------- Comment #6 from jakub at gcc dot gnu dot org 2010-05-11 10:01 ------- Created an attachment (id=20625) --> (http://gcc.gnu.org/bugzilla/attachment.cgi?id=20625&action=view) partial fix of the ICE
The ICE is when going out of cfglayout mode. When going into the cfglayout mode try_optimize_cfg deletes the following empty block with no successors: 1988 /* Delete trivially dead basic blocks. This is either 1989 blocks with no predecessors, or empty blocks with no 1990 successors. However if the empty block with no 1991 successors is the successor of the ENTRY_BLOCK, it is 1992 kept. This ensures that the ENTRY_BLOCK will have a 1993 successor which is a precondition for many RTL 1994 passes. Empty blocks may result from expanding 1995 __builtin_unreachable (). */ 1996 if (EDGE_COUNT (b->preds) == 0 1997 || (EDGE_COUNT (b->succs) == 0 ... It is fine when asm doesn't have a fallthru edge IMHO because of this, so the patch just handles that case. Unfortunately, we ICE with this patch shortly after during cfg verification once we went out of the cfglayout mode. The problem is that the empty bb was deleted in cfglayout mode and its il.footer (which contained a BARRIER) got dropped on the floor. I guess if there is a predecessor and its fallthrough edge goes to the empty bb its il.footer could be moved over to the predecessor. -- http://gcc.gnu.org/bugzilla/show_bug.cgi?id=44071
