[Bug middle-end/36550] Wrong "may be used uninitialized" warning (conditional PHIs)

["law at redhat dot com" <gcc-bugzilla at gcc dot gnu dot org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=36550

Jeffrey A. Law <law at redhat dot com> changed:

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                 CC|                            |law at redhat dot com

--- Comment #15 from Jeffrey A. Law <law at redhat dot com> ---
Note that Os throttles jump threading as jump threading often increases
codesize.  

That's why you get this warning at -Os, but not at -O2.    Jump threading does
not have a good way to estimate how much of the duplicated block will be
eliminated as dead code.

In this testcase, the contents of the duplicated block would be entirely
eliminated as dead code making threading jumps 100% free from a codesize
standpoint.

That's where I think the focus is better spent (rather than adding additional
cases to tree-ssa-uninit.c).  Improve the jump threading heuristics -- the net
result will be better code *and* the warning goes away as a side effect.