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authorSegher Boessenkool <segher@kernel.crashing.org>2016-01-08 04:58:40 +0100
committerSegher Boessenkool <segher@gcc.gnu.org>2016-01-08 04:58:40 +0100
commit52ad5601bf56aba4d5da585c6a212ce3f6509af3 (patch)
tree86689541fc8ed24ff266c281f8acac6768052b12 /gcc
parent7a127fa7c463b6b7c0285b32bac52bbdfc9a2117 (diff)
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shrink-wrap: Once more PRs 67778, 68634, and now 68909
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
Diffstat (limited to 'gcc')
-rw-r--r--gcc/ChangeLog9
-rw-r--r--gcc/shrink-wrap.c23
2 files changed, 25 insertions, 7 deletions
diff --git a/gcc/ChangeLog b/gcc/ChangeLog
index 7331599..44a2e01 100644
--- a/gcc/ChangeLog
+++ b/gcc/ChangeLog
@@ -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
diff --git a/gcc/shrink-wrap.c b/gcc/shrink-wrap.c
index e51bd36..84abd6b 100644
--- a/gcc/shrink-wrap.c
+++ b/gcc/shrink-wrap.c
@@ -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);
}