https://gcc.gnu.org/bugzilla/show_bug.cgi?id=62080
--- Comment #6 from Richard Biener <rguenth at gcc dot gnu.org> ---
(In reply to Marc Glisse from comment #5)
> With the intrinsics patch, I notice that we don't simplify in gimple either:
>
> _40 = VIEW_CONVERT_EXPR<__m128i>(_39);
> MEM[(__m128i * {ref-all})vec_4(D)] = _40;
> _60 = MEM[(const double *)vec_4(D)];
> _61 = MEM[(const double *)vec_4(D) + 8B];
> _62 = {_60, _61};
> _63 = VIEW_CONVERT_EXPR<__v4si>(_62);
>
> (_39 and _63 have the same type)
value-numbering has difficulties in seeing through so much stmts (read:
not implemented) and it doesn't have a way of expressing "partial"
values. That is, it knows that at MEM[(__m128i * {ref-all})vec_4(D)] we
stored _39 but when value-numbering the partial reads it can't assign
the value _39 to them (as said, "partial" values are not supported).
So one way to optimize this is to special-case the composition
operations and try looking up a proper memory operation.
Another possibility is to value-number compound operations also as
piecewise operations, introducing fake value-numbers (that is,
"lower" everything to component-wise operations internally).
I suppose pattern-matching
> _60 = MEM[(const double *)vec_4(D)];
> _61 = MEM[(const double *)vec_4(D) + 8B];
> _62 = {_60, _61};
and generating a single read (with eventually a permute?) would be
more profitable and easier to implement.
