24 |
do so. */ |
do so. */ |
25 |
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26 |
#include "system.h" |
#include "system.h" |
27 |
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28 |
#include "getargs.h" |
#include "getargs.h" |
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#include "symtab.h" |
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29 |
#include "gram.h" |
#include "gram.h" |
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#include "reduce.h" |
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30 |
#include "nullable.h" |
#include "nullable.h" |
31 |
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#include "reduce.h" |
32 |
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#include "symtab.h" |
33 |
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34 |
/* Linked list of rules. */ |
/* Linked list of rules. */ |
35 |
typedef struct rule_list_s |
typedef struct rule_list |
36 |
{ |
{ |
37 |
struct rule_list_s *next; |
struct rule_list *next; |
38 |
rule_t *value; |
rule *value; |
39 |
} rule_list_t; |
} rule_list; |
40 |
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41 |
bool *nullable = NULL; |
bool *nullable = NULL; |
42 |
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53 |
void |
void |
54 |
nullable_compute (void) |
nullable_compute (void) |
55 |
{ |
{ |
56 |
rule_number_t ruleno; |
rule_number ruleno; |
57 |
symbol_number_t *s1; |
symbol_number *s1; |
58 |
symbol_number_t *s2; |
symbol_number *s2; |
59 |
rule_list_t *p; |
rule_list *p; |
60 |
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61 |
symbol_number_t *squeue = XCALLOC (symbol_number_t, nvars); |
symbol_number *squeue = XCALLOC (symbol_number, nvars); |
62 |
short *rcount = XCALLOC (short, nrules); |
short *rcount = XCALLOC (short, nrules); |
63 |
/* RITEM contains all the rules, including useless productions. |
/* RITEM contains all the rules, including useless productions. |
64 |
Hence we must allocate room for useless nonterminals too. */ |
Hence we must allocate room for useless nonterminals too. */ |
65 |
rule_list_t **rsets = XCALLOC (rule_list_t *, nvars) - ntokens; |
rule_list **rsets = XCALLOC (rule_list *, nvars) - ntokens; |
66 |
/* This is said to be more elements than we actually use. |
/* This is said to be more elements than we actually use. |
67 |
Supposedly NRITEMS - NRULES is enough. But why take the risk? */ |
Supposedly NRITEMS - NRULES is enough. But why take the risk? */ |
68 |
rule_list_t *relts = XCALLOC (rule_list_t, nritems + nvars + 1); |
rule_list *relts = XCALLOC (rule_list, nritems + nvars + 1); |
69 |
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70 |
nullable = XCALLOC (bool, nvars) - ntokens; |
nullable = XCALLOC (bool, nvars) - ntokens; |
71 |
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75 |
for (ruleno = 0; ruleno < nrules; ++ruleno) |
for (ruleno = 0; ruleno < nrules; ++ruleno) |
76 |
if (rules[ruleno].useful) |
if (rules[ruleno].useful) |
77 |
{ |
{ |
78 |
rule_t *rule = &rules[ruleno]; |
rule *rules_ruleno = &rules[ruleno]; |
79 |
if (rule->rhs[0] >= 0) |
if (rules_ruleno->rhs[0] >= 0) |
80 |
{ |
{ |
81 |
/* This rule has a non empty RHS. */ |
/* This rule has a non empty RHS. */ |
82 |
item_number_t *r = NULL; |
item_number *r = NULL; |
83 |
int any_tokens = 0; |
int any_tokens = 0; |
84 |
for (r = rule->rhs; *r >= 0; ++r) |
for (r = rules_ruleno->rhs; *r >= 0; ++r) |
85 |
if (ISTOKEN (*r)) |
if (ISTOKEN (*r)) |
86 |
any_tokens = 1; |
any_tokens = 1; |
87 |
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88 |
/* This rule has only nonterminals: schedule it for the second |
/* This rule has only nonterminals: schedule it for the second |
89 |
pass. */ |
pass. */ |
90 |
if (!any_tokens) |
if (!any_tokens) |
91 |
for (r = rule->rhs; *r >= 0; ++r) |
for (r = rules_ruleno->rhs; *r >= 0; ++r) |
92 |
{ |
{ |
93 |
rcount[ruleno]++; |
rcount[ruleno]++; |
94 |
p->next = rsets[*r]; |
p->next = rsets[*r]; |
95 |
p->value = rule; |
p->value = rules_ruleno; |
96 |
rsets[*r] = p; |
rsets[*r] = p; |
97 |
p++; |
p++; |
98 |
} |
} |
100 |
else |
else |
101 |
{ |
{ |
102 |
/* This rule has an empty RHS. */ |
/* This rule has an empty RHS. */ |
103 |
if (item_number_as_rule_number (rule->rhs[0]) != ruleno) |
if (item_number_as_rule_number (rules_ruleno->rhs[0]) != ruleno) |
104 |
abort (); |
abort (); |
105 |
if (rule->useful && !nullable[rule->lhs->number]) |
if (rules_ruleno->useful && !nullable[rules_ruleno->lhs->number]) |
106 |
{ |
{ |
107 |
nullable[rule->lhs->number] = 1; |
nullable[rules_ruleno->lhs->number] = 1; |
108 |
*s2++ = rule->lhs->number; |
*s2++ = rules_ruleno->lhs->number; |
109 |
} |
} |
110 |
} |
} |
111 |
} |
} |
113 |
while (s1 < s2) |
while (s1 < s2) |
114 |
for (p = rsets[*s1++]; p; p = p->next) |
for (p = rsets[*s1++]; p; p = p->next) |
115 |
{ |
{ |
116 |
rule_t *rule = p->value; |
rule *r = p->value; |
117 |
if (--rcount[rule->number] == 0) |
if (--rcount[r->number] == 0) |
118 |
if (rule->useful && !nullable[rule->lhs->number]) |
if (r->useful && !nullable[r->lhs->number]) |
119 |
{ |
{ |
120 |
nullable[rule->lhs->number] = 1; |
nullable[r->lhs->number] = 1; |
121 |
*s2++ = rule->lhs->number; |
*s2++ = r->lhs->number; |
122 |
} |
} |
123 |
} |
} |
124 |
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