docs: automarkup: do not look up symbols twice

The automarkup code tries to look up symbols once as a function, and once
as a macro.  The Sphinx C domain code, though, totally ignores that
distinction and will return the same results either way.  So just look
things up once and be done with it; the resulting output does not change,
but htmldocs build time drops by about 5%.

Tested-by: Akira Yokosawa <akiyks@gmail.com>
Link: https://lore.kernel.org/r/20220630163630.714673-3-corbet@lwn.net
Signed-off-by: Jonathan Corbet <corbet@lwn.net>

Documentation/sphinx/automarkup.py

@@ -125,19 +125,16 @@ def markup_refs(docname, app, node):
 # do them again.
 #
 failed_lookups = { }
-def failure_seen(target, reftype):
+def failure_seen(target):
-    return (target + '::' + reftype) in failed_lookups
+    return (target) in failed_lookups
-def note_failure(target, reftype):
+def note_failure(target):
-    failed_lookups[target + '::' + reftype] = True
+    failed_lookups[target] = True
 
 #
 # In sphinx3 we can cross-reference to C macro and function, each one with its
 # own C role, but both match the same regex, so we try both.
 #
 def markup_func_ref_sphinx3(docname, app, match):
-    class_str = ['c-func', 'c-macro']
-    reftype_str = ['function', 'macro']
-
     cdom = app.env.domains['c']
     #
     # Go through the dance of getting an xref out of the C domain
@@ -153,15 +150,13 @@ def markup_func_ref_sphinx3(docname, app, match):
 
     if base_target not in Skipnames:
         for target in possible_targets:
-            if target not in Skipfuncs:
+            if (target not in Skipfuncs) and not failure_seen(target):
-                for class_s, reftype_s in zip(class_str, reftype_str):
+                lit_text = nodes.literal(classes=['xref', 'c', 'c-func'])
-                    if failure_seen(target, reftype_s):
-                        continue
-                    lit_text = nodes.literal(classes=['xref', 'c', class_s])
                 lit_text += target_text
                 pxref = addnodes.pending_xref('', refdomain = 'c',
-                                                  reftype = reftype_s,
+                                              reftype = 'function',
-                                                  reftarget = target, modname = None,
+                                              reftarget = target,
+                                              modname = None,
                                               classname = None)
                 #
                 # XXX The Latex builder will throw NoUri exceptions here,
@@ -169,14 +164,14 @@ def markup_func_ref_sphinx3(docname, app, match):
                 #
                 try:
                     xref = cdom.resolve_xref(app.env, docname, app.builder,
-                                                 reftype_s, target, pxref,
+                                             'function', target, pxref,
                                              lit_text)
                 except NoUri:
                     xref = None
 
                 if xref:
                     return xref
-                    note_failure(target, reftype_s)
+                note_failure(target)
 
     return target_text