Re: [tree-ssa] DCE and conditionals

[law at redhat dot com]

In message <1052169537.6933.1286.camel@p4>, Andrew MacLeod writes:
 >On Mon, 2003-05-05 at 16:57, law@redhat.com wrote:
 >> In message <1052167541.2909.116.camel@frodo.toronto.redhat.com>, Diego Novi
 >llo 
 >> writes:
 >>  >Ah, yes.  So, keep the conditional expression.  After you've brought the
 >>  >program out of SSA form, run the linearizer once more.  And, this time,
 >>  >you untie its hands and let it trash COND_EXPRs that have both arms
 >>  >empty.  Similarly with other empty blocks that couldn't be removed
 >>  >before because of PHI nodes.
 >>  >
 >>  >
 >>  >> And in order for that to be effective, we
 >>  >> should look at phi removal when possible since thats what ends up
 >>  >> keeping the conditions alive... 
 >>  >> 
 >>  >PHIs that have all their arguments the same can be easily checked in the
 >>  >linearizer.
 >> Note that PHI optimization/removal is pretty simple, except for one
 >> little problem.  Specifically when there is a cycle in the PHI nodes.
 >> 
 >> I've got skeleton code to do PHI -> copy transformations here, but 
 >> there wasn't much point in doing anything with it until we support
 >> handling overlapping lifetimes.  
 >
 >Well, we're within an inch and a quarter of supporting them. Ive been
 >testing it by running copy-prop, and and I only have 1 additional
 >failure with copy-prop now. Of course, there is the matter of
 >bootstrapping left :-). 
Cool.  I'm more than happy to send that prototype code your way to play
with when you're ready.

It doesn't have hooks into the cycle detection code yet and the
copy insertion code was gross at best simply because I was just
experimenting :-)

jeff