compile.c: Improve branch coverage instrumentation [Bug #16967]

Formerly, branch coverage measurement counters are generated for each
compilation traverse of the AST.  However, ensure clause node is
traversed twice; one is for normal-exit case (the resulted bytecode is
embedded in its outer scope), and the other is for exceptional case (the
resulted bytecode is used in catch table).  Two branch coverage counters
are generated for the two cases, but it is not desired.

This changeset revamps the internal representation of branch coverage
measurement.  Branch coverage counters are generated only at the first
visit of a branch node.  Visiting the same node reuses the
already-generated counter, so double counting is avoided.

1 files changed, 25 insertions, 14 deletions

diff --git a/thread.c b/thread.c
index 91a953b9ab..6fdddde720 100644
--- a/thread.c
+++ b/thread.c
@@ -5644,20 +5644,31 @@ rb_default_coverage(int n)
     RARRAY_ASET(coverage, COVERAGE_INDEX_LINES, lines);
 
     if (mode & COVERAGE_TARGET_BRANCHES) {
-	branches = rb_ary_tmp_new_fill(2);
-	/* internal data structures for branch coverage:
-	 *
-	 * [[base_type, base_first_lineno, base_first_column, base_last_lineno, base_last_column,
-	 *   target_type_1, target_first_lineno_1, target_first_column_1, target_last_lineno_1, target_last_column_1, target_counter_index_1,
-	 *   target_type_2, target_first_lineno_2, target_first_column_2, target_last_lineno_2, target_last_column_2, target_counter_index_2, ...],
-	 *  ...]
-	 *
-	 * Example: [[:case, 1, 0, 4, 3,
-	 *            :when, 2, 8, 2, 9, 0,
-	 *            :when, 3, 8, 3, 9, 1, ...],
-	 *           ...]
-	 */
-	RARRAY_ASET(branches, 0, rb_ary_tmp_new(0));
+        branches = rb_ary_tmp_new_fill(2);
+        /* internal data structures for branch coverage:
+         *
+         * { branch base node =>
+         *     [base_type, base_first_lineno, base_first_column, base_last_lineno, base_last_column, {
+         *       branch target id =>
+         *         [target_type, target_first_lineno, target_first_column, target_last_lineno, target_last_column, target_counter_index],
+         *       ...
+         *     }],
+         *   ...
+         * }
+         *
+         * Example:
+         * { NODE_CASE =>
+         *     [1, 0, 4, 3, {
+         *       NODE_WHEN => [2, 8, 2, 9, 0],
+         *       NODE_WHEN => [3, 8, 3, 9, 1],
+         *       ...
+         *     }],
+         *   ...
+         * }
+         */
+        VALUE structure = rb_hash_new();
+        rb_obj_hide(structure);
+	RARRAY_ASET(branches, 0, structure);
 	/* branch execution counters */
 	RARRAY_ASET(branches, 1, rb_ary_tmp_new(0));
     }