On Mon, Aug 16, 2010 at 5:11 PM, bernd Kopf <bayerntoni@xxxxxxxxxx> wrote: > > > > ---------------------------------------- >> From: tiago.maluta@xxxxxxxxx >> Date: Mon, 16 Aug 2010 19:55:11 +0000 >> Subject: Re: Differences between -O2 and -O3 >> To: bayerntoni@xxxxxxxxxx >> CC: gcc-help@xxxxxxxxxxx >> >> On Mon, Aug 16, 2010 at 7:45 PM, bernd Kopf wrote: >>> >>> Hello, >>> >>> Is there a way to know what are exactly the differences between -O2 and -O3? >>> >> >> $ gcc -c -Q -O3 --help=optimizers> /tmp/O3-opts >> $ gcc -c -Q -O2 --help=optimizers> /tmp/O2-opts >> $ diff /tmp/O2-opts /tmp/O3-opts | grep enabled >> >> This are described on "man gcc" >> >> --tm > It's what I meant when I said "By comparing the outputs of gcc -O2 -c -Q and gcc -O3 -c -Q" > Sorry. I misunderstood. > Like I said it returns: >> -fgcse-after-reload [enabled] >> -finline-functions [enabled] >> -fipa-cp-clone [enabled] >> -fpredictive-commoning [enabled] >> -ftree-vectorize [enabled] >> -funswitch-loops [enabled] > > But adding these options to -O2 don't give the same executable than -O3 (by far) > I had never thought of doing this test. I'll try reproduce. But I don't know why this happens... Are you using some special test case? --tm
