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Re: PRE lossage



On Oct 28, 2003, at 2:29 PM, Andrew MacLeod wrote:


On Tue, 2003-10-28 at 14:25, Daniel Berlin wrote:

On Oct 28, 2003, at 2:17 PM, law@redhat.com wrote:


In message <64E3BF94-097A-11D8-A9DD-000A95AF1FAE@dberlin.org>, Daniel
Berlin wr
ites:
I've been putting off these bugs until switch lowering happens, since
that should allow us to pre-split the critical edges without any
trouble, and once that happens, insertion shouldn't require creating
new blocks, ever, and the whole problem goes away.
I would be very wary of pre-splitting critical edges.  In my
experience, it
loses, badly.

Except that every compiler i know of does it (LLVM does it, Open64 does
it, Intel's compiler does it, etc), and the papers for SSAPRE assume it
specifically.
We also have to recompute a whole bunch of info if we split a critical
edge (dominators, dominance frontiers, etc), and can't run ESSA
minimization.

It doesnt really change that information very much does it?

No, it's more having to resize the arrays and whatnot and fill in the new info.



It should
be easily updatable when the split happens...  (dominator, etc by the
splitting routine)

It should, but i think only dominators has an interface to do incremental updates.


Andrew




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