[SYCL] Implemented SYCL 2020 sub-group size functionality. (#3444)

As specified here:
https://github.com/intel/llvm/blob/sycl/sycl/doc/extensions/SubGroup/SYCL_INTEL_sub_group.asciidoc#attributes

This patch implements the named_sub_group_size attribute as well as the
command line parameter, and creates a new spelling of
reqd_sub_group_size (sub_group_size) to work like the SYCL 2020 version.

Author: Erich Keane

clang/include/clang/Basic/Attr.td

@@ -1213,6 +1213,7 @@ def SYCLSimd : InheritableAttr {
   let Subjects = SubjectList<[Function, GlobalVar]>;
   let Documentation = [SYCLSimdDocs];
   let SupportsNonconformingLambdaSyntax = 1;
+  let SimpleHandler = 1;
 }
 
 // Available in SYCL explicit SIMD extension. Binds a file scope private
@@ -1431,15 +1432,32 @@ def LoopUnrollHint : StmtAttr {
 }
 
 def IntelReqdSubGroupSize: InheritableAttr {
-  let Spellings = [GNU<"intel_reqd_sub_group_size">,
-                   CXX11<"intel", "reqd_sub_group_size">];
+  let Spellings = [
+    GNU<"intel_reqd_sub_group_size">, CXX11<"intel", "reqd_sub_group_size">,
+    CXX11<"intel", "sub_group_size"> // SYCL2020 spelling.
+  ];
   let Args = [ExprArgument<"Value">];
   let Subjects = SubjectList<[Function], ErrorDiag>;
   let Documentation = [IntelReqdSubGroupSizeDocs];
   let LangOpts = [OpenCL, SYCLIsDevice, SilentlyIgnoreSYCLIsHost];
   let SupportsNonconformingLambdaSyntax = 1;
+  let Accessors =
+    [Accessor<"isSYCL2020Spelling", [CXX11<"intel", "sub_group_size">]>];
 }
 
+def IntelNamedSubGroupSize : InheritableAttr {
+  let Spellings = [CXX11<"intel", "named_sub_group_size">];
+  let Args = [EnumArgument<"Type", "SubGroupSizeType", ["automatic", "primary"],
+                           ["Automatic", "Primary"]>];
+  let Subjects = SubjectList<[Function], ErrorDiag>;
+  let Documentation = [IntelNamedSubGroupSizeDocs];
+  let LangOpts = [OpenCL, SYCLIsDevice, SilentlyIgnoreSYCLIsHost];
+  let SupportsNonconformingLambdaSyntax = 1;
+}
+
+def :
+  MutualExclusions<[IntelReqdSubGroupSize, IntelNamedSubGroupSize, SYCLSimd]>;
+
 // This attribute is both a type attribute, and a declaration attribute (for
 // parameter variables).
 def OpenCLAccess : Attr {

clang/include/clang/Basic/AttrDocs.td

@@ -4354,9 +4354,9 @@ This attribute can be used in both OpenCL and SYCL.
 
 OpenCL documentation:
 The optional attribute intel_reqd_sub_group_size can be used to indicate that
-the kernel must be compiled and executed with the specified subgroup size. When
+the kernel must be compiled and executed with the specified sub group size. When
 this attribute is present, get_max_sub_group_size() is guaranteed to return the
-specified integer value. This is important for the correctness of many subgroup
+specified integer value. This is important for the correctness of many sub group
 algorithms, and in some cases may be used by the compiler to generate more optimal
 code. See `cl_intel_required_subgroup_size
 <https://www.khronos.org/registry/OpenCL/extensions/intel/cl_intel_required_subgroup_size.txt>`
@@ -4367,6 +4367,13 @@ The [[intel::reqd_sub_group_size(n)]] attribute indicates that the kernel must
 be compiled and executed with a sub-group of size n. The value of n must be set
 to a sub-group size supported by the device, or device compilation will fail.
 
+The ``[[intel::sub_group_size(n)]]`` attribute has the same effect as the other
+attribute spellings, except that it follows the SYCL 2020 Attribute Rules. See
+ the ``[[intel::named_sub_group_size(NAME)]]`` documentation for clarification.
+
+This attribute is mutually exclusive with ``[[intel::named_sub_group_size(NAME)]]``
+and ``[[intel::sycl_explicit_simd]]``.
+
 In addition to device functions, the required sub-group size attribute may also
 be specified in the definition of a named functor object and lambda functions,
 as in the examples below:
@@ -4390,6 +4397,47 @@ See Sub-groups for NDRange Parallelism proposal in sycl/doc/extensions/sub_group
   }];
 }
 
+def IntelNamedSubGroupSizeDocs : Documentation {
+  let Category = DocCatFunction;
+  let Content = [{
+The ``[[intel::named_sub_group_size(NAME)]]`` attribute works similar to
+``[[intel::sub_group_size(N)]]`` attribute in that it defines the specific
+sub group size for the kernel. The ``[[intel::named_sub_group_size(NAME)]]``
+form accepts a required parameter of either ``automatic`` or ``primary``.
+
+``automatic`` specifies that the implementation is free to select any of the
+valid sub-group sizes associated with the device to which the kernel is
+submitted.  ``primary`` specifies that the implementation should select the
+device's primary sub-group size as reported by
+``info::device::primary_sub_group_size``.
+
+This attribute may not be combined with ``[[intel::sub_group_size(N)]]``, as
+the two attributes have different meanings. It is also mutually exclusive with
+``[[intel::sycl_explicit_simd]]``.
+
+In addition to the attributes, a default sub-group size strategy may be
+specified by the ``-fsycl-default-sub-group-size`` command line option, which
+accepts either ``automatic``, ``primary``, or a default size as an integer.
+These values match and have the same behavior as the ``automatic``, ``primary``,
+and ``[[intel::sub_group_size(N)]]`` values respectively.
+
+SYCL 2020 Attribute Rules:
+SYCL 2020 specifies that kernel-type attributes should only be specified on the
+kernel or a ``SYCL_EXTERNAL`` function. This implementation permits these
+attributes to appear on all function declarations for the purposes of
+self-documenting declarations. However, these attributes must match the kernel's
+sub-group size as configured by the command line, or via an attribute
+specifically.
+
+In addition to the SYCL 2020 Attribute Rules, this attribute and the
+``[[intel::sub_group_size(N)]]`` attribute also require that any
+``SYCL_EXTERNAL`` functions defined in a different translation unit must have a
+matching sub-group size specification, so ``SYCL_EXTERNAL`` functions not
+defined in this translation unit must also have a matching sub-group
+specification to the kernel function that calls it.
+}];
+}
+
 def OpenCLAccessDocs : Documentation {
   let Category = DocCatStmt;
   let Heading = "__read_only, __write_only, __read_write (read_only, write_only, read_write)";

clang/include/clang/Basic/DiagnosticSemaKinds.td

@@ -11317,6 +11317,11 @@ def note_spelling_suggestion : Note<
   "did you mean to use %0 instead?">;
 def warn_attribute_requires_non_negative_integer_argument :
   Warning<warn_impcast_integer_sign.Text>, InGroup<AcceptedAttributes>;
+def err_sycl_mismatch_group_size
+    : Error<"%select{kernel-called|undefined 'SYCL_EXTERNAL'}0 function must "
+            "have a sub group size that matches the size specified for the "
+            "kernel">;
+def note_sycl_kernel_declared_here : Note<"kernel declared here">;
 
 // errors of expect.with.probability
 def err_probability_not_constant_float : Error<

clang/include/clang/Basic/LangOptions.def

@@ -423,6 +423,14 @@ LANGOPT(RelativeCXXABIVTables, 1, 0,
 
 LANGOPT(ArmSveVectorBits, 32, 0, "SVE vector size in bits")
 
+ENUM_LANGOPT(DefaultSubGroupSizeType, SubGroupSizeType, 2,
+             SubGroupSizeType::None,
+             "Strategy via which sub group is assigned for SYCL kernel "
+             "types if not overridden via attributes")
+
+VALUE_LANGOPT(DefaultSubGroupSize, 32, 0,
+              "If DefaultSubGroupSizeType is Integer contains the value")
+
 #undef LANGOPT
 #undef COMPATIBLE_LANGOPT
 #undef BENIGN_LANGOPT

clang/include/clang/Basic/LangOptions.h

@@ -264,6 +264,8 @@ class LangOptions : public LangOptionsBase {
     Single
   };
 
+  enum class SubGroupSizeType { None, Auto, Primary, Integer };
+
 public:
   /// The used language standard.
   LangStandard::Kind LangStd;

clang/include/clang/Driver/Options.td

@@ -5728,6 +5728,14 @@ def sycl_std_EQ : Joined<["-"], "sycl-std=">, Group<sycl_Group>,
   MarshallingInfoEnum<LangOpts<"SYCLVersion">, "SYCL_None">,
   ShouldParseIf<!strconcat(fsycl_is_device.KeyPath, "||", fsycl_is_host.KeyPath)>;
 
+def fsycl_default_sub_group_size
+    : Separate<["-"], "fsycl-default-sub-group-size">,
+      HelpText<"Set the default sub group size for SYCL kernels">,
+      Flags<[CC1Option]>;
+def fsycl_default_sub_group_size_EQ
+    : Joined<["-"], "fsycl-default-sub-group-size=">,
+      Alias<fsycl_default_sub_group_size>, Flags<[CC1Option]>;
+
 defm cuda_approx_transcendentals : BoolFOption<"cuda-approx-transcendentals",
   LangOpts<"CUDADeviceApproxTranscendentals">, DefaultFalse,
   PosFlag<SetTrue, [CC1Option], "Use">, NegFlag<SetFalse, [], "Don't use">,

clang/include/clang/Sema/Sema.h

@@ -10275,6 +10275,8 @@ class Sema final {
                                 Expr *E);
   IntelReqdSubGroupSizeAttr *
   MergeIntelReqdSubGroupSizeAttr(Decl *D, const IntelReqdSubGroupSizeAttr &A);
+  IntelNamedSubGroupSizeAttr *
+  MergeIntelNamedSubGroupSizeAttr(Decl *D, const IntelNamedSubGroupSizeAttr &A);
   void AddSYCLIntelNumSimdWorkItemsAttr(Decl *D, const AttributeCommonInfo &CI,
                                         Expr *E);
   SYCLIntelNumSimdWorkItemsAttr *

clang/lib/CodeGen/CodeGenFunction.cpp

@@ -592,7 +592,7 @@ CodeGenFunction::DecodeAddrUsedInPrologue(llvm::Value *F,
 void CodeGenFunction::EmitOpenCLKernelMetadata(const FunctionDecl *FD,
                                                llvm::Function *Fn)
 {
-  if (!FD->hasAttr<OpenCLKernelAttr>())
+  if (!FD->hasAttr<OpenCLKernelAttr>() && !FD->hasAttr<SYCLDeviceAttr>())
     return;
 
   // TODO Module identifier is not reliable for this purpose since two modules
@@ -602,7 +602,8 @@ void CodeGenFunction::EmitOpenCLKernelMetadata(const FunctionDecl *FD,
 
   llvm::LLVMContext &Context = getLLVMContext();
 
-  CGM.GenOpenCLArgMetadata(Fn, FD, this);
+  if (FD->hasAttr<OpenCLKernelAttr>())
+    CGM.GenOpenCLArgMetadata(Fn, FD, this);
 
   if (const VecTypeHintAttr *A = FD->getAttr<VecTypeHintAttr>()) {
     QualType HintQTy = A->getTypeHint();
@@ -648,15 +649,52 @@ void CodeGenFunction::EmitOpenCLKernelMetadata(const FunctionDecl *FD,
                     llvm::MDNode::get(Context, AttrMDArgs));
   }
 
-  if (const IntelReqdSubGroupSizeAttr *A =
-          FD->getAttr<IntelReqdSubGroupSizeAttr>()) {
-    const auto *CE = dyn_cast<ConstantExpr>(A->getValue());
+  bool IsKernelOrDevice =
+      FD->hasAttr<SYCLKernelAttr>() || FD->hasAttr<SYCLDeviceAttr>();
+  const IntelReqdSubGroupSizeAttr *ReqSubGroup =
+      FD->getAttr<IntelReqdSubGroupSizeAttr>();
+
+  // To support the SYCL 2020 spelling with no propagation, only emit for
+  // kernel-or-device when that spelling, fall-back to old behavior.
+  if (ReqSubGroup && (IsKernelOrDevice || !ReqSubGroup->isSYCL2020Spelling())) {
+    const auto *CE = dyn_cast<ConstantExpr>(ReqSubGroup->getValue());
     assert(CE && "Not an integer constant expression");
     Optional<llvm::APSInt> ArgVal = CE->getResultAsAPSInt();
     llvm::Metadata *AttrMDArgs[] = {llvm::ConstantAsMetadata::get(
         Builder.getInt32(ArgVal->getSExtValue()))};
     Fn->setMetadata("intel_reqd_sub_group_size",
                     llvm::MDNode::get(Context, AttrMDArgs));
+  } else if (IsKernelOrDevice &&
+             CGM.getLangOpts().getDefaultSubGroupSizeType() ==
+                 LangOptions::SubGroupSizeType::Integer) {
+    llvm::Metadata *AttrMDArgs[] = {llvm::ConstantAsMetadata::get(
+        Builder.getInt32(CGM.getLangOpts().DefaultSubGroupSize))};
+    Fn->setMetadata("intel_reqd_sub_group_size",
+                    llvm::MDNode::get(Context, AttrMDArgs));
+  }
+
+  // SCYL2020 doesn't propagate attributes, so don't put it in an intermediate
+  // location.
+  if (IsKernelOrDevice) {
+    if (const auto *A = FD->getAttr<IntelNamedSubGroupSizeAttr>()) {
+      llvm::Metadata *AttrMDArgs[] = {llvm::MDString::get(
+          Context, A->getType() == IntelNamedSubGroupSizeAttr::Primary
+                       ? "primary"
+                       : "automatic")};
+      Fn->setMetadata("intel_reqd_sub_group_size",
+                      llvm::MDNode::get(Context, AttrMDArgs));
+    } else if (CGM.getLangOpts().getDefaultSubGroupSizeType() ==
+               LangOptions::SubGroupSizeType::Auto) {
+      llvm::Metadata *AttrMDArgs[] = {
+          llvm::MDString::get(Context, "automatic")};
+      Fn->setMetadata("intel_reqd_sub_group_size",
+                      llvm::MDNode::get(Context, AttrMDArgs));
+    } else if (CGM.getLangOpts().getDefaultSubGroupSizeType() ==
+               LangOptions::SubGroupSizeType::Primary) {
+      llvm::Metadata *AttrMDArgs[] = {llvm::MDString::get(Context, "primary")};
+      Fn->setMetadata("intel_reqd_sub_group_size",
+                      llvm::MDNode::get(Context, AttrMDArgs));
+    }
   }
 
   if (FD->hasAttr<SYCLSimdAttr>()) {

clang/lib/Driver/ToolChains/Clang.cpp

@@ -4394,6 +4394,9 @@ void Clang::ConstructJob(Compilation &C, const JobAction &JA,
       HeaderOpt.append(Header);
       CmdArgs.push_back(Args.MakeArgString(HeaderOpt));
     }
+
+    // Forward -fsycl-default-sub-group-size if in SYCL mode.
+    Args.AddLastArg(CmdArgs, options::OPT_fsycl_default_sub_group_size);
   }
 
   if (IsSYCL) {

clang/lib/Frontend/CompilerInvocation.cpp

@@ -3502,6 +3502,20 @@ void CompilerInvocation::GenerateLangArgs(const LangOptions &Opts,
       LangOptions::SignReturnAddressKeyKind::BKey)
     GenerateArg(Args, OPT_msign_return_address_key_EQ, "b_key", SA);
 
+  switch (Opts.getDefaultSubGroupSizeType()) {
+  case LangOptions::SubGroupSizeType::Auto:
+    GenerateArg(Args, OPT_fsycl_default_sub_group_size, "automatic", SA);
+    break;
+  case LangOptions::SubGroupSizeType::Primary:
+    GenerateArg(Args, OPT_fsycl_default_sub_group_size, "primary", SA);
+    break;
+  case LangOptions::SubGroupSizeType::Integer:
+    GenerateArg(Args, OPT_fsycl_default_sub_group_size,
+                Twine(Opts.DefaultSubGroupSize), SA);
+    break;
+  case LangOptions::SubGroupSizeType::None:
+    break;
+  }
 }
 
 bool CompilerInvocation::ParseLangArgs(LangOptions &Opts, ArgList &Args,
@@ -3592,6 +3606,28 @@ bool CompilerInvocation::ParseLangArgs(LangOptions &Opts, ArgList &Args,
     }
   }
 
+  // Parse SYCL Default Sub group size.
+  if (const Arg *A = Args.getLastArg(OPT_fsycl_default_sub_group_size)) {
+    StringRef Value = A->getValue();
+    Opts.setDefaultSubGroupSizeType(
+        llvm::StringSwitch<LangOptions::SubGroupSizeType>(Value)
+            .Case("automatic", LangOptions::SubGroupSizeType::Auto)
+            .Case("primary", LangOptions::SubGroupSizeType::Primary)
+            .Default(LangOptions::SubGroupSizeType::Integer));
+
+    if (Opts.getDefaultSubGroupSizeType() ==
+        LangOptions::SubGroupSizeType::Integer) {
+      int64_t IntResult;
+      if (!Value.getAsInteger(10, IntResult)) {
+        Opts.DefaultSubGroupSize = IntResult;
+      } else {
+        Diags.Report(diag::err_drv_invalid_value)
+            << A->getAsString(Args) << A->getValue();
+        Opts.setDefaultSubGroupSizeType(LangOptions::SubGroupSizeType::None);
+      }
+    }
+  }
+
   // These need to be parsed now. They are used to set OpenCL defaults.
   Opts.IncludeDefaultHeader = Args.hasArg(OPT_finclude_default_header);
   Opts.DeclareOpenCLBuiltins = Args.hasArg(OPT_fdeclare_opencl_builtins);