Re: [PATCH] Target hook for disabling the delay slot filler.

[Bernd Schmidt <bschmidt@redhat.com>]

On 09/17/2015 11:52 AM, Simon Dardis wrote:
> The profitability of using an ordinary branch over a delay slot branch
> depends on how the delay slot is filled. If a delay slot can be filled from
> an instruction preceding the branch or instructions proceeding that must be
> executed on both sides then it is profitable to use a delay slot branch.
>
> For cases when instructions are chosen from one side of the branch,
> the proposed optimization strategy is to not speculatively execute
> instructions when ordinary branches could be used. Performance-wise
> this avoids executing instructions which the eager delay filler picked
> wrongly.
>
> Since most branches have a compact form disabling the eager delay filler
> should be no worse than altering it not to fill delay slots in this case.

Ok, so in that case I think the patch would be reasonable if the target 
hook was named appropriately to say something like don't speculate when 
filling delay slots. It looks like fill_eager_delay_slots always 
speculates, so you needn't change your approach in reorg.c.
Possibly place the hook after rtx_cost/address_cost in target.def since 
it's cost related.


Bernd