Question on "help=optimizers"

Pawar, Amit
Mon May 11 11:28:00 GMT 2015


I am trying to get information about various flags that are enabled/disabled at each optimization levels.
I am using gcc-5.1 compiler and for getting flag information,  I used the command "gcc  -Q  (-O0 or -O1 or -O2 or -O3 or -Ofast)   --help=optimizers".
[root@udp03279771uds result]# gcc -v
Using built-in specs.
Target: x86_64-unknown-linux-gnu
Configured with: ../../gcc-5.1.0/configure --enable-bootstrap --enable-languages=all --prefix=/root/work/GCC_Team/apawar/install/gcc0501
Thread model: posix
gcc version 5.1.0 (GCC)

[root@udp03279771uds result]# gcc -Q -Ofast --help=optimizers  | grep lrs
  -ftree-lrs                            [disabled]
[root@udp03279771uds result]# gcc -Q -Ofast --help=optimizers  | grep vectori
  -ftree-loop-vectorize                 [enabled]
  -ftree-slp-vectorize                  [enabled]
  -ftree-vectorize                      [disabled]
[root@udp03279771uds result]# gcc -Q -O3 --help=optimizers  | grep fvar\-tracking
  -fvar-tracking                        [enabled]
  -fvar-tracking-assignments            [enabled]
  -fvar-tracking-assignments-toggle     [disabled]
  -fvar-tracking-uninit                 [disabled]

Can someone please clarify the following questions:

1.	-fvar-tracking-uninit, -free-lrs are shown as disabled. I searched in "gcc" internals and not able to find any description about these options. Please help me how to find the information about these.
2.	-ftree-vectorize is shown as disabled in O3 and Ofast. Should this be updated as enabled?


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