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Re: Question about how to fix PR69052


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


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