https://gcc.gnu.org/bugzilla/show_bug.cgi?id=118727
--- Comment #15 from Tamar Christina <tnfchris at gcc dot gnu.org> --- (In reply to Xi Ruoyao from comment #13) > For example for the original gcc.dg/pr108692.c: > > a.0_4 = (unsigned char) a_14; > _5 = (int) a.0_4; > b.1_6 = (unsigned char) b_16; > _7 = (int) b.1_6; > c_17 = _5 - _7; > _8 = ABS_EXPR <c_17>; > r_18 = _8 + r_23; > > becomes: > > patt_31 = .ABD (a.0_4, b.1_6); > > so when we get the ABD we already stripped the redundant (int) conversion > here, note that the (unsigned char) conversion is really needed. And for my > twisted test case: > > a.0_4 = (unsigned char) a_14; > _5 = (unsigned int) a.0_4; > _6 = (unsigned int) b_16; > _7 = _5 - _6; > c_17 = (int) _7; > _8 = ABS_EXPR <c_17>; > > becomes: > > patt_38 = (unsigned short) a.0_4; > patt_35 = (signed short) b_16; > patt_36 = (signed short) patt_38; > patt_33 = .ABD (patt_36, patt_35); > > To me this is already the "optimal" way. Correct me if I'm wrong, but > anyway even if there's a redundant conversion it should be stripped in > vect_recog_abd_pattern instead of vect_recog_sad_pattern. No, that's not correct. SAD_EXPR is the most optimal version here as SAD_EXPR performs double widening. It removes the need for the intermediate vector widening. a.0_4 = (unsigned char) a_14; patt_b_16 = (unsigned char) b_16 patt_41 = SAD_EXPR <a.0_4, patt_b_16, r_23>; is the most optimal form, as it does the operation on bytes rather than short.
