------- Comment #10 from steven at gcc dot gnu dot org 2009-02-21 16:09 -------
OK, I checked what we're PREing here. This is indeed partial-partial PRE.
I suppose something like the following is a good idea. I'll admit it's
brute-force, but I'm not sure how else to stop GCSE-PRE from doing this (it's
baked into the LCM equations).
Jeff, what do you think about this PR?
Index: gcse.c
===================================================================
--- gcse.c (revision 144303)
+++ gcse.c (working copy)
@@ -3801,16 +3801,30 @@
edge e;
edge_iterator ei;
- /* If the current block is the destination of an abnormal edge, we
- kill all trapping expressions because we won't be able to properly
- place the instruction on the edge. So make them neither
- anticipatable nor transparent. This is fairly conservative. */
- FOR_EACH_EDGE (e, ei, bb->preds)
- if (e->flags & EDGE_ABNORMAL)
- {
- sbitmap_difference (antloc[bb->index], antloc[bb->index],
trapping_expr);
- sbitmap_difference (transp[bb->index], transp[bb->index],
trapping_expr);
- break;
+ if (EDGE_COUNT (bb->preds) > 20) /* ??? Should be a PARAM */
+ {
+ /* If a block has a large number of incoming edges, then inserting
+ many expressions in the predecessors to make one/few expression
+ fully redundant is probably not a profitable transformation.
+ Make all expressions non-anticipatable and non-transparent. */
+ sbitmap_zero (antloc[bb->index]);
+ sbitmap_zero (transp[bb->index]);
+ }
+ else
+ {
+ /* If the current block is the destination of an abnormal edge, we
+ kill all trapping expressions because we won't be able to properly
+ place the instruction on the edge. So make them neither
+ anticipatable nor transparent. This is fairly conservative. */
+ FOR_EACH_EDGE (e, ei, bb->preds)
+ if (e->flags & EDGE_ABNORMAL)
+ {
+ sbitmap_difference (antloc[bb->index],
+ antloc[bb->index], trapping_expr);
+ sbitmap_difference (transp[bb->index],
+ transp[bb->index], trapping_expr);
+ break;
+ }
}
sbitmap_a_or_b (ae_kill[bb->index], transp[bb->index], comp[bb->index]);
--
steven at gcc dot gnu dot org changed:
What |Removed |Added
----------------------------------------------------------------------------
CC| |law at gcc dot gnu dot org
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=39077
