https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109154
--- Comment #63 from Tamar Christina <tnfchris at gcc dot gnu.org> --- > > It looks like `-fno-tree-pre` does the trick, but then of course, messes up > > elsewhere. The conditional statement seem to stay in the most complicated > > form possible in scalar code. > > > > I'll try to track down what to turn off and experiment with a pre2 after > > vect. > > Is before predcom a good place? > > I would avoid putting it into the loop pipeline. Instead I'd turn the > FRE pass that runs after tracer into PRE. Maybe conditional on whether > there are any loops. > > Note it's not so easy to "tame" PRE, the existing things happen at > elimination time in eliminate_dom_walker::eliminate_stmt. I would > experiment with restricting the use of inserted PHIs in innermost(!) > loops containing invariants, maybe only if the number of PHI args is > more than two ... (but that's somewhat artificial). > > That said, I'm not really convinced this is a good idea. I hear you.. there's also the added complexity that this likely only is beneficial for fully masked architectures. I wonder, if it might be feasible and better to pass on additional information from pre to ifcvt to indicate that the operation was created from a common block. In which case ifcvt could move the cond to just before the first shared statement?
