[SYCL] Initial implementation of invoke_simd and uniform extensions. (#5871)

- invoke_simd:
https://github.com/intel/llvm/blob/sycl/sycl/doc/extensions/proposed/sycl_ext_oneapi_invoke_simd.asciidoc
  Current limitations:
  * bool parameter type not supported
- uniform:
https://github.com/intel/llvm/blob/sycl/sycl/doc/extensions/proposed/sycl_ext_oneapi_uniform.asciidoc

Signed-off-by: Konstantin S Bobrovsky <konstantin.s.bobrovsky@intel.com>
Contributions from Roland Schulz (@rolandschulz) <roland.schulz@intel.com>

Author: kbobrovs

sycl/include/sycl/ext/intel/esimd/simd.hpp

@@ -19,6 +19,8 @@
 #include <sycl/ext/intel/esimd/detail/types.hpp>
 #include <sycl/ext/intel/esimd/simd_view.hpp>
 
+#include <sycl/ext/oneapi/experimental/invoke_simd.hpp>
+
 #ifndef __SYCL_DEVICE_ONLY__
 #include <iostream>
 #endif // __SYCL_DEVICE_ONLY__
@@ -77,6 +79,15 @@ class simd : public detail::simd_obj_impl<
     __esimd_dbg_print(simd(const SimdT &RHS));
   }
 
+  // Implicit conversion constructor from sycl::ext::oneapi::experimental::simd
+  template <
+      int N1 = N, class Ty1 = Ty,
+      class SFINAE = std::enable_if_t<
+          (N1 == N) && (N1 <= std::experimental::simd_abi::max_fixed_size<
+                                  Ty>)&&!detail::is_wrapper_elem_type_v<Ty1>>>
+  simd(const sycl::ext::oneapi::experimental::simd<Ty, N1> &v)
+      : simd(static_cast<raw_vector_type>(v)) {}
+
   /// Broadcast constructor with conversion. Converts given value to
   /// #element_type and replicates it in all elements.
   /// Available when \c T1 is a valid simd element type.
@@ -101,6 +112,19 @@ class simd : public detail::simd_obj_impl<
     return detail::convert_scalar<To, element_type>(base_type::data()[0]);
   }
 
+  /// Implicitly converts this object to a sycl::ext::oneapi::experimental::simd
+  /// object. Available when the number of elements does not exceed maximum
+  /// fixed size of the oneapi's simd_abi and (TODO, temporary limitation) the
+  /// element type is a primitive type (e.g. can't be sycl::half).
+  template <
+      int N1, class Ty1 = Ty,
+      class SFINAE = std::enable_if_t<
+          (N1 == N) && (N1 <= std::experimental::simd_abi::max_fixed_size<
+                                  Ty>)&&!detail::is_wrapper_elem_type_v<Ty1>>>
+  operator sycl::ext::oneapi::experimental::simd<Ty, N1>() {
+    return sycl::ext::oneapi::experimental::simd<Ty, N1>(base_type::data());
+  }
+
   /// Prefix increment, increments elements of this object.
   /// @return Reference to this object.
   simd &operator++() {

sycl/include/sycl/ext/oneapi/experimental/invoke_simd.hpp

@@ -0,0 +1,324 @@
+//==------ invoke_simd.hpp - SYCL invoke_simd extension --*- C++ -*---------==//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+// ===--------------------------------------------------------------------=== //
+// Implemenation of the sycl_ext_oneapi_invoke_simd extension.
+// https://github.com/intel/llvm/blob/sycl/sycl/doc/extensions/proposed/sycl_ext_oneapi_invoke_simd.asciidoc
+// ===--------------------------------------------------------------------=== //
+
+#pragma once
+
+// SYCL extension macro definition as required by the SYCL specification.
+// 1 - Initial extension version. Base features are supported.
+#define SYCL_EXT_ONEAPI_INVOKE_SIMD 1
+
+#include <sycl/ext/oneapi/experimental/uniform.hpp>
+
+#include <CL/sycl/sub_group.hpp>
+#include <std/experimental/simd.hpp>
+#include <sycl/detail/boost/mp11.hpp>
+
+#include <functional>
+
+// TODOs:
+// * (a) TODO bool translation in spmd2simd.
+// * (b) TODO enforce constness of a functor/lambda's () operator
+// * (c) TODO support lambdas and functors in BE
+
+/// Middle End - to - Back End interface to invoke explicit SIMD functions from
+/// SPMD SYCL context. Must not be used by user code. BEs are expected to
+/// recognize this intrinsic and transform the intrinsic call with a direct call
+/// to the SIMD target, as well as process SPMD arguments in the way described
+/// in the specification for `invoke_simd`.
+/// @tparam SpmdRet the return type. Can be `uniform<T>`.
+/// @tparam SimdCallee the type of the SIMD callee function (the "target"). Must
+///  be a function type (not lambda or functor).
+/// @tparam SpmdArgs The original SPMD arguments passed to the invoke_simd.
+template <bool IsFunc, class SpmdRet, class SimdCallee, class... SpmdArgs,
+          class = std::enable_if_t<!IsFunc>>
+SYCL_EXTERNAL __regcall SpmdRet
+__builtin_invoke_simd(SimdCallee target, const void *obj, SpmdArgs... args)
+#ifdef __SYCL_DEVICE_ONLY__
+    ;
+#else
+{
+  // __builtin_invoke_simd is not supported on the host device yet
+  throw sycl::feature_not_supported();
+}
+#endif // __SYCL_DEVICE_ONLY__
+
+template <bool IsFunc, class SpmdRet, class SimdCallee, class... SpmdArgs,
+          class = std::enable_if_t<IsFunc>>
+SYCL_EXTERNAL __regcall SpmdRet __builtin_invoke_simd(SimdCallee target,
+                                                      SpmdArgs... args)
+#ifdef __SYCL_DEVICE_ONLY__
+    ;
+#else
+{
+  // __builtin_invoke_simd is not supported on the host device yet
+  throw sycl::feature_not_supported();
+}
+#endif // __SYCL_DEVICE_ONLY__
+
+namespace sycl {
+namespace ext {
+namespace oneapi {
+namespace experimental {
+
+// --- Basic definitions prescribed by the spec.
+namespace simd_abi {
+// "Fixed-size simd width of N" ABI based on clang vectors - used as the ABI for
+// SIMD objects this implementation of invoke_simd spec is based on.
+template <class T, int N>
+using native_fixed_size = typename std::experimental::__simd_abi<
+    std::experimental::_StorageKind::_VecExt, N>;
+} // namespace simd_abi
+
+// The SIMD object type, which is the generic std::experimental::simd type with
+// the native fixed size ABI.
+template <class T, int N>
+using simd = std::experimental::simd<T, simd_abi::native_fixed_size<T, N>>;
+
+// The SIMD mask object type.
+template <class T, int N>
+using simd_mask =
+    std::experimental::simd_mask<T, simd_abi::native_fixed_size<T, N>>;
+
+// --- Helpers
+namespace detail {
+
+namespace __MP11_NS = sycl::detail::boost::mp11;
+
+// This structure performs the SPMD-to-SIMD parameter type conversion as defined
+// by the spec.
+template <class T, int N, class = void> struct spmd2simd;
+// * `uniform<T>` converts to `T`
+template <class T, int N> struct spmd2simd<uniform<T>, N> {
+  using type = T;
+};
+// * tuple of types converts to tuple of converted tuple element types.
+template <class... T, int N> struct spmd2simd<std::tuple<T...>, N> {
+  using type = std::tuple<typename spmd2simd<T, N>::type...>;
+};
+// * arithmetic type converts to a simd vector with this element type and the
+//   width equal to caller's subgroup size and passed as the `N` template
+//   argument.
+template <class T, int N>
+struct spmd2simd<T, N, std::enable_if_t<std::is_arithmetic_v<T>>> {
+  using type = simd<T, N>;
+};
+
+// This structure performs the SIMD-to-SPMD return type conversion as defined
+// by the spec.
+template <class, class = void> struct simd2spmd;
+// * `uniform<T>` stays the same
+template <class T> struct simd2spmd<uniform<T>> {
+  using type = uniform<T>;
+};
+// * `simd<T, N>` converts to T
+template <class T, int N> struct simd2spmd<simd<T, N>> {
+  using type = T;
+};
+// * tuple of types converts to tuple of converted tuple element types.
+template <class... T> struct simd2spmd<std::tuple<T...>> {
+  using type = std::tuple<typename simd2spmd<T>::type...>;
+};
+// * arithmetic type T converts to `uniform<T>`
+template <class T>
+struct simd2spmd<T, std::enable_if_t<std::is_arithmetic_v<T>>> {
+  using type = uniform<T>;
+};
+
+// Check if given type is uniform.
+template <class T> struct is_uniform_type : std::false_type {};
+template <class T> struct is_uniform_type<uniform<T>> : std::true_type {
+  using type = T;
+};
+
+// Check if given type is simd or simd_mask.
+template <class T> struct is_simd_or_mask_type : std::false_type {};
+template <class T, int N>
+struct is_simd_or_mask_type<simd<T, N>> : std::true_type {};
+template <class T, int N>
+struct is_simd_or_mask_type<simd_mask<T, N>> : std::true_type {};
+
+// Checks if the return value type and the types of arguments of given
+// SimdCallable are all uniform.
+template <class SimdCallable, class... SpmdArgs> struct has_uniform_signature {
+  constexpr operator bool() {
+    using ArgTypeList = __MP11_NS::mp_list<SpmdArgs...>;
+
+    if constexpr (__MP11_NS::mp_all_of<ArgTypeList, is_uniform_type>::value) {
+      using SimdRet = std::invoke_result_t<SimdCallable, SpmdArgs...>;
+      return is_uniform_type<SimdRet>::value ||
+             !is_simd_or_mask_type<SimdRet>::value;
+    } else {
+      return false;
+    }
+  }
+};
+
+// "Unwraps" a value of the `uniform` type (used before passing to SPMD
+//  arguments to the __builtin_invoke_simd):
+// - the case when there is nothing to unwrap
+template <typename T> struct unwrap_uniform {
+  static auto impl(T val) { return val; }
+};
+
+// - the real unwrapping case
+template <typename T> struct unwrap_uniform<uniform<T>> {
+  static T impl(uniform<T> val) { return val; }
+};
+
+// Deduces subgroup size of the caller based on given SIMD callable and
+// corresponding SPMD arguments it is being invoke with via invoke_simd.
+// Basically, for each supported subgroup size, this meta-function finds out if
+// the callable can be invoked by C++ rules given the SPMD arguments transformed
+// as prescribed by the spec assuming this subgroup size. One and only one
+// subgroup size should conform.
+template <class SimdCallable, class... SpmdArgs> struct sg_size {
+  template <class N>
+  using IsInvocableSgSize = __MP11_NS::mp_bool<std::is_invocable_v<
+      SimdCallable, typename spmd2simd<SpmdArgs, N::value>::type...>>;
+
+  constexpr operator int() {
+    using SupportedSgSizes = __MP11_NS::mp_list_c<int, 1, 2, 4, 8, 16, 32>;
+    using InvocableSgSizes =
+        __MP11_NS::mp_copy_if<SupportedSgSizes, IsInvocableSgSize>;
+    static_assert((__MP11_NS::mp_size<InvocableSgSizes>::value == 1) &&
+                  "no or multiple invoke_simd targets found");
+    return __MP11_NS::mp_front<InvocableSgSizes>::value;
+  }
+};
+
+// Determine the return type of a SIMD callable.
+template <int N, class SimdCallable, class... SpmdArgs>
+using SimdRetType =
+    std::invoke_result_t<SimdCallable,
+                         typename spmd2simd<SpmdArgs, N>::type...>;
+// Determine the return type of an invoke_simd based on the return type of a
+// SIMD callable.
+template <int N, class SimdCallable, class... SpmdArgs>
+using SpmdRetType =
+    typename simd2spmd<SimdRetType<N, SimdCallable, SpmdArgs...>>::type;
+
+template <class SimdCallable, class... SpmdArgs>
+static constexpr int get_sg_size() {
+  if constexpr (has_uniform_signature<SimdCallable, SpmdArgs...>()) {
+    return 0; // subgroup size does not matter then
+  } else {
+    return sg_size<SimdCallable, SpmdArgs...>();
+  }
+}
+
+// This function is a wrapper around a call to a functor with field or a lambda
+// with captures. Note __regcall - this is needed for efficient argument
+// forwarding.
+template <int N, class Callable, class... T>
+__regcall detail::SimdRetType<N, Callable, T...>
+simd_call_helper(const void *obj_ptr,
+                 typename detail::spmd2simd<T, N>::type... simd_args) {
+  auto f =
+      *reinterpret_cast<const std::remove_reference_t<Callable> *>(obj_ptr);
+  return f(simd_args...);
+};
+
+#ifdef _GLIBCXX_RELEASE
+#if _GLIBCXX_RELEASE < 10
+#define __INVOKE_SIMD_USE_STD_IS_FUNCTION_WA
+#endif // _GLIBCXX_RELEASE < 10
+#endif // _GLIBCXX_RELEASE
+
+#ifdef __INVOKE_SIMD_USE_STD_IS_FUNCTION_WA
+// TODO This is a workaround for libstdc++ version 9 buggy behavior which
+// returns false in the code below. Version 10 works fine. Once required
+// minimum libstdc++ version is bumped to 10, this w/a should be removed.
+//   template <class F> bool foo(F &&f) {
+//     return std::is_function_v<std::remove_reference_t<F>>;
+//   }
+// where F is a function type with __regcall.
+template <class F> struct is_regcall_function_ptr_or_ref : std::false_type {};
+
+template <class Ret, class... Args>
+struct is_regcall_function_ptr_or_ref<Ret(__regcall &)(Args...)>
+    : std::true_type {};
+
+template <class Ret, class... Args>
+struct is_regcall_function_ptr_or_ref<Ret(__regcall *)(Args...)>
+    : std::true_type {};
+
+template <class Ret, class... Args>
+struct is_regcall_function_ptr_or_ref<Ret(__regcall *&)(Args...)>
+    : std::true_type {};
+
+template <class F>
+static constexpr bool is_regcall_function_ptr_or_ref_v =
+    is_regcall_function_ptr_or_ref<F>::value;
+#endif // __INVOKE_SIMD_USE_STD_IS_FUNCTION_WA
+
+template <class Callable>
+static constexpr bool is_function_ptr_or_ref_v =
+    std::is_function_v<std::remove_pointer_t<std::remove_reference_t<Callable>>>
+#ifdef __INVOKE_SIMD_USE_STD_IS_FUNCTION_WA
+    || is_regcall_function_ptr_or_ref_v<Callable>
+#endif // __INVOKE_SIMD_USE_STD_IS_FUNCTION_WA
+    ;
+} // namespace detail
+
+// --- The main API
+
+/// The invoke_simd free function invokes a SIMD function using all work-items
+/// in a sub_group. The invoke_simd interface marshals data between the SPMD
+/// context of the calling kernel and the SIMD context of the callee, converting
+/// arguments and return values between scalar and SIMD types as appropriate.
+///
+/// @param sg the subgroup simd function is invoked from
+/// @param f represents the invoked simd function.
+///   Must be a C++ callable that can be invoked with the same number of
+///   arguments specified in the args parameter pack. Callable may be a function
+///   object, a lambda, or a function pointer (if the device supports
+///   SPV_INTEL_function_pointers). Callable must be an immutable callable with
+///   the same type and state for all work-items in the sub-group, otherwise
+///   behavior is undefined.
+/// @param args SPMD parameters to the invoked function, which undergo
+///   transformation before actual passing to the simd function, as described in
+///   the specification.
+// TODO works only for functions now, enable for other callables.
+template <class Callable, class... T>
+__attribute__((always_inline)) auto invoke_simd(sycl::sub_group sg,
+                                                Callable &&f, T... args) {
+  // If the invoke_simd call site is fully uniform, then it does not matter
+  // what the subgroup size is and arguments don't need widening and return
+  // value does not need shrinking by this library or SPMD compiler, so 0
+  // is fine in this case.
+  constexpr int N = detail::get_sg_size<Callable, T...>();
+  using RetSpmd = detail::SpmdRetType<N, Callable, T...>;
+  constexpr bool is_function = detail::is_function_ptr_or_ref_v<Callable>;
+
+  if constexpr (is_function) {
+    return __builtin_invoke_simd<is_function, RetSpmd>(
+        f, detail::unwrap_uniform<T>::impl(args)...);
+  } else {
+    // TODO support functors and lambdas which are handled in this branch.
+    // The limiting factor for now is that the LLVMIR data flow analysis
+    // implemented in LowerInvokeSimd.cpp which, finds actual invoke_simd
+    // target function, can't handle this case yet.
+    return __builtin_invoke_simd<is_function, RetSpmd>(
+        detail::simd_call_helper<N, Callable, T...>, &f,
+        detail::unwrap_uniform<T>::impl(args)...);
+  }
+// TODO Temporary macro and assert to enable API compilation testing.
+// LowerInvokeSimd.cpp does not support this case yet.
+#ifndef __INVOKE_SIMD_ENABLE_ALL_CALLABLES
+  static_assert(is_function &&
+                "invoke_simd does not support functors or lambdas yet");
+#endif // __INVOKE_SIMD_ENABLE_ALL_CALLABLES
+}
+
+} // namespace experimental
+} // namespace oneapi
+} // namespace ext
+} // namespace sycl