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Preserve loops in tail-merge 

2013-04-29  Tom de Vries  <tom@codesourcery.com>

	* tree-ssa-tail-merge.c (find_same_succ_bb): Skip loop latch bbs.
	(replace_block_by): Don't set LOOPS_NEED_FIXUP.
	(tail_merge_optimize): Handle current_loops == NULL.

	* gcc.dg/pr50763.c: Update test.

From-SVN: r198414
This commit is contained in:
Tom de Vries 2013-04-29 13:08:24 +00:00 committed by Tom de Vries
parent ebbd90d832
commit 315bbd2e3c
4 changed files with 33 additions and 14 deletions
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6
gcc/ChangeLog
View File

@ -1,3 +1,9 @@
2013-04-29 Tom de Vries <tom@codesourcery.com>
* tree-ssa-tail-merge.c (find_same_succ_bb): Skip loop latch bbs.
(replace_block_by): Don't set LOOPS_NEED_FIXUP.
(tail_merge_optimize): Handle current_loops == NULL.
2013-04-26 Jeff Law <law@redhat.com>
* tree-vrp.c (range_fits_type_p): Move to earlier point in file.

4
gcc/testsuite/ChangeLog
View File

@ -1,3 +1,7 @@
2013-04-29 Tom de Vries <tom@codesourcery.com>
* gcc.dg/pr50763.c: Update test.
2013-04-26 Jeff Law <law@redhat.com>
* gcc.dg/tree-ssa/vrp88.c: New test.

2
gcc/testsuite/gcc.dg/pr50763.c
View File

@ -12,5 +12,5 @@ foo (int c, int d)
while (c == d);
}
/* { dg-final { scan-tree-dump-times "== 33" 1 "pre"} } */
/* { dg-final { scan-tree-dump-times "== 33" 2 "pre"} } */
/* { dg-final { cleanup-tree-dump "pre" } } */

35
gcc/tree-ssa-tail-merge.c
View File

@ -691,7 +691,15 @@ find_same_succ_bb (basic_block bb, same_succ *same_p)
edge_iterator ei;
edge e;
if (bb == NULL)
if (bb == NULL
/* Be conservative with loop structure. It's not evident that this test
is sufficient. Before tail-merge, we've just called
loop_optimizer_finalize, and LOOPS_MAY_HAVE_MULTIPLE_LATCHES is now
set, so there's no guarantee that the loop->latch value is still valid.
But we assume that, since we've forced LOOPS_HAVE_SIMPLE_LATCHES at the
start of pre, we've kept that property intact throughout pre, and are
keeping it throughout tail-merge using this test. */
|| bb->loop_father->latch == bb)
return;
bitmap_set_bit (same->bbs, bb->index);
FOR_EACH_EDGE (e, ei, bb->succs)
@ -1462,17 +1470,6 @@ replace_block_by (basic_block bb1, basic_block bb2)
/* Mark the basic block as deleted. */
mark_basic_block_deleted (bb1);
/* ??? If we merge the loop preheader with the loop latch we are creating
additional entries into the loop, eventually rotating it.
Mark loops for fixup in this case.
??? This is a completely unwanted transform and will wreck most
loops at this point - but with just not considering loop latches as
merge candidates we fail to commonize the two loops in gcc.dg/pr50763.c.
A better fix to avoid that regression is needed. */
if (current_loops
&& bb2->loop_father->latch == bb2)
loops_state_set (LOOPS_NEED_FIXUP);
/* Redirect the incoming edges of bb1 to bb2. */
for (i = EDGE_COUNT (bb1->preds); i > 0 ; --i)
{
@ -1614,7 +1611,19 @@ tail_merge_optimize (unsigned int todo)
int iteration_nr = 0;
int max_iterations = PARAM_VALUE (PARAM_MAX_TAIL_MERGE_ITERATIONS);
if (!flag_tree_tail_merge || max_iterations == 0)
if (!flag_tree_tail_merge
|| max_iterations == 0
/* We try to be conservative with respect to loop structure, since:
- the cases where tail-merging could both affect loop structure and be
benificial are rare,
- it prevents us from having to fixup the loops using
loops_state_set (LOOPS_NEED_FIXUP), and
- keeping loop structure may allow us to simplify the pass.
In order to be conservative, we need loop information. In rare cases
(about 7 test-cases in the g++ testsuite) there is none (because
loop_optimizer_finalize has been called before tail-merge, and
PROP_loops is not set), so we bail out. */
|| current_loops == NULL)
return 0;
timevar_push (TV_TREE_TAIL_MERGE);