Re: [tree-ssa] Memory usage in compute_immediate_uses

[law at redhat dot com]

In message <20030916183326.GA8717@nevyn.them.org>, Daniel Jacobowitz writes:
 >This grew out of a conversation with Daniel Berlin about SSA-PRE's memory
 >usage.  It turns out PRE doesn't need compute_immediate_uses after all and
 >he's removed the call in a later snapshot than I had on disk.  But other
 >passes (CCP at least, right now) use this, so I'm writing it out anyway.
It's probably worth noting that I don't think we've done any serious
investigation on what "reasonable" starting sizes to use for our hash tables,
virtual arrays, etc -- with the possible exception of how many definitions
a statement has -- the vast majority of statements have one definition :-).
So this isn't a huge surprise.

For immediate uses, I'd really expect the distribution to be heavily
weighted at 1 use, particularly after gimplification.  It would probably
be useful to see a histogram across a large body of code.


 >And just a question.  Sometimes all the immediate_uses varrays are already
 >allocated.  Nothing ever removes from the immediate_uses list.  So...
 >doesn't any call to compute_immediate_uses after they've already been
 >computed put duplicates on the list?  It's not a problem now that CCP is the
 >only thing using it, but while SSA-PRE was using it that must have hurt
 >performance elsewhere.
Yea, seems rather lame to me as well.

Jeff