On Mon, 20 Nov 2023, Richard Biener wrote:
> 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?
Of course the other obvious alternative would be to parse
stdc_leading_zeros and friends directly, and not go through macros
and builtins.
> 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)
