> Hi,
> Ondrej Kubanek implemented profiling of loop histograms which sould be useful
> to improve
> i.e. quality of loop peeling of verctorization. However it turns out that
> most of histograms
> are lost on the way from profiling to loop peeling pass (about 90%). One
> common case is the
> following latent bug in loop header copying which forgets to update the loop
> header pointer.
>
> Curiously enough it does work to make single latch and preheader edge by
> splitting basic blocks
> but it works with wrong edge. As a consequence every loop where loop header
> was copied is
> removed from loop tree and inserted again losing all metadata included.
>
> Patch correctly updates the loop structure and also add verification
> that the loop tree is OK after all transforms which is failing without
> the patch.
>
> Bootstrapped/regtested x86_64-linux, plan to insteall this as obvious.
>
Hi,
sadly I managed to mix up patch and its WIP version in previous commit.
This patch adds the missing edge iterator and also fixes a side case
where new loop header would have multiple latches.
Bootstrapping/regtesting of x86_64-linux in progress. It was tested
previously and passed, so I hope it will again and commit it to unbreak
master then.
gcc/ChangeLog:
* tree-ssa-loop-ch.cc (ch_base::copy_headers): Fix previous
commit.
diff --git a/gcc/tree-ssa-loop-ch.cc b/gcc/tree-ssa-loop-ch.cc
index 560df39893e..9487e7f3e55 100644
--- a/gcc/tree-ssa-loop-ch.cc
+++ b/gcc/tree-ssa-loop-ch.cc
@@ -484,7 +484,10 @@ ch_base::copy_headers (function *fun)
/* Ensure that the header will have just the latch as a predecessor
inside the loop. */
if (!single_pred_p (exit->dest))
- exit = single_pred_edge (split_edge (exit));
+ {
+ header = split_edge (exit);
+ exit = single_pred_edge (header);
+ }
entry = loop_preheader_edge (loop);
@@ -547,16 +550,17 @@ ch_base::copy_headers (function *fun)
/* Find correct latch. We only duplicate chain of conditionals so
there should be precisely two edges to the new header. One entry
edge and one to latch. */
+ edge_iterator ei;
+ edge e;
FOR_EACH_EDGE (e, ei, loop->header->preds)
if (header != e->src)
{
loop->latch = e->src;
break;
}
- /* Ensure that the latch and the preheader is simple (we know that they
- are not now, since there was the loop exit condition. */
- split_edge (loop_preheader_edge (loop));
- split_edge (loop_latch_edge (loop));
+ /* Ensure that the latch is simple. */
+ if (!single_succ_p (loop_latch_edge (loop)->src))
+ split_edge (loop_latch_edge (loop));
if (dump_file && (dump_flags & TDF_DETAILS))
{
