[Coverage] Fix region termination for GNU statement expressions (#130976)

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

Author: justincady

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();
 

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: File 0, 351:35 -> 352:12 = (#0 - #1)
+  return rc;                             // CHECK-NOT: Gap
+}
+
 int main() {
   foo(0);
   foo(1);
@@ -368,5 +374,6 @@ int main() {
   ornoret();
   abstractcondnoret();
   elsecondnoret();
+  statementexprnoret(false);
   return 0;
 }

compiler-rt/test/profile/Linux/coverage-statement-expression.cpp

@@ -0,0 +1,21 @@
+// 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>
+
+// 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)
+                                                // 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|}
+// clang-format on