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.

3 files changed, 150 insertions, 63 deletions

diff --git a/compile.c b/compile.c
index c3c1921e98..972a2997ff 100644
--- a/compile.c
+++ b/compile.c
@@ -610,34 +610,74 @@ static VALUE decl_branch_base(rb_iseq_t *iseq, const NODE *node, const char *typ
 
     if (!branch_coverage_valid_p(iseq, first_lineno)) return Qundef;
 
+    /*
+     * if !structure[node]
+     *   structure[node] = [type, first_lineno, first_column, last_lineno, last_column, branches = {}]
+     * else
+     *   branches = structure[node][5]
+     * end
+     */
+
     VALUE structure = RARRAY_AREF(ISEQ_BRANCH_COVERAGE(iseq), 0);
-    VALUE branches = rb_ary_tmp_new(5);
-    rb_ary_push(structure, branches);
-    rb_ary_push(branches, ID2SYM(rb_intern(type)));
-    rb_ary_push(branches, INT2FIX(first_lineno));
-    rb_ary_push(branches, INT2FIX(first_column));
-    rb_ary_push(branches, INT2FIX(last_lineno));
-    rb_ary_push(branches, INT2FIX(last_column));
+    VALUE key = (VALUE)node | 1; // FIXNUM for hash key
+    VALUE branch_base = rb_hash_aref(structure, key);
+    VALUE branches;
+
+    if (NIL_P(branch_base)) {
+        branch_base = rb_ary_tmp_new(6);
+        rb_hash_aset(structure, key, branch_base);
+        rb_ary_push(branch_base, ID2SYM(rb_intern(type)));
+        rb_ary_push(branch_base, INT2FIX(first_lineno));
+        rb_ary_push(branch_base, INT2FIX(first_column));
+        rb_ary_push(branch_base, INT2FIX(last_lineno));
+        rb_ary_push(branch_base, INT2FIX(last_column));
+        branches = rb_hash_new();
+        rb_obj_hide(branches);
+        rb_ary_push(branch_base, branches);
+    }
+    else {
+        branches = RARRAY_AREF(branch_base, 5);
+    }
 
     return branches;
 }
 
-static void add_trace_branch_coverage(rb_iseq_t *iseq, LINK_ANCHOR *const seq, const NODE *node, const char *type, VALUE branches)
+static void add_trace_branch_coverage(rb_iseq_t *iseq, LINK_ANCHOR *const seq, const NODE *node, int branch_id, const char *type, VALUE branches)
 {
     const int first_lineno = nd_first_lineno(node), first_column = nd_first_column(node);
     const int last_lineno = nd_last_lineno(node), last_column = nd_last_column(node);
 
     if (!branch_coverage_valid_p(iseq, first_lineno)) return;
 
-    VALUE counters = RARRAY_AREF(ISEQ_BRANCH_COVERAGE(iseq), 1);
-    long counter_idx = RARRAY_LEN(counters);
-    rb_ary_push(counters, INT2FIX(0));
-    rb_ary_push(branches, ID2SYM(rb_intern(type)));
-    rb_ary_push(branches, INT2FIX(first_lineno));
-    rb_ary_push(branches, INT2FIX(first_column));
-    rb_ary_push(branches, INT2FIX(last_lineno));
-    rb_ary_push(branches, INT2FIX(last_column));
-    rb_ary_push(branches, INT2FIX(counter_idx));
+    /*
+     * if !branches[branch_id]
+     *   branches[branch_id] = [type, first_lineno, first_column, last_lineno, last_column, counter_idx]
+     * else
+     *   counter_idx= branches[branch_id][5]
+     * end
+     */
+
+    VALUE key = INT2FIX(branch_id);
+    VALUE branch = rb_hash_aref(branches, key);
+    long counter_idx;
+
+    if (NIL_P(branch)) {
+        branch = rb_ary_tmp_new(6);
+        rb_hash_aset(branches, key, branch);
+        rb_ary_push(branch, ID2SYM(rb_intern(type)));
+        rb_ary_push(branch, INT2FIX(first_lineno));
+        rb_ary_push(branch, INT2FIX(first_column));
+        rb_ary_push(branch, INT2FIX(last_lineno));
+        rb_ary_push(branch, INT2FIX(last_column));
+        VALUE counters = RARRAY_AREF(ISEQ_BRANCH_COVERAGE(iseq), 1);
+        counter_idx = RARRAY_LEN(counters);
+        rb_ary_push(branch, LONG2FIX(counter_idx));
+        rb_ary_push(counters, INT2FIX(0));
+    }
+    else {
+        counter_idx = FIX2LONG(RARRAY_AREF(branch, 5));
+    }
+
     ADD_TRACE_WITH_DATA(seq, RUBY_EVENT_COVERAGE_BRANCH, counter_idx);
     ADD_INSN(seq, last_lineno, nop);
 }
@@ -5359,6 +5399,7 @@ compile_if(rb_iseq_t *iseq, LINK_ANCHOR *const ret, const NODE *const node, int
                 iseq,
 		ret,
                 node_body ? node_body : node,
+                0,
 		type == NODE_IF ? "then" : "else",
 		branches);
 	    end_label = NEW_LABEL(line);
@@ -5374,6 +5415,7 @@ compile_if(rb_iseq_t *iseq, LINK_ANCHOR *const ret, const NODE *const node, int
                 iseq,
 		ret,
                 node_else ? node_else : node,
+                1,
 		type == NODE_IF ? "else" : "then",
 		branches);
 	}
@@ -5401,6 +5443,7 @@ compile_case(rb_iseq_t *iseq, LINK_ANCHOR *const ret, const NODE *const orig_nod
     int line;
     enum node_type type;
     VALUE branches = Qfalse;
+    int branch_id = 0;
 
     INIT_ANCHOR(head);
     INIT_ANCHOR(body_seq);
@@ -5432,6 +5475,7 @@ compile_case(rb_iseq_t *iseq, LINK_ANCHOR *const ret, const NODE *const orig_nod
                 iseq,
 		body_seq,
                 node->nd_body ? node->nd_body : node,
+                branch_id++,
 		"when",
 		branches);
 	CHECK(COMPILE_(body_seq, "when body", node->nd_body, popped));
@@ -5469,7 +5513,7 @@ compile_case(rb_iseq_t *iseq, LINK_ANCHOR *const ret, const NODE *const orig_nod
     if (node) {
 	ADD_LABEL(cond_seq, elselabel);
 	ADD_INSN(cond_seq, line, pop);
-	add_trace_branch_coverage(iseq, cond_seq, node, "else", branches);
+	add_trace_branch_coverage(iseq, cond_seq, node, branch_id, "else", branches);
 	CHECK(COMPILE_(cond_seq, "else", node, popped));
 	ADD_INSNL(cond_seq, line, jump, endlabel);
     }
@@ -5477,7 +5521,7 @@ compile_case(rb_iseq_t *iseq, LINK_ANCHOR *const ret, const NODE *const orig_nod
 	debugs("== else (implicit)\n");
 	ADD_LABEL(cond_seq, elselabel);
 	ADD_INSN(cond_seq, nd_line(orig_node), pop);
-	add_trace_branch_coverage(iseq, cond_seq, orig_node, "else", branches);
+	add_trace_branch_coverage(iseq, cond_seq, orig_node, branch_id, "else", branches);
 	if (!popped) {
 	    ADD_INSN(cond_seq, nd_line(orig_node), putnil);
 	}
@@ -5506,6 +5550,7 @@ compile_case2(rb_iseq_t *iseq, LINK_ANCHOR *const ret, const NODE *const orig_no
     LABEL *endlabel;
     DECL_ANCHOR(body_seq);
     VALUE branches = Qfalse;
+    int branch_id = 0;
 
     branches = decl_branch_base(iseq, orig_node, "case");
 
@@ -5520,6 +5565,7 @@ compile_case2(rb_iseq_t *iseq, LINK_ANCHOR *const ret, const NODE *const orig_no
                 iseq,
 		body_seq,
 		node->nd_body ? node->nd_body : node,
+                branch_id++,
 		"when",
 		branches);
 	CHECK(COMPILE_(body_seq, "when", node->nd_body, popped));
@@ -5559,6 +5605,7 @@ compile_case2(rb_iseq_t *iseq, LINK_ANCHOR *const ret, const NODE *const orig_no
         iseq,
 	ret,
         node ? node : orig_node,
+        branch_id,
 	"else",
 	branches);
     CHECK(COMPILE_(ret, "else", node, popped));
@@ -6220,6 +6267,7 @@ compile_case3(rb_iseq_t *iseq, LINK_ANCHOR *const ret, const NODE *const orig_no
     int line;
     enum node_type type;
     VALUE branches = 0;
+    int branch_id = 0;
 
     INIT_ANCHOR(head);
     INIT_ANCHOR(body_seq);
@@ -6249,6 +6297,7 @@ compile_case3(rb_iseq_t *iseq, LINK_ANCHOR *const ret, const NODE *const orig_no
             iseq,
             body_seq,
             node->nd_body ? node->nd_body : node,
+            branch_id++,
             "in",
             branches);
         CHECK(COMPILE_(body_seq, "in body", node->nd_body, popped));
@@ -6278,14 +6327,14 @@ compile_case3(rb_iseq_t *iseq, LINK_ANCHOR *const ret, const NODE *const orig_no
     if (node) {
         ADD_LABEL(cond_seq, elselabel);
         ADD_INSN(cond_seq, line, pop);
-        add_trace_branch_coverage(iseq, cond_seq, node, "else", branches);
+        add_trace_branch_coverage(iseq, cond_seq, node, branch_id, "else", branches);
         CHECK(COMPILE_(cond_seq, "else", node, popped));
         ADD_INSNL(cond_seq, line, jump, endlabel);
     }
     else {
         debugs("== else (implicit)\n");
         ADD_LABEL(cond_seq, elselabel);
-        add_trace_branch_coverage(iseq, cond_seq, orig_node, "else", branches);
+        add_trace_branch_coverage(iseq, cond_seq, orig_node, branch_id, "else", branches);
         ADD_INSN1(cond_seq, nd_line(orig_node), putspecialobject, INT2FIX(VM_SPECIAL_OBJECT_VMCORE));
         ADD_INSN1(cond_seq, nd_line(orig_node), putobject, rb_eNoMatchingPatternError);
         ADD_INSN1(cond_seq, nd_line(orig_node), topn, INT2FIX(2));
@@ -6349,6 +6398,7 @@ compile_loop(rb_iseq_t *iseq, LINK_ANCHOR *const ret, const NODE *const node, in
         iseq,
 	ret,
         node->nd_body ? node->nd_body : node,
+        0,
 	"body",
 	branches);
     CHECK(COMPILE_POPPED(ret, "while body", node->nd_body));
@@ -6923,7 +6973,7 @@ qcall_branch_start(rb_iseq_t *iseq, LINK_ANCHOR *const recv, VALUE *branches, co
     *branches = br;
     ADD_INSN(recv, line, dup);
     ADD_INSNL(recv, line, branchnil, else_label);
-    add_trace_branch_coverage(iseq, recv, node, "then", br);
+    add_trace_branch_coverage(iseq, recv, node, 0, "then", br);
     return else_label;
 }
 
@@ -6935,7 +6985,7 @@ qcall_branch_end(rb_iseq_t *iseq, LINK_ANCHOR *const ret, LABEL *else_label, VAL
     end_label = NEW_LABEL(line);
     ADD_INSNL(ret, line, jump, end_label);
     ADD_LABEL(ret, else_label);
-    add_trace_branch_coverage(iseq, ret, node, "else", branches);
+    add_trace_branch_coverage(iseq, ret, node, 1, "else", branches);
     ADD_LABEL(ret, end_label);
 }
 
diff --git a/ext/coverage/coverage.c b/ext/coverage/coverage.c
index 34b0849fc4..49f7ffa0f8 100644
--- a/ext/coverage/coverage.c
+++ b/ext/coverage/coverage.c
@@ -76,36 +76,62 @@ rb_coverage_start(int argc, VALUE *argv, VALUE klass)
     return Qnil;
 }
 
+struct branch_coverage_result_builder
+{
+    int id;
+    VALUE result;
+    VALUE children;
+    VALUE counters;
+};
+
+static int
+branch_coverage_ii(VALUE _key, VALUE branch, VALUE v)
+{
+    struct branch_coverage_result_builder *b = (struct branch_coverage_result_builder *) v;
+
+    VALUE target_label = RARRAY_AREF(branch, 0);
+    VALUE target_first_lineno = RARRAY_AREF(branch, 1);
+    VALUE target_first_column = RARRAY_AREF(branch, 2);
+    VALUE target_last_lineno = RARRAY_AREF(branch, 3);
+    VALUE target_last_column = RARRAY_AREF(branch, 4);
+    long counter_idx = FIX2LONG(RARRAY_AREF(branch, 5));
+    rb_hash_aset(b->children, rb_ary_new_from_args(6, target_label, LONG2FIX(b->id++), target_first_lineno, target_first_column, target_last_lineno, target_last_column), RARRAY_AREF(b->counters, counter_idx));
+
+    return ST_CONTINUE;
+}
+
+static int
+branch_coverage_i(VALUE _key, VALUE branch_base, VALUE v)
+{
+    struct branch_coverage_result_builder *b = (struct branch_coverage_result_builder *) v;
+
+    VALUE base_type = RARRAY_AREF(branch_base, 0);
+    VALUE base_first_lineno = RARRAY_AREF(branch_base, 1);
+    VALUE base_first_column = RARRAY_AREF(branch_base, 2);
+    VALUE base_last_lineno = RARRAY_AREF(branch_base, 3);
+    VALUE base_last_column = RARRAY_AREF(branch_base, 4);
+    VALUE branches = RARRAY_AREF(branch_base, 5);
+    VALUE children = rb_hash_new();
+    rb_hash_aset(b->result, rb_ary_new_from_args(6, base_type, LONG2FIX(b->id++), base_first_lineno, base_first_column, base_last_lineno, base_last_column), children);
+    b->children = children;
+    rb_hash_foreach(branches, branch_coverage_ii, v);
+
+    return ST_CONTINUE;
+}
+
 static VALUE
 branch_coverage(VALUE branches)
 {
-    VALUE ret = rb_hash_new();
-    VALUE structure = rb_ary_dup(RARRAY_AREF(branches, 0));
-    VALUE counters = rb_ary_dup(RARRAY_AREF(branches, 1));
-    int i, j;
-    long id = 0;
-
-    for (i = 0; i < RARRAY_LEN(structure); i++) {
-	VALUE branches = RARRAY_AREF(structure, i);
-	VALUE base_type = RARRAY_AREF(branches, 0);
-	VALUE base_first_lineno = RARRAY_AREF(branches, 1);
-	VALUE base_first_column = RARRAY_AREF(branches, 2);
-	VALUE base_last_lineno = RARRAY_AREF(branches, 3);
-	VALUE base_last_column = RARRAY_AREF(branches, 4);
-	VALUE children = rb_hash_new();
-	rb_hash_aset(ret, rb_ary_new_from_args(6, base_type, LONG2FIX(id++), base_first_lineno, base_first_column, base_last_lineno, base_last_column), children);
-	for (j = 5; j < RARRAY_LEN(branches); j += 6) {
-	    VALUE target_label = RARRAY_AREF(branches, j);
-	    VALUE target_first_lineno = RARRAY_AREF(branches, j + 1);
-	    VALUE target_first_column = RARRAY_AREF(branches, j + 2);
-	    VALUE target_last_lineno = RARRAY_AREF(branches, j + 3);
-	    VALUE target_last_column = RARRAY_AREF(branches, j + 4);
-	    int idx = FIX2INT(RARRAY_AREF(branches, j + 5));
-	    rb_hash_aset(children, rb_ary_new_from_args(6, target_label, LONG2FIX(id++), target_first_lineno, target_first_column, target_last_lineno, target_last_column), RARRAY_AREF(counters, idx));
-	}
-    }
+    VALUE structure = RARRAY_AREF(branches, 0);
+
+    struct branch_coverage_result_builder b;
+    b.id = 0;
+    b.result = rb_hash_new();
+    b.counters = RARRAY_AREF(branches, 1);
+
+    rb_hash_foreach(structure, branch_coverage_i, (VALUE)&b);
 
-    return ret;
+    return b.result;
 }
 
 static int
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));
     }