DeclSpec::TQ_unaligned, Loc, PrevSpec, DiagID,
                                  getLangOpts());
diff --git a/clang/lib/Parse/ParseExprCXX.cpp b/clang/lib/Parse/ParseExprCXX.cpp
--- a/clang/lib/Parse/ParseExprCXX.cpp
+++ b/clang/lib/Parse/ParseExprCXX.cpp
@@ -1404,6 +1404,12 @@
           ConsumeToken();
         }
 
+        // Parse HLSL addr space attribute.
+        if (Tok.is(tok::kw_groupshared)) {
+          ParseHLSLQualifiers(DS.getAttributes());
+          ConsumeToken();
+        }
+
         SourceLocation FunLocalRangeEnd = DeclEndLoc;
 
         // Parse trailing-return-type[opt].
@@ -1474,7 +1480,8 @@
                          tok::kw_constexpr, tok::kw_consteval, tok::kw_static,
                          tok::kw___private, tok::kw___global, tok::kw___local,
                          tok::kw___constant, tok::kw___generic,
-                         tok::kw_requires, tok::kw_noexcept) ||
+                         tok::kw_groupshared, tok::kw_requires,
+                         tok::kw_noexcept) ||
              (Tok.is(tok::l_square) && NextToken().is(tok::l_square))) {
     if (!getLangOpts().CPlusPlus2b)
       // It's common to forget that one needs '()' before 'mutable', an
diff --git a/clang/lib/Parse/ParseTentative.cpp b/clang/lib/Parse/ParseTentative.cpp
--- a/clang/lib/Parse/ParseTentative.cpp
+++ b/clang/lib/Parse/ParseTentative.cpp
@@ -1423,6 +1423,9 @@
     // OpenCL pipe
   case tok::kw_pipe:
 
+    // HLSL address space qualifiers
+  case tok::kw_groupshared:
+
     // GNU
   case tok::kw_restrict:
   case tok::kw__Complex:
diff --git a/clang/lib/Sema/SemaDecl.cpp b/clang/lib/Sema/SemaDecl.cpp
--- a/clang/lib/Sema/SemaDecl.cpp
+++ b/clang/lib/Sema/SemaDecl.cpp
@@ -14924,6 +14924,12 @@
                           diag::err_func_def_incomplete_result))
     FD->setInvalidDecl();
 
+  if (ResultType.getAddressSpace() != LangAS::Default && getLangOpts().HLSL) {
+    Diag(FD->getLocation(),
+         diag::err_hlsl_attribute_address_function_return_type);
+    FD->setInvalidDecl();
+  }
+
   if (FnBodyScope)
     PushDeclContext(FnBodyScope, FD);
 
diff --git a/clang/lib/Sema/SemaType.cpp b/clang/lib/Sema/SemaType.cpp
--- a/clang/lib/Sema/SemaType.cpp
+++ b/clang/lib/Sema/SemaType.cpp
@@ -2898,6 +2898,8 @@
   if (T.isVolatileQualified() && getLangOpts().CPlusPlus20)
     Diag(Loc, diag::warn_deprecated_volatile_return) << T;
 
+  if (T.getAddressSpace() != LangAS::Default && getLangOpts().HLSL)
+    return true;
   return false;
 }
 
@@ -6775,6 +6777,8 @@
     // The keyword-based type attributes imply which address space to use.
     ASIdx = S.getLangOpts().SYCLIsDevice ? Attr.asSYCLLangAS()
                                          : Attr.asOpenCLLangAS();
+    if (S.getLangOpts().HLSL)
+      ASIdx = Attr.asHLSLLangAS();
 
     if (ASIdx == LangAS::Default)
       llvm_unreachable("Invalid address space");
@@ -8388,6 +8392,7 @@
     case ParsedAttr::AT_OpenCLLocalAddressSpace:
     case ParsedAttr::AT_OpenCLConstantAddressSpace:
     case ParsedAttr::AT_OpenCLGenericAddressSpace:
+    case ParsedAttr::AT_HLSLGroupSharedAddressSpace:
     case ParsedAttr::AT_AddressSpace:
       HandleAddressSpaceTypeAttribute(type, attr, state);
       attr.setUsedAsTypeAttr();
diff --git a/clang/test/AST/HLSL/group_shared.hlsl b/clang/test/AST/HLSL/group_shared.hlsl
new file mode 100644
--- /dev/null
+++ b/clang/test/AST/HLSL/group_shared.hlsl
@@ -0,0 +1,20 @@
+// RUN: %clang_cc1 -triple dxil-pc-shadermodel6.3-library -x hlsl -ast-dump -o - %s | FileCheck %s
+
+//CHECK:VarDecl 0x[[A:[0-9a-f]+]] <{{.*}} col:24> col:20 used a 'groupshared float[10]'
+ groupshared float a[10];
+
+// CHECK:FunctionDecl 0x{{[0-9a-f]+}} <{{.*}}> line:[[@LINE+2]]:7 main 'void ()'
+ [numthreads(8,8,1)]
+ void main() {
+// CHECK:BinaryOperator 0x{{[0-9a-f]+}} <{{.*}}> 'groupshared float' lvalue '='
+// CHECK:ArraySubscriptExpr 0x{{[0-9a-f]+}} <col:4, col:7> 'groupshared float' lvalue
+// CHECK:ImplicitCastExpr 0x{{[0-9a-f]+}} <col:4> 'groupshared float *' <ArrayToPointerDecay>
+// CHECK:DeclRefExpr 0x{{[0-9a-f]+}} <col:4> 'groupshared float[10]' lvalue Var 0x[[A]] 'a' 'groupshared float[10]'
+// CHECK:IntegerLiteral 0x{{[0-9a-f]+}} <col:6> 'int' 0
+// CHECK:ImplicitCastExpr 0x{{[0-9a-f]+}} <col:11> 'float' <IntegralToFloating>
+// CHECK:IntegerLiteral 0x{{[0-9a-f]+}} <col:11> 'int' 1
+   a[0] = 1;
+ }
+
+
+// CHECK:HLSLNumThreadsAttr 0x{{[0-9a-f]+}} <{{.*}}> 8 8 1
diff --git a/clang/test/CodeGenHLSL/group_shared.hlsl b/clang/test/CodeGenHLSL/group_shared.hlsl
new file mode 100644
--- /dev/null
+++ b/clang/test/CodeGenHLSL/group_shared.hlsl
@@ -0,0 +1,15 @@
+
+// RUN: %clang_cc1 -std=hlsl2021 -finclude-default-header -x hlsl -triple \
+// RUN:   dxil-pc-shadermodel6.3-library %s \
+// RUN:   -emit-llvm -disable-llvm-passes -o - | FileCheck %s
+
+// Make sure groupshared translated into address space 3.
+// CHECK:@"?a@@3PAMA" = addrspace(3) global [10 x float]
+
+ groupshared float a[10];
+
+ [numthreads(8,8,1)]
+ void main() {
+   a[0] = 1;
+ }
+
diff --git a/clang/test/SemaHLSL/group_shared.hlsl b/clang/test/SemaHLSL/group_shared.hlsl
new file mode 100644
--- /dev/null
+++ b/clang/test/SemaHLSL/group_shared.hlsl
@@ -0,0 +1,42 @@
+// RUN: %clang_cc1 -triple dxil-pc-shadermodel6.3-library -x hlsl -o - -fsyntax-only %s -verify
+
+ groupshared float a[10];
+
+ [numthreads(8,8,1)]
+ void main() {
+   a[0] = 1;
+   // expected-error@+1 {{automatic variable qualified with an address space}}
+   groupshared float b;
+ }
+
+// expected-error@+1 {{function return type may not be qualified with an address space}}
+ groupshared float foo() {
+  static groupshared float foo0;
+    return 1;
+ }
+// expected-error@+1 {{function return type may not be qualified with an address space}}
+  groupshared void bar() {
+    extern groupshared float bar0;
+  }
+ 
+  struct S {
+    // expected-error@+1 {{field may not be qualified with an address space}}
+    groupshared float f;
+    static groupshared float g;
+  };
+
+  // expected-error@+1 {{parameter may not be qualified with an address space}}
+  float foo2(groupshared float a) {
+    return a;
+  }
+
+// expected-note@+2 {{parameter may not be qualified with an address space}}
+template<typename T>
+  T tfoo(T t) {
+     return t;
+  }
+  // expected-warning@+1 {{alias declarations are a C++11 extension}}
+ using GSF = groupshared float;
+ GSF gs;
+ // expected-error@+1 {{no matching function for call to 'tfoo'}}
+ GSF gs2 = tfoo<GSF>(gs);
diff --git a/clang/test/SemaTemplate/address_space-dependent.cpp b/clang/test/SemaTemplate/address_space-dependent.cpp
--- a/clang/test/SemaTemplate/address_space-dependent.cpp
+++ b/clang/test/SemaTemplate/address_space-dependent.cpp
@@ -43,7 +43,7 @@
 
 template <long int I>
 void tooBig() {
-  __attribute__((address_space(I))) int *bounds; // expected-error {{address space is larger than the maximum supported (8388588)}}
+  __attribute__((address_space(I))) int *bounds; // expected-error {{address space is larger than the maximum supported (8388587)}}
 }
 
 template <long int I>