Question about how to fix PR69052

[Bernd Schmidt]

On 01/26/2016 10:48 AM, Bin.Cheng wrote:
> Yes, I moved whole loop pass (also the pass_web) after combine and it
> worked.  A combine pass before loop-invariant can fix this problem.
> Below passes are currently between loop transform and combine:
>
>        NEXT_PASS (pass_web);
>        NEXT_PASS (pass_rtl_cprop);
>        NEXT_PASS (pass_cse2);
>        NEXT_PASS (pass_rtl_dse1);
>        NEXT_PASS (pass_rtl_fwprop_addr);
>        NEXT_PASS (pass_inc_dec);
>        NEXT_PASS (pass_initialize_regs);
>        NEXT_PASS (pass_ud_rtl_dce);
>
> I think pass_web needs to be after loop transform because it's used to
> handle unrolled register live range.
> pass_fwprop_addr and pass_inc_dec should stay where they are now.  And
> putting pass_inc_dec before loop unroll may be helpful to keep more
> auto increment addressing mode chosen by IVO.
> We should not need to duplicate pass_initialize_regs.
> So what's about pass_rtl_cprop, cse2 and dse1.  Should these pass be
> duplicated after loop transform thus loop transformed code can be
> cleaned up?

Hard to tell in advance - you might want to experiment a bit; set up a 
large collection of input files and see what various approaches do to 
code generation. In any case, I suspect this is gcc-7 material 
(unfortunately).


Bernd