[LLVMdev] question about PRE

Jiyu Zhang zhangjiyu at gmail.com
Mon Apr 30 14:10:49 PDT 2007

Thanks, Owen. It helps a lot:)


The old PRE never really worked properly, or at least was never
really finished.  We're planning to implement GVN-PRE (ftp://
ftp.cs.purdue.edu/pub/hosking/papers/vandrunen.pdf) as it is a more
powerful algorithm.  You are right, of course, that the ability of
the PRE to determine the equivalence of two expression.  This is an
area that can always be improved, and it's mostly an issue of if it's
worth the amount of work required to prove a given equivalence.  This
is something that'll probably have to be determined empirically.

Hope this help,


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