https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110751
--- Comment #7 from JuzheZhong <juzhe.zhong at rivai dot ai> --- (In reply to rguent...@suse.de from comment #5) > On Thu, 20 Jul 2023, kito at gcc dot gnu.org wrote: > > > https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110751 > > > > --- Comment #4 from Kito Cheng <kito at gcc dot gnu.org> --- > > > OK, so TA is either merge or all-ones. > > > > Yes, your understand is correct, just few more detail is that can be mixing > > with either merge or all-ones. > > > > e.g. > > > > An 4 x i32 vector with mask 1 0 1 0 > > > > Op = | a | b | c | d | > > Mask = | 1 | 0 | 1 | 0 | > > > > the result could be: > > | a | b | c | d | > > | a | all-1 | c | d | > > | a | all-1 | c | all-1 | > > | a | all-1 | c | d | > > > > > > > Not sure how you can use MA at the moment since you specify an existing > > > operand in your target hook. As far as > > > I can see there's no value the target hook can provide that matches any > > of the implementation semantics? > > > > That's the key point - we don't know how to return an undefined value > > there, we > > have intrinsic can generate undefined value, but it seems impossible to > > generate that within the hook. > > Well, neither *A nor *U can be specified currently. As said for 'merge' > we would need another operand. And since 'unspecified' is either merge > or all-ones we can't express that either. It's not really 'undefined' > either. > > Note this also means the proposal to define a .MASK_LOAD as zeroing > masked elements is not going to work for RISC-V, instead we'd need > an explicit 'else' value there as well. > > In fact we could follow .MASK_LOAD for .COND_* and simply omit > the 'else' operand for the case of 'unspecified', no? GIMPLE would > be fine omitting it, not sure whether there's precedent for > optabs with optional operands? I am wondering whether we can build a CONST_VECTOR with metadata in the tree attribute that can be seen in the RTL level during "expand" stage. For example, can we have some like this: tree undef = build_zero_cst (vectype) TREE_ATTRIBUTE (undef) = "undefined" Then, in the expand stage, tree t = get_tree (rtx) if (TREE_ATTRIBUTE (t) == “undefined”) { ... } This is my immature idea. Feel free to correct me.
