[clang] Fix code coverage mapping crash with generalized NTTPs (PR #85837)

[Andrey Ali Khan Bolshakov via cfe-commits]

https://github.com/bolshakov-a updated https://github.com/llvm/llvm-project/pull/85837

>From 398ad87c1e9669223def3561f4cdd72af11857c3 Mon Sep 17 00:00:00 2001
From: Bolshakov <bolsh.andrey at yandex.ru>
Date: Tue, 19 Mar 2024 19:05:36 +0300
Subject: [PATCH] [clang][c++20] Fix code coverage mapping crash with
 generalized NTTPs

Introduced in #78041, originally reported as #79957 and fixed partially
in #80050.

`OpaqueValueExpr` used with `TemplateArgument::StructuralValue` has no
corresponding source expression.

A test case with subobject-referring NTTP added.
---
 clang/lib/CodeGen/CoverageMappingGen.cpp | 3 ++-
 clang/test/CoverageMapping/templates.cpp | 3 ++-
 2 files changed, 4 insertions(+), 2 deletions(-)

diff --git a/clang/lib/CodeGen/CoverageMappingGen.cpp b/clang/lib/CodeGen/CoverageMappingGen.cpp
index 71215da362d3d0..3a87f935470673 100644
--- a/clang/lib/CodeGen/CoverageMappingGen.cpp
+++ b/clang/lib/CodeGen/CoverageMappingGen.cpp
@@ -2177,7 +2177,8 @@ struct CounterCoverageMappingBuilder
   }
 
   void VisitOpaqueValueExpr(const OpaqueValueExpr* OVE) {
-    Visit(OVE->getSourceExpr());
+    if (const Expr *SE = OVE->getSourceExpr())
+      Visit(SE);
   }
 };
 
diff --git a/clang/test/CoverageMapping/templates.cpp b/clang/test/CoverageMapping/templates.cpp
index 143e566a33cb85..7e7f2208f1145f 100644
--- a/clang/test/CoverageMapping/templates.cpp
+++ b/clang/test/CoverageMapping/templates.cpp
@@ -1,4 +1,4 @@
-// RUN: %clang_cc1 -mllvm -emptyline-comment-coverage=false -fprofile-instrument=clang -fcoverage-mapping -dump-coverage-mapping -emit-llvm-only -main-file-name templates.cpp %s | FileCheck %s
+// RUN: %clang_cc1 -std=c++20 -mllvm -emptyline-comment-coverage=false -fprofile-instrument=clang -fcoverage-mapping -dump-coverage-mapping -emit-llvm-only -main-file-name templates.cpp %s | FileCheck %s
 
 template<typename T>
 void unused(T x) {
@@ -30,5 +30,6 @@ namespace structural_value_crash {
 
   void test() {
     tpl_fn<arr>();
+    tpl_fn<&arr[1]>();
   }
 }