Re: Loop clean up fixes

[Michael Hayes <m dot hayes at elec dot canterbury dot ac dot nz>]

Franz Sirl writes:

 > With Clinton's fixes I can bootstrap again, but now I get the same regressions
 > as with Alexandre's version:
 > 
 > FAIL: gcc.c-torture/execute/991014-1.c compilation,  -O2

This test doesn't have any loops and if I make loop_optimize
immediately return it still segfaults.  So I don't think this is due
to my hacks :-)

 > What puzzles me about your REG_USERVAR_P patch is that we now abort for the
 > !REG_USERVAR_P case, but shouldn't we return 0 for some other cases? As I
 > understand it this was the situation before your patch, now the code just
 > continues.

Originally we used to abort if the iteration register was one created
during loop optimisation.  Then when try_copy_prop was introduced we
could get a new pseudo created by loop_mems propagated into the
iteration register.  Bernd's patch changed the abort to a return to
handle this new case, however, this won't allow us to unroll this loop
or to use a BCT on the PPC.  AFAICT, any pseudo created by load_mems
will have the REG_USERVAR_P bit set, so I allowed this case to work
but still made the compiler abort if the iteration register was say a
new GIV.

Hopefully as I converted the loop optimiser to use the CFG I can shake
some of this hackery out.

Michael.