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[Bug tree-optimization/81165] [8 Regression] Regression in GCC-8.0.0's optimizer
- From: "law at redhat dot com" <gcc-bugzilla at gcc dot gnu dot org>
- To: gcc-bugs at gcc dot gnu dot org
- Date: Tue, 05 Dec 2017 16:45:05 +0000
- Subject: [Bug tree-optimization/81165] [8 Regression] Regression in GCC-8.0.0's optimizer
- Auto-submitted: auto-generated
- References: <bug-81165-4@http.gcc.gnu.org/bugzilla/>
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.