https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96974
--- Comment #8 from Stam Markianos-Wright <stammark at gcc dot gnu.org> --- I have a liiitle bit more progress here, but I have a question about vect_get_smallest_scalar_type. If we look at the comment before the function: >/* Return the smallest scalar part of STMT_INFO. > This is used to determine the vectype of the stmt. We generally set the > vectype according to the type of the result (lhs). For stmts whose > result-type is different than the type of the arguments (e.g., demotion, > promotion), vectype will be reset appropriately (later). Note that we have > to visit the smallest datatype in this function, because that determines the > VF. If the smallest datatype in the loop is present only as the rhs of a > promotion operation - we'd miss it. Would this be "smallest datatype in all cases", or is this more like "the smallest datatype within the same promotion/demotion chain"? i.e. how should we react if we detect a smallest datatype on the rhs of "float" when everything else in the stmt has been in the integer chain (int or, like in this case, long int)? > Such a case, where a variable of this datatype does not appear in the lhs > anywhere in the loop, can only occur if it's an invariant: e.g.: > 'int_x = (int) short_inv', which we'd expect to have been optimized away by > invariant motion. However, we cannot rely on invariant motion to always > take invariants out of the loop, and so in the case of promotion we also > have to check the rhs. > LHS_SIZE_UNIT and RHS_SIZE_UNIT contain the sizes of the corresponding > types. */ I have found that this is why we end up with a smaller number in: TYPE_VECTOR_SUBPARTS (nunits_vectype) == 4 than in: TYPE_VECTOR_SUBPARTS (*stmt_vectype_out) == 8 So I'm thinking that either A) We shouldn't allow this, and add in some check maybe for "GET_MODE_CLASS (x) == GET_MODE_CLASS (y)" or B) Some of the logic that generates stmt_vectype_out is deficient and it should also be detecting the existence of a "float" type to get the VF.
