[Clang][HIP][CUDA] Add __cluster_dims__ and __no_cluster__ attribute

This PR adds basic frontend support for `__cluster_dims__` and `__no_cluster__` attribute.

Co-authored-by: Yaxun (Sam) Liu <yaxun.liu@amd.com>
Co-authored-by: Jay Foad <jay.foad@amd.com>

Author: 3 people

clang/include/clang/Basic/Attr.td

@@ -1572,6 +1572,23 @@ def HIPManaged : InheritableAttr {
   let Documentation = [HIPManagedAttrDocs];
 }
 
+def CUDAClusterDims : InheritableAttr {
+  let Spellings = [GNU<"cluster_dims">, Declspec<"__cluster_dims__">];
+  let Args = [ExprArgument<"X">, ExprArgument<"Y", 1>, ExprArgument<"Z", 1>];
+  let Subjects = SubjectList<[Function], ErrorDiag, "kernel functions">;
+  let LangOpts = [CUDA];
+  let Documentation = [Undocumented];
+}
+
+def CUDANoCluster : InheritableAttr {
+  let Spellings = [GNU<"no_cluster">, Declspec<"__no_cluster__">];
+  let Subjects = SubjectList<[Function], ErrorDiag, "kernel functions">;
+  let LangOpts = [CUDA];
+  let Documentation = [Undocumented];
+}
+
+def : MutualExclusions<[CUDAClusterDims, CUDANoCluster]>;
+
 def CUDAInvalidTarget : InheritableAttr {
   let Spellings = [];
   let Subjects = SubjectList<[Function]>;

clang/include/clang/Basic/DiagnosticSemaKinds.td

@@ -13070,6 +13070,14 @@ def warn_cuda_maxclusterrank_sm_90 : Warning<
   "maxclusterrank requires sm_90 or higher, CUDA arch provided: %0, ignoring "
   "%1 attribute">, InGroup<IgnoredAttributes>;
 
+def err_cuda_cluster_attr_not_supported : Error<
+  "%select{__cluster_dims__|__no_cluster__}0 is not supported for this GPU architecture"
+>;
+
+def err_cuda_cluster_dims_too_large : Error<
+  "only a maximum of %0 thread blocks in a cluster is supported"
+>;
+
 // VTable pointer authentication errors
 def err_non_polymorphic_vtable_pointer_auth : Error<
   "cannot set vtable pointer authentication on monomorphic type %0">;

clang/include/clang/Sema/Sema.h

@@ -5010,6 +5010,14 @@ class Sema final : public SemaBase {
   void AddLaunchBoundsAttr(Decl *D, const AttributeCommonInfo &CI,
                            Expr *MaxThreads, Expr *MinBlocks, Expr *MaxBlocks);
 
+  /// Add a cluster_dims attribute to a particular declaration.
+  CUDAClusterDimsAttr *createClusterDimsAttr(const AttributeCommonInfo &CI,
+                                             Expr *X, Expr *Y, Expr *Z);
+  void addClusterDimsAttr(Decl *D, const AttributeCommonInfo &CI, Expr *X,
+                          Expr *Y, Expr *Z);
+  /// Add a no_cluster attribute to a particular declaration.
+  void addNoClusterAttr(Decl *D, const AttributeCommonInfo &CI);
+
   enum class RetainOwnershipKind { NS, CF, OS };
 
   UuidAttr *mergeUuidAttr(Decl *D, const AttributeCommonInfo &CI,

clang/lib/CodeGen/Targets/AMDGPU.cpp

@@ -342,6 +342,9 @@ static bool requiresAMDGPUProtectedVisibility(const Decl *D,
 
 void AMDGPUTargetCodeGenInfo::setFunctionDeclAttributes(
     const FunctionDecl *FD, llvm::Function *F, CodeGenModule &M) const {
+  llvm::StringMap<bool> TargetFetureMap;
+  M.getContext().getFunctionFeatureMap(TargetFetureMap, FD);
+
   const auto *ReqdWGS =
       M.getLangOpts().OpenCL ? FD->getAttr<ReqdWorkGroupSizeAttr>() : nullptr;
   const bool IsOpenCLKernel =
@@ -402,6 +405,29 @@ void AMDGPUTargetCodeGenInfo::setFunctionDeclAttributes(
 
     F->addFnAttr("amdgpu-max-num-workgroups", AttrVal.str());
   }
+
+  if (auto *Attr = FD->getAttr<CUDAClusterDimsAttr>()) {
+    uint32_t X =
+        Attr->getX()->EvaluateKnownConstInt(M.getContext()).getExtValue();
+    uint32_t Y =
+        Attr->getY()
+            ? Attr->getY()->EvaluateKnownConstInt(M.getContext()).getExtValue()
+            : 1;
+    uint32_t Z =
+        Attr->getZ()
+            ? Attr->getZ()->EvaluateKnownConstInt(M.getContext()).getExtValue()
+            : 1;
+
+    llvm::SmallString<32> AttrVal;
+    llvm::raw_svector_ostream OS(AttrVal);
+    OS << X << ',' << Y << ',' << Z;
+    F->addFnAttr("amdgpu-cluster-dims", AttrVal.str());
+  }
+
+  // OpenCL doesn't support cluster feature.
+  if ((IsOpenCLKernel && TargetFetureMap.lookup("gfx1250-insts")) ||
+      FD->getAttr<CUDANoClusterAttr>())
+    F->addFnAttr("amdgpu-cluster-dims", "0,0,0");
 }
 
 void AMDGPUTargetCodeGenInfo::setTargetAttributes(

clang/lib/Headers/__clang_hip_runtime_wrapper.h

@@ -25,6 +25,8 @@
 #define __constant__ __attribute__((constant))
 #define __managed__ __attribute__((managed))
 
+#define __cluster_dims__(...) __attribute__((cluster_dims(__VA_ARGS__)))
+
 #if !defined(__cplusplus) || __cplusplus < 201103L
   #define nullptr NULL;
 #endif

clang/lib/Sema/SemaDeclAttr.cpp

@@ -5676,6 +5676,130 @@ static void handleLaunchBoundsAttr(Sema &S, Decl *D, const ParsedAttr &AL) {
                         AL.getNumArgs() > 2 ? AL.getArgAsExpr(2) : nullptr);
 }
 
+static std::pair<Expr *, int>
+makeClusterDimsArgExpr(Sema &S, Expr *E, const CUDAClusterDimsAttr &AL,
+                       const unsigned Idx) {
+  if (S.DiagnoseUnexpandedParameterPack(E))
+    return {nullptr, 0};
+
+  // Accept template arguments for now as they depend on something else.
+  // We'll get to check them when they eventually get instantiated.
+  if (E->isValueDependent())
+    return {E, 1};
+
+  std::optional<llvm::APSInt> I = llvm::APSInt(64);
+  if (!(I = E->getIntegerConstantExpr(S.Context))) {
+    S.Diag(E->getExprLoc(), diag::err_attribute_argument_n_type)
+        << &AL << Idx << AANT_ArgumentIntegerConstant << E->getSourceRange();
+    return {nullptr, 0};
+  }
+  // Make sure we can fit it in 4 bits.
+  if (!I->isIntN(4)) {
+    S.Diag(E->getExprLoc(), diag::err_ice_too_large)
+        << toString(*I, 10, false) << 4 << /* Unsigned */ 1;
+    return {nullptr, 0};
+  }
+  if (*I < 0)
+    S.Diag(E->getExprLoc(), diag::warn_attribute_argument_n_negative)
+        << &AL << Idx << E->getSourceRange();
+
+  // We may need to perform implicit conversion of the argument.
+  InitializedEntity Entity = InitializedEntity::InitializeParameter(
+      S.Context, S.Context.getConstType(S.Context.IntTy), /*consume*/ false);
+  ExprResult ValArg = S.PerformCopyInitialization(Entity, SourceLocation(), E);
+  assert(!ValArg.isInvalid() &&
+         "Unexpected PerformCopyInitialization() failure.");
+
+  return {ValArg.getAs<Expr>(), I->getZExtValue()};
+}
+
+CUDAClusterDimsAttr *Sema::createClusterDimsAttr(const AttributeCommonInfo &CI,
+                                                 Expr *X, Expr *Y, Expr *Z) {
+  CUDAClusterDimsAttr TmpAttr(Context, CI, X, Y, Z);
+
+  int ValX = 1;
+  int ValY = 1;
+  int ValZ = 1;
+
+  std::tie(X, ValX) = makeClusterDimsArgExpr(*this, X, TmpAttr, /*Idx=*/0);
+  if (!X)
+    return nullptr;
+
+  if (Y) {
+    std::tie(Y, ValY) = makeClusterDimsArgExpr(*this, Y, TmpAttr, /*Idx=*/1);
+    if (!Y)
+      return nullptr;
+  }
+
+  if (Z) {
+    std::tie(Z, ValZ) = makeClusterDimsArgExpr(*this, Z, TmpAttr, /*Idx=*/2);
+    if (!Z)
+      return nullptr;
+  }
+
+  int FlatDim = ValX * ValY * ValZ;
+  auto TT = (!Context.getLangOpts().CUDAIsDevice && Context.getAuxTargetInfo())
+                ? Context.getAuxTargetInfo()->getTriple()
+                : Context.getTargetInfo().getTriple();
+  int MaxDim = 1;
+  if (TT.isNVPTX())
+    MaxDim = 8;
+  else if (TT.isAMDGPU())
+    MaxDim = 16;
+  else
+    return nullptr;
+
+  // A maximum of 8 thread blocks in a cluster is supported as a portable
+  // cluster size in CUDA. The number is 16 for AMDGPU.
+  if (FlatDim > MaxDim) {
+    Diag(CI.getLoc(), diag::err_cuda_cluster_dims_too_large) << MaxDim;
+    return nullptr;
+  }
+
+  return ::new (Context) CUDAClusterDimsAttr(Context, CI, X, Y, Z);
+}
+
+void Sema::addClusterDimsAttr(Decl *D, const AttributeCommonInfo &CI, Expr *X,
+                              Expr *Y, Expr *Z) {
+  if (auto *Attr = createClusterDimsAttr(CI, X, Y, Z))
+    D->addAttr(Attr);
+}
+
+void Sema::addNoClusterAttr(Decl *D, const AttributeCommonInfo &CI) {
+  if (CUDANoClusterAttr *Attr = ::new (Context) CUDANoClusterAttr(Context, CI))
+    D->addAttr(Attr);
+}
+
+static void handleClusterDimsAttr(Sema &S, Decl *D, const ParsedAttr &AL) {
+  auto &TTI = S.Context.getTargetInfo();
+  auto Arch = StringToOffloadArch(TTI.getTargetOpts().CPU);
+  if ((TTI.getTriple().isNVPTX() && Arch < clang::OffloadArch::SM_90) ||
+      (TTI.getTriple().isAMDGPU() && Arch < clang::OffloadArch::GFX1250)) {
+    S.Diag(AL.getLoc(), diag::err_cuda_cluster_attr_not_supported) << 0;
+    return;
+  }
+
+  if (!AL.checkAtLeastNumArgs(S, /*Num=*/1) ||
+      !AL.checkAtMostNumArgs(S, /*Num=*/3))
+    return;
+
+  S.addClusterDimsAttr(D, AL, AL.getArgAsExpr(0),
+                       AL.getNumArgs() > 1 ? AL.getArgAsExpr(1) : nullptr,
+                       AL.getNumArgs() > 2 ? AL.getArgAsExpr(2) : nullptr);
+}
+
+static void handleNoClusterAttr(Sema &S, Decl *D, const ParsedAttr &AL) {
+  auto &TTI = S.Context.getTargetInfo();
+  auto Arch = StringToOffloadArch(TTI.getTargetOpts().CPU);
+  if ((TTI.getTriple().isNVPTX() && Arch < clang::OffloadArch::SM_90) ||
+      (TTI.getTriple().isAMDGPU() && Arch < clang::OffloadArch::GFX1250)) {
+    S.Diag(AL.getLoc(), diag::err_cuda_cluster_attr_not_supported) << 1;
+    return;
+  }
+
+  S.addNoClusterAttr(D, AL);
+}
+
 static void handleArgumentWithTypeTagAttr(Sema &S, Decl *D,
                                           const ParsedAttr &AL) {
   if (!AL.isArgIdent(0)) {
@@ -7141,6 +7265,12 @@ ProcessDeclAttribute(Sema &S, Scope *scope, Decl *D, const ParsedAttr &AL,
   case ParsedAttr::AT_CUDALaunchBounds:
     handleLaunchBoundsAttr(S, D, AL);
     break;
+  case ParsedAttr::AT_CUDAClusterDims:
+    handleClusterDimsAttr(S, D, AL);
+    break;
+  case ParsedAttr::AT_CUDANoCluster:
+    handleNoClusterAttr(S, D, AL);
+    break;
   case ParsedAttr::AT_Restrict:
     handleRestrictAttr(S, D, AL);
     break;

clang/lib/Sema/SemaTemplateInstantiateDecl.cpp

@@ -707,6 +707,38 @@ static void instantiateDependentAMDGPUMaxNumWorkGroupsAttr(
     S.AMDGPU().addAMDGPUMaxNumWorkGroupsAttr(New, Attr, XExpr, YExpr, ZExpr);
 }
 
+static void instantiateDependentCUDAClusterDimsAttr(
+    Sema &S, const MultiLevelTemplateArgumentList &TemplateArgs,
+    const CUDAClusterDimsAttr &Attr, Decl *New) {
+  EnterExpressionEvaluationContext Unevaluated(
+      S, Sema::ExpressionEvaluationContext::ConstantEvaluated);
+
+  Expr *XExpr = nullptr;
+  Expr *YExpr = nullptr;
+  Expr *ZExpr = nullptr;
+
+  if (Attr.getX()) {
+    ExprResult ResultX = S.SubstExpr(Attr.getX(), TemplateArgs);
+    if (ResultX.isUsable())
+      XExpr = ResultX.getAs<Expr>();
+  }
+
+  if (Attr.getY()) {
+    ExprResult ResultY = S.SubstExpr(Attr.getY(), TemplateArgs);
+    if (ResultY.isUsable())
+      YExpr = ResultY.getAs<Expr>();
+  }
+
+  if (Attr.getZ()) {
+    ExprResult ResultZ = S.SubstExpr(Attr.getZ(), TemplateArgs);
+    if (ResultZ.isUsable())
+      ZExpr = ResultZ.getAs<Expr>();
+  }
+
+  if (XExpr)
+    S.addClusterDimsAttr(New, Attr, XExpr, YExpr, ZExpr);
+}
+
 // This doesn't take any template parameters, but we have a custom action that
 // needs to happen when the kernel itself is instantiated. We need to run the
 // ItaniumMangler to mark the names required to name this kernel.
@@ -921,6 +953,11 @@ void Sema::InstantiateAttrs(const MultiLevelTemplateArgumentList &TemplateArgs,
           *this, TemplateArgs, *AMDGPUMaxNumWorkGroups, New);
     }
 
+    if (const auto *CUDAClusterDims = dyn_cast<CUDAClusterDimsAttr>(TmplAttr)) {
+      instantiateDependentCUDAClusterDimsAttr(*this, TemplateArgs,
+                                              *CUDAClusterDims, New);
+    }
+
     if (const auto *ParamAttr = dyn_cast<HLSLParamModifierAttr>(TmplAttr)) {
       instantiateDependentHLSLParamModifierAttr(*this, TemplateArgs, ParamAttr,
                                                 New);

clang/test/CodeGenCUDA/Inputs/cuda.h

@@ -13,6 +13,8 @@
 #endif
 #define __launch_bounds__(...) __attribute__((launch_bounds(__VA_ARGS__)))
 #define __grid_constant__ __attribute__((grid_constant))
+#define __cluster_dims__(...) __attribute__((cluster_dims(__VA_ARGS__)))
+#define __no_cluster__ __attribute__((no_cluster))
 #else
 #define __constant__
 #define __device__
@@ -22,6 +24,8 @@
 #define __managed__
 #define __launch_bounds__(...)
 #define __grid_constant__
+#define __cluster_dims__(...)
+#define __no_cluster__
 #endif
 
 struct dim3 {

clang/test/CodeGenCUDA/cluster_dims.cu

@@ -0,0 +1,38 @@
+// RUN: %clang_cc1 -triple amdgcn-amd-amdhsa -target-cpu gfx1250 -fcuda-is-device -emit-llvm -x hip -o - %s | FileCheck %s
+// RUN: %clang_cc1 -triple x86_64-pc-linux-gnu -aux-triple amdgcn-amd-amdhsa -emit-llvm -x hip -o - %s | FileCheck --check-prefix=HOST %s
+
+#include "Inputs/cuda.h"
+
+const int constint = 4;
+
+// HOST-NOT: "amdgpu-cluster-dims"
+
+// CHECK: "amdgpu-cluster-dims"="2,2,2"
+__global__ void __cluster_dims__(2, 2, 2) test_literal_3d() {}
+
+// CHECK: "amdgpu-cluster-dims"="2,2,1"
+__global__ void __cluster_dims__(2, 2) test_literal_2d() {}
+
+// CHECK: "amdgpu-cluster-dims"="4,1,1"
+__global__ void __cluster_dims__(4) test_literal_1d() {}
+
+// CHECK: "amdgpu-cluster-dims"="4,2,1"
+__global__ void __cluster_dims__(constint, constint / 2, 1) test_constant() {}
+
+// CHECK: "amdgpu-cluster-dims"="0,0,0"
+__global__ void __no_cluster__ test_no_cluster() {}
+
+// CHECK: "amdgpu-cluster-dims"="7,1,1"
+template<unsigned a>
+__global__ void __cluster_dims__(a) test_template_1d() {}
+template __global__ void test_template_1d<7>();
+
+// CHECK: "amdgpu-cluster-dims"="2,6,1"
+template<unsigned a, unsigned b>
+__global__ void __cluster_dims__(a, b) test_template_2d() {}
+template __global__ void test_template_2d<2, 6>();
+
+// CHECK: "amdgpu-cluster-dims"="1,2,3"
+template<unsigned a, unsigned b, unsigned c>
+__global__ void __cluster_dims__(a, b, c) test_template_3d() {}
+template __global__ void test_template_3d<1, 2, 3>();

clang/test/Misc/pragma-attribute-supported-attributes-list.test

@@ -35,6 +35,7 @@
 // CHECK-NEXT: CFUnknownTransfer (SubjectMatchRule_function)
 // CHECK-NEXT: CPUDispatch (SubjectMatchRule_function)
 // CHECK-NEXT: CPUSpecific (SubjectMatchRule_function)
+// CHECK-NEXT: CUDAClusterDims (SubjectMatchRule_function)
 // CHECK-NEXT: CUDAConstant (SubjectMatchRule_variable)
 // CHECK-NEXT: CUDADevice (SubjectMatchRule_function, SubjectMatchRule_variable)
 // CHECK-NEXT: CUDADeviceBuiltinSurfaceType (SubjectMatchRule_record)
@@ -43,6 +44,7 @@
 // CHECK-NEXT: CUDAGridConstant (SubjectMatchRule_variable_is_parameter)
 // CHECK-NEXT: CUDAHost (SubjectMatchRule_function)
 // CHECK-NEXT: CUDALaunchBounds (SubjectMatchRule_objc_method, SubjectMatchRule_hasType_functionType)
+// CHECK-NEXT: CUDANoCluster (SubjectMatchRule_function)
 // CHECK-NEXT: CUDAShared (SubjectMatchRule_variable)
 // CHECK-NEXT: CXX11NoReturn (SubjectMatchRule_function)
 // CHECK-NEXT: CallableWhen (SubjectMatchRule_function_is_member)