[Bug c++/70096] [6 Regression] [Invalid codegen] Read of uninitialized value in ref-qualified pointer to member function

[ppalka at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=70096

--- Comment #4 from Patrick Palka <ppalka at gcc dot gnu.org> ---
(In reply to Patrick Palka from comment #3)
> The problem ultimately seems to be that the invariant DECL_MODE (x) ==
> TYPE_MODE (TREE_TYPE (fptr)) is violated during substitution due to a change
> in the TREE_TYPE of fptr from OFFSET_TYPE to TYPE_PTRMEMFUNC_P.
> 
> I haven't looked into why r229018 causes this regression.  I suppose that
> r229018 somehow exposed this latent bug.

Before r229018, when PTRMEM_CSTs are eagerly expanded in digest_init, we
directly initialize fptr:

  h.data = 42;
  fptr.__pfn = foo;
  fptr.__delta = 0;
  _5 = fptr.__pfn;
  _6 = fptr.__delta;
  _7 = (sizetype) _6;
  _8 = &h + _7;
  _5 (_8);

After r229018, we initialize a temporary and then copy it to fptr:

  h.data = 42;
  fptr.0.__pfn = foo;
  fptr.0.__delta = 0;
  fptr = fptr.0;         // This aggregate copy is the problem, its LHS has
DImode and its RHS has TImode
  _6 = fptr.__pfn;
  _7 = fptr.__delta;
  _8 = (sizetype) _7;
  _9 = &h + _8;
  _6 (_9);