[llvm-branch-commits] [clang] release/23.x: [clang][win] Fix __global_delete breaking __attribute__((used)) (#217753) (PR #218040)

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https://github.com/llvmbot created https://github.com/llvm/llvm-project/pull/218040

Backport 061865f32607cd064ab944407cc863186702d6f1

Requested by: @dpaoliello

>From 46b438a588169e14c9bc2e8d53efb90d1d4d3797 Mon Sep 17 00:00:00 2001
From: Daniel Paoliello <danpao at microsoft.com>
Date: Fri, 21 Aug 2026 12:33:31 -0700
Subject: [PATCH] [clang][win] Fix __global_delete breaking
 __attribute__((used)) (#217753)

The `__empty_global_delete` fallback introduced in #209585 was marked
used via `llvm::appendToUsed()`, which creates a global named
"llvm.used" during codegen. `CodeGenModule::emitLLVMUsed()` later
unconditionally creates its own global of that same name at end-of-TU,
so the name collision renamed the latter to "llvm.used.1" -- a name LLVM
ignores. The result was that every `__attribute__((used))` global in the
TU silently lost its used semantics whenever a `__global_delete` wrapper
was emitted, letting those symbols be dropped.

Mark the fallback used via `CodeGenModule::addUsedGlobal()` instead, so
it joins the single llvm.used that `emitLLVMUsed()` emits.
`emitLLVMUsed()` runs well after `emitGlobalDeleteForwardingBodies()` in
`Release()`, so the fallback is still recorded in time.

Fixes a regression reported on #209585.

(cherry picked from commit 061865f32607cd064ab944407cc863186702d6f1)
---
 clang/lib/CodeGen/CodeGenModule.cpp             |  2 +-
 .../CodeGenCXX/msvc-global-delete-llvm-used.cpp | 17 +++++++++++++++++
 2 files changed, 18 insertions(+), 1 deletion(-)
 create mode 100644 clang/test/CodeGenCXX/msvc-global-delete-llvm-used.cpp

diff --git a/clang/lib/CodeGen/CodeGenModule.cpp b/clang/lib/CodeGen/CodeGenModule.cpp
index de060e31b8800..313a364e80aff 100644
--- a/clang/lib/CodeGen/CodeGenModule.cpp
+++ b/clang/lib/CodeGen/CodeGenModule.cpp
@@ -9026,7 +9026,7 @@ CodeGenModule::getOrCreateMSVCGlobalDeleteWrapper(const FunctionDecl *GlobOD) {
     // uses ::delete that alias is replaced by a real forwarding body, leaving
     // the empty otherwise unreferenced, so explicitly mark it used to ensure
     // it is always emitted (matching MSVC).
-    appendToUsed(M, {EmptyFn});
+    addUsedGlobal(EmptyFn);
   }
 
   // The wrapper defaults to a weak alias to the trapping __empty_global_delete
diff --git a/clang/test/CodeGenCXX/msvc-global-delete-llvm-used.cpp b/clang/test/CodeGenCXX/msvc-global-delete-llvm-used.cpp
new file mode 100644
index 0000000000000..07811b0f8eecc
--- /dev/null
+++ b/clang/test/CodeGenCXX/msvc-global-delete-llvm-used.cpp
@@ -0,0 +1,17 @@
+// RUN: %clang_cc1 -emit-llvm -fms-extensions %s -triple=x86_64-pc-windows-msvc -o - \
+// RUN:   | FileCheck %s --implicit-check-not="@llvm.used.1"
+
+// The __empty_global_delete fallback is marked used so it is always emitted.
+// It must join the single llvm.used that CodeGenModule emits at end-of-TU: if
+// it creates its own llvm.used first, the one holding __attribute__((used))
+// globals gets renamed to llvm.used.1, which LLVM ignores.
+
+struct S { virtual ~S(); };
+S::~S() {}
+void del(S *s) { ::delete s; }
+
+__attribute__((used)) static void keep_me() {}
+
+// CHECK: @llvm.used = appending global
+// CHECK-SAME: @"?__empty_global_delete@@YAXPEAX_K at Z"
+// CHECK-SAME: @"?keep_me@@YAXXZ"