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      1 /*	$NetBSD: d_alignof.c,v 1.12 2023/07/07 19:45:22 rillig Exp $	*/
      2 # 3 "d_alignof.c"
      3 
      4 /* https://gcc.gnu.org/onlinedocs/gcc/Alignment.html */
      5 
      6 /* lint1-extra-flags: -X 351 */
      7 
      8 unsigned long
      9 leading_and_trailing_alignof_type(void)
     10 {
     11 	return __alignof__(short);
     12 }
     13 
     14 unsigned long
     15 leading_alignof_type(void)
     16 {
     17 	return __alignof(short);
     18 }
     19 
     20 unsigned long
     21 plain_alignof_type(void)
     22 {
     23 	/* The plain word 'alignof' is not recognized by GCC. */
     24 	/* expect+2: error: function 'alignof' implicitly declared to return int [215] */
     25 	/* expect+1: error: syntax error 'short' [249] */
     26 	return alignof(short);
     27 }
     28 /* expect-1: warning: function 'plain_alignof_type' falls off bottom without returning value [217] */
     29 
     30 unsigned long
     31 leading_and_trailing_alignof_expr(void)
     32 {
     33 	return __alignof__ 3;
     34 }
     35 
     36 unsigned long
     37 leading_alignof_expr(void)
     38 {
     39 	return __alignof 3;
     40 }
     41 
     42 unsigned long
     43 plain_alignof_expr(void)
     44 {
     45 	/* The plain word 'alignof' is not recognized by GCC. */
     46 	/* expect+2: error: 'alignof' undefined [99] */
     47 	/* expect+1: error: syntax error '3' [249] */
     48 	return alignof 3;
     49 }
     50 /* expect-1: warning: function 'plain_alignof_expr' falls off bottom without returning value [217] */
     51 
     52 
     53 /*
     54  * As with 'sizeof', the keyword '__alignof__' doesn't require parentheses
     55  * when followed by an expression.  This allows for the seemingly strange
     56  * '->' after the parentheses, which in fact is perfectly fine.
     57  *
     58  * The NetBSD style guide says "We parenthesize sizeof expressions", even
     59  * though it is misleading in edge cases like this.  The GCC manual says that
     60  * '__alignof__' and 'sizeof' are syntactically the same, therefore the same
     61  * reasoning applies to '__alignof__'.
     62  */
     63 unsigned long
     64 alignof_pointer_to_member(void)
     65 {
     66 	struct s {
     67 		unsigned long member;
     68 	} var = { 0 }, *ptr = &var;
     69 
     70 	return __alignof__(ptr)->member + ptr->member;
     71 }
     72 
     73 void
     74 alignof_variants(void)
     75 {
     76 	/* expect+1: error: negative array dimension (-4) [20] */
     77 	typedef int array_int[-(int)__alignof(int[3])];
     78 
     79 	/* expect+1: error: negative array dimension (-8) [20] */
     80 	typedef int array_double[-(int)__alignof(double[3])];
     81 
     82 	/* expect+1: error: cannot take size/alignment of function type 'function(int) returning int' [144] */
     83 	typedef int func[-(int)__alignof(int(int))];
     84 
     85 	struct int_double {
     86 		int i;
     87 		double d;
     88 	};
     89 	/* expect+1: error: negative array dimension (-8) [20] */
     90 	typedef int struct_int_double[-(int)__alignof(struct int_double)];
     91 
     92 	struct chars {
     93 		char name[20];
     94 	};
     95 	/* expect+1: error: negative array dimension (-1) [20] */
     96 	typedef int struct_chars[-(int)__alignof(struct chars)];
     97 
     98 	/* expect+1: warning: struct 'incomplete_struct' never defined [233] */
     99 	struct incomplete_struct;
    100 	/* expect+1: error: cannot take size/alignment of incomplete type [143] */
    101 	typedef int incomplete_struct[-(int)__alignof(struct incomplete_struct)];
    102 
    103 	/* expect+1: warning: union 'incomplete_union' never defined [234] */
    104 	union incomplete_union;
    105 	/* expect+1: error: cannot take size/alignment of incomplete type [143] */
    106 	typedef int incomplete_union[-(int)__alignof(union incomplete_union)];
    107 
    108 	/* expect+1: warning: enum 'incomplete_enum' never defined [235] */
    109 	enum incomplete_enum;
    110 	/* expect+1: error: cannot take size/alignment of incomplete type [143] */
    111 	typedef int incomplete_enum[-(int)__alignof(enum incomplete_enum)];
    112 
    113 	/* expect+1: error: cannot take size/alignment of incomplete type [143] */
    114 	typedef int incomplete_array[-(int)__alignof(int[])];
    115 
    116 	struct bit_fields {
    117 		_Bool bit_field:1;
    118 	};
    119 	/*
    120 	 * FIXME: This is not an attempt to initialize the typedef, it's the
    121 	 * initialization of a nested expression.
    122 	 */
    123 	/* expect+2: error: cannot initialize typedef '00000000_tmp' [25] */
    124 	/* expect+1: error: cannot take size/alignment of bit-field [145] */
    125 	typedef int bit_field_1[-(int)__alignof((struct bit_fields){0}.bit_field)];
    126 
    127 	struct bit_fields bit_fields;
    128 	/* expect+1: error: cannot take size/alignment of bit-field [145] */
    129 	typedef int bit_field_2[-(int)__alignof(bit_fields.bit_field)];
    130 
    131 	/* expect+1: error: cannot take size/alignment of void [146] */
    132 	typedef int plain_void[-(int)__alignof(void)];
    133 }
    134