Re: [PATCH 1/2] Improve readability of represent helper function.

[Matthias Maennich <maennich@google.com>]

On Wed, Apr 08, 2020 at 03:24:24PM +0100, Giuliano Procida wrote:
>Hi.
>
>On Wed, 8 Apr 2020 at 13:47, Matthias Maennich <maennich@google.com> wrote:
>>
>> On Wed, Apr 08, 2020 at 01:20:43PM +0100, Giuliano Procida wrote:
>> >This change:
>> >
>> >    - makes local variables const where possible
>> >    - gives local variables more descriptive names
>> >    - factors out some more expressions as local variables
>> >    - simplifies the logic around anonymous data members
>> >
>> >There are no behavioural changes.
>> >
>> >       * src/abg-reporter-priv.cc (represent): In the var_diff_sptr
>> >       overload, rename pretty_representation to
>> >       o_pretty_representation, introduce n_pretty_representation
>> >       where needed and replace the duplicate tr1 and tr2 with these;
>> >       rename all other variables foo1 and foo2 to o_foo and n_foo
>> >       respectively, using _type instead of _t; introduce o_anon and
>> >       n_anon and use them to make the local variable
>> >       is_strict_anonymous_data_member_change const, make ABG_ASSERT
>> >       in anonymous data member handling more obvious in the case
>> >       where anonymity has changed and allow simplification of
>> >       formatting in this case; move declarations of const local
>> >       variables above those of the non-const, state-tracking,
>> >       variables.
>> >
>> >Signed-off-by: Giuliano Procida <gprocida@google.com>
>> >---
>> > src/abg-reporter-priv.cc | 117 +++++++++++++++++----------------------
>> > 1 file changed, 50 insertions(+), 67 deletions(-)
>> >
>> >diff --git a/src/abg-reporter-priv.cc b/src/abg-reporter-priv.cc
>> >index 5fb5fbc5..a46c0e9d 100644
>> >--- a/src/abg-reporter-priv.cc
>> >+++ b/src/abg-reporter-priv.cc
>> >@@ -409,14 +409,21 @@ represent(const var_diff_sptr    &diff,
>> >   if (!ctxt->get_reporter()->diff_to_be_reported(diff.get()))
>> >     return;
>> >
>> >-  var_decl_sptr o = diff->first_var();
>> >-  var_decl_sptr n = diff->second_var();
>> >-  string name1 = o->get_qualified_name();
>> >-  string name2 = n->get_qualified_name();
>> >-  uint64_t size1 = get_var_size_in_bits(o);
>> >-  uint64_t size2 = get_var_size_in_bits(n);
>> >-  uint64_t offset1 = get_data_member_offset(o);
>> >-  uint64_t offset2 = get_data_member_offset(n);
>> >+  const var_decl_sptr o = diff->first_var();
>> >+  const var_decl_sptr n = diff->second_var();
>> >+  const bool o_anon = !!is_anonymous_data_member(o);
>> >+  const bool n_anon = !!is_anonymous_data_member(n);
>> >+  const bool is_strict_anonymous_data_member_change = o_anon && n_anon;
>> >+  const string o_name = o->get_qualified_name();
>> >+  const string n_name = n->get_qualified_name();
>> >+  const uint64_t o_size = get_var_size_in_bits(o);
>> >+  const uint64_t n_size = get_var_size_in_bits(n);
>> >+  const uint64_t o_offset = get_data_member_offset(o);
>> >+  const uint64_t n_offset = get_data_member_offset(n);
>> >+  const string o_pretty_representation = o->get_pretty_representation();
>>
>> Any reason to not have n_pretty_representation also already defined
>> here?
>
>That's what I had originally. However, it may be a fairly expensive
>operation and it's only needed in relatively rare cases.

Fair enough. Maybe add a comment then.

Cheers,
Matthias

>
>Regards,
>Giuliano.
>
>> Otherwise nice cleanup!
>>
>> Reviewed-by: Matthias Maennich <maennich@google.com>
>>
>> Cheers,
>> Matthias
>>
>> >+
>> >+  const bool show_size_offset_changes = ctxt->get_allowed_category()
>> >+                                      & SIZE_OR_OFFSET_CHANGE_CATEGORY;
>> >
>> >   // Has the main diff text been output?
>> >   bool emitted = false;
>> >@@ -424,39 +431,31 @@ represent(const var_diff_sptr    &diff,
>> >   bool begin_with_and = false;
>> >   // Have we reported a size change already?
>> >   bool size_reported = false;
>> >-  // Are we reporting a change to an anonymous member?
>> >-  bool is_strict_anonymous_data_member_change = false;
>> >
>> >-  string pretty_representation = o->get_pretty_representation();
>> >-  bool show_size_offset_changes = ctxt->get_allowed_category()
>> >-                                & SIZE_OR_OFFSET_CHANGE_CATEGORY;
>> >-
>> >-  if (is_anonymous_data_member(o) && is_anonymous_data_member(n))
>> >+  if (is_strict_anonymous_data_member_change)
>> >     {
>> >-      is_strict_anonymous_data_member_change = true;
>> >-      string tr1 = o->get_pretty_representation();
>> >-      string tr2 = n->get_pretty_representation();
>> >-      type_base_sptr t1 = o->get_type(), t2 = n->get_type();
>> >-      if (tr1 != tr2)
>> >+      const string n_pretty_representation = n->get_pretty_representation();
>> >+      const type_base_sptr o_type = o->get_type(), n_type = n->get_type();
>> >+      if (o_pretty_representation != n_pretty_representation)
>> >       {
>> >         show_offset_or_size(indent + "anonymous data member at offset",
>> >-                            offset1, *ctxt, out);
>> >+                            o_offset, *ctxt, out);
>> >
>> >         out << " changed from:\n"
>> >-            << indent << "  " << tr1 << "\n"
>> >+            << indent << "  " << o_pretty_representation << "\n"
>> >             << indent << "to:\n"
>> >-            << indent << "  " << tr2 << "\n";
>> >+            << indent << "  " << n_pretty_representation << "\n";
>> >
>> >         begin_with_and = true;
>> >         emitted = true;
>> >       }
>> >-      else if (get_type_name(t1) != get_type_name(t2)
>> >-             && is_decl(t1) && is_decl(t2)
>> >-             && is_decl(t1)->get_is_anonymous()
>> >-             && is_decl(t2)->get_is_anonymous())
>> >+      else if (get_type_name(o_type) != get_type_name(n_type)
>> >+             && is_decl(o_type) && is_decl(n_type)
>> >+             && is_decl(o_type)->get_is_anonymous()
>> >+             && is_decl(n_type)->get_is_anonymous())
>> >       {
>> >         out << indent << "while looking at anonymous data member '"
>> >-            << tr1 << "':\n"
>> >+            << o_pretty_representation << "':\n"
>> >             << indent << "the internal name of that anonymous data member"
>> >                          "changed from:\n"
>> >             << indent << " " << get_type_name(o->get_type()) << "\n"
>> >@@ -472,36 +471,20 @@ represent(const var_diff_sptr    &diff,
>> >     }
>> >   else if (filtering::has_anonymous_data_member_change(diff))
>> >     {
>> >+      ABG_ASSERT(o_anon != n_anon);
>> >       // So we are looking at a non-anonymous data member change from
>> >       // or to anonymous data member.
>> >-      if (is_anonymous_data_member(o))
>> >-      {
>> >-        string repr = "anonymous data member "
>> >-          + o->get_pretty_representation()
>> >-          + " at offset";
>> >-
>> >-        show_offset_or_size(indent + repr, offset1, *ctxt, out);
>> >-        out << " became data member '"
>> >-            << n->get_pretty_representation()
>> >-            << "'\n";
>> >-      }
>> >-      else
>> >-      {
>> >-        ABG_ASSERT(is_anonymous_data_member(n));
>> >-        string repr = "data member "
>> >-          + o->get_pretty_representation()
>> >-          + " at offset";
>> >-
>> >-        show_offset_or_size(indent + repr, offset1, *ctxt, out);
>> >-        out << " became anonymous data member '"
>> >-            << n->get_pretty_representation()
>> >-            << "'\n";
>> >-      }
>> >+      const string n_pretty_representation = n->get_pretty_representation();
>> >+      out << indent << (o_anon ? "anonymous " : "")
>> >+        << "data member " << o_pretty_representation;
>> >+      show_offset_or_size(" at offset", o_offset, *ctxt, out);
>> >+      out << " became " << (n_anon ? "anonymous " : "")
>> >+        << "data member '" << n_pretty_representation << "'\n";
>> >
>> >       begin_with_and = true;
>> >       emitted = true;
>> >     }
>> >-  else if (diff_sptr d = diff->type_diff())
>> >+  else if (const diff_sptr d = diff->type_diff())
>> >     {
>> >       if (ctxt->get_reporter()->diff_to_be_reported(d.get()))
>> >       {
>> >@@ -511,7 +494,7 @@ represent(const var_diff_sptr      &diff,
>> >               << "' changed";
>> >         else
>> >           out << indent
>> >-              << "type of '" << pretty_representation << "' changed";
>> >+              << "type of '" << o_pretty_representation << "' changed";
>> >
>> >         if (d->currently_reporting())
>> >           out << ", as being reported\n";
>> >@@ -529,7 +512,7 @@ represent(const var_diff_sptr      &diff,
>> >       }
>> >     }
>> >
>> >-  if (!filtering::has_anonymous_data_member_change(diff) && name1 != name2)
>> >+  if (!filtering::has_anonymous_data_member_change(diff) && o_name != n_name)
>> >     {
>> >       if (filtering::has_harmless_name_change(o, n)
>> >         && !(ctxt->get_allowed_category()
>> >@@ -546,7 +529,7 @@ represent(const var_diff_sptr      &diff,
>> >           out << indent;
>> >         else
>> >           out << ", ";
>> >-        out << "name of '" << name1 << "' changed to '" << name2 << "'";
>> >+        out << "name of '" << o_name << "' changed to '" << n_name << "'";
>> >         report_loc_info(n, *ctxt, out);
>> >         emitted = true;
>> >       }
>> >@@ -561,7 +544,7 @@ represent(const var_diff_sptr      &diff,
>> >         begin_with_and = false;
>> >       }
>> >       else if (!emitted)
>> >-      out << indent << "'" << pretty_representation << "' ";
>> >+      out << indent << "'" << o_pretty_representation << "' ";
>> >       else
>> >       out << ", ";
>> >       if (get_data_member_is_laid_out(o))
>> >@@ -572,7 +555,7 @@ represent(const var_diff_sptr      &diff,
>> >     }
>> >   if (show_size_offset_changes)
>> >     {
>> >-      if (offset1 != offset2)
>> >+      if (o_offset != n_offset)
>> >       {
>> >         if (begin_with_and)
>> >           {
>> >@@ -584,17 +567,17 @@ represent(const var_diff_sptr    &diff,
>> >             out << indent;
>> >             if (is_strict_anonymous_data_member_change)
>> >               out << "anonymous data member ";
>> >-            out << "'" << pretty_representation << "' ";
>> >+            out << "'" << o_pretty_representation << "' ";
>> >           }
>> >         else
>> >           out << ", ";
>> >
>> >-        show_numerical_change("offset", offset1, offset2, *ctxt, out);
>> >+        show_numerical_change("offset", o_offset, n_offset, *ctxt, out);
>> >         maybe_show_relative_offset_change(diff, *ctxt, out);
>> >         emitted = true;
>> >       }
>> >
>> >-      if (!size_reported && size1 != size2)
>> >+      if (!size_reported && o_size != n_size)
>> >       {
>> >         if (begin_with_and)
>> >           {
>> >@@ -606,12 +589,12 @@ represent(const var_diff_sptr    &diff,
>> >             out << indent;
>> >             if (is_strict_anonymous_data_member_change)
>> >               out << "anonymous data member ";
>> >-            out << "'" << pretty_representation << "' ";
>> >+            out << "'" << o_pretty_representation << "' ";
>> >           }
>> >         else
>> >           out << ", ";
>> >
>> >-        show_numerical_change("size", size1, size2, *ctxt, out);
>> >+        show_numerical_change("size", o_size, n_size, *ctxt, out);
>> >         maybe_show_relative_size_change(diff, *ctxt, out);
>> >         emitted = true;
>> >       }
>> >@@ -624,7 +607,7 @@ represent(const var_diff_sptr      &diff,
>> >         begin_with_and = false;
>> >       }
>> >       else if (!emitted)
>> >-      out << indent << "'" << pretty_representation << "' ";
>> >+      out << indent << "'" << o_pretty_representation << "' ";
>> >       else
>> >       out << ", ";
>> >       out << "elf binding changed from " << o->get_binding()
>> >@@ -639,7 +622,7 @@ represent(const var_diff_sptr      &diff,
>> >         begin_with_and = false;
>> >       }
>> >       else if (!emitted)
>> >-      out << indent << "'" << pretty_representation << "' ";
>> >+      out << indent << "'" << o_pretty_representation << "' ";
>> >       else
>> >       out << ", ";
>> >       out << "visibility changed from " << o->get_visibility()
>> >@@ -656,7 +639,7 @@ represent(const var_diff_sptr      &diff,
>> >         begin_with_and = false;
>> >       }
>> >       else if (!emitted)
>> >-      out << indent << "'" << pretty_representation << "' ";
>> >+      out << indent << "'" << o_pretty_representation << "' ";
>> >       else
>> >       out << ", ";
>> >
>> >@@ -675,7 +658,7 @@ represent(const var_diff_sptr      &diff,
>> >         begin_with_and = false;
>> >       }
>> >       else if (!emitted)
>> >-      out << indent << "'" << pretty_representation << "' ";
>> >+      out << indent << "'" << o_pretty_representation << "' ";
>> >       else
>> >       out << ", ";
>> >
>> >@@ -691,7 +674,7 @@ represent(const var_diff_sptr      &diff,
>> >     ;
>> >   else if (!emitted)
>> >     // We appear to have fallen off the edge of the map.
>> >-    out << indent << "'" << pretty_representation
>> >+    out << indent << "'" << o_pretty_representation
>> >       << "' has *some* difference - please report as a bug";
>> >   else
>> >     // do nothing
>> >--
>> >2.26.0.110.g2183baf09c-goog
>> >