http://gcc.gnu.org/bugzilla/show_bug.cgi?id=55270
--- Comment #9 from Richard Biener <rguenth at gcc dot gnu.org> 2013-01-28
14:03:18 UTC ---
When propagate_rhs_into_lhs alters the CFG from
if ()
{
if ()
exit_loop;
}
to
if ()
{
exit_loop;
}
it fails to fixup loop structure:
/* Propagation into these nodes may make certain edges in
the CFG unexecutable. We want to identify them as PHI nodes
at the destination of those unexecutable edges may become
degenerates. */
else if (gimple_code (use_stmt) == GIMPLE_COND
|| gimple_code (use_stmt) == GIMPLE_SWITCH
|| gimple_code (use_stmt) == GIMPLE_GOTO)
{
...
Now, for full propagation the edge wants marking as non-executable
(which is done by removing it here - somewhat premature, as CFG cleanup
is run afterwards anyway and that handles the situation correctly
by calling fix_loop_structure).
Index: gcc/tree-ssa-dom.c
===================================================================
--- gcc/tree-ssa-dom.c (revision 195502)
+++ gcc/tree-ssa-dom.c (working copy)
@@ -3006,7 +3006,14 @@ eliminate_degenerate_phis (void)
}
if (cfg_altered)
- free_dominance_info (CDI_DOMINATORS);
+ {
+ free_dominance_info (CDI_DOMINATORS);
+ if (current_loops)
+ {
+ calculate_dominance_info (CDI_DOMINATORS);
+ fix_loop_structure (NULL);
+ }
+ }
/* Propagation of const and copies may make some EH edges dead. Purge
such edges from the CFG as needed. */
fixes this (one more reason to fix loop structure at loop_optimizer_init
instead ...)
