On Thu, 10 Jun 2021, Richard Biener wrote:
> This makes it possible to apply GCCs stable sort algorithm to vec<>
> and also use it with the qsort_r compatible interface.
>
> Alex, any comments?
I'm afraid the patch is not correct, see below; (I'll also point out
errors in comments while at it).
> Bootstrapped & tested on x86_64-unknown-linux-gnu (with some
> not here included changes to actually use stablesort)
>
> 2021-06-10 Richard Biener <rguent...@suse.de>
>
> * system.h (gcc_stablesort_r): Declare.
> * sort.cc (gcc_sort_r): Support stable sort.
> (gcc_stablesort_r): Define.
> * vec.h (vec<>::stablesort): Add.
> ---
> gcc/sort.cc | 14 +++++++++++++-
> gcc/system.h | 1 +
> gcc/vec.h | 24 ++++++++++++++++++++++++
> 3 files changed, 38 insertions(+), 1 deletion(-)
>
> diff --git a/gcc/sort.cc b/gcc/sort.cc
> index fe499b5ec73..e27b90ebbdd 100644
> --- a/gcc/sort.cc
> +++ b/gcc/sort.cc
> @@ -277,8 +277,12 @@ gcc_sort_r (void *vbase, size_t n, size_t size,
> sort_r_cmp_fn *cmp, void *data)
> {
> if (n < 2)
> return;
> + size_t nlim = 5;
> + bool stable = (ssize_t) size < 0;
> + if (stable)
> + nlim = 3, size = ~size;
> char *base = (char *)vbase;
> - sort_r_ctx c = {data, cmp, base, n, size, 5};
> + sort_r_ctx c = {data, cmp, base, n, size, nlim};
> long long scratch[32];
> size_t bufsz = (n / 2) * size;
> void *buf = bufsz <= sizeof scratch ? scratch : xmalloc (bufsz);
> @@ -296,3 +300,11 @@ gcc_stablesort (void *vbase, size_t n, size_t size,
> cmp_fn *cmp)
> {
> gcc_qsort (vbase, n, ~size, cmp);
> }
> +
> +/* Stable sort, signature-compatible to C qsort_r. */
"Glibc qsort_r" (no _r variant in C, and BSD signature differs).
> +void
> +gcc_stablesort_r (void *vbase, size_t n, size_t size, sort_r_cmp_fn *cmp,
> + void *data)
> +{
> + gcc_sort_r (vbase, n, ~size, cmp, data);
> +}
> diff --git a/gcc/system.h b/gcc/system.h
> index 3c856266cc2..adde3e264b6 100644
> --- a/gcc/system.h
> +++ b/gcc/system.h
> @@ -1250,6 +1250,7 @@ void gcc_sort_r (void *, size_t, size_t, sort_r_cmp_fn
> *, void *);
> void gcc_qsort (void *, size_t, size_t, int (*)(const void *, const void *));
> void gcc_stablesort (void *, size_t, size_t,
> int (*)(const void *, const void *));
> +void gcc_stablesort_r (void *, size_t, size_t, sort_r_cmp_fn *, void *data);
> /* Redirect four-argument qsort calls to gcc_qsort; one-argument invocations
> correspond to vec::qsort, and use C qsort internally. */
> #define PP_5th(a1, a2, a3, a4, a5, ...) a5
> diff --git a/gcc/vec.h b/gcc/vec.h
> index 24df2db0eeb..c02a834c171 100644
> --- a/gcc/vec.h
> +++ b/gcc/vec.h
> @@ -612,6 +612,7 @@ public:
> void block_remove (unsigned, unsigned);
> void qsort (int (*) (const void *, const void *));
> void sort (int (*) (const void *, const void *, void *), void *);
> + void stablesort (int (*) (const void *, const void *, void *), void *);
> T *bsearch (const void *key, int (*compar)(const void *, const void *));
> T *bsearch (const void *key,
> int (*compar)(const void *, const void *, void *), void *);
> @@ -1160,6 +1161,17 @@ vec<T, A, vl_embed>::sort (int (*cmp) (const void *,
> const void *, void *),
> gcc_sort_r (address (), length (), sizeof (T), cmp, data);
> }
>
> +/* Sort the contents of this vector with qsort. CMP is the comparison
> + function to pass to qsort. */
Not with 'qsort', but gcc_stablesort_r.
> +
> +template<typename T, typename A>
> +inline void
> +vec<T, A, vl_embed>::stablesort (int (*cmp) (const void *, const void *,
> + void *), void *data)
> +{
> + if (length () > 1)
> + gcc_stablesort_r (address (), length (), ~sizeof (T), cmp, data);
> +}
I think this is wrong. You're passing inverted size to gcc_stablesort_r, which
will invert it again, and you end up with normal non-stable sorting function.
With that fixed, I think the patch would be correct.
>
> /* Search the contents of the sorted vector with a binary search.
> CMP is the comparison function to pass to bsearch. */
> @@ -1488,6 +1500,7 @@ public:
> void block_remove (unsigned, unsigned);
> void qsort (int (*) (const void *, const void *));
> void sort (int (*) (const void *, const void *, void *), void *);
> + void stablesort (int (*) (const void *, const void *, void *), void *);
> T *bsearch (const void *key, int (*compar)(const void *, const void *));
> T *bsearch (const void *key,
> int (*compar)(const void *, const void *, void *), void *);
> @@ -2053,6 +2066,17 @@ vec<T, va_heap, vl_ptr>::sort (int (*cmp) (const void
> *, const void *,
> m_vec->sort (cmp, data);
> }
>
> +/* Sort the contents of this vector with qsort. CMP is the comparison
> + function to pass to qsort. */
Like above, copy-paste issue in comment.
> +
> +template<typename T>
> +inline void
> +vec<T, va_heap, vl_ptr>::stablesort (int (*cmp) (const void *, const void *,
> + void *), void *data)
> +{
> + if (m_vec)
> + m_vec->stablesort (cmp, data);
> +}
>
> /* Search the contents of the sorted vector with a binary search.
> CMP is the comparison function to pass to bsearch. */
>
Thanks.
Alexander
