[PATCH] vect: Merge loop mask and cond_op mask in fold-left, reduction.

[Richard Sandiford]

Richard Sandiford <richard.sandiford@arm.com> writes:
> Robin Dapp <rdapp.gcc@gmail.com> writes:
>> Hi,
>>
>> currently we discard the cond-op mask when the loop is fully masked
>> which causes wrong code in
>> gcc.dg/vect/vect-cond-reduc-in-order-2-signed-zero.c
>> when compiled with
>> -O3 -march=cascadelake --param vect-partial-vector-usage=2.
>>
>> This patch ANDs both masks instead.
>>
>> Bootstrapped and regtested on x86, aarch64 and power10.
>> Regtested on riscv64 and armv8.8-a+sve via qemu.
>>
>> Regards
>>  Robin
>>
>> gcc/ChangeLog:
>>
>> 	* tree-vect-loop.cc (vectorize_fold_left_reduction): Merge loop
>> 	mask and cond-op mask.
>
> OK, thanks.

Actually, as Richard mentioned in the PR, it would probably be better
to use prepare_vec_mask instead.  It should work in this context too
and would avoid redundant double masking.

Thanks,
Richard

>
>> ---
>>  gcc/tree-vect-loop.cc | 16 +++++++++++++++-
>>  1 file changed, 15 insertions(+), 1 deletion(-)
>>
>> diff --git a/gcc/tree-vect-loop.cc b/gcc/tree-vect-loop.cc
>> index 028692614bb..f9bf6a45611 100644
>> --- a/gcc/tree-vect-loop.cc
>> +++ b/gcc/tree-vect-loop.cc
>> @@ -7215,7 +7215,21 @@ vectorize_fold_left_reduction (loop_vec_info loop_vinfo,
>>        tree len = NULL_TREE;
>>        tree bias = NULL_TREE;
>>        if (LOOP_VINFO_FULLY_MASKED_P (loop_vinfo))
>> -	mask = vect_get_loop_mask (loop_vinfo, gsi, masks, vec_num, vectype_in, i);
>> +	{
>> +	  tree mask_loop = vect_get_loop_mask (loop_vinfo, gsi, masks,
>> +					       vec_num, vectype_in, i);
>> +	  if (is_cond_op)
>> +	    {
>> +	      /* Merge the loop mask and the cond_op mask.  */
>> +	      mask = make_ssa_name (TREE_TYPE (mask_loop));
>> +	      gassign *and_stmt = gimple_build_assign (mask, BIT_AND_EXPR,
>> +						       mask_loop,
>> +						       vec_opmask[i]);
>> +	      gsi_insert_before (gsi, and_stmt, GSI_SAME_STMT);
>> +	    }
>> +	  else
>> +	    mask = mask_loop;
>> +	}
>>        else if (is_cond_op)
>>  	mask = vec_opmask[i];
>>        if (LOOP_VINFO_FULLY_WITH_LENGTH_P (loop_vinfo))