[Bug c/45834] Redundant inter-loop edges in DDG

[bmei at broadcom dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=45834

--- Comment #5 from Bingfeng Mei <bmei at broadcom dot com> 2010-10-18 13:53:37 UTC ---
> 
> Sure, but we have other means of dealing with that (MEM_ALIAS_SET == 0).

Do you mean this check is redundant here ? I dig out the ancient code (from
1997)

  /* If both references are struct references, or both are not, nothing
     is known about aliasing.

     If either reference is QImode or BLKmode, ANSI C permits aliasing.

     If both addresses are constant, or both are not, nothing is known
     about aliasing.  */
  if (MEM_IN_STRUCT_P (x) == MEM_IN_STRUCT_P (mem)
      || mem_mode == QImode || mem_mode == BLKmode
      || GET_MODE (x) == QImode || GET_MODE (mem) == BLKmode
      || varies (x_addr) == varies (mem_addr))
    return 1;

The comment indicates that the check for QImode is for meeting aliasing rule of
char type.

> 
> > But I am not sure whether a
> > restrict qualifier will override that rule.
> 
> restrict is a different concept from type-based aliasing.
> 
Sure, but in this example, on one hand, char type pointer is supposed to alias
any other data type, on the other hand, all the char pointers have restrict
qualifiers. What is correct behaviour, alias or not?