http://gcc.gnu.org/bugzilla/show_bug.cgi?id=46590
--- Comment #36 from Richard Guenther <rguenth at gcc dot gnu.org> 2012-09-05
10:59:52 UTC ---
If I fix that (PR54489) by iterating over immediate dominators when querying
AVAIL_OUT
instead of accumulating then other loop opts quickly take over in compile-time,
but memory usage stays reasonable at -O1. LIM is now the pass that pushes
memory usage to 1.8GB - all other optimization passes are happy with just
~800MB. The issue with LIM is that it analyzes the whole function instead
of working on outermost loops at a time (PR54488). Then of course IRA
comes along and wrecks memory usage again ... (create_loop_tree_nodes).
One can tame down IRA a bit using -fno-ira-loop-pressure -fira-region=one.
We then arrive at roughly a constant 900MB memory usage for the full(!)
testcase at -O1 and
Execution times (seconds)
phase opt and generate : 495.90 (99%) usr 1.98 (98%) sys 499.91 (99%) wall
870508 kB (92%) ggc
df reaching defs : 19.16 ( 4%) usr 0.06 ( 3%) sys 19.18 ( 4%) wall
0 kB ( 0%) ggc
alias stmt walking : 28.75 ( 6%) usr 0.21 (10%) sys 29.12 ( 6%) wall
2336 kB ( 0%) ggc
tree SSA rewrite : 63.42 (13%) usr 0.02 ( 1%) sys 63.77 (13%) wall
18830 kB ( 2%) ggc
tree SSA incremental : 74.64 (15%) usr 0.03 ( 1%) sys 74.44 (15%) wall
25886 kB ( 3%) ggc
dominance frontiers : 101.71 (20%) usr 0.09 ( 4%) sys 102.17 (20%) wall
0 kB ( 0%) ggc
dominance computation : 52.56 (11%) usr 0.09 ( 4%) sys 53.35 (11%) wall
0 kB ( 0%) ggc
loop invariant motion : 101.20 (20%) usr 0.10 ( 5%) sys 101.75 (20%) wall
2700 kB ( 0%) ggc
TOTAL : 498.79 2.03 502.87
947764 kB
(all entries > 10s)
The incremental SSA stuff is complete loop unrolling / IV canonicalization
which does SSA update once per loop (similar to what loop header copying
formerly did). Fixing that leads to
Execution times (seconds)
phase opt and generate : 214.62 (99%) usr 1.53 (96%) sys 217.41 (99%) wall
870508 kB (92%) ggc
df reaching defs : 23.07 (11%) usr 0.01 ( 1%) sys 23.10 (10%) wall
0 kB ( 0%) ggc
alias stmt walking : 28.51 (13%) usr 0.23 (14%) sys 28.93 (13%) wall
2336 kB ( 0%) ggc
loop invariant motion : 105.43 (48%) usr 0.01 ( 1%) sys 106.22 (48%) wall
2700 kB ( 0%) ggc
TOTAL : 217.56 1.59 220.44
947764 kB
so RTL invariant motion is now the main offender ;)
