On Mon, 29 Jul 2019, Richard Biener wrote:
>
> The following patch addresses appearant quadraticness in PTAs
> SCC merging algorithm which does (simplified)
>
> for (node N in SCC)
> bitmap_ior_into (pred(leader), pred(N));
>
> with the linked list implementation this leads to increasingly large
> amount of walking for pred(leader).
>
> The patch changes this to
>
> while (split /= 2)
> for (node N in lower-half-of-SCC)
> bitmap_ior_into_and_free (pred (N), pred (N in upper half of SCC));
>
> so in each outer iteration reducing the number of bitmaps by a factor
> of two and thus hopefully (and in practice for the testcase) reducing
> the intermediate bitmap sizes we work on.
>
> This improves
>
> tree PTA : 8.38 ( 23%) 0.22 ( 33%) 8.62 (
> 24%) 7679 kB ( 1%)
>
> to
>
> tree PTA : 5.30 ( 16%) 0.22 ( 32%) 5.54 (
> 16%) 28081 kB ( 4%)
>
> for the reduced testcase.
>
> I somehow didn't manage a 1:1 conversion so I need to re-check details
> here still I'd like to hear comments about the new bitmap API
> which is a source-destructive variant for bitmap_ior_into, instead of
> copying elements not in A moving them from B and in the end releasing
> the rest. Note using this API with keeping the merging as-is doesn't
> help PTA time.
This is what I applied.
Bootstrapped / tested on x86_64-unknown-linux-gnu.
Richard.
2019-07-30 Richard Biener <rguent...@suse.de>
PR tree-optimization/91257
* bitmap.h (bitmap_ior_into_and_free): Declare.
* bitmap.c (bitmap_list_unlink_element): Add defaulted param
whether to add the unliked element to the freelist.
(bitmap_list_insert_element_after): Add defaulted param for
an already allocated element.
(bitmap_ior_into_and_free): New function.
* tree-ssa-structalias.c (condense_visit): Reduce the
ponts-to and edge bitmaps of the SCC members in a
logarithmic fashion rather than all to one.
Index: gcc/bitmap.c
===================================================================
--- gcc/bitmap.c (revision 273795)
+++ gcc/bitmap.c (working copy)
@@ -252,7 +252,8 @@ bitmap_list_link_element (bitmap head, b
and return it to the freelist. */
static inline void
-bitmap_list_unlink_element (bitmap head, bitmap_element *element)
+bitmap_list_unlink_element (bitmap head, bitmap_element *element,
+ bool to_freelist = true)
{
bitmap_element *next = element->next;
bitmap_element *prev = element->prev;
@@ -279,18 +280,21 @@ bitmap_list_unlink_element (bitmap head,
head->indx = 0;
}
- bitmap_elem_to_freelist (head, element);
+ if (to_freelist)
+ bitmap_elem_to_freelist (head, element);
}
-/* Insert a new uninitialized element into bitmap HEAD after element
- ELT. If ELT is NULL, insert the element at the start. Return the
- new element. */
+/* Insert a new uninitialized element (or NODE if not NULL) into bitmap
+ HEAD after element ELT. If ELT is NULL, insert the element at the start.
+ Return the new element. */
static bitmap_element *
bitmap_list_insert_element_after (bitmap head,
- bitmap_element *elt, unsigned int indx)
+ bitmap_element *elt, unsigned int indx,
+ bitmap_element *node = NULL)
{
- bitmap_element *node = bitmap_element_allocate (head);
+ if (!node)
+ node = bitmap_element_allocate (head);
node->indx = indx;
gcc_checking_assert (!head->tree_form);
@@ -2009,6 +2013,56 @@ bitmap_ior_into (bitmap a, const_bitmap
return changed;
}
+/* A |= B. Return true if A changes. Free B (re-using its storage
+ for the result). */
+
+bool
+bitmap_ior_into_and_free (bitmap a, bitmap *b_)
+{
+ bitmap b = *b_;
+ bitmap_element *a_elt = a->first;
+ bitmap_element *b_elt = b->first;
+ bitmap_element *a_prev = NULL;
+ bitmap_element **a_prev_pnext = &a->first;
+ bool changed = false;
+
+ gcc_checking_assert (!a->tree_form && !b->tree_form);
+ gcc_assert (a->obstack == b->obstack);
+ if (a == b)
+ return false;
+
+ while (b_elt)
+ {
+ /* If A lags behind B, just advance it. */
+ if (!a_elt || a_elt->indx == b_elt->indx)
+ {
+ changed = bitmap_elt_ior (a, a_elt, a_prev, a_elt, b_elt, changed);
+ b_elt = b_elt->next;
+ }
+ else if (a_elt->indx > b_elt->indx)
+ {
+ bitmap_element *b_elt_next = b_elt->next;
+ bitmap_list_unlink_element (b, b_elt, false);
+ bitmap_list_insert_element_after (a, a_prev, b_elt->indx, b_elt);
+ b_elt = b_elt_next;
+ }
+
+ a_prev = *a_prev_pnext;
+ a_prev_pnext = &a_prev->next;
+ a_elt = *a_prev_pnext;
+ }
+
+ gcc_checking_assert (!a->current == !a->first);
+ if (a->current)
+ a->indx = a->current->indx;
+
+ if (b->obstack)
+ BITMAP_FREE (*b_);
+ else
+ bitmap_clear (b);
+ return changed;
+}
+
/* DST = A ^ B */
void
Index: gcc/bitmap.h
===================================================================
--- gcc/bitmap.h (revision 273795)
+++ gcc/bitmap.h (working copy)
@@ -399,6 +399,7 @@ extern void bitmap_clear_range (bitmap,
extern void bitmap_set_range (bitmap, unsigned int, unsigned int);
extern bool bitmap_ior (bitmap, const_bitmap, const_bitmap);
extern bool bitmap_ior_into (bitmap, const_bitmap);
+extern bool bitmap_ior_into_and_free (bitmap, bitmap *);
extern void bitmap_xor (bitmap, const_bitmap, const_bitmap);
extern void bitmap_xor_into (bitmap, const_bitmap);
Index: gcc/tree-ssa-structalias.c
===================================================================
--- gcc/tree-ssa-structalias.c (revision 273795)
+++ gcc/tree-ssa-structalias.c (working copy)
@@ -2069,36 +2069,73 @@ condense_visit (constraint_graph_t graph
/* See if any components have been identified. */
if (si->dfs[n] == my_dfs)
{
- while (si->scc_stack.length () != 0
- && si->dfs[si->scc_stack.last ()] >= my_dfs)
+ if (si->scc_stack.length () != 0
+ && si->dfs[si->scc_stack.last ()] >= my_dfs)
{
- unsigned int w = si->scc_stack.pop ();
- si->node_mapping[w] = n;
-
- if (!bitmap_bit_p (graph->direct_nodes, w))
- bitmap_clear_bit (graph->direct_nodes, n);
-
- /* Unify our nodes. */
- if (graph->preds[w])
- {
- if (!graph->preds[n])
- graph->preds[n] = BITMAP_ALLOC (&predbitmap_obstack);
- bitmap_ior_into (graph->preds[n], graph->preds[w]);
- }
- if (graph->implicit_preds[w])
+ /* Find the first node of the SCC and do non-bitmap work. */
+ bool direct_p = true;
+ unsigned first = si->scc_stack.length ();
+ do
{
- if (!graph->implicit_preds[n])
- graph->implicit_preds[n] = BITMAP_ALLOC (&predbitmap_obstack);
- bitmap_ior_into (graph->implicit_preds[n],
- graph->implicit_preds[w]);
+ --first;
+ unsigned int w = si->scc_stack[first];
+ si->node_mapping[w] = n;
+ if (!bitmap_bit_p (graph->direct_nodes, w))
+ direct_p = false;
}
- if (graph->points_to[w])
+ while (first > 0
+ && si->dfs[si->scc_stack[first - 1]] >= my_dfs);
+ if (!direct_p)
+ bitmap_clear_bit (graph->direct_nodes, n);
+
+ /* Want to reduce to node n, push that first. */
+ si->scc_stack.reserve (1);
+ si->scc_stack.quick_push (si->scc_stack[first]);
+ si->scc_stack[first] = n;
+
+ unsigned scc_size = si->scc_stack.length () - first;
+ unsigned split = scc_size / 2;
+ unsigned carry = scc_size - split * 2;
+ while (split > 0)
{
- if (!graph->points_to[n])
- graph->points_to[n] = BITMAP_ALLOC (&predbitmap_obstack);
- bitmap_ior_into (graph->points_to[n],
- graph->points_to[w]);
+ for (unsigned i = 0; i < split; ++i)
+ {
+ unsigned a = si->scc_stack[first + i];
+ unsigned b = si->scc_stack[first + split + carry + i];
+
+ /* Unify our nodes. */
+ if (graph->preds[b])
+ {
+ if (!graph->preds[a])
+ std::swap (graph->preds[a], graph->preds[b]);
+ else
+ bitmap_ior_into_and_free (graph->preds[a],
+ &graph->preds[b]);
+ }
+ if (graph->implicit_preds[b])
+ {
+ if (!graph->implicit_preds[a])
+ std::swap (graph->implicit_preds[a],
+ graph->implicit_preds[b]);
+ else
+ bitmap_ior_into_and_free (graph->implicit_preds[a],
+ &graph->implicit_preds[b]);
+ }
+ if (graph->points_to[b])
+ {
+ if (!graph->points_to[a])
+ std::swap (graph->points_to[a], graph->points_to[b]);
+ else
+ bitmap_ior_into_and_free (graph->points_to[a],
+ &graph->points_to[b]);
+ }
+ }
+ unsigned remain = split + carry;
+ split = remain / 2;
+ carry = remain - split * 2;
}
+ /* Actually pop the SCC. */
+ si->scc_stack.truncate (first);
}
bitmap_set_bit (si->deleted, n);
}
