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[libc] Implement vector 'split' and 'concat' routines
Summary: This provides some helpers for the split and concatenation routines for changing the size of an existing vector. This includes a simple tuple type to do the splitting. The tuple doesn't support structured bindings yet. The concat function is more limited than what would be ideal, but the shufflevector builtin requires things of equivalent sizes and I didn't think it was worth wrangling with that just yet.
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‎libc/src/__support/CPP/CMakeLists.txt‎

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@@ -223,4 +223,7 @@ add_header_library(
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simd
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HDRS
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simd.h
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DEPENDS
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.utility
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.tuple
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)

‎libc/src/__support/CPP/simd.h‎

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@@ -16,7 +16,9 @@
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#include "hdr/stdint_proxy.h"
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#include "src/__support/CPP/algorithm.h"
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#include "src/__support/CPP/limits.h"
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#include "src/__support/CPP/tuple.h"
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#include "src/__support/CPP/type_traits.h"
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#include "src/__support/CPP/utility/integer_sequence.h"
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#include "src/__support/macros/attributes.h"
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#include "src/__support/macros/config.h"
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@@ -51,6 +53,7 @@ template <typename T> inline constexpr size_t native_vector_size = 1;
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template <typename T> LIBC_INLINE constexpr T poison() {
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return __builtin_nondeterministic_value(T());
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}
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} // namespace internal
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// Type aliases.
@@ -267,6 +270,77 @@ LIBC_INLINE constexpr simd<T, N> select(simd<bool, N> m, simd<T, N> x,
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return m ? x : y;
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}
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namespace internal {
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template <typename T, size_t N, size_t O, size_t... I>
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LIBC_INLINE constexpr static cpp::simd<T, sizeof...(I)>
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extend(cpp::simd<T, N> x, cpp::index_sequence<I...>) {
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return __builtin_shufflevector(x, x, (I < O ? static_cast<int>(I) : -1)...);
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}
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template <typename T, size_t N, size_t M, size_t O>
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LIBC_INLINE constexpr static auto extend(cpp::simd<T, N> x) {
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if constexpr (N == M)
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return x;
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else if constexpr (M <= 2 * N)
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return extend<T, N, M>(x, cpp::make_index_sequence<M>{});
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else
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return extend<T, 2 * N, M, O>(
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extend<T, N, 2 * N>(x, cpp::make_index_sequence<2 * N>{}));
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}
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template <typename T, size_t N, size_t M, size_t... I>
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LIBC_INLINE constexpr static cpp::simd<T, N + M>
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concat(cpp::simd<T, N> x, cpp::simd<T, M> y, cpp::index_sequence<I...>) {
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constexpr size_t L = (N > M ? N : M);
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auto x_ext = extend<T, N, L, N>(x);
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auto y_ext = extend<T, M, L, M>(y);
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auto remap = [](size_t idx) -> int {
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if (idx < N)
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return static_cast<int>(idx);
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if (idx < N + M)
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return static_cast<int>((idx - N) + L);
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return -1;
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};
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return __builtin_shufflevector(x_ext, y_ext, remap(I)...);
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}
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template <typename T, size_t N, size_t Count, size_t Offset, size_t... I>
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LIBC_INLINE constexpr static cpp::simd<T, Count>
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slice(cpp::simd<T, N> x, cpp::index_sequence<I...>) {
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return __builtin_shufflevector(x, x, (Offset + I)...);
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}
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template <typename T, size_t N, size_t Offset, size_t Head, size_t... Tail>
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LIBC_INLINE constexpr static auto split(cpp::simd<T, N> x) {
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auto first = cpp::make_tuple(
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slice<T, N, Head, Offset>(x, cpp::make_index_sequence<Head>{}));
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if constexpr (sizeof...(Tail) > 0)
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return cpp::tuple_cat(first, split<T, N, Offset + Head, Tail...>(x));
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else
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return first;
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}
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} // namespace internal
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// Shuffling helpers.
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template <typename T, size_t N, size_t M>
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LIBC_INLINE constexpr static auto concat(cpp::simd<T, N> x, cpp::simd<T, M> y) {
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return internal::concat(x, y, make_index_sequence<N + M>{});
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}
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template <typename T, size_t N, size_t M, typename... Rest>
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LIBC_INLINE constexpr static auto concat(cpp::simd<T, N> x, cpp::simd<T, M> y,
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Rest... rest) {
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auto xy = concat(x, y);
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if constexpr (sizeof...(Rest))
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return concat(xy, rest...);
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else
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return xy;
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}
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template <size_t... Sizes, typename T, size_t N> auto split(cpp::simd<T, N> x) {
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static_assert((... + Sizes) == N, "split sizes must sum to vector size");
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return internal::split<T, N, 0, Sizes...>(x);
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}
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// TODO: where expressions, scalar overloads, ABI types.
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} // namespace cpp

‎libc/test/src/__support/CPP/simd_test.cpp‎

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@@ -68,3 +68,28 @@ TEST(LlvmLibcSIMDTest, MaskOperations) {
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EXPECT_EQ(find_first_set(mask), 0);
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EXPECT_EQ(find_last_set(mask), 2);
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}
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TEST(LlvmLibcSIMDTest, SplitConcat) {
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simd<char, 8> v(1);
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auto [v1, v2, v3, v4] = split<2, 2, 2, 2>(v);
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static_assert(
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simd_size_v<decltype(v1)> == 2 && simd_size_v<decltype(v2)> == 2 &&
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simd_size_v<decltype(v3)> == 2 && simd_size_v<decltype(v4)> == 2,
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"invalid size");
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v1 = simd<char, 2>(1);
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v2 = simd<char, 2>(2);
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v3 = simd<char, 2>(3);
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v4 = simd<char, 2>(4);
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simd<char, 8> m = concat(v1, v2, v3, v4);
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static_assert(simd_size_v<decltype(m)> == 8, "invalid size");
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simd<char, 8> c = {1, 1, 2, 2, 3, 3, 4, 4};
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for (int i = 0; i < 8; ++i)
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EXPECT_EQ(c[i], m[i]);
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simd<char, 1> c1('\0');
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simd<char, 8> c2('\0');
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simd<char, 9> c3 = concat(c1, c2);
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static_assert(simd_size_v<decltype(c3)> == 9, "invalid size");
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}

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