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| author | Eric Botcazou <ebotcazou@libertysurf.fr> | 2004-12-16 21:01:25 +0100 |
|---|---|---|
| committer | Eric Botcazou <ebotcazou@gcc.gnu.org> | 2004-12-16 20:01:25 +0000 |
| commit | c15bc84b7b6fad8567c9fd02f51e9436c5d3f861 (patch) | |
| tree | cf52adea28f2fae4e6fc75375765ddb131f51b85 /gcc/cfgloopmanip.c | |
| parent | 59b1a766fb697329a64202089365375c042f9c40 (diff) | |
| download | gcc-c15bc84b7b6fad8567c9fd02f51e9436c5d3f861.tar.gz | |
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
Diffstat (limited to 'gcc/cfgloopmanip.c')
| -rw-r--r-- | gcc/cfgloopmanip.c | 29 |
1 files changed, 22 insertions, 7 deletions
diff --git a/gcc/cfgloopmanip.c b/gcc/cfgloopmanip.c index 77988c20c2f..c07571014af 100644 --- a/gcc/cfgloopmanip.c +++ b/gcc/cfgloopmanip.c @@ -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); |