coverage. nested decisions with only one condition do not generate branch mappings any more

Author: zhuyunxing

compiler/rustc_mir_build/src/build/coverageinfo/mcdc.rs

@@ -546,7 +546,11 @@ impl MCDCInfoBuilder {
             // MCDC is equivalent to normal branch coverage if number of conditions is less than 1, so ignore these decisions.
             // See comment of `MAX_CONDITIONS_NUM_IN_DECISION` for why decisions with oversized conditions are ignored.
             _ => {
-                self.append_normal_branches(conditions);
+                // Nested decisions with only one condition should be taken as condition of its outer decision directly
+                // in case there were duplicate branches in branch reports.
+                if decision.decision_depth == 0 || conditions.len() > 1 {
+                    self.append_normal_branches(conditions);
+                }
                 if decision.conditions_num > MAX_CONDITIONS_NUM_IN_DECISION {
                     tcx.dcx().emit_warn(MCDCExceedsConditionNumLimit {
                         span: decision.span,

tests/coverage/mcdc/nested_if.cov-map

@@ -195,22 +195,21 @@ Number of file 0 mappings: 20
     = (c3 + (c2 + (c0 - c1)))
 
 Function name: nested_if::nested_single_condition_decision
-Raw bytes (95): 0x[01, 01, 0b, 01, 05, 0b, 0d, 11, 16, 05, 11, 05, 11, 05, 11, 09, 2a, 01, 05, 0d, 27, 09, 2a, 01, 05, 0b, 01, 17, 01, 04, 09, 28, 00, 02, 04, 08, 00, 29, 30, 05, 02, 01, 02, 00, 00, 08, 00, 09, 30, 0d, 06, 02, 00, 00, 00, 0d, 00, 29, 05, 00, 10, 00, 11, 20, 11, 12, 00, 10, 00, 11, 11, 00, 14, 00, 19, 16, 00, 23, 00, 27, 0d, 00, 2a, 02, 06, 27, 02, 0c, 02, 06, 23, 03, 01, 00, 02]
+Raw bytes (86): 0x[01, 01, 0a, 01, 05, 0b, 0d, 11, 12, 05, 11, 05, 11, 09, 26, 01, 05, 0d, 23, 09, 26, 01, 05, 0a, 01, 17, 01, 04, 09, 28, 00, 02, 04, 08, 00, 29, 30, 05, 02, 01, 02, 00, 00, 08, 00, 09, 30, 0d, 06, 02, 00, 00, 00, 0d, 00, 29, 05, 00, 10, 00, 11, 11, 00, 14, 00, 19, 12, 00, 23, 00, 27, 0d, 00, 2a, 02, 06, 23, 02, 0c, 02, 06, 1f, 03, 01, 00, 02]
 Number of files: 1
 - file 0 => global file 1
-Number of expressions: 11
+Number of expressions: 10
 - expression 0 operands: lhs = Counter(0), rhs = Counter(1)
 - expression 1 operands: lhs = Expression(2, Add), rhs = Counter(3)
-- expression 2 operands: lhs = Counter(4), rhs = Expression(5, Sub)
+- expression 2 operands: lhs = Counter(4), rhs = Expression(4, Sub)
 - expression 3 operands: lhs = Counter(1), rhs = Counter(4)
 - expression 4 operands: lhs = Counter(1), rhs = Counter(4)
-- expression 5 operands: lhs = Counter(1), rhs = Counter(4)
-- expression 6 operands: lhs = Counter(2), rhs = Expression(10, Sub)
-- expression 7 operands: lhs = Counter(0), rhs = Counter(1)
-- expression 8 operands: lhs = Counter(3), rhs = Expression(9, Add)
-- expression 9 operands: lhs = Counter(2), rhs = Expression(10, Sub)
-- expression 10 operands: lhs = Counter(0), rhs = Counter(1)
-Number of file 0 mappings: 11
+- expression 5 operands: lhs = Counter(2), rhs = Expression(9, Sub)
+- expression 6 operands: lhs = Counter(0), rhs = Counter(1)
+- expression 7 operands: lhs = Counter(3), rhs = Expression(8, Add)
+- expression 8 operands: lhs = Counter(2), rhs = Expression(9, Sub)
+- expression 9 operands: lhs = Counter(0), rhs = Counter(1)
+Number of file 0 mappings: 10
 - Code(Counter(0)) at (prev + 23, 1) to (start + 4, 9)
 - MCDCDecision { bitmap_idx: 0, conditions_num: 2 } at (prev + 4, 8) to (start + 0, 41)
 - MCDCBranch { true: Counter(1), false: Expression(0, Sub), condition_id: 1, true_next_id: 2, false_next_id: 0 } at (prev + 0, 8) to (start + 0, 9)
@@ -220,15 +219,12 @@ Number of file 0 mappings: 11
     true  = c3
     false = ((c4 + (c1 - c4)) - c3)
 - Code(Counter(1)) at (prev + 0, 16) to (start + 0, 17)
-- Branch { true: Counter(4), false: Expression(4, Sub) } at (prev + 0, 16) to (start + 0, 17)
-    true  = c4
-    false = (c1 - c4)
 - Code(Counter(4)) at (prev + 0, 20) to (start + 0, 25)
-- Code(Expression(5, Sub)) at (prev + 0, 35) to (start + 0, 39)
+- Code(Expression(4, Sub)) at (prev + 0, 35) to (start + 0, 39)
     = (c1 - c4)
 - Code(Counter(3)) at (prev + 0, 42) to (start + 2, 6)
-- Code(Expression(9, Add)) at (prev + 2, 12) to (start + 2, 6)
+- Code(Expression(8, Add)) at (prev + 2, 12) to (start + 2, 6)
     = (c2 + (c0 - c1))
-- Code(Expression(8, Add)) at (prev + 3, 1) to (start + 0, 2)
+- Code(Expression(7, Add)) at (prev + 3, 1) to (start + 0, 2)
     = (c3 + (c2 + (c0 - c1)))
 

tests/coverage/mcdc/nested_if.coverage

@@ -131,7 +131,6 @@
   ------------------
   |  Branch (LL:8): [True: 2, False: 1]
   |  Branch (LL:13): [True: 1, False: 1]
-  |  Branch (LL:16): [True: 1, False: 1]
   ------------------
   |---> MC/DC Decision Region (LL:8) to (LL:41)
   |