[Bug tree-optimization/91954] [10 Regression] gcc.dg/vect/pr66142.c should not need early inlining to be vectorized since r10-3311-gff6686d2e5f797d6

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=91954

--- Comment #3 from Richard Biener <rguenth at gcc dot gnu.org> ---
IPA SRA splits the struct B parameter:

Evaluating analysis results for bar/0
  Will split parameter 0
    - component at byte offset 0, size 4
    - component at byte offset 4, size 4
    - component at byte offset 8, size 4
    - component at byte offset 12, size 4

which is passed as

  D.2220[_14].t.x = 1.0e+0;
  D.2220[_14].t.y = u_11;
  D.2220[_14].w.x = x_16;
  D.2220[_14].w.y = y_18;
  _23 = &D.2220[_14];
  _24 = bar (_23);

producing

bar.isra (const float ISRA.5, const float ISRA.6, const float ISRA.7, const
float ISRA.8)

the inlining of this then ends up as

  _23 = &D.2220[_14];
  _27 = MEM[(float *)_23];
  _28 = MEM[(float *)_23 + 4B];
  _29 = MEM[(float *)_23 + 8B];
  _30 = MEM[(float *)_23 + 12B];

where formerly forwprop ended up combining the &D.2220[_14] into the
four dereferences with the nice acccess paths which it cannot do from
the above:

  D.2220[_20].t.x = 1.0e+0;
  D.2220[_20].t.y = u_13;
  D.2220[_20].w.x = x_22;
  D.2220[_20].w.y = y_24;
  _30 = MEM <struct B[32]> [(const struct B *)&D.2220][_20].t.x;
  _34 = MEM <struct B[32]> [(const struct B *)&D.2220][_20].t.y;
  _35 = MEM <struct B[32]> [(const struct B *)&D.2220][_20].w.x;
  _36 = _30 * _35;
  _37 = MEM <struct B[32]> [(const struct B *)&D.2220][_20].w.y;

so instead we get

  D.2220[_14].t.x = 1.0e+0;
  D.2220[_14].t.y = u_11;
  D.2220[_14].w.x = x_16;
  D.2220[_14].w.y = y_18;
  _23 = &D.2220[_14];
  _27 = MEM[(float *)_23];
  _28 = MEM[(float *)_23 + 4B];
  _29 = MEM[(float *)_23 + 8B];
  _30 = MEM[(float *)_23 + 12B];

which we are not able to elide (which is of course kind-of lame).

IIRC we have a duplicate report for this somewhere assigned to me (for the VN
side).  VN already can do some tricks but it doesn't handle offsetted
MEM_REFs there (vn_reference_maybe_forwprop_address) and it doesn't somehow
work for the not offseted one either.