cgccoptimization

How to get gcc -O1 optimization without specifying -O1

I know that -O1 automatically turns on certain flags. These flags can be turned on manually though. If I don't specify -O1, it should still be possible to get -O1 optimization by specifying all the flags that -O1 turns on.

I tried

-fthread-jumps -fcprop-registers -fguess-branch-probability

but it still does not do -O1 optimization. I can tell when I use gprof because the performance is not as good.

Which flags do I turn on to get -O1 optimization?

Solution

  • One way to find out:

    gcc -O1 -c -Q -v dummy.c

    (where dummy.c is your filename.) This causes gcc to spew the flags used to the command line.

    Edit: Please see kastauyra's answer on this. It appears you cannot simulate full -O1 optimization with -f flags alone.