[Bug tree-optimization/93771] SLP produces VEC_PERM when should have used vector generation

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=93771

Richard Biener <rguenth at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2020-02-17
                 CC|                            |rguenth at gcc dot gnu.org
             Blocks|                            |53947
     Ever confirmed|0                           |1

--- Comment #2 from Richard Biener <rguenth at gcc dot gnu.org> ---
Confirmed.  I'm not sure if we should try to "fix" SLP here or rather
appropriately optimize

  v2df tem1 = *(v2df *)&t[0];
  v2df tem2 = *(v2df *)&t[2];
  __builtin_shuffle (tem1, tem2 (v2di) { 0, 3 });

which the user could write itself.  forwprop does some related transforms
splitting loads in "Rewrite loads used only in BIT_FIELD_REF extractions to
component-wise loads."


Referenced Bugs:

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=53947
[Bug 53947] [meta-bug] vectorizer missed-optimizations