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shrink-wrap: Once more PRs 67778, 68634, and now 68909

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If a candidate PRE cannot get the prologue because a block BB is
reachable from it, but PRE does not dominate BB, we try again with the
dominators of PRE.  That "try again" needs to again consider BB though,
we aren't done with it.

	PR rtl-optimization/67778
	PR rtl-optimization/68634
	PR rtl-optimization/68909
	* shrink-wrap.c (try_shrink_wrapping): Add comment.  Don't pop
	block from the stack until done with it.  Remove a superfluous
	bitmap set.  Remove a superfluous bitmap test.

From-SVN: r232148
This commit is contained in:
Segher Boessenkool 2016-01-08 04:58:40 +01:00 committed by Segher Boessenkool
parent 7a127fa7c4
commit 52ad5601bf
2 changed files with 25 additions and 7 deletions
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9
gcc/ChangeLog
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@ -1,3 +1,12 @@
2016-01-08 Segher Boessenkool <segher@kernel.crashing.org>
PR rtl-optimization/67778
PR rtl-optimization/68634
PR rtl-optimization/68909
* shrink-wrap.c (try_shrink_wrapping): Add comment. Don't pop
block from the stack until done with it. Remove a superfluous
bitmap set. Remove a superfluous bitmap test.
2016-01-07 Martin Sebor <msebor@redhat.com>
PR c/68966

23
gcc/shrink-wrap.c
View File

@ -750,9 +750,21 @@ try_shrink_wrapping (edge *entry_edge, bitmap_head *bb_with,
/* If we can move PRO back without having to duplicate more blocks, do so.
We do this because putting the prologue earlier is better for scheduling.
We can move back to a block PRE if every path from PRE will eventually
need a prologue, that is, PRO is a post-dominator of PRE. PRE needs
to dominate every block reachable from itself. */
to dominate every block reachable from itself. We keep in BB_TMP a
bitmap of the blocks reachable from PRE that we already found, and in
VEC a stack of those we still need to consider.
Any block reachable from PRE is also reachable from all predecessors
of PRE, so if we find we need to move PRE back further we can leave
everything not considered so far on the stack. Any block dominated
by PRE is also dominated by all other dominators of PRE, so anything
found good for some PRE does not need to be reconsidered later.
We don't need to update BB_WITH because none of the new blocks found
can jump to a block that does not need the prologue. */
if (pro != entry)
{
@ -775,18 +787,15 @@ try_shrink_wrapping (edge *entry_edge, bitmap_head *bb_with,
bool ok = true;
while (!vec.is_empty ())
{
basic_block bb = vec.pop ();
bitmap_set_bit (bb_tmp, pre->index);
if (!dominated_by_p (CDI_DOMINATORS, bb, pre))
if (!dominated_by_p (CDI_DOMINATORS, vec.last (), pre))
{
ok = false;
break;
}
basic_block bb = vec.pop ();
FOR_EACH_EDGE (e, ei, bb->succs)
if (!bitmap_bit_p (bb_with, e->dest->index)
&& bitmap_set_bit (bb_tmp, e->dest->index))
if (bitmap_set_bit (bb_tmp, e->dest->index))
vec.quick_push (e->dest);
}