[clang] [compiler-rt] [Coverage] Fix region termination for GNU statement expressions (PR #130976)

[Justin Cady via llvm-commits]

https://github.com/justincady updated https://github.com/llvm/llvm-project/pull/130976

>From 6f3557780d06d6a2b1a7f315c49a3ad533d821e5 Mon Sep 17 00:00:00 2001
From: Justin Cady <desk at justincady.com>
Date: Wed, 12 Mar 2025 11:23:19 -0400
Subject: [PATCH 1/2] [Coverage] Fix region termination for GNU statement
 expressions

Calls to __noreturn__ functions result in region termination for
coverage mapping. But this creates incorrect coverage results when
__noreturn__ functions (or other constructs that result in region
termination) occur within [GNU statement expressions][1].

In this scenario an extra gap region is introduced within VisitStmt,
such that if the following line does not introduce a new region it
is unconditionally counted as uncovered.

This change adjusts the mapping such that terminate statements
within statement expressions do not propagate that termination
state after the statement expression is processed.

[1]: https://gcc.gnu.org/onlinedocs/gcc/Statement-Exprs.html

Fixes #124296
---
 clang/lib/CodeGen/CoverageMappingGen.cpp      |  8 ++++++++
 .../CoverageMapping/terminate-statements.cpp  |  7 +++++++
 .../Linux/coverage-statement-expression.cpp   | 19 +++++++++++++++++++
 3 files changed, 34 insertions(+)
 create mode 100644 compiler-rt/test/profile/Linux/coverage-statement-expression.cpp

diff --git a/clang/lib/CodeGen/CoverageMappingGen.cpp b/clang/lib/CodeGen/CoverageMappingGen.cpp
index f09157771d2b5..73811d15979d5 100644
--- a/clang/lib/CodeGen/CoverageMappingGen.cpp
+++ b/clang/lib/CodeGen/CoverageMappingGen.cpp
@@ -1505,6 +1505,14 @@ struct CounterCoverageMappingBuilder
     handleFileExit(getEnd(S));
   }
 
+  void VisitStmtExpr(const StmtExpr *E) {
+    Visit(E->getSubStmt());
+    // Any region termination (such as a noreturn CallExpr) within the statement
+    // expression has been handled by visiting the sub-statement. The visitor
+    // cannot be at a terminate statement leaving the statement expression.
+    HasTerminateStmt = false;
+  }
+
   void VisitDecl(const Decl *D) {
     Stmt *Body = D->getBody();
 
diff --git a/clang/test/CoverageMapping/terminate-statements.cpp b/clang/test/CoverageMapping/terminate-statements.cpp
index 0067185fee8e6..d03e35630b317 100644
--- a/clang/test/CoverageMapping/terminate-statements.cpp
+++ b/clang/test/CoverageMapping/terminate-statements.cpp
@@ -346,6 +346,12 @@ int elsecondnoret(void) {
   return 0;
 }
 
+// CHECK-LABEL: _Z18statementexprnoretb
+int statementexprnoret(bool crash) {
+  int rc = ({ if (crash) abort(); 0; }); // CHECK-NOT: Gap,File 0, [[@LINE]]:41 -> [[@LINE+1]]:3 = 0
+  return rc;
+}
+
 int main() {
   foo(0);
   foo(1);
@@ -368,5 +374,6 @@ int main() {
   ornoret();
   abstractcondnoret();
   elsecondnoret();
+  statementexprnoret(false);
   return 0;
 }
diff --git a/compiler-rt/test/profile/Linux/coverage-statement-expression.cpp b/compiler-rt/test/profile/Linux/coverage-statement-expression.cpp
new file mode 100644
index 0000000000000..5894275b941a2
--- /dev/null
+++ b/compiler-rt/test/profile/Linux/coverage-statement-expression.cpp
@@ -0,0 +1,19 @@
+// RUN: %clangxx_profgen -std=gnu++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
+
+#include <stdio.h>
+
+__attribute__ ((__noreturn__))
+void foo(void) { while (1); }                   // CHECK:  [[@LINE]]| 0|void foo(void)
+_Noreturn void bar(void) { while (1); }         // CHECK:  [[@LINE]]| 0|_Noreturn void bar(void)
+                                                // CHECK:  [[@LINE]]|  |
+int main(int argc, char **argv) {               // CHECK:  [[@LINE]]| 1|int main(
+  int rc = ({ if (argc > 3) foo(); 0; });       // CHECK:  [[@LINE]]| 1|  int rc =
+  printf("coverage after foo is present\n");    // CHECK:  [[@LINE]]| 1|  printf(
+                                                // CHECK:  [[@LINE]]|  |
+  int rc2 = ({ if (argc > 3) bar(); 0; });      // CHECK:  [[@LINE]]| 1|  int rc2 =
+  printf("coverage after bar is present\n");    // CHECK:  [[@LINE]]| 1|  printf(
+  return rc + rc2;                              // CHECK:  [[@LINE]]| 1|  return rc
+}                                               // CHECK:  [[@LINE]]| 1|}

>From 0dc7ea6a13b34901bb6ca0253ad73e8ef5037244 Mon Sep 17 00:00:00 2001
From: Justin Cady <desk at justincady.com>
Date: Fri, 14 Mar 2025 12:32:57 -0400
Subject: [PATCH 2/2] Avoid format warning to preserve readable CHECK lines

---
 .../test/profile/Linux/coverage-statement-expression.cpp        | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/compiler-rt/test/profile/Linux/coverage-statement-expression.cpp b/compiler-rt/test/profile/Linux/coverage-statement-expression.cpp
index 5894275b941a2..7c76555e3300b 100644
--- a/compiler-rt/test/profile/Linux/coverage-statement-expression.cpp
+++ b/compiler-rt/test/profile/Linux/coverage-statement-expression.cpp
@@ -5,6 +5,7 @@
 
 #include <stdio.h>
 
+// clang-format off
 __attribute__ ((__noreturn__))
 void foo(void) { while (1); }                   // CHECK:  [[@LINE]]| 0|void foo(void)
 _Noreturn void bar(void) { while (1); }         // CHECK:  [[@LINE]]| 0|_Noreturn void bar(void)
@@ -17,3 +18,4 @@ int main(int argc, char **argv) {               // CHECK:  [[@LINE]]| 1|int main
   printf("coverage after bar is present\n");    // CHECK:  [[@LINE]]| 1|  printf(
   return rc + rc2;                              // CHECK:  [[@LINE]]| 1|  return rc
 }                                               // CHECK:  [[@LINE]]| 1|}
+// clang-format on