coverage: Instrument the RHS value of lazy logical operators

When a lazy logical operator (`&&` or `||`) occurs outside of an `if`
condition, it normally doesn't have any associated control-flow branch, so we
don't have an existing way to track whether it was true or false.

This patch adds special code to handle this case, by inserting extra MIR blocks
in a diamond shape after evaluating the RHS. This gives us a place to insert
the appropriate marker statements, which can then be given their own counters.

Author: Zalathar

compiler/rustc_mir_build/src/build/coverageinfo.rs

@@ -155,7 +155,64 @@ impl BranchInfoBuilder {
     }
 }
 
-impl Builder<'_, '_> {
+impl<'tcx> Builder<'_, 'tcx> {
+    /// If condition coverage is enabled, inject extra blocks and marker statements
+    /// that will let us track the value of the condition in `place`.
+    pub(crate) fn visit_coverage_standalone_condition(
+        &mut self,
+        mut expr_id: ExprId,     // Expression giving the span of the condition
+        place: mir::Place<'tcx>, // Already holds the boolean condition value
+        block: &mut BasicBlock,
+    ) {
+        // Bail out if condition coverage is not enabled for this function.
+        let Some(branch_info) = self.coverage_branch_info.as_mut() else { return };
+        if !self.tcx.sess.instrument_coverage_condition() {
+            return;
+        };
+
+        // Remove any wrappers, so that we can inspect the real underlying expression.
+        while let ExprKind::Use { source: inner } | ExprKind::Scope { value: inner, .. } =
+            self.thir[expr_id].kind
+        {
+            expr_id = inner;
+        }
+        // If the expression is a lazy logical op, it will naturally get branch
+        // coverage as part of its normal lowering, so we can disregard it here.
+        if let ExprKind::LogicalOp { .. } = self.thir[expr_id].kind {
+            return;
+        }
+
+        let source_info = SourceInfo { span: self.thir[expr_id].span, scope: self.source_scope };
+
+        // Using the boolean value that has already been stored in `place`, set up
+        // control flow in the shape of a diamond, so that we can place separate
+        // marker statements in the true and false blocks. The coverage MIR pass
+        // will use those markers to inject coverage counters as appropriate.
+        //
+        //          block
+        //         /     \
+        // true_block   false_block
+        //  (marker)     (marker)
+        //         \     /
+        //        join_block
+
+        let true_block = self.cfg.start_new_block();
+        let false_block = self.cfg.start_new_block();
+        self.cfg.terminate(
+            *block,
+            source_info,
+            mir::TerminatorKind::if_(mir::Operand::Copy(place), true_block, false_block),
+        );
+
+        branch_info.add_two_way_branch(&mut self.cfg, source_info, true_block, false_block);
+
+        let join_block = self.cfg.start_new_block();
+        self.cfg.goto(true_block, source_info, join_block);
+        self.cfg.goto(false_block, source_info, join_block);
+        // Any subsequent codegen in the caller should use the new join block.
+        *block = join_block;
+    }
+
     /// If branch coverage is enabled, inject marker statements into `then_block`
     /// and `else_block`, and record their IDs in the table of branch spans.
     pub(crate) fn visit_coverage_branch_condition(

compiler/rustc_mir_build/src/build/expr/into.rs

@@ -181,9 +181,13 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
                         const_: Const::from_bool(this.tcx, constant),
                     },
                 );
-                let rhs = unpack!(this.expr_into_dest(destination, continuation, rhs));
+                let mut rhs_block = unpack!(this.expr_into_dest(destination, continuation, rhs));
+                // Instrument the lowered RHS's value for condition coverage.
+                // (Does nothing if condition coverage is not enabled.)
+                this.visit_coverage_standalone_condition(rhs, destination, &mut rhs_block);
+
                 let target = this.cfg.start_new_block();
-                this.cfg.goto(rhs, source_info, target);
+                this.cfg.goto(rhs_block, source_info, target);
                 this.cfg.goto(short_circuit, source_info, target);
                 target.unit()
             }

tests/coverage/branch/conditions.cov-map

@@ -1,11 +1,11 @@
 Function name: conditions::assign_3
-Raw bytes (73): 0x[01, 01, 09, 07, 0b, 05, 09, 0d, 11, 01, 05, 01, 05, 22, 11, 01, 05, 22, 11, 01, 05, 09, 01, 17, 01, 00, 28, 03, 01, 09, 00, 0a, 01, 00, 0d, 00, 0e, 20, 05, 22, 00, 0d, 00, 0e, 22, 00, 12, 00, 13, 20, 1e, 11, 00, 12, 00, 13, 1e, 00, 17, 00, 18, 20, 09, 0d, 00, 17, 00, 18, 03, 01, 05, 01, 02]
+Raw bytes (73): 0x[01, 01, 09, 05, 07, 0b, 11, 09, 0d, 01, 05, 01, 05, 22, 11, 01, 05, 22, 11, 01, 05, 09, 01, 17, 01, 00, 28, 03, 01, 09, 00, 0a, 01, 00, 0d, 00, 0e, 20, 05, 22, 00, 0d, 00, 0e, 22, 00, 12, 00, 13, 20, 1e, 11, 00, 12, 00, 13, 1e, 00, 17, 00, 18, 20, 09, 0d, 00, 17, 00, 18, 03, 01, 05, 01, 02]
 Number of files: 1
 - file 0 => global file 1
 Number of expressions: 9
-- expression 0 operands: lhs = Expression(1, Add), rhs = Expression(2, Add)
-- expression 1 operands: lhs = Counter(1), rhs = Counter(2)
-- expression 2 operands: lhs = Counter(3), rhs = Counter(4)
+- expression 0 operands: lhs = Counter(1), rhs = Expression(1, Add)
+- expression 1 operands: lhs = Expression(2, Add), rhs = Counter(4)
+- expression 2 operands: lhs = Counter(2), rhs = Counter(3)
 - expression 3 operands: lhs = Counter(0), rhs = Counter(1)
 - expression 4 operands: lhs = Counter(0), rhs = Counter(1)
 - expression 5 operands: lhs = Expression(8, Sub), rhs = Counter(4)
@@ -15,7 +15,7 @@ Number of expressions: 9
 Number of file 0 mappings: 9
 - Code(Counter(0)) at (prev + 23, 1) to (start + 0, 40)
 - Code(Expression(0, Add)) at (prev + 1, 9) to (start + 0, 10)
-    = ((c1 + c2) + (c3 + c4))
+    = (c1 + ((c2 + c3) + c4))
 - Code(Counter(0)) at (prev + 0, 13) to (start + 0, 14)
 - Branch { true: Counter(1), false: Expression(8, Sub) } at (prev + 0, 13) to (start + 0, 14)
     true  = c1
@@ -31,7 +31,7 @@ Number of file 0 mappings: 9
     true  = c2
     false = c3
 - Code(Expression(0, Add)) at (prev + 1, 5) to (start + 1, 2)
-    = ((c1 + c2) + (c3 + c4))
+    = (c1 + ((c2 + c3) + c4))
 
 Function name: conditions::assign_3_bis
 Raw bytes (69): 0x[01, 01, 07, 07, 11, 09, 0d, 01, 05, 05, 09, 16, 1a, 05, 09, 01, 05, 09, 01, 1c, 01, 00, 2c, 03, 01, 09, 00, 0a, 01, 00, 0d, 00, 0e, 20, 05, 1a, 00, 0d, 00, 0e, 05, 00, 12, 00, 13, 20, 09, 16, 00, 12, 00, 13, 13, 00, 17, 00, 18, 20, 0d, 11, 00, 17, 00, 18, 03, 01, 05, 01, 02]
@@ -66,18 +66,18 @@ Number of file 0 mappings: 9
     = ((c2 + c3) + c4)
 
 Function name: conditions::assign_and
-Raw bytes (51): 0x[01, 01, 04, 09, 07, 0d, 0e, 01, 05, 01, 05, 07, 01, 0d, 01, 00, 21, 03, 01, 09, 00, 0a, 01, 00, 0d, 00, 0e, 20, 05, 0e, 00, 0d, 00, 0e, 05, 00, 12, 00, 13, 20, 09, 0d, 00, 12, 00, 13, 03, 01, 05, 01, 02]
+Raw bytes (51): 0x[01, 01, 04, 07, 0e, 09, 0d, 01, 05, 01, 05, 07, 01, 0d, 01, 00, 21, 03, 01, 09, 00, 0a, 01, 00, 0d, 00, 0e, 20, 05, 0e, 00, 0d, 00, 0e, 05, 00, 12, 00, 13, 20, 09, 0d, 00, 12, 00, 13, 03, 01, 05, 01, 02]
 Number of files: 1
 - file 0 => global file 1
 Number of expressions: 4
-- expression 0 operands: lhs = Counter(2), rhs = Expression(1, Add)
-- expression 1 operands: lhs = Counter(3), rhs = Expression(3, Sub)
+- expression 0 operands: lhs = Expression(1, Add), rhs = Expression(3, Sub)
+- expression 1 operands: lhs = Counter(2), rhs = Counter(3)
 - expression 2 operands: lhs = Counter(0), rhs = Counter(1)
 - expression 3 operands: lhs = Counter(0), rhs = Counter(1)
 Number of file 0 mappings: 7
 - Code(Counter(0)) at (prev + 13, 1) to (start + 0, 33)
 - Code(Expression(0, Add)) at (prev + 1, 9) to (start + 0, 10)
-    = (c2 + (c3 + (c0 - c1)))
+    = ((c2 + c3) + (c0 - c1))
 - Code(Counter(0)) at (prev + 0, 13) to (start + 0, 14)
 - Branch { true: Counter(1), false: Expression(3, Sub) } at (prev + 0, 13) to (start + 0, 14)
     true  = c1
@@ -87,7 +87,7 @@ Number of file 0 mappings: 7
     true  = c2
     false = c3
 - Code(Expression(0, Add)) at (prev + 1, 5) to (start + 1, 2)
-    = (c2 + (c3 + (c0 - c1)))
+    = ((c2 + c3) + (c0 - c1))
 
 Function name: conditions::assign_or
 Raw bytes (51): 0x[01, 01, 04, 07, 0d, 05, 09, 01, 05, 01, 05, 07, 01, 12, 01, 00, 20, 03, 01, 09, 00, 0a, 01, 00, 0d, 00, 0e, 20, 05, 0e, 00, 0d, 00, 0e, 0e, 00, 12, 00, 13, 20, 09, 0d, 00, 12, 00, 13, 03, 01, 05, 01, 02]
@@ -123,13 +123,13 @@ Number of file 0 mappings: 1
 - Code(Counter(0)) at (prev + 33, 1) to (start + 2, 2)
 
 Function name: conditions::func_call
-Raw bytes (39): 0x[01, 01, 03, 01, 05, 09, 0b, 0d, 02, 05, 01, 25, 01, 01, 0a, 20, 05, 02, 01, 09, 00, 0a, 05, 00, 0e, 00, 0f, 20, 09, 0d, 00, 0e, 00, 0f, 07, 01, 01, 00, 02]
+Raw bytes (39): 0x[01, 01, 03, 01, 05, 0b, 02, 09, 0d, 05, 01, 25, 01, 01, 0a, 20, 05, 02, 01, 09, 00, 0a, 05, 00, 0e, 00, 0f, 20, 09, 0d, 00, 0e, 00, 0f, 07, 01, 01, 00, 02]
 Number of files: 1
 - file 0 => global file 1
 Number of expressions: 3
 - expression 0 operands: lhs = Counter(0), rhs = Counter(1)
-- expression 1 operands: lhs = Counter(2), rhs = Expression(2, Add)
-- expression 2 operands: lhs = Counter(3), rhs = Expression(0, Sub)
+- expression 1 operands: lhs = Expression(2, Add), rhs = Expression(0, Sub)
+- expression 2 operands: lhs = Counter(2), rhs = Counter(3)
 Number of file 0 mappings: 5
 - Code(Counter(0)) at (prev + 37, 1) to (start + 1, 10)
 - Branch { true: Counter(1), false: Expression(0, Sub) } at (prev + 1, 9) to (start + 0, 10)
@@ -140,7 +140,7 @@ Number of file 0 mappings: 5
     true  = c2
     false = c3
 - Code(Expression(1, Add)) at (prev + 1, 1) to (start + 0, 2)
-    = (c2 + (c3 + (c0 - c1)))
+    = ((c2 + c3) + (c0 - c1))
 
 Function name: conditions::simple_assign
 Raw bytes (9): 0x[01, 01, 00, 01, 01, 08, 01, 03, 02]