[PATCH] Fix compile time regression with fortran

[Richard Guenther]

This patch may fix the compile time regression introduced with
the fix for PR 22555.  It reduces the amount of SFTs produced for
variables that are only written to in a function.

Bootstrapped and tested on x86_64-unknown-linux-gnu.

Ok for mainline?

I'd appreciate testing from the fortran folks or a preprocessed testcase
that showed the compile-time regression.

Thanks,
Richard.


2006-01-16  Richard Guenther  <rguenther@suse.de>

	* tree-ssa-alias.c (struct used_part): Add write_only field.
	(get_or_create_used_part_for): Initialize it to true.
	(create_overlap_variables_for): Don't create structure variables
	for structures that only are written to.
	(find_used_portions): Handle MODIFY_EXPR to track whether a
	structure is only written to.

	* gcc.dg/tree-ssa/20031015-1.c: Adjust testcase.

Index: tree-ssa-alias.c
===================================================================
*** tree-ssa-alias.c	(revision 109743)
--- tree-ssa-alias.c	(working copy)
*************** typedef struct used_part
*** 2424,2429 ****
--- 2424,2431 ----
       variable.  Implicit uses occur when we can't tell what part we
       are referencing, and have to make conservative assumptions.  */
    bool implicit_uses;
+   /* True if the structure is only written to or taken its address.  */
+   bool write_only;
  } *used_part_t;
  
  /* An array of used_part structures, indexed by variable uid.  */
*************** get_or_create_used_part_for (size_t uid)
*** 2509,2514 ****
--- 2511,2517 ----
        up->maxused = 0;
        up->explicit_uses = false;
        up->implicit_uses = false;
+       up->write_only = true;
      }
  
    return up;
*************** create_overlap_variables_for (tree var)
*** 2552,2561 ****
    used_part_t up;
    size_t uid = DECL_UID (var);
  
!   if (!up_lookup (uid))
      return;
  
-   up = up_lookup (uid);
    push_fields_onto_fieldstack (TREE_TYPE (var), &fieldstack, 0, NULL);
    if (VEC_length (fieldoff_s, fieldstack) != 0)
      {
--- 2555,2565 ----
    used_part_t up;
    size_t uid = DECL_UID (var);
  
!   up = up_lookup (uid);
!   if (!up
!       || up->write_only)
      return;
  
    push_fields_onto_fieldstack (TREE_TYPE (var), &fieldstack, 0, NULL);
    if (VEC_length (fieldoff_s, fieldstack) != 0)
      {
*************** create_overlap_variables_for (tree var)
*** 2691,2700 ****
     entire structure.  */
  
  static tree
! find_used_portions (tree *tp, int *walk_subtrees, void *data ATTRIBUTE_UNUSED)
  {
    switch (TREE_CODE (*tp))
      {
      case REALPART_EXPR:
      case IMAGPART_EXPR:
      case COMPONENT_REF:
--- 2695,2709 ----
     entire structure.  */
  
  static tree
! find_used_portions (tree *tp, int *walk_subtrees, void *lhs_p)
  {
    switch (TREE_CODE (*tp))
      {
+     case MODIFY_EXPR:
+       /* Recurse manually here to track whether the use is in the
+ 	 LHS of an assignment.  */
+       find_used_portions (&TREE_OPERAND (*tp, 0), walk_subtrees, tp);
+       return find_used_portions (&TREE_OPERAND (*tp, 1), walk_subtrees, NULL);
      case REALPART_EXPR:
      case IMAGPART_EXPR:
      case COMPONENT_REF:
*************** find_used_portions (tree *tp, int *walk_
*** 2723,2728 ****
--- 2732,2739 ----
  	      up->explicit_uses = true;
  	    else
  	      up->implicit_uses = true;
+ 	    if (!lhs_p)
+ 	      up->write_only = false;
  	    up_insert (uid, up);
  
  	    *walk_subtrees = 0;
Index: testsuite/gcc.dg/tree-ssa/20031015-1.c
===================================================================
*** testsuite/gcc.dg/tree-ssa/20031015-1.c	(revision 109743)
--- testsuite/gcc.dg/tree-ssa/20031015-1.c	(working copy)
*************** main(void)
*** 13,20 ****
    return 0;
  }
  
! /* The V_MUST_DEF comes from the initial assignment; the V_MAY_DEF
!    comes from the asm.  */
! /* { dg-final { scan-tree-dump-times "V_MUST_DEF" 1 "alias1" } } */
! /* { dg-final { scan-tree-dump-times "V_MAY_DEF" 1 "alias1" } } */
  /* { dg-final { cleanup-tree-dump "alias1" } } */
--- 13,18 ----
    return 0;
  }
  
! /* The V_*_DEF comes from the initial assignment and the asm.  */
! /* { dg-final { scan-tree-dump-times "_DEF" 2 "alias1" } } */
  /* { dg-final { cleanup-tree-dump "alias1" } } */