[Bug middle-end/58402] [4.9 regression] FAIL: gcc.dg/tree-ssa/phi-opt-1.c scan-tree-dump-times optimized "if" 0

[rguenth at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=58402

--- Comment #2 from Richard Biener <rguenth at gcc dot gnu.org> ---
Ok, so the testcase requires that

 1) critical edges are split (before PRE which isn't run at -O1)
 2) the next CFG cleanup (after copyprop) will end up removing the
    forwarders in a way building up a tree-argument PHI
 3) PHI-OPT executes for the third time, this time with the exact
    right CFG / PHI node present

my patch obfuscates the CFG gain by splitting edges and no CFG cleanup
running inbetween that and the late PHI-OPT pass.