[Bug tree-optimization/81165] [8 Regression] Regression in GCC-8.0.0's optimizer

law at redhat dot com gcc-bugzilla@gcc.gnu.org
Tue Dec 5 16:45:00 GMT 2017


https://gcc.gnu.org/bugzilla/show_bug.cgi?id=81165

--- Comment #12 from Jeffrey A. Law <law at redhat dot com> ---
In general we can't know if we're going to have a single argument PHI after
threading.   If the block has multiple preds that thread to the same final
destination, then we create a single copy and vector all the preds into that
single copy.

However, there the obvious special case.  If the block starts with just 2
preds, then any PHIs will be single argument PHIs in the copy.  That's probably
enough to address this particular BZ.    I don't think that's enough to address
the older BZ in this space though.


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