https://gcc.gnu.org/bugzilla/show_bug.cgi?id=118727
--- Comment #16 from Xi Ruoyao <xry111 at gcc dot gnu.org> --- (In reply to Tamar Christina from comment #15) > (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. I don't think it's correct... In the twisted test case we have something like r += abs((unsigned int)(unsigned char) a - (signed int)(signed char) b) So if a is 255 and b is 128, we should add r with abs(255 - (-128)) = 383, but with this form we'll add it with 127.
