Re: [PATCH PR69848/partial]Propagate comparison into VEC_COND_EXPR if target supports

["Bin.Cheng" <amker dot cheng at gmail dot com>]

On Fri, May 13, 2016 at 5:53 PM, Richard Biener
<richard.guenther@gmail.com> wrote:
> On May 13, 2016 6:02:27 PM GMT+02:00, Bin Cheng <Bin.Cheng@arm.com> wrote:
>>Hi,
>>As PR69848 reported, GCC vectorizer now generates comparison outside of
>>VEC_COND_EXPR for COND_REDUCTION case, as below:
>>
>>  _20 = vect__1.6_8 != { 0, 0, 0, 0 };
>>  vect_c_2.8_16 = VEC_COND_EXPR <_20, { 0, 0, 0, 0 }, vect_c_2.7_13>;
>>  _21 = VEC_COND_EXPR <_20, ivtmp_17, _19>;
>>
>>This results in inefficient expanding.  With IR like:
>>
>>vect_c_2.8_16 = VEC_COND_EXPR <vect__1.6_8 != { 0, 0, 0, 0 }, { 0, 0,
>>0, 0 }, vect_c_2.7_13>;
>>  _21 = VEC_COND_EXPR <vect__1.6_8 != { 0, 0, 0, 0 }, ivtmp_17, _19>;
>>
>>We can do:
>>1) Expanding time optimization, for example, reverting comparison
>>operator by switching VEC_COND_EXPR operands.  This is useful when
>>backend only supports some comparison operators.
>>2) For backend not supporting vcond_mask patterns, saving one LT_EXPR
>>instruction which introduced by expand_vec_cond_expr.
>>
>>This patch fixes this by propagating comparison into VEC_COND_EXPR even
>>if it's used multiple times.  For now, GCC does single_use_only
>>propagation.  Ideally, we may duplicate the comparison before each use
>>statement just before expanding, so that TER can successfully backtrack
>>it from each VEC_COND_EXPR.  Unfortunately I didn't find a good pass to
>>do this.  Tree-vect-generic.c looks like a good candidate, but it's so
>>early that following CSE could undo the transform.  Another possible
>>fix is to generate comparison inside VEC_COND_EXPR directly in function
>>vectorizable_reduction.
>
> I prefer this for now.
Hi Richard, you mean this patch, or the possible fix before your comment?
Here is an updated patch addressing comment issue pointed out by
Bernhard Reutner-Fischer.  Thanks.

Thanks,
bin
>
> Richard.
>
>>As for possible comparison CSE opportunities, I checked that it's
>>simple enough to be handled by RTL CSE.
>>
>>Bootstrap and test on x86_64 and AArch64.  Any comments?
>>
>>Thanks,
>>bin
>>
>>2016-05-12  Bin Cheng  <bin.cheng@arm.com>
>>
>>       PR tree-optimization/69848
>>       * optabs-tree.c (expand_vcond_mask_p, expand_vcond_p): New.
>>       (expand_vec_cmp_expr_p): Call above functions.
>>       * optabs-tree.h (expand_vcond_mask_p, expand_vcond_p): New.
>>       * tree-ssa-forwprop.c (optabs-tree.h): Include header file.
>>       (forward_propagate_into_cond): Propgate multiple uses for
>>       VEC_COND_EXPR.
>
>

Attachment: pr69848-1-20160515.txt
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