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On Tue, May 17, 2016 at 12:08 PM, Richard Biener <richard.guenther@gmail.com> wrote: > On Mon, May 16, 2016 at 10:09 AM, Bin.Cheng <amker.cheng@gmail.com> wrote: >> 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? > > The possible fix before my comment - make the vectorizer generate VEC_COND_EXPRs > with embedded comparison. Hi, Here is updated patch doing that. It's definitely clearer than the original version. Bootstrap and test on x86_64. Also checked the expanding time optimization still happens. Is it OK? Thanks, bin > > Thanks, > Richard. >
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pr69848-1-20160517.txt
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