-O3 failures with ? vectorization in gcc 4.9

[Tim Prince]

I get good results with -march=core-avx2 -O2 -ftree-vectorize 
-finline-functions -funswitch-loops -fpredictive-commoning 
-fgcse-after-reload -ftree-slp-vectorize -ftree-partial-pre 
-fipa-cp-clone, arrived at by trying the options listed as being enabled 
at -O3 and removing those which fail at run time.  Is this the 
recommended way to go, or should I file a PR about one or two cases 
which fail at -O3?
When running under gdb with -O3, a segfault is reported in separately 
compiled code which isn't directly affected by these options.  When 
running outside gdb, the application hangs when it reaches a vectorized 
loop containing ? operator.
It seems that -fvect-cost-model is not the only part of -O3 which 
produces failure.

-- 
Tim Prince