http://gcc.gnu.org/bugzilla/show_bug.cgi?id=59802
Richard Biener <rguenth at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Keywords| |compile-time-hog
Status|UNCONFIRMED |NEW
Last reconfirmed| |2014-01-14
Component|c |rtl-optimization
Summary|excessive compile time in |excessive compile time in
|loop unswitching |RTL optimizers (loop
| |unswitching, CPROP)
Ever confirmed|0 |1
--- Comment #1 from Richard Biener <rguenth at gcc dot gnu.org> ---
GCC 4.8 shows
CPROP : 45.00 (57%) usr 0.02 ( 4%) sys 45.01 (57%) wall
4016 kB ( 2%) ggc
TOTAL : 78.48 0.57 79.04
213705 kB
while GCC 4.9 has
loop invariant motion : 10.11 (11%) usr 0.01 ( 2%) sys 10.16 (11%) wall
2 kB ( 0%) ggc
loop unswitching : 9.81 (11%) usr 0.00 ( 0%) sys 9.83 (11%) wall
1 kB ( 0%) ggc
CPROP : 48.16 (54%) usr 0.04 ( 7%) sys 48.20 (54%) wall
4444 kB ( 2%) ggc
so I can't really confirm the unswitching slowness (this is r205857 which
is somewhat older than your test).
Generally I think we should probably consider removing RTL unswitching,
there is not a single loop unswitched by RTL for this testcase.
