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ddfb37ab17
Okay I need to introduce some vocabulary here. Suppose we have the
version 1 of a library named library-v1.so which source code is:
struct S
{
int m0;
struct S* m2;
};
int
foo(struct S* ptr)
{
return ptr;
}
And now suppose we have a version 2 of that library named
library-v2.so which source code is modified so that a new data member
is inserted into struct S:
struct S
{
int m0;
char m1; /* <--- a new data member is inserted here. */
struct S* m2;
};
int
foo(struct S* ptr)
{
return ptr;
}
struct S is said to be a cyclic type because it contains a (data)
member which type refers to struct S itself, namely, the type of the
data member S::m2 is struct S*, which refers to struct S.
So, by analogy, the diff node tree that represents the changes of
struct S is also said to be cyclic, for similar reasons: the diff
node of the change of S::m2 refers to the diff node of the change of
the type of S::m2, namely the diff node of struct S*, which refers to
the diff node for the change of struct S itself.
Now let's talk about redundancy. When walking the diff node tree of
struct S in a depth-first manner, at some point, we look at the diff
node for the data member S::m2, and we end up looking at the diff node
of its type which is the diff node for struct S*; we keep walking and
eventually we look the diff node of the change of the underlying type
of struct S, which is the diff node of struct S, and hah! that is a
redundant node because it's the first node that we visited when
visiting the diff node of ... struct S! So the diff tree node for
the change of struct S is not only a cyclic node, it's a redundant
diff node as well, and its second occurrence is located at the point
of appearance of data member S::m2. Hence the wording "cyclic
redundant diff tree node". There! We have our vocabulary all set now.
This patch enhances the code of the comparison engine so that a cyclic
diff tree node is marked as redundant from the point of its second
occurrence, onward.
First the patch separates the notion of visiting a diff node from the
notion of traversing it. Now traversing a diff node means visiting it
and visiting its children nodes. So one can visit a node without
traversing it, but one can not traverse a node without visiting it.
So, when walking diff node trees, we need to avoid ending up in
infinite loop in presence of cyclic nodes. This is why re-traversing
a node that is already being traversed is forbidden by this patch, but
visiting a node that is being visited is allowed. Before this patch,
the notions of visiting and traversing were conflated in one and were
not very clear; and one couldn't visit a node that was currently being
visited. As a result, in presence of a cyclic node, its redundant
nature wasn't being recognized, and so the diff tree node was not
being flagged as being redundant. Diff reports were then cluttered by
redundant references to changes involving cyclic types.
* include/abg-comparison.h (enum visiting_kind): Rename
enumerator DO_NOT_MARK_VISITED_NODES_AS_TRAVERSED into
DO_NOT_MARK_VISITED_NODES_AS_VISITED.
(diff_context::diff_has_been_visited): Rename
diff_context::diff_has_been_traversed into this.
(diff_context::mark_diff_as_visited): Rename
diff_context::mark_diff_as_traversed into this.
(diff_context::forget_visited_diffs): Rename
diff_context::forget_traversed_diffs into this.
(diff_context::forbid_visiting_a_node_twice): Rename
diff_context::forbid_traversing_a_node_twice into this.
(diff_context::visiting_a_node_twice_is_forbidden): Rename
diff_context::traversing_a_node_twice_is_forbidden into this.
(diff::is_traversing): Move this from protected to public.
* src/abg-comparison.cc (diff_context::priv::visited_diff_nodes_):
Rename diff_context::priv::traversed_diff_nodes_ into this.
(diff_context::priv::forbid_visiting_a_node_twice_): Rename
diff_context::priv::forbid_traversing_a_node_twice_ into this.
(diff_context::priv::priv): Adjust.
(diff_context::diff_has_been_visited): Rename
diff_context::diff_has_been_traversed into this. Adjust.
(diff_context::mark_diff_as_visited): Rename
diff_context::mark_diff_as_traversed into this. Adjust.
(diff_context::forget_visited_diffs): Rename
diff_context::forget_traversed_diffs into this. Adjust.
(diff_context::forbid_visiting_a_node_twice): Rename
diff_context::forbid_traversing_a_node_twice into this.
(diff_context::visiting_a_node_twice_is_forbidden): Rename
diff_context::traversing_a_node_twice_is_forbidden into this.
(diff_context::maybe_apply_filters): Adjust.
(diff::end_traversing): Remove the 'mark_as_traversed' parameter
of this. Remove the visited-marking code.
(diff::traverse): This is the crux of the changes of this patch.
Avoid traversing a node that is being traversed, but one can visit
a node being visited. Also, traversing a node means visiting it
and visiting its children nodes.
(diff::is_filtered_out): Simplify logic for filtering redundant
code. Basically all nodes that are redundant are filtered. All
the complicated logic that was due when diff nodes were shared is
not relevant anymore.
(corpus_diff::priv::categorize_redundant_changed_sub_nodes)
(propagate_categories, apply_suppressions)
(diff_node_printer::diff_node_printer, print_diff_tree)
(categorize_redundant_changed_sub_nodes)
(clear_redundancy_categorization)
(clear_redundancy_categorization): Adjust.
(redundancy_marking_visitor::visit_begin): Adjust. Also, if the
current diff node is already being traversed (that's a clyclic
node) then mark it as redundant.
* src/abg-comp-filter.cc (apply_filter): Adjust.
* tests/data/test-diff-filter/test16-report-2.txt: New test input data.
* tests/data/test-diff-filter/libtest25-cyclic-type-v{0,1}.so: New
test input binaries.
* tests/data/test-diff-filter/test25-cyclic-type-v{0,1}.cc: Source
code for the test input binaries.
* tests/data/test-diff-filter/test25-cyclic-type-report-0.txt: New
test input data.
* tests/data/test-diff-filter/test25-cyclic-type-report-1.txt:
Likewise.
* tests/test-diff-filter.cc (in_out_specs): Add the new test
inputs above to the list of test input data over which to run this
test harness.
* tests/data/Makefile.am: Add the new test files above to source
distribution.
* tests/data/test-diff-filter/test16-report.txt: Adjust.
* tests/data/test-diff-filter/test17-0-report.txt: Likewise.
Signed-off-by: Dodji Seketeli <dodji@redhat.com>
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||
|---|---|---|
| .. | ||
| data | ||
| Makefile.am | ||
| print-diff-tree.cc | ||
| test-abicompat.cc | ||
| test-abidiff.cc | ||
| test-alt-dwarf-file.cc | ||
| test-core-diff.cc | ||
| test-diff2.cc | ||
| test-diff-dwarf.cc | ||
| test-diff-filter.cc | ||
| test-diff-suppr.cc | ||
| test-dot.cc | ||
| test-ir-walker.cc | ||
| test-lookup-syms.cc | ||
| test-read-dwarf.cc | ||
| test-read-write.cc | ||
| test-svg.cc | ||
| test-utils.cc | ||
| test-utils.h | ||
| test-write-read-archive.cc | ||