Re: -O2 vs -O3

From: Graham Stoney (greyham@research.canon.com.au)
Date: Fri May 26 2000 - 04:16:25 EDT

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    Christopher Thompson writes:
    > -O0: fails compile
    > -O1: 7 min 22 s --> 807594 bytes
    > -O2: 8 min 38 s --> 830397 bytes
    > -O3: 8 min 55 s --> 869151 bytes
    > -Os: 8 min 36 s --> 819874 bytes

    I couldn't duplicate this discrepancy between -Os and -O1 with gcc-2.95.2 on
    PowerPC: -Os gives the smallest kernel as you would expect, by a small margin:

    % powerpc-linux-size vmlinux.O1
       text data bss dec hex filename
     872076 70512 99356 1041944 fe618 vmlinux.O1
    % powerpc-linux-size vmlinux.O2
       text data bss dec hex filename
     864624 70512 99356 1034492 fc8fc vmlinux.O2
    % powerpc-linux-size vmlinux.Os
       text data bss dec hex filename
     859596 70512 99356 1029464 fb558 vmlinux.Os

    Regards,
    Graham

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