O0 used for debugging

[bmyerz]

It seems that things build fine with O0, so why not use it for debugging instead of O1?

[nelsonje]

We chose -O1 so that we'd still get inlining in debug mode.

I thought there used to be build/correctness problems; that may have been with an old compiler or with an incorrect use of includes, since these days things seem to run okay There is a significant performance difference, as you can see from this 15-node, 8-core-per-node demo-gups4 run (both sizeA and sizeB 2^30):

optimization level	GUPS
-O0	0.118
-O1	0.392
-O3	0.442

I think that performance gap is too large to make -O0 the default in debug mode, but we could add a switch to the build.