Re: Would alias analysis help WRT builtin memmove -> builtin memcpy ?

["Kaveh R. Ghazi" <ghazi@caip.rutgers.edu>]

 > From: Jeffrey A Law <law@cygnus.com>
 > 
 >   In message < 200003292334.SAA02200@caip.rutgers.edu >you write:
 >   > Right, but then shouldn't it have returned set 0, not 11? 
 > 
 > Depends on the code :-)  I believe if you had casted the arg to a void *
 > then you would have got an alias set zero.  Actually, wait, you have two
 > pointers, not two MEMs -- how are you checking alias sets in that case
 > since the alias set is a property of the MEM, not the address.

I wasn't doing any casting, but the prototype of memmove may have done
that for me.

Anway, here is what I am talking about.  Assume the following is in a
new expand_builtin_memmove() routine, where `arglist' is the tree
chain of parameters passed to the expanded memmove call:

+      tree dst = TREE_VALUE (arglist);
+      tree src = TREE_VALUE (TREE_CHAIN (arglist));
+      tree len = TREE_VALUE (TREE_CHAIN (TREE_CHAIN (arglist)));
+      const int dst_set = get_alias_set (dst);
+      const int src_set = get_alias_set (src);
+      const int len_set = get_alias_set (len);
+
+      fprintf (stderr, "src=%d, dst=%d, len=%d\n",
+              src_set, dst_set, len_set);
+
+      if (src_set <= 0 || dst_set <= 0 || src_set == dst_set)
+       return 0;
+      else
+       return expand_builtin_memcpy (arglist);

Given a call to memmove(int[], char[], size_t) I was getting 11, 11, 9
for the alias sets.  Maybe I'm not using the type based aliasing
correctly.  (Docs somewhere?)  In any case, I'm now interested in the
base ptr aliasing code.


 > So, no, I don't see a way to do easily what you want since our aliasing
 > code is designed to work on MEMs, not addresses.
 > 
 > You might be able to generate a MEM with the unknown alias set (-1 I think)
 > and pass that to the aliasing routines.  Not really sure.
 > jeff

Okay, what routine?

I couldn't figure out what the relevant exported interface to the base
ptr aliasing I should try.  Randomly looking in alias.c wasn't very
productive.

		--Kaveh
--
Kaveh R. Ghazi			Engagement Manager / Project Services
ghazi@caip.rutgers.edu		Qwest Internet Solutions