dwarf2out: Stop using wide_int in GC structures

  Hi!

On Tue, Oct 10, 2023 at 09:30:31AM +0000, Richard Biener wrote:
> On Mon, 9 Oct 2023, Jakub Jelinek wrote:
> > > This makes wide_int unusable in GC structures, so for dwarf2out
> > > which was the only place which needed it there is a new rwide_int type
> > > (restricted wide_int) which supports only up to RWIDE_INT_MAX_ELTS limbs
> > > inline and is trivially copyable (dwarf2out should never deal with large
> > > _BitInt constants, those should have been lowered earlier).
> > 
> > As discussed on IRC, the dwarf2out.{h,cc} needs are actually quite limited,
> > it just needs to allocate new GC structures val_wide points to (constructed
> > from some const wide_int_ref &) and needs to call operator==,
> > get_precision, elt, get_len and get_val methods on it.
> > Even trailing_wide_int would be overkill for that, the following just adds
> > a new struct with precision/len and trailing val array members and
> > implements the needed methods (only 2 of them using wide_int_ref constructed
> > from those).
> > 
> > Incremental patch, so far compile time tested only:
> 
> LGTM, wonder if we can push this separately as prerequesite?

Here it is as a separate independent patch.  Even without the
wide_int changing patch it should save some memory, by not always
allocating room for 9 limbs, but say just the 2/3 or how many we actually
need.  And, another advantage is that if we really need it at some point,
it could support even more than 9 limbs if it is created from a wide_int_ref
with get_len () > 9.

Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk?

2023-10-10  Jakub Jelinek  <jakub@redhat.com>

	* dwarf2out.h (wide_int_ptr): Remove.
	(dw_wide_int_ptr): New typedef.
	(struct dw_val_node): Change type of val_wide from wide_int_ptr
	to dw_wide_int_ptr.
	(struct dw_wide_int): New type.
	(dw_wide_int::elt): New method.
	(dw_wide_int::operator ==): Likewise.
	* dwarf2out.cc (get_full_len): Change argument type to
	const dw_wide_int & from const wide_int &.  Use CEIL.  Call
	get_precision method instead of calling wi::get_precision.
	(alloc_dw_wide_int): New function.
	(add_AT_wide): Change w argument type to const wide_int_ref &
	from const wide_int &.  Use alloc_dw_wide_int.
	(mem_loc_descriptor, loc_descriptor): Use alloc_dw_wide_int.
	(insert_wide_int): Change val argument type to const wide_int_ref &
	from const wide_int &.
	(add_const_value_attribute): Pass rtx_mode_t temporary directly to
	add_AT_wide instead of using a temporary variable.



	Jakub
  

On Tue, 10 Oct 2023, Jakub Jelinek wrote:

> Hi!
> 
> On Tue, Oct 10, 2023 at 09:30:31AM +0000, Richard Biener wrote:
> > On Mon, 9 Oct 2023, Jakub Jelinek wrote:
> > > > This makes wide_int unusable in GC structures, so for dwarf2out
> > > > which was the only place which needed it there is a new rwide_int type
> > > > (restricted wide_int) which supports only up to RWIDE_INT_MAX_ELTS limbs
> > > > inline and is trivially copyable (dwarf2out should never deal with large
> > > > _BitInt constants, those should have been lowered earlier).
> > > 
> > > As discussed on IRC, the dwarf2out.{h,cc} needs are actually quite limited,
> > > it just needs to allocate new GC structures val_wide points to (constructed
> > > from some const wide_int_ref &) and needs to call operator==,
> > > get_precision, elt, get_len and get_val methods on it.
> > > Even trailing_wide_int would be overkill for that, the following just adds
> > > a new struct with precision/len and trailing val array members and
> > > implements the needed methods (only 2 of them using wide_int_ref constructed
> > > from those).
> > > 
> > > Incremental patch, so far compile time tested only:
> > 
> > LGTM, wonder if we can push this separately as prerequesite?
> 
> Here it is as a separate independent patch.  Even without the
> wide_int changing patch it should save some memory, by not always
> allocating room for 9 limbs, but say just the 2/3 or how many we actually
> need.  And, another advantage is that if we really need it at some point,
> it could support even more than 9 limbs if it is created from a wide_int_ref
> with get_len () > 9.
> 
> Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk?

OK by me if Jason doesn't object.

Thanks,
Richard.

> 2023-10-10  Jakub Jelinek  <jakub@redhat.com>
> 
> 	* dwarf2out.h (wide_int_ptr): Remove.
> 	(dw_wide_int_ptr): New typedef.
> 	(struct dw_val_node): Change type of val_wide from wide_int_ptr
> 	to dw_wide_int_ptr.
> 	(struct dw_wide_int): New type.
> 	(dw_wide_int::elt): New method.
> 	(dw_wide_int::operator ==): Likewise.
> 	* dwarf2out.cc (get_full_len): Change argument type to
> 	const dw_wide_int & from const wide_int &.  Use CEIL.  Call
> 	get_precision method instead of calling wi::get_precision.
> 	(alloc_dw_wide_int): New function.
> 	(add_AT_wide): Change w argument type to const wide_int_ref &
> 	from const wide_int &.  Use alloc_dw_wide_int.
> 	(mem_loc_descriptor, loc_descriptor): Use alloc_dw_wide_int.
> 	(insert_wide_int): Change val argument type to const wide_int_ref &
> 	from const wide_int &.
> 	(add_const_value_attribute): Pass rtx_mode_t temporary directly to
> 	add_AT_wide instead of using a temporary variable.
> 
> --- gcc/dwarf2out.h.jj	2023-10-09 14:37:45.890939965 +0200
> +++ gcc/dwarf2out.h	2023-10-09 16:46:14.705816928 +0200
> @@ -30,7 +30,7 @@ typedef struct dw_cfi_node *dw_cfi_ref;
>  typedef struct dw_loc_descr_node *dw_loc_descr_ref;
>  typedef struct dw_loc_list_struct *dw_loc_list_ref;
>  typedef struct dw_discr_list_node *dw_discr_list_ref;
> -typedef wide_int *wide_int_ptr;
> +typedef struct dw_wide_int *dw_wide_int_ptr;
>  
>  
>  /* Call frames are described using a sequence of Call Frame
> @@ -252,7 +252,7 @@ struct GTY(()) dw_val_node {
>        unsigned HOST_WIDE_INT
>  	GTY ((tag ("dw_val_class_unsigned_const"))) val_unsigned;
>        double_int GTY ((tag ("dw_val_class_const_double"))) val_double;
> -      wide_int_ptr GTY ((tag ("dw_val_class_wide_int"))) val_wide;
> +      dw_wide_int_ptr GTY ((tag ("dw_val_class_wide_int"))) val_wide;
>        dw_vec_const GTY ((tag ("dw_val_class_vec"))) val_vec;
>        struct dw_val_die_union
>  	{
> @@ -313,6 +313,35 @@ struct GTY(()) dw_discr_list_node {
>    int dw_discr_range;
>  };
>  
> +struct GTY((variable_size)) dw_wide_int {
> +  unsigned int precision;
> +  unsigned int len;
> +  HOST_WIDE_INT val[1];
> +
> +  unsigned int get_precision () const { return precision; }
> +  unsigned int get_len () const { return len; }
> +  const HOST_WIDE_INT *get_val () const { return val; }
> +  inline HOST_WIDE_INT elt (unsigned int) const;
> +  inline bool operator == (const dw_wide_int &) const;
> +};
> +
> +inline HOST_WIDE_INT
> +dw_wide_int::elt (unsigned int i) const
> +{
> +  if (i < len)
> +    return val[i];
> +  wide_int_ref ref = wi::storage_ref (val, len, precision);
> +  return wi::sign_mask (ref);
> +}
> +
> +inline bool
> +dw_wide_int::operator == (const dw_wide_int &o) const
> +{
> +  wide_int_ref ref1 = wi::storage_ref (val, len, precision);
> +  wide_int_ref ref2 = wi::storage_ref (o.val, o.len, o.precision);
> +  return ref1 == ref2;
> +}
> +
>  /* Interface from dwarf2out.cc to dwarf2cfi.cc.  */
>  extern struct dw_loc_descr_node *build_cfa_loc
>    (dw_cfa_location *, poly_int64);
> --- gcc/dwarf2out.cc.jj	2023-10-09 14:37:45.894939909 +0200
> +++ gcc/dwarf2out.cc	2023-10-09 16:48:24.565014459 +0200
> @@ -397,11 +397,9 @@ dump_struct_debug (tree type, enum debug
>     of the number.  */
>  
>  static unsigned int
> -get_full_len (const wide_int &op)
> +get_full_len (const dw_wide_int &op)
>  {
> -  int prec = wi::get_precision (op);
> -  return ((prec + HOST_BITS_PER_WIDE_INT - 1)
> -	  / HOST_BITS_PER_WIDE_INT);
> +  return CEIL (op.get_precision (), HOST_BITS_PER_WIDE_INT);
>  }
>  
>  static bool
> @@ -3900,7 +3898,7 @@ static void add_data_member_location_att
>  						struct vlr_context *);
>  static bool add_const_value_attribute (dw_die_ref, machine_mode, rtx);
>  static void insert_int (HOST_WIDE_INT, unsigned, unsigned char *);
> -static void insert_wide_int (const wide_int &, unsigned char *, int);
> +static void insert_wide_int (const wide_int_ref &, unsigned char *, int);
>  static unsigned insert_float (const_rtx, unsigned char *);
>  static rtx rtl_for_decl_location (tree);
>  static bool add_location_or_const_value_attribute (dw_die_ref, tree, bool);
> @@ -4594,19 +4592,31 @@ AT_unsigned (dw_attr_node *a)
>    return a->dw_attr_val.v.val_unsigned;
>  }
>  
> +dw_wide_int *
> +alloc_dw_wide_int (const wide_int_ref &w)
> +{
> +  dw_wide_int *p
> +    = (dw_wide_int *) ggc_internal_alloc (sizeof (dw_wide_int)
> +					  + ((w.get_len () - 1)
> +					     * sizeof (HOST_WIDE_INT)));
> +  p->precision = w.get_precision ();
> +  p->len = w.get_len ();
> +  memcpy (p->val, w.get_val (), p->len * sizeof (HOST_WIDE_INT));
> +  return p;
> +}
> +
>  /* Add an unsigned wide integer attribute value to a DIE.  */
>  
>  static inline void
>  add_AT_wide (dw_die_ref die, enum dwarf_attribute attr_kind,
> -	     const wide_int& w)
> +	     const wide_int_ref &w)
>  {
>    dw_attr_node attr;
>  
>    attr.dw_attr = attr_kind;
>    attr.dw_attr_val.val_class = dw_val_class_wide_int;
>    attr.dw_attr_val.val_entry = NULL;
> -  attr.dw_attr_val.v.val_wide = ggc_alloc<wide_int> ();
> -  *attr.dw_attr_val.v.val_wide = w;
> +  attr.dw_attr_val.v.val_wide = alloc_dw_wide_int (w);
>    add_dwarf_attr (die, &attr);
>  }
>  
> @@ -16714,8 +16724,8 @@ mem_loc_descriptor (rtx rtl, machine_mod
>  	  mem_loc_result->dw_loc_oprnd1.v.val_die_ref.external = 0;
>  	  mem_loc_result->dw_loc_oprnd2.val_class
>  	    = dw_val_class_wide_int;
> -	  mem_loc_result->dw_loc_oprnd2.v.val_wide = ggc_alloc<wide_int> ();
> -	  *mem_loc_result->dw_loc_oprnd2.v.val_wide = rtx_mode_t (rtl, mode);
> +	  mem_loc_result->dw_loc_oprnd2.v.val_wide
> +	    = alloc_dw_wide_int (rtx_mode_t (rtl, mode));
>  	}
>        break;
>  
> @@ -17288,8 +17298,8 @@ loc_descriptor (rtx rtl, machine_mode mo
>  	  loc_result = new_loc_descr (DW_OP_implicit_value,
>  				      GET_MODE_SIZE (int_mode), 0);
>  	  loc_result->dw_loc_oprnd2.val_class = dw_val_class_wide_int;
> -	  loc_result->dw_loc_oprnd2.v.val_wide = ggc_alloc<wide_int> ();
> -	  *loc_result->dw_loc_oprnd2.v.val_wide = rtx_mode_t (rtl, int_mode);
> +	  loc_result->dw_loc_oprnd2.v.val_wide
> +	    = alloc_dw_wide_int (rtx_mode_t (rtl, int_mode));
>  	}
>        break;
>  
> @@ -20189,7 +20199,7 @@ extract_int (const unsigned char *src, u
>  /* Writes wide_int values to dw_vec_const array.  */
>  
>  static void
> -insert_wide_int (const wide_int &val, unsigned char *dest, int elt_size)
> +insert_wide_int (const wide_int_ref &val, unsigned char *dest, int elt_size)
>  {
>    int i;
>  
> @@ -20274,8 +20284,7 @@ add_const_value_attribute (dw_die_ref di
>  	  && (GET_MODE_PRECISION (int_mode)
>  	      & (HOST_BITS_PER_WIDE_INT - 1)) == 0)
>  	{
> -	  wide_int w = rtx_mode_t (rtl, int_mode);
> -	  add_AT_wide (die, DW_AT_const_value, w);
> +	  add_AT_wide (die, DW_AT_const_value, rtx_mode_t (rtl, int_mode));
>  	  return true;
>  	}
>        return false;
> 
> 
> 	Jakub
> 
>