Re: [PATCH] c-family, middle-end: Add __builtin_c[lt]zg (arg, 0ULL) exception

[Richard Biener <rguenther@suse.de>]

On Sat, 18 Nov 2023, Jakub Jelinek wrote:

> Hi!
> 
> In https://sourceware.org/pipermail/libc-alpha/2023-November/152819.html
> Florian Weimer raised concern that the type-generic stdbit.h macros
> currently being considered suffer from similar problem as old tgmath.h
> implementation, in particular that the macros expand during preprocessing
> their arguments multiple times and if one nests these stdbit.h type-generic
> macros several times, that can result in extremely large preprocessed source
> and long compile times, even when the argument is only actually evaluated
> once at runtime for side-effects.
> 
> As I'd strongly prefer not to add new builtins for all the 14 stdbit.h
> type-generic macros, I think it is better to build the macros from
> smaller building blocks.
> 
> The following patch adds the first one.
> While one can say implement e.g. stdc_leading_zeros(value) macro
> as ((unsigned int) __builtin_clzg (value, __builtin_popcountg ((__typeof (value)) ~(__typeof (value)) 0)))
> that expands the argument 3 times, and even if it just used
> ((unsigned int) __builtin_clzg (value, __builtin_popcountg ((__typeof (value)) -1)))
> relying on 2-s complement, that is still twice.
> 
> I'd prefer not to add optional 3rd argument to these, but given that the
> second argument if specified right now has to have signed int type,
> the following patch adds an exception that it allows 0ULL as a magic
> value for the argument to mean fill in the precision of the first argument.

Ugh.  First of all I don't like that the exception is applied during
folding.  As for the problem of multi evaluation can't consumers use
stmt expressions for this, say

{( auto __tem = value; __builtin_xyz (__tem, __typeof (__tem)); ... )}

?  Thus use 'auto' to avoid spelling 'value' multiple times?

Richard.

> Ok for trunk if it passes bootstrap/regtest?
> 
> 2023-11-18  Jakub Jelinek  <jakub@redhat.com>
> 
> 	PR c/111309
> gcc/
> 	* builtins.cc (fold_builtin_bit_query): If arg1 is 0ULL, use
> 	TYPE_PRECISION (arg0_type) instead of it.
> 	* fold-const-call.cc (fold_const_call_sss): Rename arg0_type
> 	argument to arg_type, add arg1_type argument, if for CLZ/CTZ
> 	second argument is unsigned long long, use
> 	TYPE_PRECISION (arg0_type).
> 	(fold_const_call_1): Pass also TREE_TYPE (arg1) to
> 	fold_const_call_sss.
> 	* doc/extend.texi (__builtin_clzg, __builtin_ctzg): Document
> 	behavior for second argument 0ULL.
> gcc/c-family/
> 	* c-common.cc (check_builtin_function_arguments): If args[1] is
> 	0ULL, use TYPE_PRECISION (TREE_TYPE (args[0])) instead of it.
> gcc/testsuite/
> 	* c-c++-common/pr111309-3.c: New test.
> 	* gcc.dg/torture/bitint-43.c: Add tests with 0ULL second argument.
> 
> --- gcc/builtins.cc.jj	2023-11-14 10:52:16.170276318 +0100
> +++ gcc/builtins.cc	2023-11-18 13:55:02.996395917 +0100
> @@ -9591,6 +9591,10 @@ fold_builtin_bit_query (location_t loc,
>      case BUILT_IN_CLZG:
>        if (arg1 && TREE_CODE (arg1) != INTEGER_CST)
>  	return NULL_TREE;
> +      if (arg1
> +	  && (TYPE_MAIN_VARIANT (TREE_TYPE (arg1))
> +	      == long_long_unsigned_type_node))
> +	arg1 = build_int_cst (integer_type_node, TYPE_PRECISION (arg0_type));
>        ifn = IFN_CLZ;
>        fcodei = BUILT_IN_CLZ;
>        fcodel = BUILT_IN_CLZL;
> @@ -9599,6 +9603,10 @@ fold_builtin_bit_query (location_t loc,
>      case BUILT_IN_CTZG:
>        if (arg1 && TREE_CODE (arg1) != INTEGER_CST)
>  	return NULL_TREE;
> +      if (arg1
> +	  && (TYPE_MAIN_VARIANT (TREE_TYPE (arg1))
> +	      == long_long_unsigned_type_node))
> +	arg1 = build_int_cst (integer_type_node, TYPE_PRECISION (arg0_type));
>        ifn = IFN_CTZ;
>        fcodei = BUILT_IN_CTZ;
>        fcodel = BUILT_IN_CTZL;
> --- gcc/fold-const-call.cc.jj	2023-11-14 10:52:16.186276097 +0100
> +++ gcc/fold-const-call.cc	2023-11-18 13:49:57.514641417 +0100
> @@ -1543,13 +1543,13 @@ fold_const_call_sss (real_value *result,
>  
>        *RESULT = FN (ARG0, ARG1)
>  
> -   where ARG_TYPE is the type of ARG0 and PRECISION is the number of bits in
> -   the result.  Return true on success.  */
> +   where ARG0_TYPE is the type of ARG0, ARG1_TYPE is the type of ARG1 and
> +   PRECISION is the number of bits in the result.  Return true on success.  */
>  
>  static bool
>  fold_const_call_sss (wide_int *result, combined_fn fn,
>  		     const wide_int_ref &arg0, const wide_int_ref &arg1,
> -		     unsigned int precision, tree arg_type ATTRIBUTE_UNUSED)
> +		     unsigned int precision, tree arg0_type, tree arg1_type)
>  {
>    switch (fn)
>      {
> @@ -1559,6 +1559,8 @@ fold_const_call_sss (wide_int *result, c
>  	int tmp;
>  	if (wi::ne_p (arg0, 0))
>  	  tmp = wi::clz (arg0);
> +	else if (TYPE_MAIN_VARIANT (arg1_type) == long_long_unsigned_type_node)
> +	  tmp = TYPE_PRECISION (arg0_type);
>  	else
>  	  tmp = arg1.to_shwi ();
>  	*result = wi::shwi (tmp, precision);
> @@ -1571,6 +1573,8 @@ fold_const_call_sss (wide_int *result, c
>  	int tmp;
>  	if (wi::ne_p (arg0, 0))
>  	  tmp = wi::ctz (arg0);
> +	else if (TYPE_MAIN_VARIANT (arg1_type) == long_long_unsigned_type_node)
> +	  tmp = TYPE_PRECISION (arg0_type);
>  	else
>  	  tmp = arg1.to_shwi ();
>  	*result = wi::shwi (tmp, precision);
> @@ -1625,7 +1629,7 @@ fold_const_call_1 (combined_fn fn, tree
>  	  wide_int result;
>  	  if (fold_const_call_sss (&result, fn, wi::to_wide (arg0),
>  				   wi::to_wide (arg1), TYPE_PRECISION (type),
> -				   TREE_TYPE (arg0)))
> +				   TREE_TYPE (arg0), TREE_TYPE (arg1)))
>  	    return wide_int_to_tree (type, result);
>  	}
>        return NULL_TREE;
> --- gcc/doc/extend.texi.jj	2023-11-16 17:27:39.838028110 +0100
> +++ gcc/doc/extend.texi	2023-11-18 13:17:40.982551766 +0100
> @@ -15031,6 +15031,9 @@ optional second argument with int type.
>  are performed on the first argument.  If two arguments are specified,
>  and first argument is 0, the result is the second argument.  If only
>  one argument is specified and it is 0, the result is undefined.
> +As an exception, if two arguments are specified and the second argument
> +is 0ULL, it is as if the second argument was the bit width of the first
> +argument.
>  @enddefbuiltin
>  
>  @defbuiltin{int __builtin_ctzg (...)}
> @@ -15040,6 +15043,9 @@ optional second argument with int type.
>  are performed on the first argument.  If two arguments are specified,
>  and first argument is 0, the result is the second argument.  If only
>  one argument is specified and it is 0, the result is undefined.
> +As an exception, if two arguments are specified and the second argument
> +is 0ULL, it is as if the second argument was the bit width of the first
> +argument.
>  @enddefbuiltin
>  
>  @defbuiltin{int __builtin_clrsbg (...)}
> --- gcc/c-family/c-common.cc.jj	2023-11-14 18:26:05.193616416 +0100
> +++ gcc/c-family/c-common.cc	2023-11-18 13:20:55.751844490 +0100
> @@ -6540,6 +6540,13 @@ check_builtin_function_arguments (locati
>  			"%qE does not have integral type", 2, fndecl);
>  	      return false;
>  	    }
> +	  if (integer_zerop (args[1])
> +	      && (TYPE_MAIN_VARIANT (TREE_TYPE (args[1]))
> +		  == long_long_unsigned_type_node))
> +	    args[1] = build_int_cst (integer_type_node,
> +				     INTEGRAL_TYPE_P (TREE_TYPE (args[0]))
> +				     ? TYPE_PRECISION (TREE_TYPE (args[0]))
> +				     : 0);
>  	  if ((TYPE_PRECISION (TREE_TYPE (args[1]))
>  	       > TYPE_PRECISION (integer_type_node))
>  	      || (TYPE_PRECISION (TREE_TYPE (args[1]))
> --- gcc/testsuite/c-c++-common/pr111309-3.c.jj	2023-11-18 13:22:22.084644472 +0100
> +++ gcc/testsuite/c-c++-common/pr111309-3.c	2023-11-18 13:26:12.894436233 +0100
> @@ -0,0 +1,26 @@
> +/* PR c/111309 */
> +/* { dg-do run } */
> +/* { dg-options "-O2" } */
> +
> +int
> +main ()
> +{
> +  if (__builtin_clzg ((unsigned char) 0, 0ULL) != __CHAR_BIT__
> +      || __builtin_clzg ((unsigned short) 0, 0ULL) != __SIZEOF_SHORT__ * __CHAR_BIT__
> +      || __builtin_clzg (0U, 0ULL) != __SIZEOF_INT__ * __CHAR_BIT__
> +      || __builtin_clzg (0UL, 0ULL) != __SIZEOF_LONG__ * __CHAR_BIT__
> +      || __builtin_clzg (0ULL, 0ULL) != __SIZEOF_LONG_LONG__ * __CHAR_BIT__
> +#ifdef __SIZEOF_INT128__
> +      || __builtin_clzg ((unsigned __int128) 0, 0ULL) != __SIZEOF_INT128__ * __CHAR_BIT__
> +#endif
> +      || __builtin_clzg ((unsigned char) 1, 0ULL) != __CHAR_BIT__ - 1
> +      || __builtin_clzg ((unsigned short) 2, 0ULL) != __SIZEOF_SHORT__ * __CHAR_BIT__ - 2
> +      || __builtin_clzg (4U, 0ULL) != __SIZEOF_INT__ * __CHAR_BIT__ - 3
> +      || __builtin_clzg (8UL, 0ULL) != __SIZEOF_LONG__ * __CHAR_BIT__ - 4
> +      || __builtin_clzg (16ULL, 0ULL) != __SIZEOF_LONG_LONG__ * __CHAR_BIT__ - 5
> +#ifdef __SIZEOF_INT128__
> +      || __builtin_clzg ((unsigned __int128) 32, 0ULL) != __SIZEOF_INT128__ * __CHAR_BIT__ - 6
> +#endif
> +      || 0)
> +    __builtin_abort ();
> +}
> --- gcc/testsuite/gcc.dg/torture/bitint-43.c.jj	2023-11-14 10:52:16.191276028 +0100
> +++ gcc/testsuite/gcc.dg/torture/bitint-43.c	2023-11-18 13:28:49.335261722 +0100
> @@ -141,7 +141,9 @@ main ()
>        || parity156 (0) != 0
>        || popcount156 (0) != 0
>        || __builtin_clzg ((unsigned _BitInt(156)) 0, 156 + 32) != 156 + 32
> +      || __builtin_clzg ((unsigned _BitInt(156)) 0, 0ULL) != 156
>        || __builtin_ctzg ((unsigned _BitInt(156)) 0, 156) != 156
> +      || __builtin_ctzg ((unsigned _BitInt(156)) 0, 0ULL) != 156
>        || __builtin_clrsbg ((_BitInt(156)) 0) != 156 - 1
>        || __builtin_ffsg ((_BitInt(156)) 0) != 0
>        || __builtin_parityg ((unsigned _BitInt(156)) 0) != 0
> @@ -159,8 +161,10 @@ main ()
>        || popcount156 (-1) != 156
>        || __builtin_clzg ((unsigned _BitInt(156)) -1) != 0
>        || __builtin_clzg ((unsigned _BitInt(156)) -1, 156 + 32) != 0
> +      || __builtin_clzg ((unsigned _BitInt(156)) -1, 0ULL) != 0
>        || __builtin_ctzg ((unsigned _BitInt(156)) -1) != 0
>        || __builtin_ctzg ((unsigned _BitInt(156)) -1, 156) != 0
> +      || __builtin_ctzg ((unsigned _BitInt(156)) -1, 0ULL) != 0
>        || __builtin_clrsbg ((_BitInt(156)) -1) != 156 - 1
>        || __builtin_ffsg ((_BitInt(156)) -1) != 1
>        || __builtin_parityg ((unsigned _BitInt(156)) -1) != 0
> 
> 	Jakub
> 
> 

-- 
Richard Biener <rguenther@suse.de>
SUSE Software Solutions Germany GmbH,
Frankenstrasse 146, 90461 Nuernberg, Germany;
GF: Ivo Totev, Andrew McDonald, Werner Knoblich; (HRB 36809, AG Nuernberg)