Re: Dom patch

[Jeffrey A Law <law at redhat dot com>]

On Thu, 2005-08-25 at 02:42 -0400, James Morrison wrote:
>  Hey,
> 
>   I'm going to do more testing on this, but it seems this patch reduces the
> number of DOM iterations from the number of else if statements in pr19097 to
> 2 DOM iterations.
Certainly any time we can optimize more of the comparisons in a smaller
number of iterations, it's going to be a compile-time win.  



>   This is a massive savings and the savings if from
> calling fold_build2 (cond_code, boolean_type_node, op0, op1) in 
> thread_across_edge since the folded expression is now saved for the rest of
> the iteration where the folded expression wasn't before.
Huh?  I don't follow this explanation.   Nor after a quick read of
the code do I see how you've made any real change here.  Both before
and after your change we still fold the condition and store the
result in cached_lhs. 

Also note that both cached_lhs and the dummy condition are only valid
for a single call to thread_across_edge -- so if you're saving a value
from one call and expecting it to be valid across another call (from the
standpoint of the correctness of the target program), then it's clearly
wrong.

Jeff