[Bug tree-optimization/81884] Invalid code generation with zero size arrays or flexible array members

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=81884

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |ASSIGNED
   Last reconfirmed|                            |2017-08-18
          Component|c++                         |tree-optimization
           Assignee|unassigned at gcc dot gnu.org      |rguenth at gcc dot gnu.org
     Ever confirmed|0                           |1

--- Comment #1 from Richard Biener <rguenth at gcc dot gnu.org> ---
Confirmed.  Mine.  DSE is optimizing

void initialize() ()
{
  long unsigned int SR.19;
  struct value_t D.2321;
  struct X * x.0_1;
  struct X * x.3_4;

  <bb 2> [100.00%]:
  x.0_1 = x;
  x.0_1->arr[0] = 11;
  x.0_1->arr[1] = 12;
  MEM[(struct X *)x.0_1] = 10;
  x.3_4 = x;
  x.3_4->arr[2] = 13;
  x.3_4->arr[3] = 14;
  return;

to

__attribute__((noinline, noclone))
void initialize() ()
{
  long unsigned int SR.19;
  struct value_t D.2321;
  struct X * x.0_1;
  struct X * x.3_4;

  <bb 2> [100.00%]:
  x.0_1 = x;
  MEM[(struct X *)x.0_1] = 10;
  x.3_4 = x;
  x.3_4->arr[2] = 13;
  x.3_4->arr[3] = 14;
  return;

so it appears that it treats the "aggregate" assignment as a must-def.