[Bug fortran/70856] [6/7 Regression] ICE with -fopenacc in get_constraint_for_ssa_var, at tree-ssa-structalias.c:2952

["rguenth at gcc dot gnu.org" <gcc-bugzilla at gcc dot gnu dot org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=70856

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |hubicka at gcc dot gnu.org,
                   |                            |mliska at suse dot cz

--- Comment #6 from Richard Biener <rguenth at gcc dot gnu.org> ---
(In reply to vries from comment #5)
> before icf, we have:
> ...
>   static real(kind=4) A.4[2] = {1.0e+0, 2.0e+0};
>   static real(kind=4) A.1[2] = {1.0e+0, 2.0e+0};
> ...
> 
> Then icf does:
> ...
> Semantic equality hit:A.4->A.1
> Assembler symbol names:A.4.3435->A.1.3429
> Unified; Variable alias has been created.
> ...
> 
> And after icf, we have:
> ...
>   static real(kind=4) A.4[2] = {1.0e+0, 2.0e+0};
>   static real(kind=4) A.1[2];
> ...
> 
> What openacc does, is run ipa-pta before and after icf.
> 
> The compilation succeeds with -fno-ipa-icf.

Hmm, indeed running ICF after IPA PTA invalidates points-to info (eventually
even causing wrong-code).  There is nothing ICF can do here (it would need to
adjust all points-to bitmaps).

Note that this is true also for non-IPA PTA info.

The wrong-code possibilities (given that we only merge readonly decls in ICF)
restrict themselves to equality/inequality compares which constitute an area
in ICF that is fishy anyway.

That said - if ICF would adjust DECL_PT_UID then a testcase like

static const int a[] = { 1, 2, 3, 4 };
static const int b[] = { 1, 2, 3, 4 };

bool isA (int *p) { return p == a; }
bool isB (int *p) { return p == b; }
int main()
{
  if (! (isA (a) || isB (a)))
    abort (); 
}

could start to abort (it's a bit tricky and would involve some disabling
of some CCP I guess).

Honza, Martin - I suppose if we start to comare DECL_PT_UID in ICF then
this effectively disables ICF of variables.  Any ideas besides adjusting
DECL_PT_UID in ICF and hoping for the best (on the wrong-code issue)?