[HLSL][SPIR-V] Add support for SV_Target semantic

clang/include/clang/Basic/DiagnosticSemaKinds.td

@@ -13213,6 +13213,8 @@ def err_hlsl_semantic_indexing_not_supported
 def err_hlsl_init_priority_unsupported : Error<
   "initializer priorities are not supported in HLSL">;
 def err_hlsl_semantic_index_overlap : Error<"semantic index overlap %0">;
+def err_hlsl_semantic_unsupported_direction_for_stage
+    : Error<"semantic %0 is unsupported as %1 for stage %2">;
 
 def warn_hlsl_user_defined_type_missing_member: Warning<"binding type '%select{t|u|b|s|c}0' only applies to types containing %select{SRV resources|UAV resources|constant buffer resources|sampler state|numeric types}0">, InGroup<LegacyConstantRegisterBinding>;
 def err_hlsl_binding_type_mismatch: Error<"binding type '%select{t|u|b|s|c}0' only applies to %select{SRV resources|UAV resources|constant buffer resources|sampler state|numeric variables in the global scope}0">;

clang/include/clang/Sema/SemaHLSL.h

@@ -134,9 +134,6 @@ class SemaHLSL : public SemaBase {
   void CheckEntryPoint(FunctionDecl *FD);
   bool CheckResourceBinOp(BinaryOperatorKind Opc, Expr *LHSExpr, Expr *RHSExpr,
                           SourceLocation Loc);
-  void DiagnoseAttrStageMismatch(
-      const Attr *A, llvm::Triple::EnvironmentType Stage,
-      std::initializer_list<llvm::Triple::EnvironmentType> AllowedStages);
 
   QualType handleVectorBinOpConversion(ExprResult &LHS, ExprResult &RHS,
                                        QualType LHSType, QualType RHSType,
@@ -244,26 +241,50 @@ class SemaHLSL : public SemaBase {
     std::optional<uint32_t> Index;
   };
 
+  enum IOType {
+    In = 0b01,
+    Out = 0b10,
+    InOut = 0b11,
+  };
+
+  struct SemanticStageInfo {
+    llvm::Triple::EnvironmentType Stage;
+    IOType Direction;
+  };
+
 private:
   void collectResourceBindingsOnVarDecl(VarDecl *D);
   void collectResourceBindingsOnUserRecordDecl(const VarDecl *VD,
                                                const RecordType *RT);
 
   void checkSemanticAnnotation(FunctionDecl *EntryPoint, const Decl *Param,
-                               const HLSLAppliedSemanticAttr *SemanticAttr);
+                               const HLSLAppliedSemanticAttr *SemanticAttr,
+                               bool IsInput);
+
   bool determineActiveSemanticOnScalar(FunctionDecl *FD,
                                        DeclaratorDecl *OutputDecl,
                                        DeclaratorDecl *D,
                                        SemanticInfo &ActiveSemantic,
-                                       llvm::StringSet<> &ActiveInputSemantics);
+                                       llvm::StringSet<> &ActiveSemantics,
+                                       bool IsInput);
+
   bool determineActiveSemantic(FunctionDecl *FD, DeclaratorDecl *OutputDecl,
                                DeclaratorDecl *D, SemanticInfo &ActiveSemantic,
-                               llvm::StringSet<> &ActiveInputSemantics);
+                               llvm::StringSet<> &ActiveSemantics,
+                               bool IsInput);
 
   void processExplicitBindingsOnDecl(VarDecl *D);
 
   void diagnoseAvailabilityViolations(TranslationUnitDecl *TU);
 
+  void diagnoseAttrStageMismatch(
+      const Attr *A, llvm::Triple::EnvironmentType Stage,
+      std::initializer_list<llvm::Triple::EnvironmentType> AllowedStages);
+
+  void diagnoseSemanticStageMismatch(
+      const Attr *A, llvm::Triple::EnvironmentType Stage, bool IsInput,
+      std::initializer_list<SemanticStageInfo> AllowedStages);
+
   uint32_t getNextImplicitBindingOrderID() {
     return ImplicitBindingNextOrderID++;
   }

clang/lib/CodeGen/CGHLSLRuntime.cpp

@@ -730,10 +730,18 @@ llvm::Value *CGHLSLRuntime::emitSystemSemanticLoad(
   }
 
   if (SemanticName == "SV_POSITION") {
-    if (CGM.getTriple().getEnvironment() == Triple::EnvironmentType::Pixel)
-      return createSPIRVBuiltinLoad(B, CGM.getModule(), Type,
-                                    Semantic->getAttrName()->getName(),
-                                    /* BuiltIn::FragCoord */ 15);
+    if (CGM.getTriple().getEnvironment() == Triple::EnvironmentType::Pixel) {
+      if (CGM.getTarget().getTriple().isSPIRV())
+        return createSPIRVBuiltinLoad(B, CGM.getModule(), Type,
+                                      Semantic->getAttrName()->getName(),
+                                      /* BuiltIn::FragCoord */ 15);
+      if (CGM.getTarget().getTriple().isDXIL())
+        return emitDXILUserSemanticLoad(B, Type, Semantic, Index);
+    }
+
+    if (CGM.getTriple().getEnvironment() == Triple::EnvironmentType::Vertex) {
+      return emitUserSemanticLoad(B, Type, Decl, Semantic, Index);
+    }
   }
 
   llvm_unreachable("non-handled system semantic. FIXME.");
@@ -759,11 +767,16 @@ void CGHLSLRuntime::emitSystemSemanticStore(IRBuilder<> &B, llvm::Value *Source,
                                             std::optional<unsigned> Index) {
 
   std::string SemanticName = Semantic->getAttrName()->getName().upper();
-  if (SemanticName == "SV_POSITION")
-    createSPIRVBuiltinStore(B, CGM.getModule(), Source,
-                            Semantic->getAttrName()->getName(),
-                            /* BuiltIn::Position */ 0);
-  else
+  if (SemanticName == "SV_POSITION") {
+    if (CGM.getTarget().getTriple().isDXIL())
+      emitDXILUserSemanticStore(B, Source, Semantic, Index);
+    else if (CGM.getTarget().getTriple().isSPIRV())
+      createSPIRVBuiltinStore(B, CGM.getModule(), Source,
+                              Semantic->getAttrName()->getName(),
+                              /* BuiltIn::Position */ 0);
+  } else if (SemanticName == "SV_TARGET") {
+    emitUserSemanticStore(B, Source, Decl, Semantic, Index);
+  } else
     llvm_unreachable("non-handled system semantic. FIXME.");
 }
 

clang/lib/Sema/SemaHLSL.cpp

@@ -771,9 +771,12 @@ void SemaHLSL::ActOnTopLevelFunction(FunctionDecl *FD) {
   }
 }
 
-bool SemaHLSL::determineActiveSemanticOnScalar(
-    FunctionDecl *FD, DeclaratorDecl *OutputDecl, DeclaratorDecl *D,
-    SemanticInfo &ActiveSemantic, llvm::StringSet<> &UsedSemantics) {
+bool SemaHLSL::determineActiveSemanticOnScalar(FunctionDecl *FD,
+                                               DeclaratorDecl *OutputDecl,
+                                               DeclaratorDecl *D,
+                                               SemanticInfo &ActiveSemantic,
+                                               llvm::StringSet<> &UsedSemantics,
+                                               bool IsInput) {
   if (ActiveSemantic.Semantic == nullptr) {
     ActiveSemantic.Semantic = D->getAttr<HLSLParsedSemanticAttr>();
     if (ActiveSemantic.Semantic)
@@ -792,7 +795,7 @@ bool SemaHLSL::determineActiveSemanticOnScalar(
   if (!A)
     return false;
 
-  checkSemanticAnnotation(FD, D, A);
+  checkSemanticAnnotation(FD, D, A, IsInput);
   OutputDecl->addAttr(A);
 
   unsigned Location = ActiveSemantic.Index.value_or(0);
@@ -820,7 +823,8 @@ bool SemaHLSL::determineActiveSemantic(FunctionDecl *FD,
                                        DeclaratorDecl *OutputDecl,
                                        DeclaratorDecl *D,
                                        SemanticInfo &ActiveSemantic,
-                                       llvm::StringSet<> &UsedSemantics) {
+                                       llvm::StringSet<> &UsedSemantics,
+                                       bool IsInput) {
   if (ActiveSemantic.Semantic == nullptr) {
     ActiveSemantic.Semantic = D->getAttr<HLSLParsedSemanticAttr>();
     if (ActiveSemantic.Semantic)
@@ -833,12 +837,13 @@ bool SemaHLSL::determineActiveSemantic(FunctionDecl *FD,
   const RecordType *RT = dyn_cast<RecordType>(T);
   if (!RT)
     return determineActiveSemanticOnScalar(FD, OutputDecl, D, ActiveSemantic,
-                                           UsedSemantics);
+                                           UsedSemantics, IsInput);
 
   const RecordDecl *RD = RT->getDecl();
   for (FieldDecl *Field : RD->fields()) {
     SemanticInfo Info = ActiveSemantic;
-    if (!determineActiveSemantic(FD, OutputDecl, Field, Info, UsedSemantics)) {
+    if (!determineActiveSemantic(FD, OutputDecl, Field, Info, UsedSemantics,
+                                 IsInput)) {
       Diag(Field->getLocation(), diag::note_hlsl_semantic_used_here) << Field;
       return false;
     }
@@ -868,14 +873,14 @@ void SemaHLSL::CheckEntryPoint(FunctionDecl *FD) {
   case llvm::Triple::Miss:
   case llvm::Triple::Callable:
     if (const auto *NT = FD->getAttr<HLSLNumThreadsAttr>()) {
-      DiagnoseAttrStageMismatch(NT, ST,
+      diagnoseAttrStageMismatch(NT, ST,
                                 {llvm::Triple::Compute,
                                  llvm::Triple::Amplification,
                                  llvm::Triple::Mesh});
       FD->setInvalidDecl();
     }
     if (const auto *WS = FD->getAttr<HLSLWaveSizeAttr>()) {
-      DiagnoseAttrStageMismatch(WS, ST,
+      diagnoseAttrStageMismatch(WS, ST,
                                 {llvm::Triple::Compute,
                                  llvm::Triple::Amplification,
                                  llvm::Triple::Mesh});
@@ -920,7 +925,7 @@ void SemaHLSL::CheckEntryPoint(FunctionDecl *FD) {
 
     // FIXME: Verify output semantics in parameters.
     if (!determineActiveSemantic(FD, Param, Param, ActiveSemantic,
-                                 ActiveInputSemantics)) {
+                                 ActiveInputSemantics, /* IsInput= */ true)) {
       Diag(Param->getLocation(), diag::note_previous_decl) << Param;
       FD->setInvalidDecl();
     }
@@ -932,12 +937,13 @@ void SemaHLSL::CheckEntryPoint(FunctionDecl *FD) {
   if (ActiveSemantic.Semantic)
     ActiveSemantic.Index = ActiveSemantic.Semantic->getSemanticIndex();
   if (!FD->getReturnType()->isVoidType())
-    determineActiveSemantic(FD, FD, FD, ActiveSemantic, ActiveOutputSemantics);
+    determineActiveSemantic(FD, FD, FD, ActiveSemantic, ActiveOutputSemantics,
+                            /* IsInput= */ false);
 }
 
 void SemaHLSL::checkSemanticAnnotation(
     FunctionDecl *EntryPoint, const Decl *Param,
-    const HLSLAppliedSemanticAttr *SemanticAttr) {
+    const HLSLAppliedSemanticAttr *SemanticAttr, bool IsInput) {
   auto *ShaderAttr = EntryPoint->getAttr<HLSLShaderAttr>();
   assert(ShaderAttr && "Entry point has no shader attribute");
   llvm::Triple::EnvironmentType ST = ShaderAttr->getType();
@@ -948,7 +954,8 @@ void SemaHLSL::checkSemanticAnnotation(
       SemanticName == "SV_GROUPID") {
 
     if (ST != llvm::Triple::Compute)
-      DiagnoseAttrStageMismatch(SemanticAttr, ST, {llvm::Triple::Compute});
+      diagnoseSemanticStageMismatch(SemanticAttr, ST, IsInput,
+                                    {{llvm::Triple::Compute, IOType::In}});
 
     if (SemanticAttr->getSemanticIndex() != 0) {
       std::string PrettyName =
@@ -961,11 +968,15 @@ void SemaHLSL::checkSemanticAnnotation(
   }
 
   if (SemanticName == "SV_POSITION") {
-    // TODO(#143523): allow use on other shader types & output once the overall
-    // semantic logic is implemented.
-    if (ST == llvm::Triple::Pixel)
-      return;
-    DiagnoseAttrStageMismatch(SemanticAttr, ST, {llvm::Triple::Pixel});
+    diagnoseSemanticStageMismatch(SemanticAttr, ST, IsInput,
+                                  {{llvm::Triple::Vertex, IOType::InOut},
+                                   {llvm::Triple::Pixel, IOType::In}});
+    return;
+  }
+
+  if (SemanticName == "SV_TARGET") {
+    diagnoseSemanticStageMismatch(SemanticAttr, ST, IsInput,
+                                  {{llvm::Triple::Pixel, IOType::Out}});
     return;
   }
 
@@ -975,7 +986,7 @@ void SemaHLSL::checkSemanticAnnotation(
     llvm_unreachable("Unknown SemanticAttr");
 }
 
-void SemaHLSL::DiagnoseAttrStageMismatch(
+void SemaHLSL::diagnoseAttrStageMismatch(
     const Attr *A, llvm::Triple::EnvironmentType Stage,
     std::initializer_list<llvm::Triple::EnvironmentType> AllowedStages) {
   SmallVector<StringRef, 8> StageStrings;
@@ -989,6 +1000,37 @@ void SemaHLSL::DiagnoseAttrStageMismatch(
       << (AllowedStages.size() != 1) << join(StageStrings, ", ");
 }
 
+void SemaHLSL::diagnoseSemanticStageMismatch(
+    const Attr *A, llvm::Triple::EnvironmentType Stage, bool IsInput,
+    std::initializer_list<SemanticStageInfo> Allowed) {
+
+  for (auto &Case : Allowed) {
+    if (Case.Stage != Stage)
+      continue;
+
+    if (IsInput && Case.Direction & IOType::In)
+      return;
+    if (!IsInput && Case.Direction & IOType::Out)
+      return;
+
+    Diag(A->getLoc(), diag::err_hlsl_semantic_unsupported_direction_for_stage)
+        << A->getAttrName() << (IsInput ? "input" : "output")
+        << llvm::Triple::getEnvironmentTypeName(Case.Stage);
+    return;
+  }
+
+  SmallVector<StringRef, 8> StageStrings;
+  llvm::transform(
+      Allowed, std::back_inserter(StageStrings), [](SemanticStageInfo Case) {
+        return StringRef(
+            HLSLShaderAttr::ConvertEnvironmentTypeToStr(Case.Stage));
+      });
+
+  Diag(A->getLoc(), diag::err_hlsl_attr_unsupported_in_stage)
+      << A->getAttrName() << llvm::Triple::getEnvironmentTypeName(Stage)
+      << (Allowed.size() != 1) << join(StageStrings, ", ");
+}
+
 template <CastKind Kind>
 static void castVector(Sema &S, ExprResult &E, QualType &Ty, unsigned Sz) {
   if (const auto *VTy = Ty->getAs<VectorType>())
@@ -1790,6 +1832,16 @@ void SemaHLSL::diagnoseSystemSemanticAttr(Decl *D, const ParsedAttr &AL,
     return;
   }
 
+  if (SemanticName == "SV_TARGET") {
+    const auto *VT = ValueType->getAs<VectorType>();
+    if (!ValueType->hasFloatingRepresentation() ||
+        (VT && VT->getNumElements() > 4))
+      Diag(AL.getLoc(), diag::err_hlsl_attr_invalid_type)
+          << AL << "float/float1/float2/float3/float4";
+    D->addAttr(createSemanticAttr<HLSLParsedSemanticAttr>(AL, Index));
+    return;
+  }
+
   Diag(AL.getLoc(), diag::err_hlsl_unknown_semantic) << AL;
 }
 

clang/test/CodeGenHLSL/semantics/SV_Position.ps.hlsl

@@ -1,11 +1,21 @@
-// RUN: %clang_cc1 -triple spirv-unknown-vulkan1.3-pixel -x hlsl -emit-llvm -finclude-default-header -disable-llvm-passes -o - %s | FileCheck %s
+// RUN: %clang_cc1 -triple spirv-pc-vulkan1.3-pixel -x hlsl -emit-llvm -finclude-default-header -disable-llvm-passes -o - %s | FileCheck %s --check-prefix=CHECK-SPIRV
+// RUN: %clang_cc1 -triple dxil-pc-shadermodel6.3-pixel -x hlsl -emit-llvm -finclude-default-header -disable-llvm-passes -o - %s | FileCheck %s --check-prefix=CHECK-DXIL
 
-// CHECK: @SV_Position = external hidden thread_local addrspace(7) externally_initialized constant <4 x float>, !spirv.Decorations !0
+// CHECK-SPIRV: @SV_Position = external hidden thread_local addrspace(7) externally_initialized constant <4 x float>, !spirv.Decorations ![[#MD_0:]]
 
 // CHECK: define void @main() {{.*}} {
 float4 main(float4 p : SV_Position) : A {
-  // CHECK: %[[#P:]] = load <4 x float>, ptr addrspace(7) @SV_Position, align 16
-  // CHECK: %[[#R:]] = call spir_func <4 x float> @_Z4mainDv4_f(<4 x float> %[[#P]])
-  // CHECK:            store <4 x float> %[[#R]], ptr addrspace(8) @A0, align 16
+  // CHECK-SPIRV: %[[#P:]] = load <4 x float>, ptr addrspace(7) @SV_Position, align 16
+  // CHECK-SPIRV: %[[#R:]] = call spir_func <4 x float> @_Z4mainDv4_f(<4 x float> %[[#P]])
+  // CHECK-SPIRV:            store <4 x float> %[[#R]], ptr addrspace(8) @A0, align 16
+
+  // CHECK-DXIL: %SV_Position0 = call <4 x float> @llvm.dx.load.input.v4f32(i32 4, i32 0, i32 0, i8 0, i32 poison)
+  // CHECK-DXIL:    %[[#TMP:]] = call <4 x float> @_Z4mainDv4_f(<4 x float> %SV_Position0)
+  // CHECK-DXIL:                 call void @llvm.dx.store.output.v4f32(i32 4, i32 0, i32 0, i8 0, i32 poison, <4 x float> %[[#TMP]])
   return p;
 }
+
+// CHECK-SPIRV-DAG: ![[#MD_0]] = !{![[#MD_1:]]}
+// CHECK-SPIRV-DAG: ![[#MD_1]] = !{i32 11, i32 15}
+//                                      |       `-> BuiltIn Position
+//                                      `-> SPIR-V decoration 'FragCoord'

clang/test/CodeGenHLSL/semantics/SV_Position.vs.hlsl

@@ -0,0 +1,26 @@
+// RUN: %clang_cc1 -triple dxil-unknown-shadermodel6.8-vertex -x hlsl -emit-llvm -finclude-default-header -disable-llvm-passes -o - %s | FileCheck --check-prefix=CHECK-DXIL %s
+// RUN: %clang_cc1 -triple spirv-unknown-vulkan1.3-vertex -x hlsl -emit-llvm -finclude-default-header -disable-llvm-passes -o - %s | FileCheck --check-prefix=CHECK-SPIRV  %s
+
+// CHECK-SPIRV: @SV_Position0 = external hidden thread_local addrspace(7) externally_initialized constant <4 x float>, !spirv.Decorations ![[#MD_0:]]
+// CHECK-SPIRV: @SV_Position = external hidden thread_local addrspace(8) global <4 x float>, !spirv.Decorations ![[#MD_2:]]
+
+// CHECK: define void @main() {{.*}} {
+float4 main(float4 p : SV_Position) : SV_Position {
+  // CHECK-SPIRV: %[[#P:]] = load <4 x float>, ptr addrspace(7) @SV_Position0, align 16
+  // CHECK-SPIRV: %[[#R:]] = call spir_func <4 x float> @_Z4mainDv4_f(<4 x float> %[[#P]])
+  // CHECK-SPIRV:            store <4 x float> %[[#R]], ptr addrspace(8) @SV_Position, align 16
+
+  // CHECK-DXIL: %SV_Position0 = call <4 x float> @llvm.dx.load.input.v4f32(i32 4, i32 0, i32 0, i8 0, i32 poison)
+  // CHECK-DXIL:    %[[#TMP:]] = call <4 x float> @_Z4mainDv4_f(<4 x float> %SV_Position0)
+  // CHECK-DXIL:                 call void @llvm.dx.store.output.v4f32(i32 4, i32 0, i32 0, i8 0, i32 poison, <4 x float> %[[#TMP]])
+  return p;
+}
+
+// CHECK-SPIRV-DAG: ![[#MD_0]] = !{![[#MD_1:]]}
+// CHECK-SPIRV-DAG: ![[#MD_2]] = !{![[#MD_3:]]}
+// CHECK-SPIRV-DAG: ![[#MD_1]] = !{i32 30, i32 0}
+//                                      |       `-> Location 0
+//                                      `-> SPIR-V decoration 'Location'
+// CHECK-SPIRV-DAG: ![[#MD_3]] = !{i32 11, i32 0}
+//                                      |       `-> BuiltIn Position
+//                                      `-> SPIR-V decoration 'BuiltIn'

clang/test/CodeGenHLSL/semantics/SV_Target.ps.hlsl

@@ -0,0 +1,19 @@
+// RUN: %clang_cc1 -triple spirv-pc-vulkan1.3-pixel -x hlsl -emit-llvm -finclude-default-header -disable-llvm-passes -o - %s | FileCheck %s --check-prefix=CHECK-SPIRV
+// RUN: %clang_cc1 -triple dxil-pc-shadermodel6.3-pixel -x hlsl -emit-llvm -finclude-default-header -disable-llvm-passes -o - %s | FileCheck %s --check-prefix=CHECK-DXIL
+
+// CHECK-SPIRV: @SV_Target0 = external hidden thread_local addrspace(8) global <4 x float>, !spirv.Decorations ![[#MD_2:]]
+
+// CHECK: define void @main() {{.*}} {
+float4 main(float4 p : SV_Position) : SV_Target {
+  // CHECK-SPIRV: %[[#R:]] = call spir_func <4 x float> @_Z4mainDv4_f(<4 x float> %[[#]])
+  // CHECK-SPIRV:            store <4 x float> %[[#R]], ptr addrspace(8) @SV_Target0, align 16
+
+  // CHECK-DXIL:    %[[#TMP:]] = call <4 x float> @_Z4mainDv4_f(<4 x float> %SV_Position0)
+  // CHECK-DXIL:                 call void @llvm.dx.store.output.v4f32(i32 4, i32 0, i32 0, i8 0, i32 poison, <4 x float> %[[#TMP]])
+  return p;
+}
+
+// CHECK-SPIRV-DAG: ![[#MD_2]] = !{![[#MD_3:]]}
+// CHECK-SPIRV-DAG: ![[#MD_3]] = !{i32 30, i32 0}
+//                                      |       `-> Location index
+//                                      `-> SPIR-V decoration 'Location'

clang/test/SemaHLSL/Semantics/position.ps.hlsl

@@ -1,13 +1,7 @@
-// RUN: %clang_cc1 -triple dxil-pc-shadermodel6.0-pixel -x hlsl -finclude-default-header -o - %s -ast-dump | FileCheck %s
+// RUN: %clang_cc1 -triple dxil-pc-shadermodel6.3-pixel -finclude-default-header -x hlsl -verify -o - %s
+// RUN: %clang_cc1 -triple spirv-pc-vulkan1.3-pixel -finclude-default-header -x hlsl -verify -o - %s
 
-// FIXME(Keenuts): change output semantic to something valid for pixels shaders
-float4 main(float4 a : SV_Position2) : A {
-// CHECK: FunctionDecl 0x{{[0-9a-fA-F]+}} <{{.*}}> line:[[@LINE-1]]:8 main 'float4 (float4)'
-// CHECK-NEXT: ParmVarDecl 0x{{[0-9a-fA-F]+}} <{{.*}}> col:20 used a 'float4':'vector<float, 4>'
-// CHECK-NEXT:  HLSLParsedSemanticAttr 0x{{[0-9a-f]+}} <col:24> "SV_Position" 2
-// CHECK-NEXT:  HLSLAppliedSemanticAttr 0x{{[0-9a-f]+}} <col:24> "SV_Position" 2
-
-// CHECK:       HLSLParsedSemanticAttr 0x{{[0-9a-f]+}} <line:4:40> "A" 0
-// CHECK:       HLSLAppliedSemanticAttr 0x{{[0-9a-f]+}} <col:40> "A" 0
+float4 main(float4 a : A) : SV_Position {
+// expected-error@-1 {{semantic 'SV_Position' is unsupported as output for stage pixel}}
   return a;
 }