[Qemu-devel] [PATCH v10 04/13] qapi: Drop pointless gotos in generated code

[Eric Blake]

There's no point in emitting a goto if the very next thing
emitted will be the label.  A bit of cleverness in gen_visit_fields()
will let us choose when to omit a final error check (basically,
swap the order of emitted text within the loop, with the error
check omitted on the first pass, then checking whether to emit a
final check after the loop); and in turn omit unused labels.

The change to generated code is a bit easier because we split out
the reindentation of the remaining gotos in the previous patch.
For example, in visit_type_ChardevReturn_fields():

|     if (visit_optional(v, "pty", &obj->has_pty)) {
|         visit_type_str(v, "pty", &obj->pty, &err);
|     }
|-    if (err) {
|-        goto out;
|-    }
|-
|-out:
|     error_propagate(errp, err);

Signed-off-by: Eric Blake <address@hidden>

---
v10: new patch
---
 scripts/qapi-event.py |  7 +++++--
 scripts/qapi-visit.py | 10 ++++++----
 scripts/qapi.py       |  8 ++++++--
 3 files changed, 17 insertions(+), 8 deletions(-)

diff --git a/scripts/qapi-event.py b/scripts/qapi-event.py
index 544ae12..b50ac29 100644
--- a/scripts/qapi-event.py
+++ b/scripts/qapi-event.py
@@ -68,9 +68,12 @@ def gen_event_send(name, arg_type):
                      name=name)
         ret += gen_err_check()
         ret += gen_visit_fields(arg_type.members, need_cast=True,
-                                label='out_obj')
-        ret += mcgen('''
+                                label='out_obj', skiplast=True)
+        if len(arg_type.members) > 1:
+            ret += mcgen('''
 out_obj:
+''')
+        ret += mcgen('''
     visit_end_struct(v, err ? NULL : &err);
     if (err) {
         goto out;
diff --git a/scripts/qapi-visit.py b/scripts/qapi-visit.py
index 0cc9b08..0be396b 100644
--- a/scripts/qapi-visit.py
+++ b/scripts/qapi-visit.py
@@ -92,12 +92,14 @@ static void visit_type_%(c_name)s_fields(Visitor *v, 
%(c_name)s **obj, Error **e
     visit_type_%(c_type)s_fields(v, (%(c_type)s **)obj, &err);
 ''',
                      c_type=base.c_name())
-        ret += gen_err_check()
+        if members:
+            ret += gen_err_check()

-    ret += gen_visit_fields(members, prefix='(*obj)->')
+    ret += gen_visit_fields(members, prefix='(*obj)->', skiplast=True)

-    # 'goto out' produced for base, and by gen_visit_fields() for each member
-    if base or members:
+    # 'goto out' produced for base, and by gen_visit_fields() for each
+    # member except the last
+    if bool(base) + len(members) > 1:
         ret += mcgen('''

 out:
diff --git a/scripts/qapi.py b/scripts/qapi.py
index fab5001..4d75d75 100644
--- a/scripts/qapi.py
+++ b/scripts/qapi.py
@@ -1645,14 +1645,17 @@ def gen_err_check(label='out', skiperr=False):


 def gen_visit_fields(members, prefix='', need_cast=False, skiperr=False,
-                     label='out'):
+                     label='out', skiplast=False):
     ret = ''
     if skiperr:
         errparg = 'NULL'
     else:
         errparg = '&err'
+    local_skiperr = True

     for memb in members:
+        ret += gen_err_check(skiperr=local_skiperr, label=label)
+        local_skiperr = skiperr
         if memb.optional:
             ret += mcgen('''
     if (visit_optional(v, "%(name)s", &%(prefix)shas_%(c_name)s)) {
@@ -1679,8 +1682,9 @@ def gen_visit_fields(members, prefix='', need_cast=False, 
skiperr=False,
             ret += mcgen('''
     }
 ''')
+
+    if members and not skiplast:
         ret += gen_err_check(skiperr=skiperr, label=label)
-
     return ret


-- 
2.5.0