Re: [PATCH V2] Use subscalar mode to move struct block for parameter

[Jeff Law <jeffreyalaw@gmail.com>]

On 11/28/22 20:53, Jiufu Guo wrote:

>>
>> Right, but the number of registers is target dependent, so I don't see
>> how using "8" or any number of that matter is correct here.
> I understand.  And even for the same struct type, using how many
> registers to pass a parameter, it also dependends on the size of the
> parameter and how many leading parameters there is.
> So, as you said, "8" or any numbers are not always accurate.
> 
> Because, the enhancement in this patch is just make "block move" to be
> more friendly for follow optiomizations(cse/dse/dce...) by moving
> through sub-mode.  So, I just selected one arbitrary number which may
> not too large and also tolerable.
> I also through to query the max number registers from targets for
> param/ret passing, but it may not very accurate neither.
> 
> Any sugguestions are welcome! and thanks!
OK, so it's just a magic number and (in theory) any number should still 
generate correct code -- the number merely places limits on when we'll 
consider performing this optimization.

It may be overkill, but you might consider making it a PARAM that can be 
adjusted.


> 
> For this patch, only simple stuffs are handled like "D.xxx = param_1",
> where the source and dest of the assignment are all in memory which is
> the DECL_RTL(of D.xx/param_xx) in MEM_P/BLK.
> And to avoid complicate, this patch only handle the case where
> "(size % mode_size) == 0".
> 
> If any misunderstandings, please point out, thanks.
> And thanks for comments!
How values are justified varies on the PA depending on whether the 
parameter is passed in registers or in memory.   Though thinking more 
about things, I don't think you're changing how the parameter is passed. 
  Just how it's subsequently pulled out of memory.

jeff