Google SoC Project Proposal: Better Uninitialized Warnings

[Joe Buck]

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.