[Bug tree-optimization/125672] Jump threading hurts conditional select formation

[ktkachov at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=125672

--- Comment #6 from ktkachov at gcc dot gnu.org ---
Can we teach the threader in tree-ssa-threadbackward.cc profitable_path_p to
reject paths that are likely to be if-converted i.e. it is a diamond with pure
operations and no memory ops that ends in a 2-operand PHI of a mode that
can_conditionally_move_p ? I have a prototype for that that fixes the benchmark
in question and seems to be relatively clean testsuite-wise