removing movemask from platform (facebook#2302)

Summary:
Pull Request resolved: facebook#2302

stepping stone for simd::contains.

We want to do less things in simd platform if possbile, so moving out non essential things.

Differential Revision: D63388617

CMakeLists.txt

@@ -649,6 +649,8 @@ if (BUILD_TESTS OR BUILD_BENCHMARKS)
     DIRECTORY algorithm/simd/detail/test/
       TEST algorithm_simd_detail_simd_any_of_test SOURCES SimdAnyOfTest.cpp
       TEST algorithm_simd_detail_simd_for_each_test SOURCES SimdForEachTest.cpp
+      TEST algorithm_simd_detail_simd_for_each_test SOURCES SimdForEachTest.cpp
+      TEST algorithm_simd_detail_ignore_test SOURCES IgnoreTest.cpp
       TEST algorithm_simd_detail_unroll_utils_test SOURCES UnrollUtilsTest.cpp
       # disabled until C++20
       # TEST algorithm_simd_detail_simd_traits_test SOURCES TraitsTest.cpp

folly/algorithm/simd/FindFixed.h

@@ -194,7 +194,7 @@ std::optional<std::size_t> findSplitFirstRegister(
 
 template <typename Scalar, typename Reg>
 std::optional<std::size_t> firstTrue(Reg reg) {
-  auto [bits, bitsPerElement] = folly::movemask<Scalar>(reg);
+  auto [bits, bitsPerElement] = folly::simd::movemask<Scalar>(reg);
   if (bits) {
     return std::countr_zero(bits) / bitsPerElement();
   }

folly/algorithm/simd/Movemask.h

@@ -33,7 +33,7 @@
 FOLLY_PUSH_WARNING
 FOLLY_GCC_DISABLE_WARNING("-Wignored-attributes")
 
-namespace folly {
+namespace folly::simd {
 
 /*
  * This is a low level utility used for simd search algorithms.
@@ -43,7 +43,7 @@ namespace folly {
  * for both x86 and arm.
  *
  * Interface looks like this:
- * folly::movemask<-scalar type->(nativeRegister)
+ * folly::simd::movemask<-scalar type->(nativeRegister)
  *   -> std::pair<Bits, BitsPerElement>;
  *
  *  Bits - unsigned integral, containing the bitmask (first is lowest bit).
@@ -53,7 +53,7 @@ namespace folly {
  *
  *  std::optional<std::uint32_t> firstTrueUint16(auto simdRegister) {
  *    auto [bits, bitsPerElement] =
- *        folly::movemask<std::uint16_t>(simdRegister);
+ *        folly::simd::movemask<std::uint16_t>(simdRegister);
  *    if (!bits) {
  *      return std::nullopt;
  *    }
@@ -71,7 +71,11 @@ template <typename Scalar, typename Reg>
 auto movemask(Reg reg) {
   std::integral_constant<std::uint32_t, sizeof(Scalar) == 2 ? 2 : 1>
       bitsPerElement;
-  auto mmask = static_cast<std::uint32_t>([&] {
+
+  using uint_t = std::
+      conditional_t<std::is_same_v<Reg, __m128i>, std::uint16_t, std::uint32_t>;
+
+  auto mmask = static_cast<uint_t>([&] {
     if constexpr (std::is_same_v<Reg, __m128i>) {
       if constexpr (sizeof(Scalar) <= 2) {
         return _mm_movemask_epi8(reg);
@@ -142,6 +146,13 @@ auto movemask(Reg reg) {
 
 #endif
 
-} // namespace folly
+#if !FOLLY_X64 && !FOLLY_AARCH64
+
+template <typename Scalar, typename Reg>
+void movemask(Reg reg) = delete;
+
+#endif
+
+} // namespace folly::simd
 
 FOLLY_POP_WARNING

folly/algorithm/simd/detail/BUCK

@@ -5,6 +5,14 @@ load("@fbcode_macros//build_defs:cpp_library.bzl", "cpp_library")
 
 oncall("fbcode_entropy_wardens_folly")
 
+cpp_library(
+    name = "ignore",
+    headers = ["Ignore.h"],
+    exported_deps = [
+        "//folly/lang:bits",
+    ],
+)
+
 cpp_library(
     name = "simd_any_of",
     headers = ["SimdAnyOf.h"],
@@ -19,7 +27,7 @@ cpp_library(
     name = "simd_char_platform",
     headers = ["SimdCharPlatform.h"],
     exported_deps = [
-        ":simd_for_each",
+        ":ignore",
         "//folly:portability",
         "//folly/algorithm/simd:movemask",
         "//folly/lang:bits",
@@ -30,9 +38,10 @@ cpp_library(
     name = "simd_for_each",
     headers = ["SimdForEach.h"],
     exported_deps = [
+        ":ignore",
+        ":unroll_utils",
         "//folly:c_portability",
         "//folly:traits",
-        "//folly/algorithm/simd/detail:unroll_utils",
     ],
 )
 

folly/algorithm/simd/detail/Ignore.h

@@ -0,0 +1,61 @@
+/*
+ * Copyright (c) Meta Platforms, Inc. and affiliates.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#pragma once
+
+#include <folly/lang/Bits.h>
+
+#include <type_traits>
+
+namespace folly::simd::detail {
+
+/**
+ * ignore(_none/_extrema)
+ *
+ * Tag types for handling the tails.
+ * ignore_none indicates that the whole register is used.
+ * ignore_extrema.first, .last show how many elements are out of the data.
+ *
+ * For example 3 elements, starting from the second for an 8 element register
+ * will be ignore_extrema{.first = 1, .last = 4}
+ */
+
+struct ignore_extrema {
+  int first = 0;
+  int last = 0;
+};
+
+struct ignore_none {};
+
+/*
+ * NOTE: for ignore none we don't clear anything, even if some bits are not
+ * doing anything. We expect mmask to only have zeroes in masked out elements.
+ *
+ * Maybe we need to revisit that at some point.
+ */
+template <int Cardinal, typename Uint, typename BitsPerElement, typename Ignore>
+void mmaskClearIgnored(std::pair<Uint, BitsPerElement>& mmask, Ignore ignore) {
+  if constexpr (std::is_same_v<Ignore, ignore_extrema>) {
+    mmask.first = set_rzero(mmask.first, ignore.first * BitsPerElement{});
+
+    static constexpr int kTopBitsAlwaysIgnored =
+        sizeof(Uint) * 8 - Cardinal * BitsPerElement{};
+    mmask.first = set_lzero(
+        mmask.first, ignore.last * BitsPerElement{} + kTopBitsAlwaysIgnored);
+  }
+}
+
+} // namespace folly::simd::detail

folly/algorithm/simd/detail/SimdCharPlatform.h

@@ -18,7 +18,8 @@
 
 #include <folly/Portability.h>
 #include <folly/algorithm/simd/Movemask.h>
-#include <folly/algorithm/simd/detail/SimdForEach.h>
+#include <folly/algorithm/simd/detail/Ignore.h>
+#include <folly/algorithm/simd/detail/SimdCharPlatform.h>
 #include <folly/lang/Bits.h>
 
 #include <array>
@@ -68,47 +69,16 @@ namespace simd::detail {
  *  - le_unsigned(reg_t, char) - by lane less than or equal to char.
  *
  * logical ops:
- *   - movemask - take a bitmask
  *   - any(logical_t, ignore) - return true if any the lanes are true
  *   - logical_or(logical_t, logical_t) - by lane logical or
  *
- * mmask ops:
- *   - clear(mmask, ignore) - sets ignored bits to 0
- *
  */
 
 #if FOLLY_X64 || FOLLY_AARCH64
 
 template <typename Platform>
 struct SimdCharPlatformCommon : Platform {
   using logical_t = typename Platform::logical_t;
-  using movemask_result_t =
-      decltype(folly::movemask<std::uint8_t>(logical_t{}));
-  using mmask_t = typename movemask_result_t::first_type;
-  static constexpr std::uint32_t kMmaskBitsPerElement =
-      typename movemask_result_t::second_type{}();
-
-  template <typename Uint>
-  FOLLY_NODISCARD FOLLY_ALWAYS_INLINE static Uint setLowerNBits(int n) {
-    if (sizeof(Uint) == 8 && n == 64) {
-      return static_cast<Uint>(-1);
-    }
-    return static_cast<Uint>((std::uint64_t{1} << n) - 1);
-  }
-
-  FOLLY_NODISCARD FOLLY_ALWAYS_INLINE static mmask_t clear(
-      mmask_t mmask, ignore_extrema ignore) {
-    mmask_t clearFirst =
-        ~setLowerNBits<mmask_t>(ignore.first * kMmaskBitsPerElement);
-    mmask_t clearLast = setLowerNBits<mmask_t>(
-        (Platform::kCardinal - ignore.last) * kMmaskBitsPerElement);
-    return mmask & clearFirst & clearLast;
-  }
-
-  FOLLY_NODISCARD FOLLY_ALWAYS_INLINE static mmask_t clear(
-      mmask_t mmask, ignore_none) {
-    return mmask;
-  }
 
   // These are aligned loads but there is no point in generating
   // aligned load instructions, so we call loadu.
@@ -122,18 +92,13 @@ struct SimdCharPlatformCommon : Platform {
     return Platform::unsafeLoadu(ptr, ignore_none{});
   }
 
-  FOLLY_ALWAYS_INLINE
-  static mmask_t movemask(logical_t log) {
-    return folly::movemask<std::uint8_t>(log).first;
-  }
-
   using Platform::any;
 
   FOLLY_ALWAYS_INLINE
   static bool any(typename Platform::logical_t log, ignore_extrema ignore) {
-    auto mmask = movemask(log);
-    mmask = clear(mmask, ignore);
-    return mmask;
+    auto mmask = movemask<std::uint8_t>(log);
+    mmaskClearIgnored<Platform::kCardinal>(mmask, ignore);
+    return mmask.first;
   }
 
   static auto toArray(typename Platform::reg_t x) {
@@ -186,7 +151,7 @@ struct SimdCharSse2PlatformSpecific {
 
   FOLLY_ALWAYS_INLINE
   static bool any(logical_t log, ignore_none) {
-    return folly::movemask<std::uint8_t>(log).first;
+    return movemask<std::uint8_t>(log).first;
   }
 };
 
@@ -234,7 +199,7 @@ struct SimdCharAvx2PlatformSpecific {
 
   FOLLY_ALWAYS_INLINE
   static bool any(logical_t log, ignore_none) {
-    return folly::movemask<std::uint8_t>(log).first;
+    return simd::movemask<std::uint8_t>(log).first;
   }
 };
 

folly/algorithm/simd/detail/SimdForEach.h

@@ -18,6 +18,7 @@
 
 #include <folly/CPortability.h>
 #include <folly/Traits.h>
+#include <folly/algorithm/simd/detail/Ignore.h>
 #include <folly/algorithm/simd/detail/UnrollUtils.h>
 
 #include <array>
@@ -35,23 +36,6 @@ namespace simd::detail {
 // to mess that up.
 //
 
-/**
- * ignore(_none/_extrema)
- *
- * Tag types for handling the tails.
- * ignore_none indicates that the whole register is used.
- * ignore_extrema.first, .last show how many elements are out of the data.
- *
- * For example 3 elements, starting from the second for an 8 element register
- * will be ignore_extrema{.first = 1, .last = 4}
- */
-struct ignore_extrema {
-  int first = 0;
-  int last = 0;
-};
-
-struct ignore_none {};
-
 /**
  * simdForEachAligning<unrolling>(cardinal, f, l, delegate);
  *

folly/algorithm/simd/detail/test/BUCK

@@ -24,6 +24,15 @@ cpp_unittest(
     ],
 )
 
+cpp_unittest(
+    name = "ignore_test",
+    srcs = ["IgnoreTest.cpp"],
+    deps = [
+        "//folly/algorithm/simd/detail:ignore",
+        "//folly/portability:gtest",
+    ],
+)
+
 cpp_unittest(
     name = "traits_test",
     srcs = ["TraitsTest.cpp"],

folly/algorithm/simd/detail/test/IgnoreTest.cpp

@@ -0,0 +1,45 @@
+/*
+ * Copyright (c) Meta Platforms, Inc. and affiliates.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#include <folly/algorithm/simd/detail/Ignore.h>
+
+#include <cstdint>
+
+#include <folly/portability/GTest.h>
+
+namespace folly::simd::detail {
+
+struct IgnoreTest : ::testing::Test {};
+
+TEST_F(IgnoreTest, MaskClearIgnored) {
+  auto mmask =
+      std::pair{std::uint8_t{0xff}, std::integral_constant<std::uint32_t, 2>{}};
+
+  // mostly relying on folly::clear_<>_n_bits working correctly
+  // simd any of also covers a lot of cases.
+  // this is just the bare minimal smoke test.
+
+  mmaskClearIgnored<4>(mmask, ignore_none{});
+  EXPECT_EQ(0xff, mmask.first);
+
+  mmaskClearIgnored<4>(mmask, ignore_extrema{1, 2});
+  EXPECT_EQ(0b0000'1100, mmask.first);
+
+  mmaskClearIgnored<2>(mmask, ignore_extrema{0, 1});
+  EXPECT_EQ(0b0000'0000, mmask.first);
+}
+
+} // namespace folly::simd::detail

folly/algorithm/simd/detail/test/SimdAnyOfTest.cpp

@@ -83,7 +83,7 @@ TEST(SimdAnyOfSimple, Ignore) {
   buffer.fill(' ');
   for (auto& c : buffer) {
     c = 'a';
-    anySpacesTest({&c, 1}, false);
+    ASSERT_NO_FATAL_FAILURE(anySpacesTest({&c, 1}, false));
     c = ' ';
   }
 }

folly/algorithm/simd/test/MovemaskTest.cpp

@@ -55,11 +55,11 @@ void allOneTrueTests() {
   std::array<T, N> arr;
   arr.fill(kFalse);
 
-  ASSERT_EQ(0, folly::movemask<T>(loadReg<Reg>(arr)).first);
+  ASSERT_EQ(0, folly::simd::movemask<T>(loadReg<Reg>(arr)).first);
 
   for (std::size_t i = 0; i != N; ++i) {
     arr[i] = kTrue;
-    auto [bits, bitsPerElement] = folly::movemask<T>(loadReg<Reg>(arr));
+    auto [bits, bitsPerElement] = folly::simd::movemask<T>(loadReg<Reg>(arr));
     std::uint64_t oneElement = safeShift(1, bitsPerElement()) - 1;
     std::uint64_t expectedBits = safeShift(oneElement, i * bitsPerElement());
 

folly/detail/BUCK

@@ -269,6 +269,8 @@ cpp_library(
     exported_deps = [
         "//folly:portability",
         "//folly:range",
+        "//folly/algorithm/simd:movemask",
+        "//folly/algorithm/simd/detail:ignore",
         "//folly/algorithm/simd/detail:simd_char_platform",
         "//folly/algorithm/simd/detail:simd_for_each",
         "//folly/lang:bits",