Re: Gcc-mcore -O3?

[Nick Clifton <nickc at redhat dot com>]

Hi Yanbo,

: Me again. You are the expert of GCC for MCore. Can I have your help
: again?

Sure, send $5 in unmarked bills to.... :-)

: When I compile several c modules and run on the MCore EVB with "-g
: -c", everything is OK. But, when I apply "-c -O3" on the same files,
: the activities become unpredictable. I don't know why? Please help
: me. 

This is probably due to a bug in the MCore port.  Most likely an
optimisation is being performed that is generating incorrect code.
Without any more information I cannot narrow down the source of the
problem.

Here are some things you can try, in order to help locate the problem:

  * Does the problem occur at -O2 ?  How about -Os ?

  * Are there any other switches that you are passing to gcc ?
    If so, does the problem go away when you remove them from the
    command line ?

  * Does the problem still occur if you add the -g flag to gcc's
    command line, in order to enable debugging ?  If so, then cvan you
    use a debugger to narrow down where this unpredictable behavior
    is occurring ?

  * Can you create a small, reproducible test case that demonstrates
    the problem ?  If so, if you past that test case to the list,
    along with instructions on how to make the problem happen, then
    other people can have a go at tracking down the bug.

  * Does the problem happen in the simulator as well as on the
    hardware ?  can you use the instruction tracing feature of the
    simulator to track down where the misbehavior occurs ?

Cheers
	Nick