Regex impl (facebook#2607)

Summary:
Pull Request resolved: facebook#2607

Execution style chosen: All of them.

This uses a backtracking implementation by default, but, unless it can prove it isn't needed, will track the number of backtracks that occur and fall back to the NFA, or, if available, DFA executor, if too many occur. This gets the perf benefits for the backtracking implementation by default in most cases, while also countering the worst-case-scenario.

For the benchmarks, Folly's implementation manages at least one, sometimes two, orders of magnitude improvement vs. the other regex implementations. The only implementations it currently falls behind in are a couple where CTRE wins. It also manages to beat CTRE in quite a few others, and importantly, is consistently fast. There are a number of patterns in the benchmarks where CTRE shows catastrophic performance, all of which this implementation handles without issue.

Work is still ongoing, the PR is only to see how the OSS tests behave.

Differential Revision: D97922157

Author: Orvid

folly/CMakeLists.txt

@@ -1507,6 +1507,7 @@ if (PYTHON_EXTENSIONS)
   add_subdirectory(python)
 endif()
 add_subdirectory(random)
+add_subdirectory(regex)
 add_subdirectory(result)
 add_subdirectory(settings)
 add_subdirectory(ssl)

folly/portability/Constexpr.h

@@ -141,4 +141,28 @@ constexpr bool is_constant_evaluated_or(
 #endif
 }
 
+//  constexpr_memcpy
+//
+//  constexpr-compatible memcpy. Uses __builtin_memcpy when available as a
+//  constexpr builtin (dramatically faster in constexpr evaluation), otherwise
+//  falls back to a trivial byte-by-byte copy loop.
+template <typename T>
+constexpr T* constexpr_memcpy(
+    T* dest, const T* src, std::size_t count) noexcept {
+#if defined(__has_constexpr_builtin)
+#if __has_constexpr_builtin(__builtin_memcpy)
+  __builtin_memcpy(dest, src, count * sizeof(T));
+#else
+  for (std::size_t i = 0; i < count; ++i) {
+    dest[i] = src[i];
+  }
+#endif
+#else
+  for (std::size_t i = 0; i < count; ++i) {
+    dest[i] = src[i];
+  }
+#endif
+  return dest;
+}
+
 } // namespace folly

folly/regex/BUCK

@@ -0,0 +1,23 @@
+load("@fbsource//tools/build_defs/dirsync:fb_dirsync_cpp_library.bzl", "fb_dirsync_cpp_library")
+
+oncall("fbcode_entropy_wardens_folly")
+
+fb_dirsync_cpp_library(
+    name = "regex",
+    headers = [
+        "Regex.h",
+    ],
+    use_raw_headers = True,
+    exported_deps = [
+        "//folly/regex/detail:ast",
+        "//folly/regex/detail:ast_optimizer",
+        "//folly/regex/detail:char_class",
+        "//folly/regex/detail:dfa",
+        "//folly/regex/detail:dfa_executor",
+        "//folly/regex/detail:direction",
+        "//folly/regex/detail:executor",
+        "//folly/regex/detail:nfa",
+        "//folly/regex/detail:nfa_executor",
+        "//folly/regex/detail:parser",
+    ],
+)

folly/regex/CMakeLists.txt

@@ -0,0 +1,34 @@
+# 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.
+
+# @generated by folly/facebook/generate_cmake.py
+
+folly_add_library(
+  NAME regex
+  HEADERS
+    Regex.h
+  EXPORTED_DEPS
+    folly_regex_detail_ast
+    folly_regex_detail_ast_optimizer
+    folly_regex_detail_char_class
+    folly_regex_detail_dfa
+    folly_regex_detail_dfa_executor
+    folly_regex_detail_direction
+    folly_regex_detail_executor
+    folly_regex_detail_nfa
+    folly_regex_detail_nfa_executor
+    folly_regex_detail_parser
+)
+
+add_subdirectory(detail)