[RFC] fix char* restrict

[Dan Nicolaescu <dann at godzilla dot ICS dot UCI dot EDU>]

As can be seen in the message archived at:

http://gcc.gnu.rg/ml/gcc-patches/2002-03/msg00274.html

char *restrict does not work as expected, restricted char*s are put in
alias set 0.

Why? alias.c:get_alias_set calls c-common.c:c_common_get_alias_set
that returns zero for a char*.  get_alias_set sees the zero and
returns without checking if the "char*" is a "char* restrict". That
check would have occurred later in the code.

One way to fix make char* restrict is to somehow make language
specific lang_hooks.get_alias_set function signal that even though the
value it returns is 0 the processing in alias.c:get_alias_set should
continue to check for restricted pointers. This can be done by adding
another parameter to lang_hooks.get_alias_set. 

Does anybody see a better solution? 
A proposed patch follows. If it is acceptable I will submit it
properly. Right now I just want to make sure I am on the right track. 

Thanks.
        --dan
  

2002-05-12  Dan Nicolaescu  <dann@ics.uci.edu>

	* c-common.c (c_common_get_alias_set): Add extra parameter. Set it
	in for a char*. 

	* alias.c (get_alias_set): Don't return for a restrict candidate. 


*** alias.c.~1.170.~	Sat May 11 12:47:36 2002
--- alias.c	Sun May 12 15:36:17 2002
***************
*** 470,479 ****
        /* Remove any nops, then give the language a chance to do
  	 something with this tree before we look at it.  */
        STRIP_NOPS (t);
!       set = (*lang_hooks.get_alias_set) (t);
!       if (set != -1)
! 	return set;
! 
        /* First see if the actual object referenced is an INDIRECT_REF from a
  	 restrict-qualified pointer or a "void *".  Replace
  	 PLACEHOLDER_EXPRs.  */
--- 470,482 ----
        /* Remove any nops, then give the language a chance to do
  	 something with this tree before we look at it.  */
        STRIP_NOPS (t);
!       {
!         int restrict_candidate_p = 0;
!         set = (*lang_hooks.get_alias_set) (t, &restrict_candidate_p);
!         if (set != -1 && (set == 0 && !restrict_candidate_p))
!           return set;
!       }
!       
        /* First see if the actual object referenced is an INDIRECT_REF from a
  	 restrict-qualified pointer or a "void *".  Replace
  	 PLACEHOLDER_EXPRs.  */


*** c-common.c.~1.320.~	Sat May 11 12:47:37 2002
--- c-common.c	Sun May 12 16:10:39 2002
***************
*** 2484,2494 ****
  }
  
  /* Return the typed-based alias set for T, which may be an expression
!    or a type.  Return -1 if we don't do anything special.  */
  
  HOST_WIDE_INT
! c_common_get_alias_set (t)
       tree t;
  {
    tree u;
    
--- 2484,2497 ----
  }
  
  /* Return the typed-based alias set for T, which may be an expression
!    or a type.  Return -1 if we don't do anything special.
!    Set RESTRICT_CANDIDATE_P in case T should be checked if it's a
!    restricted char pointer.  */
  
  HOST_WIDE_INT
! c_common_get_alias_set (t, restrict_candidate_p)
       tree t;
+      int *restrict_candidate_p;
  {
    tree u;
    
***************
*** 2514,2520 ****
    if (TREE_CODE_CLASS (TREE_CODE (t)) == 'r'
        && TREE_CODE (TREE_TYPE (t)) == INTEGER_TYPE
        && TYPE_PRECISION (TREE_TYPE (t)) == TYPE_PRECISION (char_type_node))
!     return 0;
  
    /* That's all the expressions we handle specially.  */
    if (! TYPE_P (t))
--- 2517,2526 ----
    if (TREE_CODE_CLASS (TREE_CODE (t)) == 'r'
        && TREE_CODE (TREE_TYPE (t)) == INTEGER_TYPE
        && TYPE_PRECISION (TREE_TYPE (t)) == TYPE_PRECISION (char_type_node))
!     {
!       *restrict_candidate_p = 1;
!       return 0;
!     }
  
    /* That's all the expressions we handle specially.  */
    if (! TYPE_P (t))