On Mon, Mar 19, 2007 at 03:32:19PM -0400, David Edelsohn wrote: > >>>>> Joe Buck writes: > > Joe> What worries me is that we can't afford to make -O0 run significantly > Joe> slower than it does now. Cycle speeds are no longer increasing, we have > Joe> to be very careful about slowing things down. > > Adding more passes does not necessarily slow down the compiler, as > IBM found with XLC. If one can remove enough dead code / statements / > insns / IR, one performs more processing on less data leading to less > overall work and faster compilation at -O0.
Agreed; -O0 could in principle be sped up; the important thing is making sure that it happens. In this case, adding a pass that computes SSA information that is used only for uninitialized variable warnings costs time; it could be compensated for by finding other speedups, but taken alone it is a slowdown.
