X-Git-Url: https://git.saurik.com/bison.git/blobdiff_plain/d7913476c462b480f11e14b6829942f2691c6c01..bec30531f782a6f4fe1466fb62b61352d873cb58:/src/nullable.c

diff --git a/src/nullable.c b/src/nullable.c
index dae7a62a..f8c9b32e 100644
--- a/src/nullable.c
+++ b/src/nullable.c
@@ -1,5 +1,5 @@
 /* Part of the bison parser generator,
-   Copyright (C) 1984, 1989, 2000 Free Software Foundation, Inc.
+   Copyright 1984, 1989, 2000, 2001 Free Software Foundation, Inc.
 
    This file is part of Bison, the GNU Compiler Compiler.
 
@@ -24,108 +24,105 @@
    do so.  */
 
 #include "system.h"
+#include "getargs.h"
+#include "symtab.h"
 #include "types.h"
 #include "gram.h"
-#include "xalloc.h"
+#include "reduce.h"
 #include "nullable.h"
 
 char *nullable = NULL;
 
+static void
+nullable_print (FILE *out)
+{
+  int i;
+  fputs ("NULLABLE\n", out);
+  for (i = ntokens; i < nsyms; i++)
+    fprintf (out, "\t%s: %s\n", symbols[i]->tag, nullable[i] ? "yes" : "no");
+  fputs ("\n\n", out);
+}
+
 void
 set_nullable (void)
 {
-  short *r;
+  int ruleno;
   short *s1;
   short *s2;
-  int ruleno;
-  int symbol;
   shorts *p;
 
-  short *squeue;
-  short *rcount;
-  shorts **rsets;
-  shorts *relts;
-  char any_tokens;
-  short *r1;
+  short *squeue = XCALLOC (short, nvars);
+  short *rcount = XCALLOC (short, nrules + 1);
+  /* RITEM contains all the rules, including useless productions.
+     Hence we must allocate room for useless nonterminals too.  */
+  shorts **rsets = XCALLOC (shorts *, nvars) - ntokens;
+  /* This is said to be more elements than we actually use.
+     Supposedly NRITEMS - NRULES is enough.  But why take the risk?  */
+  shorts *relts = XCALLOC (shorts, nritems + nvars + 1);
 
-#ifdef	TRACE
-  fprintf (stderr, _("Entering set_nullable"));
-#endif
+  if (trace_flag)
+    fprintf (stderr, "Entering set_nullable\n");
 
   nullable = XCALLOC (char, nvars) - ntokens;
 
-  squeue = XCALLOC (short, nvars);
   s1 = s2 = squeue;
-
-  rcount = XCALLOC (short, nrules + 1);
-  rsets = XCALLOC (shorts *, nvars) - ntokens;
-  /* This is said to be more elements than we actually use.
-     Supposedly nitems - nrules is enough.
-     But why take the risk?  */
-  relts = XCALLOC (shorts, nitems + nvars + 1);
   p = relts;
 
-  r = ritem;
-  while (*r)
-    {
-      if (*r < 0)
-	{
-	  symbol = rlhs[-(*r++)];
-	  if (symbol >= 0 && !nullable[symbol])
-	    {
-	      nullable[symbol] = 1;
-	      *s2++ = symbol;
-	    }
-	}
-      else
-	{
-	  r1 = r;
-	  any_tokens = 0;
-	  for (symbol = *r++; symbol > 0; symbol = *r++)
-	    {
-	      if (ISTOKEN (symbol))
+  for (ruleno = 1; ruleno < nrules + 1; ++ruleno)
+    if (rules[ruleno].useful)
+      {
+	if (ritem[rules[ruleno].rhs] >= 0)
+	  {
+	    /* This rule has a non empty RHS. */
+	    short *r;
+	    int any_tokens = 0;
+	    for (r = &ritem[rules[ruleno].rhs]; *r >= 0; ++r)
+	      if (ISTOKEN (*r))
 		any_tokens = 1;
-	    }
 
-	  if (!any_tokens)
-	    {
-	      ruleno = -symbol;
-	      r = r1;
-	      for (symbol = *r++; symbol > 0; symbol = *r++)
+	    /* This rule has only nonterminals: schedule it for the second
+	       pass.  */
+	    if (!any_tokens)
+	      for (r = &ritem[rules[ruleno].rhs]; *r >= 0; ++r)
 		{
 		  rcount[ruleno]++;
-		  p->next = rsets[symbol];
+		  p->next = rsets[*r];
 		  p->value = ruleno;
-		  rsets[symbol] = p;
+		  rsets[*r] = p;
 		  p++;
 		}
-	    }
-	}
-    }
+	  }
+	else
+	  {
+	    /* This rule has an empty RHS. */
+	    assert (ritem[rules[ruleno].rhs] == -ruleno);
+	    if (rules[ruleno].useful && !nullable[rules[ruleno].lhs])
+	      {
+		nullable[rules[ruleno].lhs] = 1;
+		*s2++ = rules[ruleno].lhs;
+	      }
+	  }
+      }
 
   while (s1 < s2)
-    {
-      p = rsets[*s1++];
-      while (p)
-	{
-	  ruleno = p->value;
-	  p = p->next;
-	  if (--rcount[ruleno] == 0)
+    for (p = rsets[*s1++]; p; p = p->next)
+      {
+	ruleno = p->value;
+	if (--rcount[ruleno] == 0)
+	  if (rules[ruleno].useful && !nullable[rules[ruleno].lhs])
 	    {
-	      symbol = rlhs[ruleno];
-	      if (symbol >= 0 && !nullable[symbol])
-		{
-		  nullable[symbol] = 1;
-		  *s2++ = symbol;
-		}
+	      nullable[rules[ruleno].lhs] = 1;
+	      *s2++ = rules[ruleno].lhs;
 	    }
-	}
-    }
+      }
 
   XFREE (squeue);
   XFREE (rcount);
   XFREE (rsets + ntokens);
   XFREE (relts);
+
+  if (trace_flag)
+    nullable_print (stderr);
 }