[llvm] [llvm-cov][CoverageMapping] Fix LineCoverageStats incorrectly using gap region count (PR #203740)
Maksim Levental via llvm-commits
llvm-commits at lists.llvm.org
Sun Jun 14 10:20:57 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 1/3] [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
zcmd1FDa%dHFUw_QfB>NxECLMiQRW3j`N^rp#Yv30iJ5si5IISx8a5!!B*ws^Uy at rO
zke*neTUeS|l&xE4q?cS!09B)$utcfzhd`MPkRQ?F$psSD{#tXU%}D+)BM`81FtST<
zGchu8GVmy{GBE%tRt8>%zJ`Vd4ps&}CN?G}HpW&EkBO0$m5+gmg|QjL`*pSVxmn88
W+nhl2BtV7&0m57cMn(}HW+ni7u`AgC
literal 0
HcmV?d00001
diff --git a/llvm/test/tools/llvm-cov/Inputs/gap-region-quirk/gap-quirk.profdata b/llvm/test/tools/llvm-cov/Inputs/gap-region-quirk/gap-quirk.profdata
new file mode 100644
index 0000000000000000000000000000000000000000..3acc509754fcf1cce00538e0b8d6f33f2a924602
GIT binary patch
literal 720
zcmeyLQ&5zjmf6V5fE}!0LKQ!N#y<h&vq6;!KxvpVW+<N#jfQd=VCn?aVIrvXf;N~=
zRB;Dhn8~Q(4<@sq3P5=cQZN^yN-Hd62MfS#fw|{^Iww}~gmqk4#TiU_u!=9(4GCFv
z^FP$_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%
>From 20456954046bfd16e2f46ba32e22d5f06d03cd49 Mon Sep 17 00:00:00 2001
From: makslevental <maksim.levental at gmail.com>
Date: Sat, 13 Jun 2026 21:49:48 -0700
Subject: [PATCH 2/3] [llvm-cov] Fix undercounting lines wrapped by gap regions
Lines with no region entry that are wrapped by a gap region were
reported with the gap's count (often 0), even when non-gap segments
on the line indicated the line was actually executed. This caused
llvm-cov to undercount coverage for lines that continue a covered
region after a gap (e.g., closing braces, simple statements following
an if/else).
Check for non-gap segments with HasCount on such lines and use their
max count instead of the gap region's count.
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply at anthropic.com>
---
llvm/lib/ProfileData/Coverage/CoverageMapping.cpp | 13 ++++++++++++-
1 file changed, 12 insertions(+), 1 deletion(-)
diff --git a/llvm/lib/ProfileData/Coverage/CoverageMapping.cpp b/llvm/lib/ProfileData/Coverage/CoverageMapping.cpp
index 0d9a5a6758f06..797ef9c55bfa6 100644
--- a/llvm/lib/ProfileData/Coverage/CoverageMapping.cpp
+++ b/llvm/lib/ProfileData/Coverage/CoverageMapping.cpp
@@ -1604,8 +1604,19 @@ LineCoverageStats::LineCoverageStats(
// wrapped count.
if (WrappedSegment)
ExecutionCount = WrappedSegment->Count;
- if (!MinRegionCount)
+ if (!MinRegionCount) {
+ // If no region entries on this line and the wrapping segment is a gap
+ // region, check for non-gap segments with HasCount (e.g., continuation
+ // of a covered region after a gap). Use their max count instead of the
+ // gap's count of 0.
+ if (WrappedSegment && WrappedSegment->IsGapRegion) {
+ for (const auto *LS : LineSegments) {
+ if (!LS->IsGapRegion && LS->HasCount)
+ ExecutionCount = std::max(ExecutionCount, LS->Count);
+ }
+ }
return;
+ }
for (const auto *LS : LineSegments)
if (isStartOfRegion(LS))
ExecutionCount = std::max(ExecutionCount, LS->Count);
>From 6bda63ccc96867ba1c15e34aea06e2f88814f5f0 Mon Sep 17 00:00:00 2001
From: makslevental <maksim.levental at gmail.com>
Date: Sun, 14 Jun 2026 10:20:09 -0700
Subject: [PATCH 3/3] [llvm-cov] Replace binary test blobs with text formats
Replace .covmapping and .profdata binary blobs with .yaml (obj2yaml)
and .proftext respectively. The test now uses yaml2obj and
llvm-profdata merge to produce inputs at test time.
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply at anthropic.com>
---
.../gap-region-quirk/gap-quirk.covmapping | Bin 213 -> 0 bytes
.../gap-region-quirk/gap-quirk.profdata | Bin 720 -> 0 bytes
.../gap-region-quirk/gap-quirk.proftext | 16 +++++
.../Inputs/gap-region-quirk/gap-quirk.yaml | 57 ++++++++++++++++++
.../llvm-cov/gap-region-line-coverage.test | 25 +++-----
5 files changed, 80 insertions(+), 18 deletions(-)
delete mode 100644 llvm/test/tools/llvm-cov/Inputs/gap-region-quirk/gap-quirk.covmapping
delete mode 100644 llvm/test/tools/llvm-cov/Inputs/gap-region-quirk/gap-quirk.profdata
create mode 100644 llvm/test/tools/llvm-cov/Inputs/gap-region-quirk/gap-quirk.proftext
create mode 100644 llvm/test/tools/llvm-cov/Inputs/gap-region-quirk/gap-quirk.yaml
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
deleted file mode 100644
index b10fa7cf82d731eaa88f171ed8e7b2eca7693f05..0000000000000000000000000000000000000000
GIT binary patch
literal 0
HcmV?d00001
literal 213
zcmd1FDa%dHFUw_QfB>NxECLMiQRW3j`N^rp#Yv30iJ5si5IISx8a5!!B*ws^Uy at rO
zke*neTUeS|l&xE4q?cS!09B)$utcfzhd`MPkRQ?F$psSD{#tXU%}D+)BM`81FtST<
zGchu8GVmy{GBE%tRt8>%zJ`Vd4ps&}CN?G}HpW&EkBO0$m5+gmg|QjL`*pSVxmn88
W+nhl2BtV7&0m57cMn(}HW+ni7u`AgC
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
deleted file mode 100644
index 3acc509754fcf1cce00538e0b8d6f33f2a924602..0000000000000000000000000000000000000000
GIT binary patch
literal 0
HcmV?d00001
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
diff --git a/llvm/test/tools/llvm-cov/Inputs/gap-region-quirk/gap-quirk.proftext b/llvm/test/tools/llvm-cov/Inputs/gap-region-quirk/gap-quirk.proftext
new file mode 100644
index 0000000000000..d27d279e954af
--- /dev/null
+++ b/llvm/test/tools/llvm-cov/Inputs/gap-region-quirk/gap-quirk.proftext
@@ -0,0 +1,16 @@
+_Z7processb
+# Func Hash:
+172590168
+# Num Counters:
+2
+# Counter Values:
+1
+0
+
+main
+# Func Hash:
+24
+# Num Counters:
+1
+# Counter Values:
+1
diff --git a/llvm/test/tools/llvm-cov/Inputs/gap-region-quirk/gap-quirk.yaml b/llvm/test/tools/llvm-cov/Inputs/gap-region-quirk/gap-quirk.yaml
new file mode 100644
index 0000000000000..d34e65270bc6f
--- /dev/null
+++ b/llvm/test/tools/llvm-cov/Inputs/gap-region-quirk/gap-quirk.yaml
@@ -0,0 +1,57 @@
+--- !ELF
+FileHeader:
+ Class: ELFCLASS64
+ Data: ELFDATA2LSB
+ OSABI: ELFOSABI_GNU
+ Type: ET_REL
+ Machine: EM_X86_64
+ SectionHeaderStringTable: .strtab
+Sections:
+ - Name: __llvm_covfun
+ Type: SHT_PROGBITS
+ Flags: [ SHF_GNU_RETAIN ]
+ AddressAlign: 0x8
+ Content: 2360A42289F810763C0000005884490A0000000012E9CC181F5D5C9C0101010105080107180B02010209000C2005020009000C05000D008E8080800805000E0206020206018580808008020105050E000204018380808008
+ - Name: '__llvm_covfun (1)'
+ Type: SHT_PROGBITS
+ Flags: [ SHF_GNU_RETAIN ]
+ AddressAlign: 0x8
+ Content: FAD58DE7366495DB09000000180000000000000012E9CC181F5D5C9C0101000101140C0302
+ - Name: __llvm_covmap
+ Type: SHT_PROGBITS
+ Flags: [ SHF_GNU_RETAIN ]
+ AddressAlign: 0x8
+ Content: 0000000015000000000000000600000002120000106761702D717569726B2D76322E637070000000
+ - Name: __llvm_prf_names
+ Type: SHT_PROGBITS
+ Flags: [ SHF_ALLOC, SHF_GNU_RETAIN ]
+ AddressAlign: 0x1
+ Content: 10005F5A3770726F6365737362016D61696E
+ - Type: SectionHeaderTable
+ Sections:
+ - Name: .strtab
+ - Name: __llvm_covfun
+ - Name: '__llvm_covfun (1)'
+ - Name: __llvm_covmap
+ - Name: __llvm_prf_names
+ - Name: .symtab
+Symbols:
+ - Name: __llvm_covmap
+ Type: STT_SECTION
+ Section: __llvm_covmap
+ - Name: __llvm_prf_names
+ Type: STT_SECTION
+ Section: __llvm_prf_names
+ - Name: __covrec_7610F88922A46023u
+ Type: STT_OBJECT
+ Section: __llvm_covfun
+ Binding: STB_WEAK
+ Size: 0x58
+ Other: [ STV_HIDDEN ]
+ - Name: __covrec_DB956436E78DD5FAu
+ Type: STT_OBJECT
+ Section: '__llvm_covfun (1)'
+ Binding: STB_WEAK
+ Size: 0x25
+ Other: [ STV_HIDDEN ]
+...
diff --git a/llvm/test/tools/llvm-cov/gap-region-line-coverage.test b/llvm/test/tools/llvm-cov/gap-region-line-coverage.test
index 6f1d48c8b2b27..00d33922f37ea 100644
--- a/llvm/test/tools/llvm-cov/gap-region-line-coverage.test
+++ b/llvm/test/tools/llvm-cov/gap-region-line-coverage.test
@@ -5,30 +5,19 @@
// 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: yaml2obj %S/Inputs/gap-region-quirk/gap-quirk.yaml -o %t.o
+// RUN: llvm-profdata merge %S/Inputs/gap-region-quirk/gap-quirk.proftext -o %t.profdata
+
+// RUN: llvm-cov show %t.o -instr-profile %t.profdata \
+// RUN: -path-equivalence=.,%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: llvm-cov report %t.o -instr-profile %t.profdata \
+// RUN: -path-equivalence=.,%S/Inputs/gap-region-quirk \
// RUN: --show-branch-summary=false \
// RUN: 2>&1 | FileCheck -check-prefix=REPORT %s
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