Re: middle-end/9997: Coelesce stack slots for disjoint scopes.

[Daniel Jacobowitz <drow@mvista.com>]

The following reply was made to PR middle-end/9997; it has been noted by GNATS.

From: Daniel Jacobowitz <drow@mvista.com>
To: rth@redhat.com
Cc: gcc-gnats@gcc.gnu.org
Subject: Re: middle-end/9997: Coelesce stack slots for disjoint scopes.
Date: Sat, 8 Mar 2003 12:54:07 -0500

 On Sat, Mar 08, 2003 at 12:56:24AM -0000, rth@redhat.com wrote:
 > 
 > >Number:         9997
 > >Category:       middle-end
 > >Synopsis:       Coelesce stack slots for disjoint scopes.
 > >Confidential:   no
 > >Severity:       non-critical
 > >Priority:       medium
 > >Responsible:    unassigned
 > >State:          open
 > >Class:          change-request
 > >Submitter-Id:   net
 > >Arrival-Date:   Sat Mar 08 01:06:00 UTC 2003
 > >Closed-Date:
 > >Last-Modified:
 > >Originator:     Richard Henderson
 > >Release:        all
 > >Organization:
 > >Environment:
 > any
 > >Description:
 > Given
 > 
 > struct big { char x[1024]; };
 > extern void bar(struct big *);
 > 
 > void foo(void)
 > {
 >   {
 >     struct big one;
 >     bar(&one);
 >   }
 >   {
 >     struct big one;
 >     bar(&one);
 >   }
 > }
 > 
 > we should allocate only one structure on the stack.
 
 Here's some interesting numbers I got for this testcase.  HEAD+stack is
 the -fstack-reorg patch posted some time ago.
 
 Compiler	Flags			Stack size
 
 gcc 3.2.2	-O0			2068
 gcc 3.2.2	-O2			2068
 gcc HEAD+stack	-O0			2072
 gcc HEAD+stack	-O2			2072
 gcc HEAD+stack	-O0 -fstack-reorg	2072
 gcc HEAD+stack	-O2 -fstack-reorg	2072
 
 Here's a patch I've been playing with:
 gcc HEAD+patch	-O0			1048
 gcc HEAD+patch	-O2			1044
 
 The patch bootstrapped on i686-pc-linux-gnu, and I'm running make check
 now.  I think it's correct; basically, when we close the SCOPE_EXPR,
 mark all stack slots associated with locals as dead.
 
 -- 
 Daniel Jacobowitz
 MontaVista Software                         Debian GNU/Linux Developer
 
 2003-03-08  Daniel Jacobowitz  <drow@mvista.com>
 
 	* c-semantics.c (genrtl_scope_stmt): Call free_named_temp_slots.
 	* expr.c (expand_expr): Update calls to assign_stack_temp_for_type.
 	* function.c (struct temp_slot): Add DECL.
 	(assign_stack_temp_for_type): Add DECL argument; save it in the
 	temp_slot.
 	(assign_stack_temp): Update call to assign_stack_temp_for_type.
 	(assign_temp): Pass the DECL to assign_stack_temp_for_type.
 	(free_named_stack_slots): New function.
 	* rtl.h (assign_stack_temp_for_type): Update prototype.
 	* tree.h (assign_stack_temp_for_type): Add prototype.
 
 Index: c-semantics.c
 ===================================================================
 RCS file: /cvs/gcc/gcc/gcc/c-semantics.c,v
 retrieving revision 1.53
 diff -u -p -r1.53 c-semantics.c
 --- c-semantics.c	22 Feb 2003 00:32:02 -0000	1.53
 +++ c-semantics.c	8 Mar 2003 17:48:53 -0000
 @@ -622,7 +622,11 @@ genrtl_scope_stmt (t)
        if (SCOPE_BEGIN_P (t))
  	expand_start_bindings_and_block (2 * SCOPE_NULLIFIED_P (t), block);
        else if (SCOPE_END_P (t))
 -	expand_end_bindings (NULL_TREE, !SCOPE_NULLIFIED_P (t), 0);
 +	{
 +	  expand_end_bindings (NULL_TREE, !SCOPE_NULLIFIED_P (t), 0);
 +	  if (block)
 +	    free_named_temp_slots (block);
 +	}
      }
    else if (!SCOPE_NULLIFIED_P (t))
      {
 Index: expr.c
 ===================================================================
 RCS file: /cvs/gcc/gcc/gcc/expr.c,v
 retrieving revision 1.510
 diff -u -p -r1.510 expr.c
 --- expr.c	5 Mar 2003 00:12:40 -0000	1.510
 +++ expr.c	8 Mar 2003 17:48:55 -0000
 @@ -7863,7 +7863,8 @@ expand_expr (exp, target, tmode, modifie
  	    target
  	      = assign_stack_temp_for_type
  		(TYPE_MODE (inner_type),
 -		 GET_MODE_SIZE (TYPE_MODE (inner_type)), 0, inner_type);
 +		 GET_MODE_SIZE (TYPE_MODE (inner_type)), 0, inner_type,
 +		 NULL_TREE);
  
  	  emit_move_insn (target, op0);
  	  op0 = target;
 @@ -7887,7 +7888,8 @@ expand_expr (exp, target, tmode, modifie
  		= MAX (int_size_in_bytes (inner_type),
  		       (HOST_WIDE_INT) GET_MODE_SIZE (TYPE_MODE (type)));
  	      rtx new = assign_stack_temp_for_type (TYPE_MODE (type),
 -						    temp_size, 0, type);
 +						    temp_size, 0, type,
 +						    NULL_TREE);
  	      rtx new_with_op0_mode = adjust_address (new, GET_MODE (op0), 0);
  
  	      if (TREE_ADDRESSABLE (exp))
 @@ -9189,7 +9191,8 @@ expand_expr (exp, target, tmode, modifie
  		   : int_size_in_bytes (inner_type),
  		   1, build_qualified_type (inner_type,
  					    (TYPE_QUALS (inner_type)
 -					     | TYPE_QUAL_CONST)));
 +					     | TYPE_QUAL_CONST)),
 +		   NULL_TREE);
  
  	      if (TYPE_ALIGN_OK (inner_type))
  		abort ();
 Index: function.c
 ===================================================================
 RCS file: /cvs/gcc/gcc/gcc/function.c,v
 retrieving revision 1.405
 diff -u -p -r1.405 function.c
 --- function.c	4 Mar 2003 06:20:12 -0000	1.405
 +++ function.c	8 Mar 2003 17:48:57 -0000
 @@ -165,7 +165,8 @@ static GTY(()) varray_type sibcall_epilo
  
     Automatic variables are also assigned temporary slots, at the nesting
     level where they are defined.  They are marked a "kept" so that
 -   free_temp_slots will not free them.  */
 +   free_temp_slots will not free them, although a decl is associated
 +   with each so that it can be freed when the decl goes out of scope.  */
  
  struct temp_slot GTY(())
  {
 @@ -201,6 +202,9 @@ struct temp_slot GTY(())
    /* The size of the slot, including extra space for alignment.  This
       info is for combine_temp_slots.  */
    HOST_WIDE_INT full_size;
 +  /* The decl associated with this stack slot, for automatic variables.  This
 +     info is for free_named_temp_slots.  */
 +  tree decl;
  };
  \f
  /* This structure is used to record MEMs or pseudos used to replace VAR, any
 @@ -649,14 +653,17 @@ assign_stack_local (mode, size, align)
     if we are to allocate something at an inner level to be treated as
     a variable in the block (e.g., a SAVE_EXPR).
  
 -   TYPE is the type that will be used for the stack slot.  */
 +   TYPE is the type that will be used for the stack slot.
 +
 +   DECL is the decl that will be associated with the stack slot.  */
  
  rtx
 -assign_stack_temp_for_type (mode, size, keep, type)
 +assign_stack_temp_for_type (mode, size, keep, type, decl)
       enum machine_mode mode;
       HOST_WIDE_INT size;
       int keep;
       tree type;
 +     tree decl;
  {
    unsigned int align;
    struct temp_slot *p, *best_p = 0;
 @@ -789,6 +796,7 @@ assign_stack_temp_for_type (mode, size, 
    p->addr_taken = 0;
    p->rtl_expr = seq_rtl_expr;
    p->type = type;
 +  p->decl = decl;
  
    if (keep == 2)
      {
 @@ -838,7 +846,7 @@ assign_stack_temp (mode, size, keep)
       HOST_WIDE_INT size;
       int keep;
  {
 -  return assign_stack_temp_for_type (mode, size, keep, NULL_TREE);
 +  return assign_stack_temp_for_type (mode, size, keep, NULL_TREE, NULL_TREE);
  }
  \f
  /* Assign a temporary.
 @@ -904,7 +912,7 @@ assign_temp (type_or_decl, keep, memory_
  	  size = 1;
  	}
  
 -      tmp = assign_stack_temp_for_type (mode, size, keep, type);
 +      tmp = assign_stack_temp_for_type (mode, size, keep, type, decl);
        return tmp;
      }
  
 @@ -1177,6 +1185,23 @@ preserve_temp_slots (x)
    for (p = temp_slots; p; p = p->next)
      if (p->in_use && p->level == temp_slot_level && ! p->keep)
        p->level--;
 +}
 +
 +/* For every VAR_DECL in BLOCK, mark the associated temporary slot as dead
 +   so that it can be reused.  */
 +
 +void
 +free_named_temp_slots (block)
 +     tree block;
 +{
 +  struct temp_slot *p;
 +  tree decl;
 +
 +  for (decl = BLOCK_VARS (block); decl; decl = TREE_CHAIN (decl))
 +    if (TREE_CODE (decl) == VAR_DECL)
 +      for (p = temp_slots; p; p = p->next)
 +	if (p->decl == decl)
 +	    p->in_use = 0;
  }
  
  /* X is the result of an RTL_EXPR.  If it is a temporary slot associated
 Index: rtl.h
 ===================================================================
 RCS file: /cvs/gcc/gcc/gcc/rtl.h,v
 retrieving revision 1.386
 diff -u -p -r1.386 rtl.h
 --- rtl.h	28 Feb 2003 07:06:33 -0000	1.386
 +++ rtl.h	8 Mar 2003 17:48:57 -0000
 @@ -1459,7 +1459,8 @@ extern rtx assign_stack_local		PARAMS ((
  extern rtx assign_stack_temp		PARAMS ((enum machine_mode,
  					       HOST_WIDE_INT, int));
  extern rtx assign_stack_temp_for_type	PARAMS ((enum machine_mode,
 -						 HOST_WIDE_INT, int, tree));
 +						 HOST_WIDE_INT, int, tree,
 +						 tree));
  extern rtx assign_temp			PARAMS ((tree, int, int, int));
  /* In emit-rtl.c */
  extern rtx emit_insn_before		PARAMS ((rtx, rtx));
 Index: tree.h
 ===================================================================
 RCS file: /cvs/gcc/gcc/gcc/tree.h,v
 retrieving revision 1.385
 diff -u -p -r1.385 tree.h
 --- tree.h	2 Mar 2003 21:18:15 -0000	1.385
 +++ tree.h	8 Mar 2003 17:49:00 -0000
 @@ -2999,6 +2999,7 @@ extern void pop_temp_slots		PARAMS ((voi
  extern void push_temp_slots		PARAMS ((void));
  extern void preserve_temp_slots		PARAMS ((rtx));
  extern void preserve_rtl_expr_temps	PARAMS ((tree));
 +extern void free_named_temp_slots	PARAMS ((tree));
  extern int aggregate_value_p		PARAMS ((tree));
  extern void free_temps_for_rtl_expr	PARAMS ((tree));
  extern void instantiate_virtual_regs	PARAMS ((tree, rtx));