[refactor, performance] Remove unused 'spids' field on compound_word.

AFTER:

$ _bin/osh_parse.opt -n benchmarks/testdata/configure

dumb_alloc:
        gNumNew = 824496
        gNumDelete = 67267
        gMemPos = 18352488

        gNumMalloc = 83244
        gNumFree = 0
        gMemPos2 = 1113888

$ _bin/osh_parse.opt -n benchmarks/testdata/configure-coreutils

dumb_alloc:
        gNumNew = 2282545
        gNumDelete = 187457
        gMemPos = 55296584

        gNumMalloc = 237032
        gNumFree = 0
	gMemPos2 = 3353424

frontend/syntax.asdl

@@ -185,7 +185,8 @@ module syntax
   | ExprSub(Token left, expr child)
   attributes (int* spids)
 
-  compound_word = (word_part* parts, int* spids)
+  compound_word = (word_part* parts)
+
   word = 
     -- Empty is for the RHS of 'x=', 'declare x=', and the argument in "${x:-}".
     -- Semantically, we need it for "${x:-}" (see osh/word_parse.py).  Other 

osh/braces.py

@@ -236,7 +236,7 @@ def _BraceDetect(w):
         # ?  We're forcing braces right now but not commas.
         if len(stack):
           stack[-1].saw_comma = True
-          stack[-1].alt_part.words.append(compound_word(cur_parts, None))
+          stack[-1].alt_part.words.append(compound_word(cur_parts))
           cur_parts = []  # clear
           append = False
 
@@ -272,7 +272,7 @@ def _BraceDetect(w):
           if not stack[-1].saw_comma:  # {foo} is not a real alternative
             return None  # early return
 
-          stack[-1].alt_part.words.append(compound_word(cur_parts, None))
+          stack[-1].alt_part.words.append(compound_word(cur_parts))
 
           frame = stack.pop()
           cur_parts = frame.cur_parts
@@ -481,7 +481,7 @@ def BraceExpandWords(words):
       if case(word_e.BracedTree):
         w = cast(word__BracedTree, UP_w)
         parts_list = _BraceExpand(w.parts)
-        tmp = [compound_word(p, None) for p in parts_list]
+        tmp = [compound_word(p) for p in parts_list]
         out.extend(tmp)
 
       elif case(word_e.Compound):

osh/cmd_exec.py

@@ -580,7 +580,7 @@ def _EvalRedirect(self, n):
 
     elif n.tag == redir_e.HereDoc:
       # HACK: Wrap it in a word to evaluate.
-      w = compound_word(n.stdin_parts, None)
+      w = compound_word(n.stdin_parts)
       val = self.word_ev.EvalWordToString(w)
       assert val.tag == value_e.Str, val
       return redirect.HereDoc(fd, val.s, n.op.span_id)

osh/cmd_parse.py

@@ -243,7 +243,7 @@ def _MakeAssignPair(parse_ctx, preparsed, arena):
   if part_offset == n:
     val = word.Empty()  # type: word_t
   else:
-    val = compound_word(w.parts[part_offset:], None)
+    val = compound_word(w.parts[part_offset:])
     tilde = word_.TildeDetect(val)
     if tilde:
       val = tilde
@@ -273,7 +273,7 @@ def _AppendMoreEnv(preparsed_list, more_env):
     if part_offset == n:
       val = word.Empty()  # type: word_t
     else:
-      val = compound_word(w.parts[part_offset:], None)
+      val = compound_word(w.parts[part_offset:])
 
     pair = syntax_asdl.env_pair(var_name, val, [left_token.span_id])
     more_env.append(pair)

osh/word_.py

@@ -367,7 +367,7 @@ def TildeDetect(UP_w):
 
   if len(w.parts) == 1:  # can't be zero
     tilde_part = word_part.TildeSub(tok0)
-    return compound_word([tilde_part], None)
+    return compound_word([tilde_part])
 
   UP_part1 = w.parts[1]
   # NOTE: We could inspect the raw tokens.
@@ -378,7 +378,7 @@ def TildeDetect(UP_w):
 
       parts = [tilde_part_]
       parts.extend(w.parts[1:])
-      return compound_word(parts, None)
+      return compound_word(parts)
 
   # It could be something like '~foo:bar', which doesn't have a slash.
   return None
@@ -528,8 +528,8 @@ def DetectAssocPair(w):
     id_ = _LiteralId(parts[i])
     if id_ == Id.Lit_ArrayLhsClose: # ]=
       # e.g. if we have [$x$y]=$a$b
-      key = compound_word(parts[1:i], None)  # $x$y 
-      value = compound_word(parts[i+1:], None)  # $a$b from
+      key = compound_word(parts[1:i])  # $x$y 
+      value = compound_word(parts[i+1:])  # $a$b from
 
       # Type-annotated intermediate value for mycpp translation
       ret = key, value  # type: Optional[Tuple[compound_word, compound_word]]
@@ -715,7 +715,7 @@ def ErrorWord(fmt, err):
     # type: (str, _ErrorWithLocation) -> compound_word
     error_str = fmt % err.UserErrorString()
     t = Token(Id.Lit_Chars, runtime.NO_SPID, error_str)
-    return compound_word([t], None)
+    return compound_word([t])
 
 
 def Pretty(w):