[Bug middle-end/65330] restrict should be considered when folding through references from global vars

[hubicka at ucw dot cz]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65330

--- Comment #3 from Jan Hubicka <hubicka at ucw dot cz> ---
> I was thinking of sth else first - make sure that points-to analysis processes
> initializers of readonly globals (when they bind to the current def).  In
when ctor_for_folding returns non-NULL;
> your testcase the globals are not readonly - or did you mean to write
> 
> int * const varptr = &var;
> int * const __restrict__ varptr2 = &var;
> 
> ?  Your testcase also misses a declaration of 'var'.

I did not quite finish the testcase because the restrict qualifier I was
interested in was ignored.  Yes, they would need to be declared either const or
static (so the DECL_READONLY is derived by IPA code).

This should be full testcase (-fmerge-all-constants is needed to get merging
done, but to expose any problems testrestrict/testrestrict2 codegen would need
to differ):

int var;
static const int *varptr=&var;
static const int *__restrict__ varptr2=&var;
static int *__restrict__ varptr3 = &var;
static int *__restrict__ varptr4 = &var;
int *
return_valptr(int i)
{
  return varptr[i];
}
int * __restrict__
return_valptr2(int i)
{
  return varptr2[i];
}
int
testrestrict ()
{
  int *ptr = return_valptr (0);
  *ptr = 0;
  *varptr3 = 1;
  return *ptr;
}
int
testrestrict2 ()
{
  int *ptr = return_valptr2 (0);
  *ptr = 0;
  *varptr3 = 1;
  return *ptr;
}
int
testrestrict4 ()
{
  *varptr4 = 0;
  *varptr3 = 1;
  return *varptr4;
}