Revert "[libc] Improve qsort" (#121303)

Reverts #120450

Author: SchrodingerZhu

libc/src/stdlib/heap_sort.h

@@ -18,12 +18,11 @@ namespace internal {
 // A simple in-place heapsort implementation.
 // Follow the implementation in https://en.wikipedia.org/wiki/Heapsort.
 
-template <typename A, typename F>
-LIBC_INLINE void heap_sort(const A &array, const F &is_less) {
-  size_t end = array.len();
+LIBC_INLINE void heap_sort(const Array &array) {
+  size_t end = array.size();
   size_t start = end / 2;
 
-  const auto left_child = [](size_t i) -> size_t { return 2 * i + 1; };
+  auto left_child = [](size_t i) -> size_t { return 2 * i + 1; };
 
   while (end > 1) {
     if (start > 0) {
@@ -41,11 +40,12 @@ LIBC_INLINE void heap_sort(const A &array, const F &is_less) {
     while (left_child(root) < end) {
       size_t child = left_child(root);
       // If there are two children, set child to the greater.
-      if ((child + 1 < end) && is_less(array.get(child), array.get(child + 1)))
+      if (child + 1 < end &&
+          array.elem_compare(child, array.get(child + 1)) < 0)
         ++child;
 
       // If the root is less than the greater child
-      if (!is_less(array.get(root), array.get(child)))
+      if (array.elem_compare(root, array.get(child)) >= 0)
         break;
 
       // Swap the root with the greater child and continue sifting down.

libc/src/stdlib/qsort.cpp

@@ -18,12 +18,14 @@ namespace LIBC_NAMESPACE_DECL {
 LLVM_LIBC_FUNCTION(void, qsort,
                    (void *array, size_t array_size, size_t elem_size,
                     int (*compare)(const void *, const void *))) {
+  if (array == nullptr || array_size == 0 || elem_size == 0)
+    return;
+  internal::Comparator c(compare);
 
-  const auto is_less = [compare](const void *a, const void *b) -> bool {
-    return compare(a, b) < 0;
-  };
+  auto arr = internal::Array(reinterpret_cast<uint8_t *>(array), array_size,
+                             elem_size, c);
 
-  internal::unstable_sort(array, array_size, elem_size, is_less);
+  internal::sort(arr);
 }
 
 } // namespace LIBC_NAMESPACE_DECL

libc/src/stdlib/qsort_data.h

@@ -17,122 +17,91 @@
 namespace LIBC_NAMESPACE_DECL {
 namespace internal {
 
-class ArrayGenericSize {
-  cpp::byte *array_base;
-  size_t array_len;
-  size_t elem_size;
-
-  LIBC_INLINE cpp::byte *get_internal(size_t i) const {
-    return array_base + (i * elem_size);
-  }
-
-public:
-  LIBC_INLINE ArrayGenericSize(void *a, size_t s, size_t e)
-      : array_base(reinterpret_cast<cpp::byte *>(a)), array_len(s),
-        elem_size(e) {}
-
-  static constexpr bool has_fixed_size() { return false; }
-
-  LIBC_INLINE void *get(size_t i) const { return get_internal(i); }
-
-  LIBC_INLINE void swap(size_t i, size_t j) const {
-    // It's possible to use 8 byte blocks with `uint64_t`, but that
-    // generates more machine code as the remainder loop gets
-    // unrolled, plus 4 byte operations are more likely to be
-    // efficient on a wider variety of hardware. On x86 LLVM tends
-    // to unroll the block loop again into 2 16 byte swaps per
-    // iteration which is another reason that 4 byte blocks yields
-    // good performance even for big types.
-    using block_t = uint32_t;
-    constexpr size_t BLOCK_SIZE = sizeof(block_t);
-
-    alignas(block_t) cpp::byte tmp_block[BLOCK_SIZE];
-
-    cpp::byte *elem_i = get_internal(i);
-    cpp::byte *elem_j = get_internal(j);
-
-    const size_t elem_size_rem = elem_size % BLOCK_SIZE;
-    const cpp::byte *elem_i_block_end = elem_i + (elem_size - elem_size_rem);
-
-    while (elem_i != elem_i_block_end) {
-      __builtin_memcpy(tmp_block, elem_i, BLOCK_SIZE);
-      __builtin_memcpy(elem_i, elem_j, BLOCK_SIZE);
-      __builtin_memcpy(elem_j, tmp_block, BLOCK_SIZE);
-
-      elem_i += BLOCK_SIZE;
-      elem_j += BLOCK_SIZE;
-    }
-
-    for (size_t n = 0; n < elem_size_rem; ++n) {
-      cpp::byte tmp = elem_i[n];
-      elem_i[n] = elem_j[n];
-      elem_j[n] = tmp;
+using Compare = int(const void *, const void *);
+using CompareWithState = int(const void *, const void *, void *);
+
+enum class CompType { COMPARE, COMPARE_WITH_STATE };
+
+struct Comparator {
+  union {
+    Compare *comp_func;
+    CompareWithState *comp_func_r;
+  };
+  const CompType comp_type;
+
+  void *arg;
+
+  Comparator(Compare *func)
+      : comp_func(func), comp_type(CompType::COMPARE), arg(nullptr) {}
+
+  Comparator(CompareWithState *func, void *arg_val)
+      : comp_func_r(func), comp_type(CompType::COMPARE_WITH_STATE),
+        arg(arg_val) {}
+
+#if defined(__clang__)
+  // Recent upstream changes to -fsanitize=function find more instances of
+  // function type mismatches. One case is with the comparator passed to this
+  // class. Libraries will tend to pass comparators that take pointers to
+  // varying types while this comparator expects to accept const void pointers.
+  // Ideally those tools would pass a function that strictly accepts const
+  // void*s to avoid UB, or would use qsort_r to pass their own comparator.
+  [[clang::no_sanitize("function")]]
+#endif
+  int comp_vals(const void *a, const void *b) const {
+    if (comp_type == CompType::COMPARE) {
+      return comp_func(a, b);
+    } else {
+      return comp_func_r(a, b, arg);
     }
   }
-
-  LIBC_INLINE size_t len() const { return array_len; }
-
-  // Make an Array starting at index |i| and length |s|.
-  LIBC_INLINE ArrayGenericSize make_array(size_t i, size_t s) const {
-    return ArrayGenericSize(get_internal(i), s, elem_size);
-  }
-
-  // Reset this Array to point at a different interval of the same
-  // items starting at index |i|.
-  LIBC_INLINE void reset_bounds(size_t i, size_t s) {
-    array_base = get_internal(i);
-    array_len = s;
-  }
 };
 
-// Having a specialized Array type for sorting that knows at
-// compile-time what the size of the element is, allows for much more
-// efficient swapping and for cheaper offset calculations.
-template <size_t ELEM_SIZE> class ArrayFixedSize {
-  cpp::byte *array_base;
-  size_t array_len;
-
-  LIBC_INLINE cpp::byte *get_internal(size_t i) const {
-    return array_base + (i * ELEM_SIZE);
-  }
+class Array {
+  uint8_t *array;
+  size_t array_size;
+  size_t elem_size;
+  Comparator compare;
 
 public:
-  LIBC_INLINE ArrayFixedSize(void *a, size_t s)
-      : array_base(reinterpret_cast<cpp::byte *>(a)), array_len(s) {}
-
-  // Beware this function is used a heuristic for cheap to swap types, so
-  // instantiating `ArrayFixedSize` with `ELEM_SIZE > 100` is probably a bad
-  // idea perf wise.
-  static constexpr bool has_fixed_size() { return true; }
-
-  LIBC_INLINE void *get(size_t i) const { return get_internal(i); }
-
-  LIBC_INLINE void swap(size_t i, size_t j) const {
-    alignas(32) cpp::byte tmp[ELEM_SIZE];
-
-    cpp::byte *elem_i = get_internal(i);
-    cpp::byte *elem_j = get_internal(j);
+  Array(uint8_t *a, size_t s, size_t e, Comparator c)
+      : array(a), array_size(s), elem_size(e), compare(c) {}
+
+  uint8_t *get(size_t i) const { return array + i * elem_size; }
+
+  void swap(size_t i, size_t j) const {
+    uint8_t *elem_i = get(i);
+    uint8_t *elem_j = get(j);
+    for (size_t b = 0; b < elem_size; ++b) {
+      uint8_t temp = elem_i[b];
+      elem_i[b] = elem_j[b];
+      elem_j[b] = temp;
+    }
+  }
 
-    __builtin_memcpy(tmp, elem_i, ELEM_SIZE);
-    __builtin_memmove(elem_i, elem_j, ELEM_SIZE);
-    __builtin_memcpy(elem_j, tmp, ELEM_SIZE);
+  int elem_compare(size_t i, const uint8_t *other) const {
+    // An element must compare equal to itself so we don't need to consult the
+    // user provided comparator.
+    if (get(i) == other)
+      return 0;
+    return compare.comp_vals(get(i), other);
   }
 
-  LIBC_INLINE size_t len() const { return array_len; }
+  size_t size() const { return array_size; }
 
-  // Make an Array starting at index |i| and length |s|.
-  LIBC_INLINE ArrayFixedSize<ELEM_SIZE> make_array(size_t i, size_t s) const {
-    return ArrayFixedSize<ELEM_SIZE>(get_internal(i), s);
+  // Make an Array starting at index |i| and size |s|.
+  LIBC_INLINE Array make_array(size_t i, size_t s) const {
+    return Array(get(i), s, elem_size, compare);
   }
 
-  // Reset this Array to point at a different interval of the same
-  // items starting at index |i|.
-  LIBC_INLINE void reset_bounds(size_t i, size_t s) {
-    array_base = get_internal(i);
-    array_len = s;
+  // Reset this Array to point at a different interval of the same items.
+  LIBC_INLINE void reset_bounds(uint8_t *a, size_t s) {
+    array = a;
+    array_size = s;
   }
 };
 
+using SortingRoutine = void(const Array &);
+
 } // namespace internal
 } // namespace LIBC_NAMESPACE_DECL
 

libc/src/stdlib/qsort_pivot.h

@@ -19,12 +19,13 @@ LLVM_LIBC_FUNCTION(void, qsort_r,
                    (void *array, size_t array_size, size_t elem_size,
                     int (*compare)(const void *, const void *, void *),
                     void *arg)) {
+  if (array == nullptr || array_size == 0 || elem_size == 0)
+    return;
+  internal::Comparator c(compare, arg);
+  auto arr = internal::Array(reinterpret_cast<uint8_t *>(array), array_size,
+                             elem_size, c);
 
-  const auto is_less = [compare, arg](const void *a, const void *b) -> bool {
-    return compare(a, b, arg) < 0;
-  };
-
-  internal::unstable_sort(array, array_size, elem_size, is_less);
+  internal::sort(arr);
 }
 
 } // namespace LIBC_NAMESPACE_DECL