[clang] [Clang][CodeGen] Fix crash in EmitParmDecl for bodyless destructors with -fextend-variable-liveness (PR #218830)

[via cfe-commits]

https://github.com/AZero13 created https://github.com/llvm/llvm-project/pull/218830

The fake-use coroutine check in EmitParmDecl calls FnDecl->getBody()->getStmtClass() without guarding against a null getBody(). This crashes when processing implicit parameters (e.g. should_call_delete) of MSVC deleting destructors whose base destructor is only declared, not defined.

>From d1fa49dded08aa29ed019190b506e64e0caf1c88 Mon Sep 17 00:00:00 2001
From: AZero13 <gfunni234 at gmail.com>
Date: Tue, 25 Aug 2026 23:32:14 -0400
Subject: [PATCH] [Clang][CodeGen] Fix crash in EmitParmDecl for bodyless
 destructors with -fextend-variable-liveness

The fake-use coroutine check in EmitParmDecl calls FnDecl->getBody()->getStmtClass() without guarding against a null getBody(). This crashes when processing implicit parameters (e.g. should_call_delete) of MSVC deleting destructors whose base destructor is only declared, not defined.
---
 clang/lib/CodeGen/CGDecl.cpp              |  2 +-
 clang/test/CodeGen/fake-use-msvc-dtor.cpp | 17 +++++++++++++++++
 2 files changed, 18 insertions(+), 1 deletion(-)
 create mode 100644 clang/test/CodeGen/fake-use-msvc-dtor.cpp

diff --git a/clang/lib/CodeGen/CGDecl.cpp b/clang/lib/CodeGen/CGDecl.cpp
index b8fae352d41d7..1ed8989d3f627 100644
--- a/clang/lib/CodeGen/CGDecl.cpp
+++ b/clang/lib/CodeGen/CGDecl.cpp
@@ -2856,7 +2856,7 @@ void CodeGenFunction::EmitParmDecl(const VarDecl &D, ParamValue Arg,
        &D == CXXABIThisDecl)) {
     // We don't emit fake uses for coroutine parameters, other than `this`.
     if (auto *FnDecl = dyn_cast_or_null<FunctionDecl>(CurCodeDecl);
-        &D == CXXABIThisDecl || !FnDecl ||
+        &D == CXXABIThisDecl || !FnDecl || !FnDecl->getBody() ||
         FnDecl->getBody()->getStmtClass() != Stmt::CoroutineBodyStmtClass) {
       if (shouldExtendLifetime(getContext(), CurCodeDecl, D, CXXABIThisDecl))
         EHStack.pushCleanup<FakeUse>(NormalFakeUse, DeclPtr);
diff --git a/clang/test/CodeGen/fake-use-msvc-dtor.cpp b/clang/test/CodeGen/fake-use-msvc-dtor.cpp
new file mode 100644
index 0000000000000..3988b4b2242ec
--- /dev/null
+++ b/clang/test/CodeGen/fake-use-msvc-dtor.cpp
@@ -0,0 +1,17 @@
+// RUN: %clang_cc1 %s -triple x86_64-pc-windows-msvc -emit-llvm -fextend-variable-liveness=all -O1 -mconstructor-aliases -o /dev/null
+// Verify that we do not crash when generating fake uses for parameters
+// of destructor declarations that have no body (the should_call_delete
+// implicit parameter in MSVC deleting destructors).
+
+struct A {
+  virtual ~A(void);
+};
+struct B {
+  virtual ~B(void);
+};
+
+struct C : A, B {};
+
+void foo() {
+  C c;
+}