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