Re: [committed] [RISC-V] Allow uarchs to set TARGET_OVERLAP_OP_BY_PIECES_P

[Jeff Law <jeffreyalaw@gmail.com>]

On 5/7/24 3:24 PM, Palmer Dabbelt wrote:

>> @@ -529,6 +536,7 @@ static const struct riscv_tune_param generic_ooo_tune_info = {
>>     4,						/* fmv_cost */
>>     false,					/* slow_unaligned_access */
>>     false,					/* use_divmod_expansion */
>> +  false,					/* overlap_op_by_pieces */
> 
> IMO we should turn this on for the generic OOO tuning -- the benchmarks
> say it's not faster for the T-Head OOO cores, but we were all so
> surprised to find that I don't think we even fully trust the benchmarks.
> I'd assume OOO cores are faster with the overlapping stores, so we
> should just lean into it and let vendors say something if that's the
> wrong assumption.
Several factors likely come into play (branch prediction, OOO 
properties, write combining, etc etc).

But sure, I don't think that'd be terribly controversial.  I can go 
ahead and make that change now given its triviality.

Jeff