Compilation performance comparison of 3.5.0 and TreeSSA trees on MICO sources as requested in: [tree-ssa] Merge status 2004-05-03

[Richard Kenner]

    Mostly because of the breaking down of expressions into small trees,
    which are friendlier to the RTL expanders.  That's the reason we have a
    tree recombination pass at the end of tree optimization.

Sure, but my question is why do that breaking down and recombining with -O0?