| Message ID | 1456443528-13901-16-git-send-email-eblake@redhat.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
Eric Blake <eblake@redhat.com> writes: > When first introduced, neither branch of gen_visit_members_call() > would output a goto. But now that the implicit struct visit > always ends with a goto, we should do the same for regular > struct visits, so that callers don't have to worry about whether > they are creating two identical goto's in a row. > > Generated code gets slightly larger; if desired, we could patch > qapi.py:gen_visit_members() to have a mode where it skips the > final goto and leave it up to the callers when to use that mode, > but that adds more maintenance burden when the compiler should > be smart enough to not bloat the .o file just because the .c > file got larger. > > Signed-off-by: Eric Blake <eblake@redhat.com> > > --- > v2: rebase onto s/fields/members/ change > --- > scripts/qapi-visit.py | 8 ++++---- > 1 file changed, 4 insertions(+), 4 deletions(-) > > diff --git a/scripts/qapi-visit.py b/scripts/qapi-visit.py > index e281d21..a17ecc1 100644 > --- a/scripts/qapi-visit.py > +++ b/scripts/qapi-visit.py > @@ -48,6 +48,7 @@ def gen_visit_members_call(typ, direct_name, implicit_name=None): assert isinstance(typ, QAPISchemaObjectType) if typ.is_empty(): pass elif typ.is_implicit(): assert implicit_name assert not typ.variants ret += gen_visit_members(typ.members, prefix=implicit_name) This is the goto-generating part mentioned in the commit message. else: ret += mcgen(''' > visit_type_%(c_type)s_members(v, %(c_name)s, &err); > ''', > c_type=typ.c_name(), c_name=direct_name) > + ret += gen_err_check() > return ret Emitting the gen_err_check() right after emitting the call it checks makes for simpler and more robust code. > > > @@ -63,7 +64,6 @@ void visit_type_%(c_name)s_members(Visitor *v, %(c_name)s *obj, Error **errp) > > if base: > ret += gen_visit_members_call(base, '(%s *)obj' % base.c_name()) > - ret += gen_err_check() > > ret += gen_visit_members(members, prefix='obj->') > Adding more context to show the other use of gen_visit_members_call(): if variants: ret += mcgen(''' switch (obj->%(c_name)s) { ''', c_name=c_name(variants.tag_member.name)) for var in variants.variants: ret += mcgen(''' case %(case)s: ''', case=c_enum_const(variants.tag_member.type.name, var.name, variants.tag_member.type.prefix)) push_indent() ret += gen_visit_members_call(var.type, '&obj->u.' + c_name(var.name), 'obj->u.' + c_name(var.name) + '.') This is where the generated code grows. Before the patch, we sometimes omit the goto on error, which works, because the label comes right after the switch. pop_indent() ret += mcgen(''' break; ''') ret += mcgen(''' default: abort(); } ''') I wonder whether it would be simpler to make gen_visit_members_call() add the goto from the start. > @@ -95,9 +95,9 @@ void visit_type_%(c_name)s_members(Visitor *v, %(c_name)s *obj, Error **errp) > } > ''') > > - # 'goto out' produced for base, by gen_visit_members() for each member, > - # and if variants were present > - if base or members or variants: > + # 'goto out' produced for non-empty base, by gen_visit_members() for > + # each member, and if variants were present > + if (base and not base.is_empty()) or members or variants: > ret += mcgen(''' > > out: Uh, sure this hunk belongs to this patch?
On 03/03/2016 04:56 AM, Markus Armbruster wrote: > Eric Blake <eblake@redhat.com> writes: > >> When first introduced, neither branch of gen_visit_members_call() >> would output a goto. But now that the implicit struct visit >> always ends with a goto, we should do the same for regular >> struct visits, so that callers don't have to worry about whether >> they are creating two identical goto's in a row. >> >> Generated code gets slightly larger; if desired, we could patch >> qapi.py:gen_visit_members() to have a mode where it skips the >> final goto and leave it up to the callers when to use that mode, >> but that adds more maintenance burden when the compiler should >> be smart enough to not bloat the .o file just because the .c >> file got larger. >> >> Signed-off-by: Eric Blake <eblake@redhat.com> >> >> +++ b/scripts/qapi-visit.py >> @@ -48,6 +48,7 @@ def gen_visit_members_call(typ, direct_name, implicit_name=None): > assert isinstance(typ, QAPISchemaObjectType) > if typ.is_empty(): > pass > elif typ.is_implicit(): > assert implicit_name > assert not typ.variants > ret += gen_visit_members(typ.members, prefix=implicit_name) > > This is the goto-generating part mentioned in the commit message. > >> @@ -95,9 +95,9 @@ void visit_type_%(c_name)s_members(Visitor *v, %(c_name)s *obj, Error **errp) >> } >> ''') >> >> - # 'goto out' produced for base, by gen_visit_members() for each member, >> - # and if variants were present >> - if base or members or variants: >> + # 'goto out' produced for non-empty base, by gen_visit_members() for >> + # each member, and if variants were present >> + if (base and not base.is_empty()) or members or variants: >> ret += mcgen(''' >> >> out: > > Uh, sure this hunk belongs to this patch? Unfortunately, yeah - because the empty base case doesn't generate a goto. I'm leaning more and more towards not bothering to special case empty types on the next round. I've already started playing with making type.c_name() work on implicit types - it generates names like '_obj_Foo_wrapper', which won't collide (because we reserved leading underscore for our own use), but also doesn't quite match conventional naming conventions - but as long as it is used only in generated code, it isn't that bad. And with an implicit type directly laid out, I can then just blindly call visit_type_FOO_members(), even for implicit base or variant. The v4 spin of the second half of this series is looking promising...
diff --git a/scripts/qapi-visit.py b/scripts/qapi-visit.py index e281d21..a17ecc1 100644 --- a/scripts/qapi-visit.py +++ b/scripts/qapi-visit.py @@ -48,6 +48,7 @@ def gen_visit_members_call(typ, direct_name, implicit_name=None): visit_type_%(c_type)s_members(v, %(c_name)s, &err); ''', c_type=typ.c_name(), c_name=direct_name) + ret += gen_err_check() return ret @@ -63,7 +64,6 @@ void visit_type_%(c_name)s_members(Visitor *v, %(c_name)s *obj, Error **errp) if base: ret += gen_visit_members_call(base, '(%s *)obj' % base.c_name()) - ret += gen_err_check() ret += gen_visit_members(members, prefix='obj->') @@ -95,9 +95,9 @@ void visit_type_%(c_name)s_members(Visitor *v, %(c_name)s *obj, Error **errp) } ''') - # 'goto out' produced for base, by gen_visit_members() for each member, - # and if variants were present - if base or members or variants: + # 'goto out' produced for non-empty base, by gen_visit_members() for + # each member, and if variants were present + if (base and not base.is_empty()) or members or variants: ret += mcgen(''' out:
When first introduced, neither branch of gen_visit_members_call() would output a goto. But now that the implicit struct visit always ends with a goto, we should do the same for regular struct visits, so that callers don't have to worry about whether they are creating two identical goto's in a row. Generated code gets slightly larger; if desired, we could patch qapi.py:gen_visit_members() to have a mode where it skips the final goto and leave it up to the callers when to use that mode, but that adds more maintenance burden when the compiler should be smart enough to not bloat the .o file just because the .c file got larger. Signed-off-by: Eric Blake <eblake@redhat.com> --- v2: rebase onto s/fields/members/ change --- scripts/qapi-visit.py | 8 ++++---- 1 file changed, 4 insertions(+), 4 deletions(-)