[PATCH][alias-improvements] Fix glitch get_deref_alias_set patch

[Richard Guenther <rguenther at suse dot de>]

The patch that introduced get_deref_alias_set causes us to always fall
back to the base indirect-ref alias set.  This was of course not intended.
The following fixes it and adds a testcase for the missed-optimization.

Bootstrapped and tested on x86_64-unknown-linux-gnu, applied to the
branch.  This brings tramp3d performance back to trunk level.  Yay.

Richard.

2009-01-11  Richard Guenther  <rguenther@suse.de>

	* tree-ssa-structalias.c (set_uids_in_ptset): Use get_deref_alias_set.
	* alias.c (get_deref_alias_set_1): Split out from
	(get_deref_alias_set): Fall back to access type alias-set here.
	(get_alias_set): Use get_deref_alias_set_1.

	* gcc.dg/tree-ssa/alias-20.c: New testcase.

Index: gcc/tree-ssa-structalias.c
===================================================================
*** gcc/tree-ssa-structalias.c	(revision 143251)
--- gcc/tree-ssa-structalias.c	(working copy)
*************** set_uids_in_ptset (tree ptr, bitmap into
*** 4789,4795 ****
  	    {
  	      alias_set_type var_alias_set, mem_alias_set;
  	      var_alias_set = get_alias_set (vi->decl);
! 	      mem_alias_set = get_alias_set (TREE_TYPE (TREE_TYPE (ptr)));
  	      if (!may_alias_p (SSA_NAME_VAR (ptr), mem_alias_set,
  				vi->decl, var_alias_set))
  		{
--- 4794,4800 ----
  	    {
  	      alias_set_type var_alias_set, mem_alias_set;
  	      var_alias_set = get_alias_set (vi->decl);
! 	      mem_alias_set = get_deref_alias_set (ptr);
  	      if (!may_alias_p (SSA_NAME_VAR (ptr), mem_alias_set,
  				vi->decl, var_alias_set))
  		{
Index: gcc/alias.c
===================================================================
*** gcc/alias.c	(revision 143251)
--- gcc/alias.c	(working copy)
*************** component_uses_parent_alias_set (const_t
*** 483,492 ****
  }
  
  /* Return the alias set for the memory pointed to by T, which may be
!    either a type or an expression.  */
  
! alias_set_type
! get_deref_alias_set (tree t)
  {
    /* If we're not doing any alias analysis, just assume everything
       aliases everything else.  */
--- 483,493 ----
  }
  
  /* Return the alias set for the memory pointed to by T, which may be
!    either a type or an expression.  Return -1 if there is nothing
!    special about dereferencing T.  */
  
! static alias_set_type
! get_deref_alias_set_1 (tree t)
  {
    /* If we're not doing any alias analysis, just assume everything
       aliases everything else.  */
*************** get_deref_alias_set (tree t)
*** 551,558 ****
        || TYPE_REF_CAN_ALIAS_ALL (t))
      return 0;
  
    /* Fall back to the alias-set of the pointed-to type.  */
!   return get_alias_set (TREE_TYPE (t));
  }
  
  /* Return the alias set for T, which may be either a type or an
--- 552,577 ----
        || TYPE_REF_CAN_ALIAS_ALL (t))
      return 0;
  
+   return -1;
+ }
+ 
+ /* Return the alias set for the memory pointed to by T, which may be
+    either a type or an expression.  */
+ 
+ alias_set_type
+ get_deref_alias_set (tree t)
+ {
+   alias_set_type set = get_deref_alias_set_1 (t);
+ 
    /* Fall back to the alias-set of the pointed-to type.  */
!   if (set == -1)
!     {
!       if (! TYPE_P (t))
! 	t = TREE_TYPE (t);
!       set = get_alias_set (TREE_TYPE (t));
!     }
! 
!   return set;
  }
  
  /* Return the alias set for T, which may be either a type or an
*************** get_alias_set (tree t)
*** 596,602 ****
  	}
  
        if (INDIRECT_REF_P (inner))
! 	return get_deref_alias_set (TREE_OPERAND (inner, 0));
  
        /* Otherwise, pick up the outermost object that we could have a pointer
  	 to, processing conversions as above.  */
--- 615,625 ----
  	}
  
        if (INDIRECT_REF_P (inner))
! 	{
! 	  set = get_deref_alias_set_1 (TREE_OPERAND (inner, 0));
! 	  if (set != -1)
! 	    return set;
! 	}
  
        /* Otherwise, pick up the outermost object that we could have a pointer
  	 to, processing conversions as above.  */
Index: gcc/testsuite/gcc.dg/tree-ssa/alias-20.c
===================================================================
*** gcc/testsuite/gcc.dg/tree-ssa/alias-20.c	(revision 0)
--- gcc/testsuite/gcc.dg/tree-ssa/alias-20.c	(revision 0)
***************
*** 0 ****
--- 1,24 ----
+ /* { dg-do compile } */
+ /* { dg-options "-O -fstrict-aliasing -fdump-tree-optimized" } */
+ 
+ struct S { float f; int i; };
+ struct R { int x; int i; };
+ 
+ /* Strict-aliasing rules say that int and float do not alias.  */
+ int bar(struct S *s, int *i)
+ {
+   *i = 0;
+   s->f = 1.0;
+   return *i;
+ }
+ 
+ /* Strict-aliasing rules say that S and R do not alias.  */
+ int foo(struct S *s, struct R *r)
+ {
+   r->i = 0;
+   s->f = 1.0;
+   return r->i;
+ }
+ 
+ /* { dg-final { scan-tree-dump-times "return 0;" 2 "optimized" } } */
+ /* { dg-final { cleanup-tree-dump "optimized" } } */