--- /dev/null
+/* Platform-independent deterministic sort function.
+ Copyright (C) 2018 Free Software Foundation, Inc.
+ Contributed by Alexander Monakov.
+
+This file is part of GCC.
+
+GCC is free software; you can redistribute it and/or modify it
+under the terms of the GNU General Public License as published by the
+Free Software Foundation; either version 3, or (at your option) any
+later version.
+
+GCC is distributed in the hope that it will be useful, but WITHOUT
+ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
+for more details.
+
+You should have received a copy of the GNU General Public License
+along with GCC; see the file COPYING3. If not see
+<http://www.gnu.org/licenses/>. */
+
+/* This implements a sort function suitable for GCC use cases:
+ - signature-compatible to C qsort, but relaxed contract:
+ - may apply the comparator to elements in a temporary buffer
+ - may abort on allocation failure
+ - deterministic (but not necessarily stable)
+ - fast, especially for common cases (0-5 elements of size 8 or 4)
+
+ The implementation uses a network sort for up to 5 elements and
+ a merge sort on top of that. Neither stage has branches depending on
+ comparator result, trading extra arithmetic for branch mispredictions. */
+
+#ifdef GENERATOR_FILE
+#include "bconfig.h"
+#else
+#include "config.h"
+#endif
+
+#include "system.h"
+
+#define likely(cond) __builtin_expect ((cond), 1)
+
+#ifdef __GNUC__
+#define noinline __attribute__ ((__noinline__))
+#else
+#define noinline
+#endif
+
+/* C-style qsort comparator function type. */
+typedef int cmp_fn (const void *, const void *);
+
+/* Structure holding read-mostly (read-only in netsort) context. */
+struct sort_ctx
+{
+ cmp_fn *cmp; // pointer to comparator
+ char *out; // output buffer
+ size_t n; // number of elements
+ size_t size; // element size
+};
+
+/* Helper for netsort. Permute, possibly in-place, 2 or 3 elements,
+ placing E0 to C->OUT, E1 to C->OUT + C->SIZE, and so on. */
+static void
+reorder23 (sort_ctx *c, char *e0, char *e1, char *e2)
+{
+#define REORDER_23(SIZE, STRIDE, OFFSET) \
+do { \
+ size_t t0, t1; \
+ memcpy (&t0, e0 + OFFSET, SIZE); \
+ memcpy (&t1, e1 + OFFSET, SIZE); \
+ char *out = c->out + OFFSET; \
+ if (likely (c->n == 3)) \
+ memcpy (out + 2*STRIDE, e2 + OFFSET, SIZE); \
+ memcpy (out, &t0, SIZE); out += STRIDE; \
+ memcpy (out, &t1, SIZE); \
+} while (0)
+
+ if (sizeof (size_t) == 8 && likely (c->size == 8))
+ REORDER_23 (8, 8, 0);
+ else if (likely (c->size == 4))
+ REORDER_23 (4, 4, 0);
+ else
+ {
+ size_t offset = 0, step = sizeof (size_t);
+ for (; offset + step <= c->size; offset += step)
+ REORDER_23 (step, c->size, offset);
+ for (; offset < c->size; offset++)
+ REORDER_23 (1, c->size, offset);
+ }
+}
+
+/* Like reorder23, but permute 4 or 5 elements. */
+static void
+reorder45 (sort_ctx *c, char *e0, char *e1, char *e2, char *e3, char *e4)
+{
+#define REORDER_45(SIZE, STRIDE, OFFSET) \
+do { \
+ size_t t0, t1, t2, t3; \
+ memcpy (&t0, e0 + OFFSET, SIZE); \
+ memcpy (&t1, e1 + OFFSET, SIZE); \
+ memcpy (&t2, e2 + OFFSET, SIZE); \
+ memcpy (&t3, e3 + OFFSET, SIZE); \
+ char *out = c->out + OFFSET; \
+ if (likely (c->n == 5)) \
+ memcpy (out + 4*STRIDE, e4 + OFFSET, SIZE); \
+ memcpy (out, &t0, SIZE); out += STRIDE; \
+ memcpy (out, &t1, SIZE); out += STRIDE; \
+ memcpy (out, &t2, SIZE); out += STRIDE; \
+ memcpy (out, &t3, SIZE); \
+} while (0)
+
+ if (sizeof (size_t) == 8 && likely (c->size == 8))
+ REORDER_45 (8, 8, 0);
+ else if (likely(c->size == 4))
+ REORDER_45 (4, 4, 0);
+ else
+ {
+ size_t offset = 0, step = sizeof (size_t);
+ for (; offset + step <= c->size; offset += step)
+ REORDER_45 (step, c->size, offset);
+ for (; offset < c->size; offset++)
+ REORDER_45 (1, c->size, offset);
+ }
+}
+
+/* Helper for netsort. Invoke comparator CMP on E0 and E1.
+ Return E0^E1 if E0 compares less than E1, zero otherwise.
+ This is noinline to avoid code growth and confine invocation
+ to a single call site, assisting indirect branch prediction. */
+noinline static intptr_t
+cmp1 (char *e0, char *e1, cmp_fn *cmp)
+{
+ intptr_t x = (intptr_t)e0 ^ (intptr_t)e1;
+ return x & (cmp (e0, e1) >> 31);
+}
+
+/* Execute network sort on 2 to 5 elements from IN, placing them into C->OUT.
+ IN may be equal to C->OUT, in which case elements are sorted in place. */
+static void
+netsort (char *in, sort_ctx *c)
+{
+#define CMP(e0, e1) \
+do { \
+ intptr_t x = cmp1 (e1, e0, c->cmp); \
+ e0 = (char *)((intptr_t)e0 ^ x); \
+ e1 = (char *)((intptr_t)e1 ^ x); \
+} while (0)
+
+ char *e0 = in, *e1 = e0 + c->size, *e2 = e1 + c->size;
+ CMP (e0, e1);
+ if (likely (c->n == 3))
+ {
+ CMP (e1, e2);
+ CMP (e0, e1);
+ }
+ if (c->n <= 3)
+ return reorder23 (c, e0, e1, e2);
+ char *e3 = e2 + c->size, *e4 = e3 + c->size;
+ if (likely (c->n == 5))
+ {
+ CMP (e3, e4);
+ CMP (e2, e4);
+ }
+ CMP (e2, e3);
+ if (likely (c->n == 5))
+ {
+ CMP (e0, e3);
+ CMP (e1, e4);
+ }
+ CMP (e0, e2);
+ CMP (e1, e3);
+ CMP (e1, e2);
+ reorder45 (c, e0, e1, e2, e3, e4);
+}
+
+/* Execute merge sort on N elements from IN, placing them into OUT,
+ using TMP as temporary storage if IN is equal to OUT.
+ This is a stable sort if netsort is used only for 2 or 3 elements. */
+static void
+mergesort (char *in, sort_ctx *c, size_t n, char *out, char *tmp)
+{
+ if (likely (n <= 5))
+ {
+ c->out = out;
+ c->n = n;
+ return netsort (in, c);
+ }
+ size_t nl = n / 2, nr = n - nl, sz = nl * c->size;
+ char *mid = in + sz, *r = out + sz, *l = in == out ? tmp : in;
+ /* Sort the right half, outputting to right half of OUT. */
+ mergesort (mid, c, nr, r, tmp);
+ /* Sort the left half, leaving left half of OUT free. */
+ mergesort (in, c, nl, l, mid);
+ /* Merge sorted halves given by L, R to [OUT, END). */
+#define MERGE_ELTSIZE(SIZE) \
+do { \
+ intptr_t mr = c->cmp (r, l) >> 31; \
+ intptr_t lr = (intptr_t)l ^ (intptr_t)r; \
+ lr = (intptr_t)l ^ (lr & mr); \
+ out = (char *)memcpy (out, (char *)lr, SIZE); \
+ out += SIZE; \
+ r += mr & SIZE; \
+ if (r == out) return; \
+ l += ~mr & SIZE; \
+} while (r != end)
+
+ if (likely (c->cmp(r, l + (r - out) - c->size) < 0))
+ {
+ char *end = out + n * c->size;
+ if (sizeof (size_t) == 8 && likely (c->size == 8))
+ MERGE_ELTSIZE (8);
+ else if (likely (c->size == 4))
+ MERGE_ELTSIZE (4);
+ else
+ MERGE_ELTSIZE (c->size);
+ }
+ memcpy (out, l, r - out);
+}
+
+void
+gcc_qsort (void *vbase, size_t n, size_t size, cmp_fn *cmp)
+{
+ if (n < 2)
+ return;
+ char *base = (char *)vbase;
+ sort_ctx c = {cmp, base, n, size};
+ long long scratch[32];
+ size_t bufsz = (n / 2) * size;
+ void *buf = bufsz <= sizeof scratch ? scratch : xmalloc (bufsz);
+ mergesort (base, &c, n, base, (char *)buf);
+ if (buf != scratch)
+ free (buf);
+}
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