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re PR tree-optimization/18707 (Performance regression at -O2 with gzip) 

PR tree-optimization/18707
	* cfgloopmanip.c (create_preheader): Move the preheader
	only if the latch was falling through to the header.

Co-Authored-By: Roger Sayle <roger@eyesopen.com>

From-SVN: r92282
This commit is contained in:
Eric Botcazou 2004-12-16 21:01:25 +01:00 committed by Eric Botcazou
parent 59b1a766fb
commit c15bc84b7b
2 changed files with 29 additions and 7 deletions
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7
gcc/ChangeLog
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@ -1,3 +1,10 @@
2004-12-16 Eric Botcazou <ebotcazou@libertysurf.fr>
Roger Sayle <roger@eyesopen.com>
PR tree-optimization/18707
* cfgloopmanip.c (create_preheader): Move the preheader
only if the latch was falling through to the header.
2004-12-16 Danny Smith <dannysmith@users.sourceforge.net>
PR target/18997

29
gcc/cfgloopmanip.c
View File

@ -1142,6 +1142,8 @@ create_preheader (struct loop *loop, int flags)
struct loop *cloop, *ploop;
int nentry = 0;
bool irred = false;
bool latch_edge_was_fallthru;
edge one_succ_pred = 0;
edge_iterator ei;
cloop = loop->outer;
@ -1152,6 +1154,8 @@ create_preheader (struct loop *loop, int flags)
continue;
irred |= (e->flags & EDGE_IRREDUCIBLE_LOOP) != 0;
nentry++;
if (EDGE_COUNT (e->src->succs) == 1)
one_succ_pred = e;
}
gcc_assert (nentry);
if (nentry == 1)
@ -1166,6 +1170,7 @@ create_preheader (struct loop *loop, int flags)
}
mfb_kj_edge = loop_latch_edge (loop);
latch_edge_was_fallthru = (mfb_kj_edge->flags & EDGE_FALLTHRU) != 0;
fallthru = make_forwarder_block (loop->header, mfb_keep_just,
mfb_update_loops);
dummy = fallthru->src;
@ -1177,13 +1182,23 @@ create_preheader (struct loop *loop, int flags)
if (ploop->latch == dummy)
ploop->latch = fallthru->dest;
/* Reorganize blocks so that the preheader is not stuck in the middle of the
loop. */
/* Get an edge that is different from the one from loop->latch to
dummy. */
e = EDGE_PRED (dummy, EDGE_PRED (dummy, 0)->src == loop->latch);
move_block_after (dummy, e->src);
/* Try to be clever in placing the newly created preheader. The idea is to
avoid breaking any "fallthruness" relationship between blocks.
The preheader was created just before the header and all incoming edges
to the header were redirected to the preheader, except the latch edge.
So the only problematic case is when this latch edge was a fallthru
edge: it is not anymore after the preheader creation so we have broken
the fallthruness. We're therefore going to look for a better place. */
if (latch_edge_was_fallthru)
{
if (one_succ_pred)
e = one_succ_pred;
else
e = EDGE_PRED (dummy, 0);
move_block_after (dummy, e->src);
}
loop->header->loop_father = loop;
add_bb_to_loop (dummy, cloop);