http://gcc.gnu.org/bugzilla/show_bug.cgi?id=54146
--- Comment #17 from Steven Bosscher <steven at gcc dot gnu.org> 2012-08-05
18:48:55 UTC ---
(In reply to comment #14)
> if-conversion : 177.26 (but due to loop_optimizer_init)
Hmm, this is not loop_optimizer_init. All time is spent in the two memset calls
in cond_move_process_if_block:
/* Build a mapping for each block to the value used for each
register. */
max_reg = max_reg_num ();
size = (max_reg + 1) * sizeof (rtx);
then_vals = (rtx *) alloca (size);
else_vals = (rtx *) alloca (size);
memset (then_vals, 0, size);
memset (else_vals, 0, size);
There are O(1e6) registers in the test case, and O(1e5) basic blocks. So we end
up memset'ing O(10)MB X O(1e5)times = O(1e6)MB (assuming 64 bits pointers so
that each rtx is O(10) bytes).
I have a few ideas to fix this problem.
