RE: optimization issue about -O2 and -Os

["Dave Korn" <dk at artimi dot com>]

> -----Original Message-----
> From: gcc-owner On Behalf Of Jim Wilson
> Sent: 30 April 2004 05:06

> On Thu, 2004-04-29 at 19:34, Ebony Zhu wrote:
> > Have you ever been troubled in the same problem? Are you 
> sure it's a gcc
> > bug, and not a mistake I probably made when building the cross tool?
> > (e.g. missed some important options when building gcc).
> 
> If something compiled with -O2 works and something compiled with -Os
> does not work, then the logical conclusion is that the -Os option is
> buggy.
> 
> However, it is possible that something went wrong with your build, if
> you are trying to do something complicated.  Since you didn't say
> anything about how you built the toolchain, or what you built, I can't
> comment on this.  I was just assuming that you had one toolchain, and
> the only thing that changed was the -O2/-Os option when using it.
> 
> I deal with gcc bugs everyday, but I don't have any specific knowledge
> about -Os PPC gcc-3.3.2 bugs.
> 
> You might try debugging the problem a bit to see what is 
> wrong.  Run the
> programs under gdb and see where they fail.  Put a breakpoint 
> in main to
> see if maybe they fail before main is reached.  Etc.

  Use -fverbose-asm in conjunction with --save-temps to get a list of the
optimisations in effect at the top of each assembler code file.  Try it with
-Os and -O2, and note the differences between them.  You may be able to
narrow it down to a specific -f flag by starting with -O2 and introducing
the changes between that and -Os one at a time. 


    cheers, 
      DaveK
-- 
Can't think of a witty .sigline today....