[llvm] [llvm-cov][CoverageMapping] Fix LineCoverageStats incorrectly using gap region count (PR #203740)
Maksim Levental via llvm-commits
llvm-commits at lists.llvm.org
Sat Jun 13 21:16:13 PDT 2026
https://github.com/makslevental updated https://github.com/llvm/llvm-project/pull/203740
>From 0034a6791064811f7b342283b457468a6d0807e3 Mon Sep 17 00:00:00 2001
From: makslevental <maksim.levental at gmail.com>
Date: Sat, 13 Jun 2026 16:33:04 -0700
Subject: [PATCH] [llvm-cov] Add failing test for gap region line coverage bug
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit
LineCoverageStats incorrectly reports lines as uncovered when a gap
region with count=0 wraps into a line that has non-entry segments
with count > 0.
The test uses a minimal reproducer: a scoped block with a never-taken
early return followed by a statement. The closing "}" produces a gap
region that wraps to the next line, suppressing its execution count.
The extra statement after the if-block is required — without it,
clang emits a region entry (MinRegionCount > 0) and the bug doesn't
trigger.
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply at anthropic.com>
---
.../Inputs/gap-region-quirk/gap-quirk-v2.cpp | 23 +++++++++++
.../gap-region-quirk/gap-quirk.covmapping | Bin 0 -> 213 bytes
.../gap-region-quirk/gap-quirk.profdata | Bin 0 -> 720 bytes
.../llvm-cov/gap-region-line-coverage.test | 37 ++++++++++++++++++
4 files changed, 60 insertions(+)
create mode 100644 llvm/test/tools/llvm-cov/Inputs/gap-region-quirk/gap-quirk-v2.cpp
create mode 100644 llvm/test/tools/llvm-cov/Inputs/gap-region-quirk/gap-quirk.covmapping
create mode 100644 llvm/test/tools/llvm-cov/Inputs/gap-region-quirk/gap-quirk.profdata
create mode 100644 llvm/test/tools/llvm-cov/gap-region-line-coverage.test
diff --git a/llvm/test/tools/llvm-cov/Inputs/gap-region-quirk/gap-quirk-v2.cpp b/llvm/test/tools/llvm-cov/Inputs/gap-region-quirk/gap-quirk-v2.cpp
new file mode 100644
index 0000000000000..f235382db64e8
--- /dev/null
+++ b/llvm/test/tools/llvm-cov/Inputs/gap-region-quirk/gap-quirk-v2.cpp
@@ -0,0 +1,23 @@
+// A scoped block with a never-taken early return followed by at least one
+// statement is needed to produce the gap region pattern. Without the extra
+// statement after the if-block, clang emits a region entry on the line after
+// the closing "}" (MinRegionCount > 0) and the bug doesn't trigger. With the
+// extra statement, the closing "}" produces a gap region that wraps forward,
+// and the next line has only a non-entry segment (MinRegionCount == 0).
+bool process(bool err) {
+ {
+ if (err) {
+ return false;
+ }
+ int fd = 1;
+ (void)fd;
+ }
+ int result = 42;
+ (void)result;
+ return true;
+}
+
+int main() {
+ process(false);
+ return 0;
+}
diff --git a/llvm/test/tools/llvm-cov/Inputs/gap-region-quirk/gap-quirk.covmapping b/llvm/test/tools/llvm-cov/Inputs/gap-region-quirk/gap-quirk.covmapping
new file mode 100644
index 0000000000000000000000000000000000000000..b10fa7cf82d731eaa88f171ed8e7b2eca7693f05
GIT binary patch
literal 213
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W+nhl2BtV7&0m57cMn(}HW+ni7u`AgC
literal 0
HcmV?d00001
diff --git a/llvm/test/tools/llvm-cov/Inputs/gap-region-quirk/gap-quirk.profdata b/llvm/test/tools/llvm-cov/Inputs/gap-region-quirk/gap-quirk.profdata
new file mode 100644
index 0000000000000000000000000000000000000000..3acc509754fcf1cce00538e0b8d6f33f2a924602
GIT binary patch
literal 720
zcmeyLQ&5zjmf6V5fE}!0LKQ!N#y<h&vq6;!KxvpVW+<N#jfQd=VCn?aVIrvXf;N~=
zRB;Dhn8~Q(4<@sq3P5=cQZN^yN-Hd62MfS#fw|{^Iww}~gmqk4#TiU_u!=9(4GCFv
z^FP$_VO4J+&5u<)!VbIm9Y^fqW=`0}?Qw`RG5osP``j#L>TOu~X at K3qz>u4mnI{2d
z!+Zgwp~4ItP=<2C5~a=`0%hD#z5$euk1_`)v*gs`;-rWcPjCpr0vg>YbR(gBm@=3)
L4j2Qb9!diMX9^?n
literal 0
HcmV?d00001
diff --git a/llvm/test/tools/llvm-cov/gap-region-line-coverage.test b/llvm/test/tools/llvm-cov/gap-region-line-coverage.test
new file mode 100644
index 0000000000000..6f1d48c8b2b27
--- /dev/null
+++ b/llvm/test/tools/llvm-cov/gap-region-line-coverage.test
@@ -0,0 +1,37 @@
+// Tests that LineCoverageStats correctly handles lines where a gap region
+// with count=0 wraps into a line that has a non-entry segment with count > 0.
+//
+// In this test, line 15 ("int result = 42;") follows a scoped block containing
+// a never-taken early return. The gap region from the block's closing "}" wraps
+// to line 15, but line 15 has a non-entry segment with count=1 (the function
+// body continues). LineCoverageStats should report count=1 for line 15.
+//
+// Test inputs generated with (CWD and source must be in /tmp for path-equivalence):
+// cp Inputs/gap-region-quirk/gap-quirk-v2.cpp /tmp/gap-quirk-v2.cpp
+// cd /tmp
+// %clang -fprofile-instr-generate -fcoverage-mapping -O0 \
+// -mllvm -enable-name-compression=false \
+// -c -o gap-quirk.o gap-quirk-v2.cpp
+// llvm-cov convert-for-testing gap-quirk.o -o gap-quirk.covmapping
+// %clang -fprofile-instr-generate -fcoverage-mapping -O0 \
+// -o gap-quirk gap-quirk-v2.cpp
+// LLVM_PROFILE_FILE=gap-quirk.profraw ./gap-quirk
+// llvm-profdata merge --sparse gap-quirk.profraw -o gap-quirk.profdata
+
+// RUN: llvm-cov show %S/Inputs/gap-region-quirk/gap-quirk.covmapping \
+// RUN: -instr-profile %S/Inputs/gap-region-quirk/gap-quirk.profdata \
+// RUN: -path-equivalence=/tmp,%S/Inputs/gap-region-quirk \
+// RUN: 2>&1 | FileCheck -check-prefix=SHOW %s
+
+// Line 15 ("int result = 42;") should show count 1, not 0.
+// SHOW: 15| 1| int result = 42;
+
+// RUN: llvm-cov report %S/Inputs/gap-region-quirk/gap-quirk.covmapping \
+// RUN: -instr-profile %S/Inputs/gap-region-quirk/gap-quirk.profdata \
+// RUN: -path-equivalence=/tmp,%S/Inputs/gap-region-quirk \
+// RUN: --show-branch-summary=false \
+// RUN: 2>&1 | FileCheck -check-prefix=REPORT %s
+
+// Line 15 should NOT be counted as missed (16 total lines, 2 missed).
+// REPORT: Filename{{.*}}Regions{{.*}}Missed Regions{{.*}}Cover{{.*}}Functions{{.*}}Missed Functions{{.*}}Executed{{.*}}Lines{{.*}}Missed Lines{{.*}}Cover
+// REPORT: gap-quirk-v2.cpp{{[[:space:]]+}}5{{[[:space:]]+}}1{{[[:space:]]+}}80.00%{{[[:space:]]+}}2{{[[:space:]]+}}0{{[[:space:]]+}}100.00%{{[[:space:]]+}}16{{[[:space:]]+}}2{{[[:space:]]+}}87.50%
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