built in memset

built in memset

[John Carr]

My alias changes revealed a bug in setting MEM_IN_STRUCT_P when
calling builtin memset.  This patch improves the situation but there
are still potential bugs.  memcpy probably also needs to be fixed.

I think it would be correct to always set MEM_IN_STRUCT_P, or always
set it except in cases where the argument is the address of a scalar
(i.e. &foo but not ptr = &foo; memset(ptr).)

The specific bug was compiling cse.c:simplify_plus_or_minus:

  rtx ops[8];
  bzero ((char *) ops, sizeof ops);

After removing casts, ops is a pointer to a pointer, not a pointer to
a structure.  That is all the existing code checks: is the type a
pointer to aggregate.


Tue Apr 21 20:36:28 1998  John Carr  <jfc@mit.edu>

	* expr.c (expand_builtin, case MEMSET): Set MEM_IN_STRUCT_P
	if the argument is the adress of a structure or array.

*** expr.c	1998/04/16 23:56:03	1.48
--- expr.c	1998/04/22 00:36:51
*************** expand_builtin (exp, target, subtarget, 
*** 8634,8640 ****
  	  /* There could be a void* cast on top of the object.  */
  	  while (TREE_CODE (dest) == NOP_EXPR)
  	    dest = TREE_OPERAND (dest, 0);
! 	  type = TREE_TYPE (TREE_TYPE (dest));
  	  MEM_IN_STRUCT_P (dest_mem) = AGGREGATE_TYPE_P (type);
  
  	  dest_addr = clear_storage (dest_mem, len_rtx, dest_align);
--- 8634,8646 ----
  	  /* There could be a void* cast on top of the object.  */
  	  while (TREE_CODE (dest) == NOP_EXPR)
  	    dest = TREE_OPERAND (dest, 0);
! 
! 	  if (TREE_CODE (dest) == ADDR_EXPR)
! 	    /* If this is the address of an object, check whether the
! 	       object is an array.  */
! 	    type = TREE_TYPE (TREE_OPERAND (dest, 0));
! 	  else
! 	    type = TREE_TYPE (TREE_TYPE (dest));
  	  MEM_IN_STRUCT_P (dest_mem) = AGGREGATE_TYPE_P (type);
  
  	  dest_addr = clear_storage (dest_mem, len_rtx, dest_align);

Re: built in memset

[Jim Wilson]

	* expr.c (expand_builtin, case MEMSET): Set MEM_IN_STRUCT_P
	if the argument is the adress of a structure or array.

This patch looks OK to me.

Jim