247 lines
7.9 KiB
C++
247 lines
7.9 KiB
C++
/* Platform-independent deterministic sort function.
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Copyright (C) 2018-2019 Free Software Foundation, Inc.
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Contributed by Alexander Monakov.
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This file is part of GCC.
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GCC is free software; you can redistribute it and/or modify it
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under the terms of the GNU General Public License as published by the
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Free Software Foundation; either version 3, or (at your option) any
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later version.
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GCC is distributed in the hope that it will be useful, but WITHOUT
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ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
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FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
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for more details.
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You should have received a copy of the GNU General Public License
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along with GCC; see the file COPYING3. If not see
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<http://www.gnu.org/licenses/>. */
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/* This implements a sort function suitable for GCC use cases:
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- signature-compatible to C qsort, but relaxed contract:
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- may apply the comparator to elements in a temporary buffer
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- may abort on allocation failure
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- deterministic (but not necessarily stable)
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- fast, especially for common cases (0-5 elements of size 8 or 4)
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The implementation uses a network sort for up to 5 elements and
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a merge sort on top of that. Neither stage has branches depending on
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comparator result, trading extra arithmetic for branch mispredictions. */
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#ifdef GENERATOR_FILE
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#include "bconfig.h"
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#else
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#include "config.h"
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#endif
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#include "system.h"
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#define likely(cond) __builtin_expect ((cond), 1)
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#ifdef __GNUC__
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#define noinline __attribute__ ((__noinline__))
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#else
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#define noinline
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#endif
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/* C-style qsort comparator function type. */
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typedef int cmp_fn (const void *, const void *);
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/* Structure holding read-mostly (read-only in netsort) context. */
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struct sort_ctx
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{
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cmp_fn *cmp; // pointer to comparator
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char *out; // output buffer
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size_t n; // number of elements
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size_t size; // element size
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size_t nlim; // limit for network sort
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};
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/* Helper for netsort. Permute, possibly in-place, 2 or 3 elements,
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placing E0 to C->OUT, E1 to C->OUT + C->SIZE, and so on. */
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static void
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reorder23 (sort_ctx *c, char *e0, char *e1, char *e2)
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{
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#define REORDER_23(TYPE, STRIDE, OFFSET) \
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do { \
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TYPE t0, t1; \
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memcpy (&t0, e0 + OFFSET, sizeof (TYPE)); \
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memcpy (&t1, e1 + OFFSET, sizeof (TYPE)); \
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char *out = c->out + OFFSET; \
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if (likely (c->n == 3)) \
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memmove (out + 2*STRIDE, e2 + OFFSET, sizeof (TYPE));\
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memcpy (out, &t0, sizeof (TYPE)); out += STRIDE; \
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memcpy (out, &t1, sizeof (TYPE)); \
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} while (0)
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if (likely (c->size == sizeof (size_t)))
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REORDER_23 (size_t, sizeof (size_t), 0);
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else if (likely (c->size == sizeof (int)))
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REORDER_23 (int, sizeof (int), 0);
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else
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{
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size_t offset = 0, step = sizeof (size_t);
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for (; offset + step <= c->size; offset += step)
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REORDER_23 (size_t, c->size, offset);
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for (; offset < c->size; offset++)
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REORDER_23 (char, c->size, offset);
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}
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}
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/* Like reorder23, but permute 4 or 5 elements. */
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static void
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reorder45 (sort_ctx *c, char *e0, char *e1, char *e2, char *e3, char *e4)
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{
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#define REORDER_45(TYPE, STRIDE, OFFSET) \
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do { \
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TYPE t0, t1, t2, t3; \
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memcpy (&t0, e0 + OFFSET, sizeof (TYPE)); \
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memcpy (&t1, e1 + OFFSET, sizeof (TYPE)); \
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memcpy (&t2, e2 + OFFSET, sizeof (TYPE)); \
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memcpy (&t3, e3 + OFFSET, sizeof (TYPE)); \
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char *out = c->out + OFFSET; \
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if (likely (c->n == 5)) \
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memmove (out + 4*STRIDE, e4 + OFFSET, sizeof (TYPE));\
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memcpy (out, &t0, sizeof (TYPE)); out += STRIDE; \
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memcpy (out, &t1, sizeof (TYPE)); out += STRIDE; \
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memcpy (out, &t2, sizeof (TYPE)); out += STRIDE; \
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memcpy (out, &t3, sizeof (TYPE)); \
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} while (0)
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if (likely (c->size == sizeof (size_t)))
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REORDER_45 (size_t, sizeof (size_t), 0);
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else if (likely(c->size == sizeof (int)))
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REORDER_45 (int, sizeof (int), 0);
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else
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{
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size_t offset = 0, step = sizeof (size_t);
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for (; offset + step <= c->size; offset += step)
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REORDER_45 (size_t, c->size, offset);
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for (; offset < c->size; offset++)
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REORDER_45 (char, c->size, offset);
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}
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}
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/* Helper for netsort. Invoke comparator CMP on E0 and E1.
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Return E0^E1 if E0 compares less than E1, zero otherwise.
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This is noinline to avoid code growth and confine invocation
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to a single call site, assisting indirect branch prediction. */
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noinline static intptr_t
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cmp1 (char *e0, char *e1, cmp_fn *cmp)
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{
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intptr_t x = (intptr_t)e0 ^ (intptr_t)e1;
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return x & (cmp (e0, e1) >> 31);
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}
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/* Execute network sort on 2 to 5 elements from IN, placing them into C->OUT.
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IN may be equal to C->OUT, in which case elements are sorted in place. */
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static void
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netsort (char *in, sort_ctx *c)
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{
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#define CMP(e0, e1) \
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do { \
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intptr_t x = cmp1 (e1, e0, c->cmp); \
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e0 = (char *)((intptr_t)e0 ^ x); \
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e1 = (char *)((intptr_t)e1 ^ x); \
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} while (0)
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char *e0 = in, *e1 = e0 + c->size, *e2 = e1 + c->size;
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CMP (e0, e1);
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if (likely (c->n == 3))
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{
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CMP (e1, e2);
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CMP (e0, e1);
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}
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if (c->n <= 3)
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return reorder23 (c, e0, e1, e2);
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char *e3 = e2 + c->size, *e4 = e3 + c->size;
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if (likely (c->n == 5))
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{
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CMP (e3, e4);
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CMP (e2, e4);
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}
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CMP (e2, e3);
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if (likely (c->n == 5))
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{
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CMP (e0, e3);
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CMP (e1, e4);
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}
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CMP (e0, e2);
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CMP (e1, e3);
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CMP (e1, e2);
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reorder45 (c, e0, e1, e2, e3, e4);
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}
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/* Execute merge sort on N elements from IN, placing them into OUT,
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using TMP as temporary storage if IN is equal to OUT.
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This is a stable sort if netsort is used only for 2 or 3 elements. */
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static void
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mergesort (char *in, sort_ctx *c, size_t n, char *out, char *tmp)
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{
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if (likely (n <= c->nlim))
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{
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c->out = out;
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c->n = n;
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return netsort (in, c);
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}
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size_t nl = n / 2, nr = n - nl, sz = nl * c->size;
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char *mid = in + sz, *r = out + sz, *l = in == out ? tmp : in;
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/* Sort the right half, outputting to right half of OUT. */
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mergesort (mid, c, nr, r, tmp);
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/* Sort the left half, leaving left half of OUT free. */
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mergesort (in, c, nl, l, mid);
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/* Merge sorted halves given by L, R to [OUT, END). */
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#define MERGE_ELTSIZE(SIZE) \
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do { \
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intptr_t mr = c->cmp (r, l) >> 31; \
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intptr_t lr = (intptr_t)l ^ (intptr_t)r; \
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lr = (intptr_t)l ^ (lr & mr); \
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out = (char *)memcpy (out, (char *)lr, SIZE); \
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out += SIZE; \
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r += mr & SIZE; \
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if (r == out) return; \
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l += ~mr & SIZE; \
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} while (r != end)
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if (likely (c->cmp(r, l + (r - out) - c->size) < 0))
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{
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char *end = out + n * c->size;
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if (sizeof (size_t) == 8 && likely (c->size == 8))
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MERGE_ELTSIZE (8);
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else if (likely (c->size == 4))
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MERGE_ELTSIZE (4);
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else
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MERGE_ELTSIZE (c->size);
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}
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memcpy (out, l, r - out);
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}
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void
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gcc_qsort (void *vbase, size_t n, size_t size, cmp_fn *cmp)
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{
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if (n < 2)
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return;
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size_t nlim = 5;
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bool stable = (ssize_t) size < 0;
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if (stable)
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nlim = 3, size = ~size;
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char *base = (char *)vbase;
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sort_ctx c = {cmp, base, n, size, nlim};
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long long scratch[32];
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size_t bufsz = (n / 2) * size;
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void *buf = bufsz <= sizeof scratch ? scratch : xmalloc (bufsz);
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mergesort (base, &c, n, base, (char *)buf);
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if (buf != scratch)
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free (buf);
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#if CHECKING_P
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qsort_chk (vbase, n, size, cmp);
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#endif
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}
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void
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gcc_stablesort (void *vbase, size_t n, size_t size, cmp_fn *cmp)
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{
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gcc_qsort (vbase, n, ~size, cmp);
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}
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