diff --git a/tools/clang/include/clang/Basic/Attr.td b/tools/clang/include/clang/Basic/Attr.td
index 6d2295dc4a..25a70c6664 100644
--- a/tools/clang/include/clang/Basic/Attr.td
+++ b/tools/clang/include/clang/Basic/Attr.td
@@ -671,6 +671,11 @@ def HLSLNumThreads: InheritableAttr {
   let Args = [IntArgument<"X">, IntArgument<"Y">, IntArgument<"Z">];
   let Documentation = [Undocumented];
 }
+def HLSLSpirvNumThreads : InheritableAttr {
+  let Spellings = [CXX11<"vk", "LocalSizeId", 2015>];
+  let Args = [ExprArgument<"X">, ExprArgument<"Y">, ExprArgument<"Z">];
+  let Documentation = [Undocumented];
+}
 def HLSLRootSignature: InheritableAttr {
   let Spellings = [CXX11<"", "RootSignature", 2015>];
   let Args = [StringArgument<"SignatureName">];
diff --git a/tools/clang/include/clang/SPIRV/SpirvBuilder.h b/tools/clang/include/clang/SPIRV/SpirvBuilder.h
index f03735115b..59471a7be3 100644
--- a/tools/clang/include/clang/SPIRV/SpirvBuilder.h
+++ b/tools/clang/include/clang/SPIRV/SpirvBuilder.h
@@ -607,6 +607,14 @@ class SpirvBuilder {
                                             SourceLocation,
                                             bool useIdParams = false);
 
+  /// \brief Adds an execution mode to the module under construction if it does
+  /// not already exist. Return the newly added instruction or the existing
+  /// instruction, if one already exists.
+  inline SpirvInstruction *
+  addExecutionModeId(SpirvFunction *entryPoint, spv::ExecutionMode em,
+                     llvm::ArrayRef<SpirvInstruction *> params,
+                     SourceLocation loc);
+
   /// \brief Adds an OpModuleProcessed instruction to the module under
   /// construction.
   void addModuleProcessed(llvm::StringRef process);
@@ -954,7 +962,7 @@ SpirvBuilder::addExecutionMode(SpirvFunction *entryPoint, spv::ExecutionMode em,
                                llvm::ArrayRef<uint32_t> params,
                                SourceLocation loc, bool useIdParams) {
   SpirvExecutionMode *mode = nullptr;
-  SpirvExecutionMode *existingInstruction =
+  SpirvExecutionModeBase *existingInstruction =
       mod->findExecutionMode(entryPoint, em);
 
   if (!existingInstruction) {
@@ -962,7 +970,38 @@ SpirvBuilder::addExecutionMode(SpirvFunction *entryPoint, spv::ExecutionMode em,
         SpirvExecutionMode(loc, entryPoint, em, params, useIdParams);
     mod->addExecutionMode(mode);
   } else {
-    mode = existingInstruction;
+    // No execution mode can be used with both OpExecutionMode and
+    // OpExecutionModeId. If this assert is triggered, then either this
+    // `addExecutionModeId` should have been called with `em` or the existing
+    // instruction is wrong.
+    assert(existingInstruction->getKind() ==
+           SpirvInstruction::IK_ExecutionMode);
+    mode = cast<SpirvExecutionMode>(existingInstruction);
+  }
+
+  return mode;
+}
+
+SpirvInstruction *SpirvBuilder::addExecutionModeId(
+    SpirvFunction *entryPoint, spv::ExecutionMode em,
+    llvm::ArrayRef<SpirvInstruction *> params, SourceLocation loc) {
+  SpirvExecutionModeId *mode = nullptr;
+  SpirvExecutionModeBase *existingInstruction =
+      mod->findExecutionMode(entryPoint, em);
+  assert(!existingInstruction || existingInstruction->getKind() ==
+                                     SpirvInstruction::IK_ExecutionModeId);
+
+  if (!existingInstruction) {
+    mode = new (context) SpirvExecutionModeId(loc, entryPoint, em, params);
+    mod->addExecutionMode(mode);
+  } else {
+    // No execution mode can be used with both OpExecutionMode and
+    // OpExecutionModeId. If this assert is triggered, then either this
+    // `addExecutionMode` should have been called with `em` or the existing
+    // instruction is wrong.
+    assert(existingInstruction->getKind() ==
+           SpirvInstruction::IK_ExecutionMode);
+    mode = cast<SpirvExecutionModeId>(existingInstruction);
   }
 
   return mode;
diff --git a/tools/clang/include/clang/SPIRV/SpirvInstruction.h b/tools/clang/include/clang/SPIRV/SpirvInstruction.h
index 7ec1375bde..6a95f79b23 100644
--- a/tools/clang/include/clang/SPIRV/SpirvInstruction.h
+++ b/tools/clang/include/clang/SPIRV/SpirvInstruction.h
@@ -53,6 +53,7 @@ class SpirvInstruction {
     IK_MemoryModel,     // OpMemoryModel
     IK_EntryPoint,      // OpEntryPoint
     IK_ExecutionMode,   // OpExecutionMode
+    IK_ExecutionModeId, // OpExecutionModeId
     IK_String,          // OpString (debug)
     IK_Source,          // OpSource (debug)
     IK_ModuleProcessed, // OpModuleProcessed (debug)
@@ -396,8 +397,31 @@ class SpirvEntryPoint : public SpirvInstruction {
   llvm::SmallVector<SpirvVariable *, 8> interfaceVec;
 };
 
+class SpirvExecutionModeBase : public SpirvInstruction {
+public:
+  SpirvExecutionModeBase(Kind kind, spv::Op opcode, SourceLocation loc,
+                         SpirvFunction *entryPointFunction,
+                         spv::ExecutionMode executionMode)
+      : SpirvInstruction(kind, opcode, QualType(), loc),
+        entryPoint(entryPointFunction), execMode(executionMode) {}
+
+  DEFINE_RELEASE_MEMORY_FOR_CLASS(SpirvExecutionModeBase)
+
+  // For LLVM-style RTTI
+  static bool classof(const SpirvInstruction *inst) { return false; }
+
+  bool invokeVisitor(Visitor *v) override;
+
+  SpirvFunction *getEntryPoint() const { return entryPoint; }
+  spv::ExecutionMode getExecutionMode() const { return execMode; }
+
+private:
+  SpirvFunction *entryPoint;
+  spv::ExecutionMode execMode;
+};
+
 /// \brief OpExecutionMode and OpExecutionModeId instructions
-class SpirvExecutionMode : public SpirvInstruction {
+class SpirvExecutionMode : public SpirvExecutionModeBase {
 public:
   SpirvExecutionMode(SourceLocation loc, SpirvFunction *entryPointFunction,
                      spv::ExecutionMode, llvm::ArrayRef<uint32_t> params,
@@ -412,16 +436,34 @@ class SpirvExecutionMode : public SpirvInstruction {
 
   bool invokeVisitor(Visitor *v) override;
 
-  SpirvFunction *getEntryPoint() const { return entryPoint; }
-  spv::ExecutionMode getExecutionMode() const { return execMode; }
   llvm::ArrayRef<uint32_t> getParams() const { return params; }
 
 private:
-  SpirvFunction *entryPoint;
-  spv::ExecutionMode execMode;
   llvm::SmallVector<uint32_t, 4> params;
 };
 
+/// \brief OpExecutionModeId
+class SpirvExecutionModeId : public SpirvExecutionModeBase {
+public:
+  SpirvExecutionModeId(SourceLocation loc, SpirvFunction *entryPointFunction,
+                       spv::ExecutionMode em,
+                       llvm::ArrayRef<SpirvInstruction *> params);
+
+  DEFINE_RELEASE_MEMORY_FOR_CLASS(SpirvExecutionModeId)
+
+  // For LLVM-style RTTI
+  static bool classof(const SpirvInstruction *inst) {
+    return inst->getKind() == IK_ExecutionModeId;
+  }
+
+  bool invokeVisitor(Visitor *v) override;
+
+  llvm::ArrayRef<SpirvInstruction *> getParams() const { return params; }
+
+private:
+  llvm::SmallVector<SpirvInstruction *, 4> params;
+};
+
 /// \brief OpString instruction
 class SpirvString : public SpirvInstruction {
 public:
diff --git a/tools/clang/include/clang/SPIRV/SpirvModule.h b/tools/clang/include/clang/SPIRV/SpirvModule.h
index 298c06d65e..9ab0c296b8 100644
--- a/tools/clang/include/clang/SPIRV/SpirvModule.h
+++ b/tools/clang/include/clang/SPIRV/SpirvModule.h
@@ -119,11 +119,11 @@ class SpirvModule {
 
   // Returns an existing execution mode instruction that is the same as em if it
   // exists. Return nullptr otherwise.
-  SpirvExecutionMode *findExecutionMode(SpirvFunction *entryPoint,
-                                        spv::ExecutionMode em);
+  SpirvExecutionModeBase *findExecutionMode(SpirvFunction *entryPoint,
+                                            spv::ExecutionMode em);
 
   // Adds an execution mode to the module.
-  void addExecutionMode(SpirvExecutionMode *);
+  void addExecutionMode(SpirvExecutionModeBase *em);
 
   // Adds an extension to the module. Returns true if the extension was added.
   // Returns false otherwise (e.g. if the extension already existed).
@@ -194,7 +194,7 @@ class SpirvModule {
   llvm::SmallVector<SpirvExtInstImport *, 1> extInstSets;
   SpirvMemoryModel *memoryModel;
   llvm::SmallVector<SpirvEntryPoint *, 1> entryPoints;
-  llvm::SmallVector<SpirvExecutionMode *, 4> executionModes;
+  llvm::SmallVector<SpirvExecutionModeBase *, 4> executionModes;
   llvm::SmallVector<SpirvString *, 4> constStrings;
   std::vector<SpirvSource *> sources;
   std::vector<SpirvModuleProcessed *> moduleProcesses;
diff --git a/tools/clang/include/clang/SPIRV/SpirvVisitor.h b/tools/clang/include/clang/SPIRV/SpirvVisitor.h
index 303a4600a1..a3737f5387 100644
--- a/tools/clang/include/clang/SPIRV/SpirvVisitor.h
+++ b/tools/clang/include/clang/SPIRV/SpirvVisitor.h
@@ -60,7 +60,7 @@ class Visitor {
   DEFINE_VISIT_METHOD(SpirvExtInstImport)
   DEFINE_VISIT_METHOD(SpirvMemoryModel)
   DEFINE_VISIT_METHOD(SpirvEntryPoint)
-  DEFINE_VISIT_METHOD(SpirvExecutionMode)
+  DEFINE_VISIT_METHOD(SpirvExecutionModeBase)
   DEFINE_VISIT_METHOD(SpirvString)
   DEFINE_VISIT_METHOD(SpirvSource)
   DEFINE_VISIT_METHOD(SpirvModuleProcessed)
diff --git a/tools/clang/lib/SPIRV/CapabilityVisitor.cpp b/tools/clang/lib/SPIRV/CapabilityVisitor.cpp
index 50a7ab0905..4771a5f835 100644
--- a/tools/clang/lib/SPIRV/CapabilityVisitor.cpp
+++ b/tools/clang/lib/SPIRV/CapabilityVisitor.cpp
@@ -634,7 +634,7 @@ bool CapabilityVisitor::visit(SpirvEntryPoint *entryPoint) {
   return true;
 }
 
-bool CapabilityVisitor::visit(SpirvExecutionMode *execMode) {
+bool CapabilityVisitor::visit(SpirvExecutionModeBase *execMode) {
   spv::ExecutionMode executionMode = execMode->getExecutionMode();
   SourceLocation execModeSourceLocation = execMode->getSourceLocation();
   SourceLocation entryPointSourceLocation =
diff --git a/tools/clang/lib/SPIRV/CapabilityVisitor.h b/tools/clang/lib/SPIRV/CapabilityVisitor.h
index 95db110cce..35d4b5a18b 100644
--- a/tools/clang/lib/SPIRV/CapabilityVisitor.h
+++ b/tools/clang/lib/SPIRV/CapabilityVisitor.h
@@ -31,7 +31,7 @@ class CapabilityVisitor : public Visitor {
 
   bool visit(SpirvDecoration *decor) override;
   bool visit(SpirvEntryPoint *) override;
-  bool visit(SpirvExecutionMode *) override;
+  bool visit(SpirvExecutionModeBase *execMode) override;
   bool visit(SpirvImageQuery *) override;
   bool visit(SpirvImageOp *) override;
   bool visit(SpirvImageSparseTexelsResident *) override;
diff --git a/tools/clang/lib/SPIRV/EmitVisitor.cpp b/tools/clang/lib/SPIRV/EmitVisitor.cpp
index 468fdee4a4..579f5df255 100644
--- a/tools/clang/lib/SPIRV/EmitVisitor.cpp
+++ b/tools/clang/lib/SPIRV/EmitVisitor.cpp
@@ -613,18 +613,29 @@ bool EmitVisitor::visit(SpirvEntryPoint *inst) {
   return true;
 }
 
-bool EmitVisitor::visit(SpirvExecutionMode *inst) {
+bool EmitVisitor::visit(SpirvExecutionModeBase *inst) {
   initInstruction(inst);
   curInst.push_back(getOrAssignResultId<SpirvFunction>(inst->getEntryPoint()));
   curInst.push_back(static_cast<uint32_t>(inst->getExecutionMode()));
   if (inst->getopcode() == spv::Op::OpExecutionMode) {
-    curInst.insert(curInst.end(), inst->getParams().begin(),
-                   inst->getParams().end());
+    ArrayRef<uint32_t> params =
+        static_cast<SpirvExecutionMode *>(inst)->getParams();
+    curInst.insert(curInst.end(), params.begin(), params.end());
   } else {
-    for (uint32_t param : inst->getParams()) {
-      curInst.push_back(typeHandler.getOrCreateConstantInt(
-          llvm::APInt(32, param), context.getUIntType(32),
-          /*isSpecConst */ false));
+    if (inst->getKind() == SpirvInstruction::IK_ExecutionModeId) {
+      auto *exeModeId = static_cast<SpirvExecutionModeId *>(inst);
+      for (SpirvInstruction *param : exeModeId->getParams()) {
+        uint32_t id = getOrAssignResultId<SpirvInstruction>(param);
+        curInst.push_back(id);
+      }
+    } else {
+      ArrayRef<uint32_t> params =
+          static_cast<SpirvExecutionMode *>(inst)->getParams();
+      for (uint32_t param : params) {
+        curInst.push_back(typeHandler.getOrCreateConstantInt(
+            llvm::APInt(32, param), context.getUIntType(32),
+            /*isSpecConst */ false));
+      }
     }
   }
   finalizeInstruction(&preambleBinary);
diff --git a/tools/clang/lib/SPIRV/EmitVisitor.h b/tools/clang/lib/SPIRV/EmitVisitor.h
index 2f5d99b89d..2726b4e64f 100644
--- a/tools/clang/lib/SPIRV/EmitVisitor.h
+++ b/tools/clang/lib/SPIRV/EmitVisitor.h
@@ -228,7 +228,7 @@ class EmitVisitor : public Visitor {
   bool visit(SpirvEmitVertex *) override;
   bool visit(SpirvEndPrimitive *) override;
   bool visit(SpirvEntryPoint *) override;
-  bool visit(SpirvExecutionMode *) override;
+  bool visit(SpirvExecutionModeBase *) override;
   bool visit(SpirvString *) override;
   bool visit(SpirvSource *) override;
   bool visit(SpirvModuleProcessed *) override;
diff --git a/tools/clang/lib/SPIRV/SpirvEmitter.cpp b/tools/clang/lib/SPIRV/SpirvEmitter.cpp
index 0d47e1fa32..53c11eab58 100644
--- a/tools/clang/lib/SPIRV/SpirvEmitter.cpp
+++ b/tools/clang/lib/SPIRV/SpirvEmitter.cpp
@@ -34,6 +34,7 @@
 
 #ifdef SUPPORT_QUERY_GIT_COMMIT_INFO
 #include "clang/Basic/Version.h"
+#include "clang/Sema/Lookup.h"
 #else
 namespace clang {
 uint32_t getGitCommitCount() { return 0; }
@@ -13226,14 +13227,26 @@ void SpirvEmitter::processPixelShaderAttributes(const FunctionDecl *decl) {
 
 void SpirvEmitter::processComputeShaderAttributes(const FunctionDecl *decl) {
   auto *numThreadsAttr = decl->getAttr<HLSLNumThreadsAttr>();
-  assert(numThreadsAttr && "thread group size missing from entry-point");
+  auto *localSizeIdAttr = decl->getAttr<HLSLSpirvNumThreadsAttr>();
+  assert((numThreadsAttr || localSizeIdAttr) &&
+         "thread group size missing from entry-point");
 
-  uint32_t x = static_cast<uint32_t>(numThreadsAttr->getX());
-  uint32_t y = static_cast<uint32_t>(numThreadsAttr->getY());
-  uint32_t z = static_cast<uint32_t>(numThreadsAttr->getZ());
+  if (numThreadsAttr) {
+    uint32_t x = static_cast<uint32_t>(numThreadsAttr->getX());
+    uint32_t y = static_cast<uint32_t>(numThreadsAttr->getY());
+    uint32_t z = static_cast<uint32_t>(numThreadsAttr->getZ());
 
-  spvBuilder.addExecutionMode(entryFunction, spv::ExecutionMode::LocalSize,
-                              {x, y, z}, decl->getLocation());
+    spvBuilder.addExecutionMode(entryFunction, spv::ExecutionMode::LocalSize,
+                                {x, y, z}, decl->getLocation());
+  } else {
+    auto *exprX = localSizeIdAttr->getX();
+    auto *x = doExpr(exprX);
+    auto *y = doExpr(localSizeIdAttr->getY());
+    auto *z = doExpr(localSizeIdAttr->getZ());
+    spvBuilder.addExecutionModeId(entryFunction,
+                                  spv::ExecutionMode::LocalSizeId, {x, y, z},
+                                  decl->getLocation());
+  }
 
   auto *waveSizeAttr = decl->getAttr<HLSLWaveSizeAttr>();
   if (waveSizeAttr) {
@@ -13461,6 +13474,13 @@ bool SpirvEmitter::processMeshOrAmplificationShaderAttributes(
     z = static_cast<uint32_t>(numThreadsAttr->getZ());
     spvBuilder.addExecutionMode(entryFunction, spv::ExecutionMode::LocalSize,
                                 {x, y, z}, decl->getLocation());
+  } else if (auto *localSizeIdAttr = decl->getAttr<HLSLSpirvNumThreadsAttr>()) {
+    auto *x = doExpr(localSizeIdAttr->getX());
+    auto *y = doExpr(localSizeIdAttr->getY());
+    auto *z = doExpr(localSizeIdAttr->getZ());
+    spvBuilder.addExecutionModeId(entryFunction,
+                                  spv::ExecutionMode::LocalSizeId, {x, y, z},
+                                  decl->getLocation());
   }
 
   // Early return for amplification shaders as they only take the 'numthreads'
@@ -15022,9 +15042,14 @@ bool SpirvEmitter::spirvToolsValidate(std::vector<uint32_t> *mod,
 void SpirvEmitter::addDerivativeGroupExecutionMode() {
   assert(spvContext.isCS());
 
-  SpirvExecutionMode *numThreadsEm = spvBuilder.getModule()->findExecutionMode(
-      entryFunction, spv::ExecutionMode::LocalSize);
-  auto numThreads = numThreadsEm->getParams();
+  SpirvExecutionModeBase *numThreadsEm =
+      spvBuilder.getModule()->findExecutionMode(entryFunction,
+                                                spv::ExecutionMode::LocalSize);
+
+  // TODO: Need to handle LocalSizeID as well.
+  assert(numThreadsEm->getKind() == SpirvInstruction::IK_ExecutionMode);
+  auto numThreads =
+      static_cast<SpirvExecutionMode *>(numThreadsEm)->getParams();
 
   // The layout of the quad is determined by the numer of threads in each
   // dimention. From the HLSL spec
diff --git a/tools/clang/lib/SPIRV/SpirvInstruction.cpp b/tools/clang/lib/SPIRV/SpirvInstruction.cpp
index 21aada9e82..e28f7e506c 100644
--- a/tools/clang/lib/SPIRV/SpirvInstruction.cpp
+++ b/tools/clang/lib/SPIRV/SpirvInstruction.cpp
@@ -29,7 +29,9 @@ DEFINE_INVOKE_VISITOR_FOR_CLASS(SpirvExtension)
 DEFINE_INVOKE_VISITOR_FOR_CLASS(SpirvExtInstImport)
 DEFINE_INVOKE_VISITOR_FOR_CLASS(SpirvMemoryModel)
 DEFINE_INVOKE_VISITOR_FOR_CLASS(SpirvEntryPoint)
+DEFINE_INVOKE_VISITOR_FOR_CLASS(SpirvExecutionModeBase)
 DEFINE_INVOKE_VISITOR_FOR_CLASS(SpirvExecutionMode)
+DEFINE_INVOKE_VISITOR_FOR_CLASS(SpirvExecutionModeId)
 DEFINE_INVOKE_VISITOR_FOR_CLASS(SpirvString)
 DEFINE_INVOKE_VISITOR_FOR_CLASS(SpirvSource)
 DEFINE_INVOKE_VISITOR_FOR_CLASS(SpirvModuleProcessed)
@@ -203,11 +205,17 @@ SpirvExecutionMode::SpirvExecutionMode(SourceLocation loc, SpirvFunction *entry,
                                        spv::ExecutionMode em,
                                        llvm::ArrayRef<uint32_t> paramsVec,
                                        bool usesIdParams)
-    : SpirvInstruction(IK_ExecutionMode,
-                       usesIdParams ? spv::Op::OpExecutionModeId
-                                    : spv::Op::OpExecutionMode,
-                       QualType(), loc),
-      entryPoint(entry), execMode(em),
+    : SpirvExecutionModeBase(IK_ExecutionMode,
+                             usesIdParams ? spv::Op::OpExecutionModeId
+                                          : spv::Op::OpExecutionMode,
+                             loc, entry, em),
+      params(paramsVec.begin(), paramsVec.end()) {}
+
+SpirvExecutionModeId::SpirvExecutionModeId(
+    SourceLocation loc, SpirvFunction *entry, spv::ExecutionMode em,
+    llvm::ArrayRef<SpirvInstruction *> paramsVec)
+    : SpirvExecutionModeBase(IK_ExecutionModeId, spv::Op::OpExecutionModeId,
+                             loc, entry, em),
       params(paramsVec.begin(), paramsVec.end()) {}
 
 SpirvString::SpirvString(SourceLocation loc, llvm::StringRef stringLiteral)
diff --git a/tools/clang/lib/SPIRV/SpirvModule.cpp b/tools/clang/lib/SPIRV/SpirvModule.cpp
index 9c6a826a5b..ed6aca7488 100644
--- a/tools/clang/lib/SPIRV/SpirvModule.cpp
+++ b/tools/clang/lib/SPIRV/SpirvModule.cpp
@@ -294,9 +294,10 @@ void SpirvModule::addEntryPoint(SpirvEntryPoint *ep) {
   entryPoints.push_back(ep);
 }
 
-SpirvExecutionMode *SpirvModule::findExecutionMode(SpirvFunction *entryPoint,
-                                                   spv::ExecutionMode em) {
-  for (SpirvExecutionMode *cem : executionModes) {
+SpirvExecutionModeBase *
+SpirvModule::findExecutionMode(SpirvFunction *entryPoint,
+                               spv::ExecutionMode em) {
+  for (SpirvExecutionModeBase *cem : executionModes) {
     if (cem->getEntryPoint() != entryPoint)
       continue;
     if (cem->getExecutionMode() != em)
@@ -306,7 +307,7 @@ SpirvExecutionMode *SpirvModule::findExecutionMode(SpirvFunction *entryPoint,
   return nullptr;
 }
 
-void SpirvModule::addExecutionMode(SpirvExecutionMode *em) {
+void SpirvModule::addExecutionMode(SpirvExecutionModeBase *em) {
   assert(em && "cannot add null execution mode");
   executionModes.push_back(em);
 }
diff --git a/tools/clang/lib/Sema/SemaHLSL.cpp b/tools/clang/lib/Sema/SemaHLSL.cpp
index ba0801dd52..7b7ef08359 100644
--- a/tools/clang/lib/Sema/SemaHLSL.cpp
+++ b/tools/clang/lib/Sema/SemaHLSL.cpp
@@ -13349,6 +13349,18 @@ void hlsl::HandleDeclAttributeForHLSL(Sema &S, Decl *D, const AttributeList &A,
     }
     break;
   }
+  case AttributeList::AT_HLSLSpirvNumThreads: {
+    // TODO: require SPIR-V 1.2
+    // TODO: require expression to be C++11ConstantExpr or a spec constant.
+    // We we want to allow things with SpecConstantOp?
+    auto *X = A.getArgAsExpr(0);
+    auto *Y = A.getArgAsExpr(1);
+    auto *Z = A.getArgAsExpr(2);
+    auto numThreads = ::new (S.Context) HLSLSpirvNumThreadsAttr(
+        A.getRange(), S.Context, X, Y, Z, A.getAttributeSpellingListIndex());
+    declAttr = numThreads;
+    break;
+  }
   case AttributeList::AT_HLSLRootSignature:
     declAttr = ::new (S.Context) HLSLRootSignatureAttr(
         A.getRange(), S.Context,
@@ -15570,7 +15582,8 @@ void DiagnoseDispatchGridSemantics(Sema &S, RecordDecl *NodeRecordStruct,
 void DiagnoseAmplificationEntry(Sema &S, FunctionDecl *FD,
                                 llvm::StringRef StageName) {
 
-  if (!(FD->getAttr<HLSLNumThreadsAttr>()))
+  if (!(FD->getAttr<HLSLNumThreadsAttr>()) &&
+      !(FD->getAttr<HLSLSpirvNumThreadsAttr>()))
     S.Diags.Report(FD->getLocation(), diag::err_hlsl_missing_attr)
         << StageName << "numthreads";
 
@@ -15594,7 +15607,8 @@ void DiagnoseVertexEntry(Sema &S, FunctionDecl *FD, llvm::StringRef StageName) {
 
 void DiagnoseMeshEntry(Sema &S, FunctionDecl *FD, llvm::StringRef StageName) {
 
-  if (!(FD->getAttr<HLSLNumThreadsAttr>()))
+  if (!(FD->getAttr<HLSLNumThreadsAttr>()) &&
+      !(FD->getAttr<HLSLSpirvNumThreadsAttr>()))
     S.Diags.Report(FD->getLocation(), diag::err_hlsl_missing_attr)
         << StageName << "numthreads";
   if (!(FD->getAttr<HLSLOutputTopologyAttr>()))
@@ -15649,7 +15663,8 @@ void DiagnoseGeometryEntry(Sema &S, FunctionDecl *FD,
 void DiagnoseComputeEntry(Sema &S, FunctionDecl *FD, llvm::StringRef StageName,
                           bool isActiveEntry) {
   if (isActiveEntry) {
-    if (!(FD->getAttr<HLSLNumThreadsAttr>()))
+    if (!(FD->getAttr<HLSLNumThreadsAttr>()) &&
+        !(FD->getAttr<HLSLSpirvNumThreadsAttr>()))
       S.Diags.Report(FD->getLocation(), diag::err_hlsl_missing_attr)
           << StageName << "numthreads";
     if (auto WaveSizeAttr = FD->getAttr<HLSLWaveSizeAttr>()) {
diff --git a/tools/clang/test/CodeGenSPIRV/spec_constant.numthreads.hlsl b/tools/clang/test/CodeGenSPIRV/spec_constant.numthreads.hlsl
new file mode 100644
index 0000000000..24a75a01c5
--- /dev/null
+++ b/tools/clang/test/CodeGenSPIRV/spec_constant.numthreads.hlsl
@@ -0,0 +1,9 @@
+// RUN: %dxc -T cs_6_0 -E main -fspv-target-env=vulkan1.3 -fcgl  %s -spirv | FileCheck %s
+
+// CHECK: OpEntryPoint GLCompute %main "main"
+// CHECK: OpExecutionModeId %main LocalSizeId [[spec_constant:%[0-9a-zA-Z]+]] %int_8 %int_1
+// CHECK: [[spec_constant]] = OpSpecConstant %uint 8
+
+[[vk::constant_id(1)]] const uint specConstant = 8;
+[[vk::LocalSizeId(specConstant, 8, 1)]]
+void main() {}