https://github.com/int-zjt created
https://github.com/llvm/llvm-project/pull/149085
## Issue Summary
We identified an inaccuracy in line coverage reporting when short-circuit
evaluation occurs in multi-line conditional expressions. Specifically:
1. Un-executed conditions following line breaks may be incorrectly marked as
covered
(e.g., conditionB in a non-executed && chain shows coverage)
```
1| |#include <iostream>
2| |
3| 1|int main() {
4| 1| bool conditionA = false;
5| 1| bool conditionB = true;
6| 1| if (conditionA &&
7| 1| conditionB) {
8| 0| std::cout << "IF-THEN" << std::endl;
9| 0| }
10| 1| return 0;
11| 1|}
```
2. Inconsistent coverage reporting across un-executed conditions
*(adjacent un-executed conditions may show 1 vs 0 line coverage)*
```
1| |#include <iostream>
2| |
3| 1|int main() {
4| 1| bool conditionA = false;
5| 1| bool conditionB = true;
6| 1| bool conditionC = true;
7| 1| if (conditionA &&
8| 1| (conditionB ||
9| 0| conditionC)) {
10| 0| std::cout << "IF-THEN" << std::endl;
11| 0| }
12| 1| return 0;
13| 1|}
```
## Root Cause Analysis
The current `WrappedSegment` mechanism may propagates coverage data from the
last segment of the LHS line to subsequent RHS lines. Because the LHS line's
coverage data depends on count of its segments and `WrappedSegment`'s count, it
may causes false positive coverage for un-executed RHS conditions.
## Proposed Solution
The current implementation correctly handles single-statement if bodies through
GapRegion insertion:
```
if (cond) // Line 1
statement; // Line 2
```
Processing workflow:
1. A GapRegion is created spanning from the end of the condition (Line 1) to
the start of the body statement (Line 2)
2. This GapRegion inherits the execution counter from Line 2
3. During coverage calculation:
* Line 2 uses this GapRegion as its WrappedSegment
* Prevents propagation of Line 1's coverage data to Line 2
Generalize the GapRegion insertion strategy from if-statements to logical
operators, placing RHS-synchronized segments at LHS-line-end to isolate
coverage contexts during short-circuit evaluation.
>From 763293b20bb79bb28c0187edc4b282a1536993dc Mon Sep 17 00:00:00 2001
From: int-zjt <zhangjiaton...@bytedance.com>
Date: Wed, 16 Jul 2025 19:03:11 +0800
Subject: [PATCH] [llvm-cov] Add gap region after binary operator && and ||
---
clang/lib/CodeGen/CoverageMappingGen.cpp | 10 ++++++
.../profile/Linux/coverage_short_circuit.cpp | 36 +++++++++++++++++++
2 files changed, 46 insertions(+)
create mode 100644 compiler-rt/test/profile/Linux/coverage_short_circuit.cpp
diff --git a/clang/lib/CodeGen/CoverageMappingGen.cpp
b/clang/lib/CodeGen/CoverageMappingGen.cpp
index 4aafac349e3e9..f55290a5feee6 100644
--- a/clang/lib/CodeGen/CoverageMappingGen.cpp
+++ b/clang/lib/CodeGen/CoverageMappingGen.cpp
@@ -2269,6 +2269,11 @@ struct CounterCoverageMappingBuilder
// Track LHS True/False Decision.
const auto DecisionLHS = MCDCBuilder.pop();
+ if (auto Gap =
+ findGapAreaBetween(getEnd(E->getLHS()), getStart(E->getRHS()))) {
+ fillGapAreaWithCount(Gap->getBegin(), Gap->getEnd(),
getRegionCounter(E));
+ }
+
// Counter tracks the right hand side of a logical and operator.
extendRegion(E->getRHS());
propagateCounts(getRegionCounter(E), E->getRHS());
@@ -2330,6 +2335,11 @@ struct CounterCoverageMappingBuilder
// Track LHS True/False Decision.
const auto DecisionLHS = MCDCBuilder.pop();
+ if (auto Gap =
+ findGapAreaBetween(getEnd(E->getLHS()), getStart(E->getRHS()))) {
+ fillGapAreaWithCount(Gap->getBegin(), Gap->getEnd(),
getRegionCounter(E));
+ }
+
// Counter tracks the right hand side of a logical or operator.
extendRegion(E->getRHS());
propagateCounts(getRegionCounter(E), E->getRHS());
diff --git a/compiler-rt/test/profile/Linux/coverage_short_circuit.cpp
b/compiler-rt/test/profile/Linux/coverage_short_circuit.cpp
new file mode 100644
index 0000000000000..cc4022bc3c286
--- /dev/null
+++ b/compiler-rt/test/profile/Linux/coverage_short_circuit.cpp
@@ -0,0 +1,36 @@
+// RUN: %clangxx_profgen -std=c++17 -fuse-ld=lld -fcoverage-mapping -o %t %s
+// RUN: env LLVM_PROFILE_FILE=%t.profraw %run %t
+// RUN: llvm-profdata merge -o %t.profdata %t.profraw
+// RUN: llvm-cov show %t -instr-profile=%t.profdata 2>&1 | FileCheck %s
+
+void foo() { // CHECK: [[@LINE]]| 1|void foo() {
+ bool cond1 = false; // CHECK-NEXT: [[@LINE]]| 1| bool cond1 = false;
+ bool cond2 = true; // CHECK-NEXT: [[@LINE]]| 1| bool cond2 = true;
+ if (cond1 && // CHECK-NEXT: [[@LINE]]| 1| if (cond1 &&
+ cond2) { // CHECK-NEXT: [[@LINE]]| 0| cond2) {
+ } // CHECK-NEXT: [[@LINE]]| 0| }
+} // CHECK-NEXT: [[@LINE]]| 1|}
+
+void bar() { // CHECK: [[@LINE]]| 1|void bar() {
+ bool cond1 = true; // CHECK-NEXT: [[@LINE]]| 1| bool cond1 = true;
+ bool cond2 = false; // CHECK-NEXT: [[@LINE]]| 1| bool cond2 = false;
+ if (cond1 && // CHECK-NEXT: [[@LINE]]| 1| if (cond1 &&
+ cond2) { // CHECK-NEXT: [[@LINE]]| 1| cond2) {
+ } // CHECK-NEXT: [[@LINE]]| 0| }
+} // CHECK-NEXT: [[@LINE]]| 1|}
+
+void baz() { // CHECK: [[@LINE]]| 1|void baz() {
+ bool cond1 = false; // CHECK-NEXT: [[@LINE]]| 1| bool cond1 = false;
+ bool cond2 = true; // CHECK-NEXT: [[@LINE]]| 1| bool cond2 = true;
+ if (cond1 // CHECK-NEXT: [[@LINE]]| 1| if (cond1
+ && // CHECK-NEXT: [[@LINE]]| 0| &&
+ cond2) { // CHECK-NEXT: [[@LINE]]| 0| cond2) {
+ } // CHECK-NEXT: [[@LINE]]| 0| }
+} // CHECK-NEXT: [[@LINE]]| 1|}
+
+int main() {
+ foo();
+ bar();
+ baz();
+ return 0;
+}
_______________________________________________
cfe-commits mailing list
cfe-commits@lists.llvm.org
https://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-commits
