On Tue, Sep 01, 2020 at 04:09:53PM +0800, luoxhu wrote:
> On 2020/9/1 01:04, Segher Boessenkool wrote:
> > For v a V4SI, x a SI, j some int, what do we generate for
> > v[j&3] = x;
> > ?
> > This should be exactly the same as we generate for
> > vec_insert(x, v, j);
> > (the builtin does a modulo 4 automatically).
>
> No, even with my patch "stxv 34,-16(1);stwx 5,9,6;lxv 34,-16(1)" generated
> currently.
I think you should solve the problem in the generic case, then, since it
is (presumably) much more frequent.
> Is it feasible and acceptable to expand some kind of pattern in expander
> directly without
> builtin transition?
I don't understand what you mean?
> I borrowed some of implementation from vec_extract. For vec_extract, the
> issue also exists:
>
> source: gimple:
> expand: asm:
> 1) i = vec_extract (v, n); => i = __builtin_vec_ext_v4si (v, n); =>
> {r120:SI=unspec[r118:V4SI,r119:DI] 134;...} => slwi 9,6,2 vextuwrx
> 3,9,2
> 2) i = vec_extract (v, 3); => i = __builtin_vec_ext_v4si (v, 3); =>
> {r120:SI=vec_select(r118:V4SI,parallel)...} => li 9,12 vextuwrx
> 3,9,2
> 3) i = v[n%4]; => _1 = n & 3; i = VIEW_CONVERT_EXPR<int[4]>(v)[_1]; =>
> ... => stxv 34,-16(1);addi 9,1,-16; rldic 5,5,2,60; lwax 3,9,5
> 4) i = v[3]; => i = BIT_FIELD_REF <v, 32, 96>; =>
> {r120:SI=vec_select(r118:V4SI,parallel)...} => li 9,12; vextuwrx 3,9,2
>
> Case 3) also couldn't handle the similar usage, and case 4) doesn't generate
> builtin as expected,
> it just expand to vec_select by coincidence. So does this mean both
> vec_insert and vec_extract
> and all other similar vector builtins should use IFN as suggested by Richard
> Biener, to match the
> pattern in gimple and expand both constant and variable index in expander?
> Will this also be
> beneficial for other targets except power? Or we should do that gradually
> after this patch
> approved as it seems another independent issue? Thanks:)
I don't think we should do that at all? IFNs just complicate
everything, there is no added value here: this is just data movement!
We need to avoid the data aliasing some generic way.
Segher
