CLEANUP: Clause indexing code.

Split into smaller functions, use `bool` type, avoid `goto`,
add more comments, etc. This is a preparation before improvements.

src/pl-comp.c

@@ -4812,9 +4812,11 @@ machine code.
 
 NOTE: this function must  be  kept   consistent  with  indexOfWord()  in
 pl-index.c.
+
+@return `true` when argument can be indexed
 - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */
 
-int
+bool
 argKey(Code PC, int skip, word *key)
 { if ( skip > 0 )
     PC = skipArgs(PC, skip);
@@ -4887,7 +4889,7 @@ argKey(Code PC, int skip, word *key)
       case I_SSU_COMMIT:
       case I_SSU_CHOICE:
 	*key = 0;
-	fail;
+	return false;
       case I_NOP:
       case I_CHP:
 	continue;
@@ -4900,7 +4902,7 @@ argKey(Code PC, int skip, word *key)
 	Sdprintf("Unexpected VM code %" PRIuPTR " at %p\n", c, PC);
 	Sdprintf("\topcode=%s\n", codeTable[c].name);
 	assert(0);
-	fail;
+	return false;
     }
   }
 }
@@ -4912,7 +4914,7 @@ first argument. This is used  by   listSupervisor().  This used to share
 with argKey(), but argKey() is time critical and merging complicates it.
 - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */
 
-int
+bool
 arg1Key(Code PC, word *key)
 { for(;;)
   { code c = decode(*PC++);
@@ -4964,7 +4966,7 @@ arg1Key(Code PC, word *key)
       case I_SSU_CHOICE:
       case I_SSU_COMMIT:
 	*key = 0;
-	fail;
+	return false;
       case I_NOP:
       case I_CHP:
 	continue;
@@ -4975,7 +4977,7 @@ arg1Key(Code PC, word *key)
 #endif
       default:
 	assert(0);
-	fail;
+	return false;
     }
   }
 

src/pl-comp.h

@@ -70,8 +70,8 @@ bool		decompileHead(Clause clause, term_t head);
 int		det_goal_error(LocalFrame fr, Code PC,
 			       atom_t found);
 Code		skipArgs(Code PC, int skip);
-int		argKey(Code PC, int skip, word *key);
-int		arg1Key(Code PC, word *key);
+bool		argKey(Code PC, int skip, word *key);
+bool		arg1Key(Code PC, word *key);
 bool		decompile(Clause clause, term_t term, term_t bindings);
 word		pl_nth_clause(term_t p, term_t n, term_t ref,
 			      control_t h);

src/pl-incl.h

@@ -1292,6 +1292,8 @@ We assume the compiler will optimise this properly.
 	  } \
 	}
 
+typedef unsigned char iarg_t;	/* index argument */
+
 /* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
 Structure declarations that must be shared across multiple files.
 - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */
@@ -1449,7 +1451,6 @@ typedef struct impl_local
   LocalDefinitions local;		/* P_THREAD_LOCAL predicates */
 } impl_local, *ImplLocal;
 
-
 typedef struct clause_list
 { arg_info     *args;			/* Meta and indexing info */
   ClauseRef	first_clause;		/* clause list of procedure */
@@ -1458,7 +1459,8 @@ typedef struct clause_list
   unsigned int	number_of_clauses;	/* number of associated clauses */
   unsigned int	erased_clauses;		/* number of erased clauses in set */
   unsigned int	number_of_rules;	/* number of real rules */
-  unsigned int	jiti_tried;		/* number of times we tried to find */
+  iarg_t	jiti_tried;		/* number of times we tried to find */
+  iarg_t	primary_index;		/* Index used to link clauses */
 } clause_list, *ClauseList;
 
 typedef struct clause_ref
@@ -1610,12 +1612,10 @@ struct clause_bucket
 };
 
 #define MAX_MULTI_INDEX  4
-#define MAXINDEXARG    254
+#define MAXINDEXARG    254		/* must fit iarg_t  */
 #define MAXINDEXDEPTH    7
 #define END_INDEX_POS  255
 
-typedef unsigned char iarg_t;		/* index argument */
-
 struct clause_index
 { unsigned int	 buckets;		/* # entries */
   unsigned int	 size;			/* # clauses */
@@ -1625,6 +1625,7 @@ struct clause_index
   unsigned	 is_list : 1;		/* Index with lists */
   unsigned	 incomplete : 1;	/* Index is incomplete */
   unsigned	 invalid : 1;		/* Index is invalid */
+  unsigned	 good : 1;		/* Index is (near) perfect */
   iarg_t	 args[MAX_MULTI_INDEX];	/* Indexed arguments */
   iarg_t	 position[MAXINDEXDEPTH+1]; /* Deep index position */
   float		 speedup;		/* Estimated speedup */
@@ -1658,10 +1659,6 @@ struct definition
 #if defined(__SANITIZE_ADDRESS__)
   char	       *name;			/* Name for debugging */
 #endif
-#ifdef O_PROF_PENTIUM
-  int		prof_index;		/* index in profiling */
-  char	       *prof_name;		/* name in profiling */
-#endif
 };
 
 struct definition_chain