Details
-
Type:
RFC
-
Status: Implemented
-
Resolution: Done
-
Component/s: DM
-
Labels:None
Description
By default, our builds are not optimised (-O0), which requires everyone who doesn't want to wait until the heat death of the universe to set SCONSFLAGS="opt=3", but other packages that are built with scons may not recognise this. This default is also contrary to the standard practise for open-source software, which is that by default builds are optimised. I propose to change the default optimisation level to opt=3 from the current opt=0. It's a very simple change in sconsUtils:
--- a/python/lsst/sconsUtils/state.py
|
+++ b/python/lsst/sconsUtils/state.py
|
@@ -98,7 +98,7 @@ def _initVariables():
|
SCons.Script.BoolVariable('force', 'Set to force possibly dangerous behaviours', False),
|
('optfile', 'Specify a file to read default options from', None),
|
('prefix', 'Specify the install destination', None),
|
- SCons.Script.EnumVariable('opt', 'Set the optimisation level', 0,
|
+ SCons.Script.EnumVariable('opt', 'Set the optimisation level', 3,
|
allowed_values=('0', '1', '2', '3')),
|
SCons.Script.EnumVariable('profile', 'Compile/link for profiler', 0,
|
allowed_values=('0', '1', 'pg', 'gcov')),
|
Attachments
Issue Links
Activity
I don't think so. You either want optimisation on full (2 or 3) for production-style builds, or you want it off completely (0) for debugging builds. I don't think there's any helpful middle ground.
Note also that even with optimisation turned off completely (-O0), debugging C++ in gdb can still be very difficult because it inlines stuff anyway.
Paul Price
added a comment - I don't think so. You either want optimisation on full (2 or 3) for production-style builds, or you want it off completely (0) for debugging builds. I don't think there's any helpful middle ground.
Note also that even with optimisation turned off completely ( -O0 ), debugging C++ in gdb can still be very difficult because it inlines stuff anyway. -Og (4.8 or later) is a good middle ground for debug?
Aside: I wasn't aware of -Og. I don't think we've currently got a means for setting it through sconsUtils (short of putting it in SCONSFLAGS). I'll fix that when I change the default optimisation setting.
Paul Price
added a comment - Aside: I wasn't aware of -Og . I don't think we've currently got a means for setting it through sconsUtils (short of putting it in SCONSFLAGS ). I'll fix that when I change the default optimisation setting. It shall be done in DM-7010.
Paul Price
added a comment - It shall be done in DM-7010 . 
Would it be worth using a lower optimization (e.g. 1 or 2) to make debugging feasible? I guess the tradeoff is general run time for everyone vs. people who want to use gdb having to rebuild lots of things without optimization.