Re: [PATCH-1, combine] Don't widen shift mode when target has rotate/mask instruction on original mode [PR93738]

[HAO CHEN GUI <guihaoc@linux.ibm.com>]

Sorry for the typo
s/change/chance

在 2023/7/21 8:59, HAO CHEN GUI 写道:
> Hi Jeff,
> 
> 在 2023/7/21 5:27, Jeff Law 写道:
>> Wouldn't it make more sense to just try rotate/mask in the original mode before trying a shift in a widened mode?  I'm not sure why we need a target hook here.
> 
> There is no change to try rotate/mask with the original mode when
> expensive_optimizations is set. The subst widens the shift mode.
> 
>       if (flag_expensive_optimizations)
>         {
>           /* Pass pc_rtx so no substitutions are done, just
>              simplifications.  */
>           if (i1)
>             {
>               subst_low_luid = DF_INSN_LUID (i1);
>               i1src = subst (i1src, pc_rtx, pc_rtx, 0, 0, 0);
>             }
> 
>           subst_low_luid = DF_INSN_LUID (i2);
>           i2src = subst (i2src, pc_rtx, pc_rtx, 0, 0, 0);
>         }
> 
> I don't know if the wider mode is helpful to other targets, so
> I added the target hook.
> 
> Thanks
> Gui Haochen