[Bug middle-end/92088] New: aggregates with VLAs and nested functions are broken

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=92088

            Bug ID: 92088
           Summary: aggregates with VLAs and nested functions are broken
           Product: gcc
           Version: 9.2.1
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: middle-end
          Assignee: unassigned at gcc dot gnu.org
          Reporter: rguenth at gcc dot gnu.org
  Target Milestone: ---

Tried to see where we might miscompile things due to the inliner remapping
types...

void foo(int n)
{
  struct X { int a[n]; } y;

  struct X baz (struct X x)
    {
      x.a[0] = 1;
      return x;
    }

  y.a[0] = 0;
  y = baz(y);
  if (y.a[0] != 1)
    __builtin_abort ();
}

ICEs left and right.  After fixing the most obvious we end up with

t.c: In function ‘foo’:
t.c:1:6: error: size of variable ‘x’ is too large
    1 | void foo(int n)
      |      ^~~

when inlining because the inliner fails to appropriately "allocate" the
parameter space for baz 'x':

foo (int n)
{
  struct X x;
  struct X * y.1;
  sizetype _1;
  int _7;
  sizetype _8;

  <bb 2> [local count: 1073741824]:
  __builtin_dwarf_cfa (0);
  _1 = (sizetype) n_2(D);
  _8 = _1 * 4;
  y.1_10 = __builtin_alloca_with_align (_8, 32);
  y.1_10->a[0] = 0;
  x = [with_size_expr] WITH_SIZE_EXPR <*y.1_10, _8>;
  x.a[0] = 1;
  __builtin_memcpy (y.1_10, &x, _8);
  x ={v} {CLOBBER};
  _7 = y.1_10->a[0];