dwarf2out: Fix up CONST_WIDE_INT handling once more [PR103046]

  Hi!

My last change to CONST_WIDE_INT handling in add_const_value_attribute broke
handling of CONST_WIDE_INT constants like ((__uint128_t) 1 << 120).
wi::min_precision (w1, UNSIGNED) in that case 121, but wide_int::from
creates a wide_int that has 0 and 0xff00000000000000ULL in its elts and
precision 121.  When we output that, we output both elements and thus emit
0, 0xff00000000000000 instead of the desired 0, 0x0100000000000000.

The following patch fixes that by ensuring the precision is equal to what
we'll actually use, whole multiples of 64 bits.

Bootstrapped/regtested on x86_64-linux and i686-linux.

Though, thinking more about it, maybe better would be to actually pass
machine_mode to add_const_value_attribute from callers, so that we know
exactly what precision we want.  Because hypothetically, if say mode is
OImode and the CONST_WIDE_INT value fits into 128 bits or 192 bits,
we'd emit just those 128 or 192 bits but debug info users would expect
256 bits.

2021-11-03  Jakub Jelinek  <jakub@redhat.com>

	PR debug/103046
	* dwarf2out.c (add_const_value_attribute) <case CONST_WIDE_INT>: Round
	prec up to next HOST_BITS_PER_WIDE_INT multiple.


	Jakub
  

On Wed, Nov 03, 2021 at 09:35:38AM +0100, Jakub Jelinek wrote:
> Though, thinking more about it, maybe better would be to actually pass
> machine_mode to add_const_value_attribute from callers, so that we know
> exactly what precision we want.  Because hypothetically, if say mode is
> OImode and the CONST_WIDE_INT value fits into 128 bits or 192 bits,
> we'd emit just those 128 or 192 bits but debug info users would expect
> 256 bits.

The other option would be something like untested patch below.
On
typedef unsigned __int128 U;

int
main ()
{
  U a = (U) 1 << 120;
  U b = 0xffffffffffffffffULL;
  U c = ((U) 0xffffffff00000000ULL) << 64;
  return 0;
}
vanilla gcc incorrectly emits 0, 0xff00000000000000 for a,
0xffffffffffffffff alone (DW_FORM_data8) for b and 0, 0xffffffff00000000
for c.  gcc with the previously posted PR103046 patch emits
0, 0x0100000000000000 for a, 0xffffffffffffffff alone for b and
0, 0xffffffff00000000 for c.  And with this patch we emit
0, 0x0100000000000000 for a, 0xffffffffffffffff, 0 for b and
0, 0xffffffff00000000 for c.
So, the patch below certainly causes larger debug info (well, 128-bit
integers are pretty rare), but in this case the question is if it isn't
more correct, as debug info consumers generally will not know if they
should sign or zero extend the value in DW_AT_const_value.
The previous code assumes they will always zero extend it...

2021-11-03  Jakub Jelinek  <jakub@redhat.com>

	PR debug/103046
	* dwarf2out.c (add_const_value_attribute): Add MODE argument, use it
	in CONST_WIDE_INT handling.  Adjust recursive calls.
	(add_location_or_const_value_attribute): Pass DECL_MODE (decl) to
	new add_const_value_attribute argument.
	(tree_add_const_value_attribute): Pass TYPE_MODE (type) to new
	add_const_value_attribute argument.

--- gcc/dwarf2out.c.jj	2021-10-08 10:52:47.086531820 +0200
+++ gcc/dwarf2out.c	2021-11-03 09:45:52.160841764 +0100
@@ -3854,7 +3854,7 @@ static void add_AT_location_description
 					 dw_loc_list_ref);
 static void add_data_member_location_attribute (dw_die_ref, tree,
 						struct vlr_context *);
-static bool add_const_value_attribute (dw_die_ref, rtx);
+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 unsigned insert_float (const_rtx, unsigned char *);
@@ -20081,8 +20081,10 @@ insert_float (const_rtx rtl, unsigned ch
    constants do not necessarily get memory "homes".  */
 
 static bool
-add_const_value_attribute (dw_die_ref die, rtx rtl)
+add_const_value_attribute (dw_die_ref die, machine_mode mode, rtx rtl)
 {
+  scalar_mode int_mode;
+
   switch (GET_CODE (rtl))
     {
     case CONST_INT:
@@ -20097,14 +20099,13 @@ add_const_value_attribute (dw_die_ref di
       return true;
 
     case CONST_WIDE_INT:
-      {
-	wide_int w1 = rtx_mode_t (rtl, MAX_MODE_INT);
-	unsigned int prec = MIN (wi::min_precision (w1, UNSIGNED),
-				 (unsigned int) CONST_WIDE_INT_NUNITS (rtl)
-				 * HOST_BITS_PER_WIDE_INT);
-	wide_int w = wide_int::from (w1, prec, UNSIGNED);
-	add_AT_wide (die, DW_AT_const_value, w);
-      }
+      if (is_int_mode (mode, &int_mode)
+	  && (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);
+	}
       return true;
 
     case CONST_DOUBLE:
@@ -20190,7 +20191,7 @@ add_const_value_attribute (dw_die_ref di
 
     case CONST:
       if (CONSTANT_P (XEXP (rtl, 0)))
-	return add_const_value_attribute (die, XEXP (rtl, 0));
+	return add_const_value_attribute (die, mode, XEXP (rtl, 0));
       /* FALLTHROUGH */
     case SYMBOL_REF:
       if (!const_ok_for_output (rtl))
@@ -20703,7 +20704,7 @@ add_location_or_const_value_attribute (d
 
   rtl = rtl_for_decl_location (decl);
   if (rtl && (CONSTANT_P (rtl) || GET_CODE (rtl) == CONST_STRING)
-      && add_const_value_attribute (die, rtl))
+      && add_const_value_attribute (die, DECL_MODE (decl), rtl))
     return true;
 
   /* See if we have single element location list that is equivalent to
@@ -20724,7 +20725,7 @@ add_location_or_const_value_attribute (d
       if (GET_CODE (rtl) == EXPR_LIST)
 	rtl = XEXP (rtl, 0);
       if ((CONSTANT_P (rtl) || GET_CODE (rtl) == CONST_STRING)
-	  && add_const_value_attribute (die, rtl))
+	  && add_const_value_attribute (die, DECL_MODE (decl), rtl))
 	 return true;
     }
   /* If this decl is from BLOCK_NONLOCALIZED_VARS, we might need its
@@ -20799,7 +20800,7 @@ tree_add_const_value_attribute (dw_die_r
      symbols.  */
   rtl = rtl_for_decl_init (init, type);
   if (rtl && !early_dwarf)
-    return add_const_value_attribute (die, rtl);
+    return add_const_value_attribute (die, TYPE_MODE (type), rtl);
   /* If the host and target are sane, try harder.  */
   if (CHAR_BIT == 8 && BITS_PER_UNIT == 8
       && initializer_constant_valid_p (init, type))


	Jakub
  

On Wed, Nov 03, 2021 at 01:59:27PM +0100, Richard Biener wrote:
> >      case CONST_WIDE_INT:
> > -      {
> > -	wide_int w1 = rtx_mode_t (rtl, MAX_MODE_INT);
> > -	unsigned int prec = MIN (wi::min_precision (w1, UNSIGNED),
> > -				 (unsigned int) CONST_WIDE_INT_NUNITS (rtl)
> > -				 * HOST_BITS_PER_WIDE_INT);
> > -	wide_int w = wide_int::from (w1, prec, UNSIGNED);
> > -	add_AT_wide (die, DW_AT_const_value, w);
> > -      }
> > +      if (is_int_mode (mode, &int_mode)
> > +	  && (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);
> > +	}
> 
> ... this at least deserves a comment why we return true doing
> nothing when the mode precision isn't a multiple of 64.  The other
> patch simply extended things.

Oops, that is obviously a bug.  For non-integral mode or mode with
precision not a multiple of 64 I meant to punt.  The reason for the latter
is that if precision is something weird like 123 bits, then the printing
code will print the whole 64-bit elt which would be wrong for at least
unsigned numbers with MSB set.  I guess such modes are still very rare to
non-existing.

2021-11-03  Jakub Jelinek  <jakub@redhat.com>

	PR debug/103046
	* dwarf2out.c (add_const_value_attribute): Add MODE argument, use it
	in CONST_WIDE_INT handling.  Adjust recursive calls.
	(add_location_or_const_value_attribute): Pass DECL_MODE (decl) to
	new add_const_value_attribute argument.
	(tree_add_const_value_attribute): Pass TYPE_MODE (type) to new
	add_const_value_attribute argument.

--- gcc/dwarf2out.c.jj	2021-10-08 10:52:47.086531820 +0200
+++ gcc/dwarf2out.c	2021-11-03 14:06:22.750387774 +0100
@@ -3854,7 +3854,7 @@ static void add_AT_location_description
 					 dw_loc_list_ref);
 static void add_data_member_location_attribute (dw_die_ref, tree,
 						struct vlr_context *);
-static bool add_const_value_attribute (dw_die_ref, rtx);
+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 unsigned insert_float (const_rtx, unsigned char *);
@@ -20081,8 +20081,10 @@ insert_float (const_rtx rtl, unsigned ch
    constants do not necessarily get memory "homes".  */
 
 static bool
-add_const_value_attribute (dw_die_ref die, rtx rtl)
+add_const_value_attribute (dw_die_ref die, machine_mode mode, rtx rtl)
 {
+  scalar_mode int_mode;
+
   switch (GET_CODE (rtl))
     {
     case CONST_INT:
@@ -20097,15 +20099,15 @@ add_const_value_attribute (dw_die_ref di
       return true;
 
     case CONST_WIDE_INT:
-      {
-	wide_int w1 = rtx_mode_t (rtl, MAX_MODE_INT);
-	unsigned int prec = MIN (wi::min_precision (w1, UNSIGNED),
-				 (unsigned int) CONST_WIDE_INT_NUNITS (rtl)
-				 * HOST_BITS_PER_WIDE_INT);
-	wide_int w = wide_int::from (w1, prec, UNSIGNED);
-	add_AT_wide (die, DW_AT_const_value, w);
-      }
-      return true;
+      if (is_int_mode (mode, &int_mode)
+	  && (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);
+	  return true;
+	}
+      return false;
 
     case CONST_DOUBLE:
       /* Note that a CONST_DOUBLE rtx could represent either an integer or a
@@ -20190,7 +20192,7 @@ add_const_value_attribute (dw_die_ref di
 
     case CONST:
       if (CONSTANT_P (XEXP (rtl, 0)))
-	return add_const_value_attribute (die, XEXP (rtl, 0));
+	return add_const_value_attribute (die, mode, XEXP (rtl, 0));
       /* FALLTHROUGH */
     case SYMBOL_REF:
       if (!const_ok_for_output (rtl))
@@ -20703,7 +20705,7 @@ add_location_or_const_value_attribute (d
 
   rtl = rtl_for_decl_location (decl);
   if (rtl && (CONSTANT_P (rtl) || GET_CODE (rtl) == CONST_STRING)
-      && add_const_value_attribute (die, rtl))
+      && add_const_value_attribute (die, DECL_MODE (decl), rtl))
     return true;
 
   /* See if we have single element location list that is equivalent to
@@ -20724,7 +20726,7 @@ add_location_or_const_value_attribute (d
       if (GET_CODE (rtl) == EXPR_LIST)
 	rtl = XEXP (rtl, 0);
       if ((CONSTANT_P (rtl) || GET_CODE (rtl) == CONST_STRING)
-	  && add_const_value_attribute (die, rtl))
+	  && add_const_value_attribute (die, DECL_MODE (decl), rtl))
 	 return true;
     }
   /* If this decl is from BLOCK_NONLOCALIZED_VARS, we might need its
@@ -20799,7 +20801,7 @@ tree_add_const_value_attribute (dw_die_r
      symbols.  */
   rtl = rtl_for_decl_init (init, type);
   if (rtl && !early_dwarf)
-    return add_const_value_attribute (die, rtl);
+    return add_const_value_attribute (die, TYPE_MODE (type), rtl);
   /* If the host and target are sane, try harder.  */
   if (CHAR_BIT == 8 && BITS_PER_UNIT == 8
       && initializer_constant_valid_p (init, type))


	Jakub
  

On Wed, 3 Nov 2021, Jakub Jelinek wrote:

> On Wed, Nov 03, 2021 at 01:59:27PM +0100, Richard Biener wrote:
> > >      case CONST_WIDE_INT:
> > > -      {
> > > -	wide_int w1 = rtx_mode_t (rtl, MAX_MODE_INT);
> > > -	unsigned int prec = MIN (wi::min_precision (w1, UNSIGNED),
> > > -				 (unsigned int) CONST_WIDE_INT_NUNITS (rtl)
> > > -				 * HOST_BITS_PER_WIDE_INT);
> > > -	wide_int w = wide_int::from (w1, prec, UNSIGNED);
> > > -	add_AT_wide (die, DW_AT_const_value, w);
> > > -      }
> > > +      if (is_int_mode (mode, &int_mode)
> > > +	  && (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);
> > > +	}
> > 
> > ... this at least deserves a comment why we return true doing
> > nothing when the mode precision isn't a multiple of 64.  The other
> > patch simply extended things.
> 
> Oops, that is obviously a bug.  For non-integral mode or mode with
> precision not a multiple of 64 I meant to punt.  The reason for the latter
> is that if precision is something weird like 123 bits, then the printing
> code will print the whole 64-bit elt which would be wrong for at least
> unsigned numbers with MSB set.  I guess such modes are still very rare to
> non-existing.

Agreed.  The patch looks good to me now.

Thanks,
Richard.

> 2021-11-03  Jakub Jelinek  <jakub@redhat.com>
> 
> 	PR debug/103046
> 	* dwarf2out.c (add_const_value_attribute): Add MODE argument, use it
> 	in CONST_WIDE_INT handling.  Adjust recursive calls.
> 	(add_location_or_const_value_attribute): Pass DECL_MODE (decl) to
> 	new add_const_value_attribute argument.
> 	(tree_add_const_value_attribute): Pass TYPE_MODE (type) to new
> 	add_const_value_attribute argument.
> 
> --- gcc/dwarf2out.c.jj	2021-10-08 10:52:47.086531820 +0200
> +++ gcc/dwarf2out.c	2021-11-03 14:06:22.750387774 +0100
> @@ -3854,7 +3854,7 @@ static void add_AT_location_description
>  					 dw_loc_list_ref);
>  static void add_data_member_location_attribute (dw_die_ref, tree,
>  						struct vlr_context *);
> -static bool add_const_value_attribute (dw_die_ref, rtx);
> +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 unsigned insert_float (const_rtx, unsigned char *);
> @@ -20081,8 +20081,10 @@ insert_float (const_rtx rtl, unsigned ch
>     constants do not necessarily get memory "homes".  */
>  
>  static bool
> -add_const_value_attribute (dw_die_ref die, rtx rtl)
> +add_const_value_attribute (dw_die_ref die, machine_mode mode, rtx rtl)
>  {
> +  scalar_mode int_mode;
> +
>    switch (GET_CODE (rtl))
>      {
>      case CONST_INT:
> @@ -20097,15 +20099,15 @@ add_const_value_attribute (dw_die_ref di
>        return true;
>  
>      case CONST_WIDE_INT:
> -      {
> -	wide_int w1 = rtx_mode_t (rtl, MAX_MODE_INT);
> -	unsigned int prec = MIN (wi::min_precision (w1, UNSIGNED),
> -				 (unsigned int) CONST_WIDE_INT_NUNITS (rtl)
> -				 * HOST_BITS_PER_WIDE_INT);
> -	wide_int w = wide_int::from (w1, prec, UNSIGNED);
> -	add_AT_wide (die, DW_AT_const_value, w);
> -      }
> -      return true;
> +      if (is_int_mode (mode, &int_mode)
> +	  && (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);
> +	  return true;
> +	}
> +      return false;
>  
>      case CONST_DOUBLE:
>        /* Note that a CONST_DOUBLE rtx could represent either an integer or a
> @@ -20190,7 +20192,7 @@ add_const_value_attribute (dw_die_ref di
>  
>      case CONST:
>        if (CONSTANT_P (XEXP (rtl, 0)))
> -	return add_const_value_attribute (die, XEXP (rtl, 0));
> +	return add_const_value_attribute (die, mode, XEXP (rtl, 0));
>        /* FALLTHROUGH */
>      case SYMBOL_REF:
>        if (!const_ok_for_output (rtl))
> @@ -20703,7 +20705,7 @@ add_location_or_const_value_attribute (d
>  
>    rtl = rtl_for_decl_location (decl);
>    if (rtl && (CONSTANT_P (rtl) || GET_CODE (rtl) == CONST_STRING)
> -      && add_const_value_attribute (die, rtl))
> +      && add_const_value_attribute (die, DECL_MODE (decl), rtl))
>      return true;
>  
>    /* See if we have single element location list that is equivalent to
> @@ -20724,7 +20726,7 @@ add_location_or_const_value_attribute (d
>        if (GET_CODE (rtl) == EXPR_LIST)
>  	rtl = XEXP (rtl, 0);
>        if ((CONSTANT_P (rtl) || GET_CODE (rtl) == CONST_STRING)
> -	  && add_const_value_attribute (die, rtl))
> +	  && add_const_value_attribute (die, DECL_MODE (decl), rtl))
>  	 return true;
>      }
>    /* If this decl is from BLOCK_NONLOCALIZED_VARS, we might need its
> @@ -20799,7 +20801,7 @@ tree_add_const_value_attribute (dw_die_r
>       symbols.  */
>    rtl = rtl_for_decl_init (init, type);
>    if (rtl && !early_dwarf)
> -    return add_const_value_attribute (die, rtl);
> +    return add_const_value_attribute (die, TYPE_MODE (type), rtl);
>    /* If the host and target are sane, try harder.  */
>    if (CHAR_BIT == 8 && BITS_PER_UNIT == 8
>        && initializer_constant_valid_p (init, type))
> 
> 
> 	Jakub
> 
>