#_FLAGS="$_FLAGS -fomit-frame-pointer"
_FLAGS="$_FLAGS -fno-ident -fivopts -fbranch-target-load-optimize"
_FLAGS="$_FLAGS -finline-small-functions -findirect-inlining"
_FLAGS="$_FLAGS -ffast-math"
# ?
#_FLAGS="$_FLAGS -fgcse-sm -fgcse-las"
# O2
_FLAGS="$_FLAGS -fschedule-insns2 -fsched-spec-load -fsched-pressure"
# broken on x86 (https://gcc.gnu.org/bugzilla/show_bug.cgi?id=38768). I get worked exlude elfutils -ftracer
#_FLAGS="$_FLAGS -fschedule-insns"
# O3
_FLAGS="$_FLAGS -fgcse-after-reload -fipa-cp-clone -fpredictive-commoning -ftree-loop-distribute-patterns -funswitch-loops -ftree-vectorize"
# O3 4.8
_FLAGS="$_FLAGS -fvect-cost-model -ftree-partial-pre"
# 4.9
#_FLAGS="$_FLAGS -fno-var-tracking-assignments"

# looks like help other optimizers, but too increase code size
#_FLAGS="$_FLAGS -ftracer"

# modulo
_FLAGS="$_FLAGS -fmodulo-sched -fmodulo-sched-allow-regmoves -freschedule-modulo-scheduled-loops"

#_FLAGS="$_FLAGS -fno-stack-protector"

# 5 "improve code quality"? to grok
#_FLAGS="$_FLAGS -fno-semantic-interposition"