The dominance info is incorrect for entry and exit blocks.
According to dominated_by_p, nothing dominates the exit block (which is wrong),
and nothing post-dominates the entry block (which is also wrong).
A simple example:
(gdb) p dominated_by_p (CDI_POST_DOMINATORS, ENTRY_BLOCK_PTR, EXIT_BLOCK_PTR)
$4 = 0 '\0'
(gdb) p dominated_by_p (CDI_DOMINATORS, EXIT_BLOCK_PTR, ENTRY_BLOCK_PTR)
$5 = 0 '\0'
Both of these should return true.
Zdenek said he thought he knew why this was.