intent in cfg_layout_initialize

[DJ Delorie]

> > I think best fix is to simply add parameter of cfglayout_initialize
> > specifying whether the liveness shall be preserved, as for tracer
> > the cfglayout_initialize is called before liveness is built.
> 
> The one that I'm seeing is the call from the start of
> reorder_basic_blocks().

Didn't work.  x86 failed many tests because update_life got confused
about the FPU registers ($st, $st(1), etc) and deleted a few sets of
$st that it shouldn't have :-P

Any ideas?  Should I disable jump elimination for CLEANUP_CFGLAYOUT ?