Re: Problem with Delayed Branch Scheduling

[Balaji S <sivanbalaji at acmet dot com>]

_On 05-Jul-2005 00:14, Ian Lance Taylor san wrote_:
> Steven Bosscher <stevenb@suse.de> writes:
>
> > So you have a few instructions bundled into a VLIW instruction, and
> > one of the instructions in the bundle is moved into the delay slot,
> > thus breaking your VLIW bundle.  Right?
>
>
> I think there are two natural approaches.
>
> 1) Do the VLIW bundling after delayed branch scheduling.  The way to
>    do that is to the bundling in TARGET_ASM_FUNCTION_PROLOGUE.  The
>    FRV backend does this.  I've done this successfully in the past.
I think this is a good workaround but nullifying the possibility of having a VLIW bundled instruction in a branch delay slot.

> 2) When you do the VLIW bundling, put the instructions into a
>    PARALLEL.
I think this is the right solution which rectifies the problems. Please provide the pointer to where it has to be done.

> In general the gcc scheduler does not handle VLIW scheduling very
> well, and it needs a fair amount of target specific help.
I dont know the list of known requirements (help), but from my side, currently insns are marked by TImode to signify the start of a VLIW bundle but some assemblers may require to signify the end of a VLIW bundle. There is no provision for that. Currently i have hacked GCC to meet this requirement.