llvmorg-github-actions[bot] wrote:
<!--LLVM PR SUMMARY COMMENT-->
@llvm/pr-subscribers-clang-codegen
Author: Emery Conrad (conrade-ctc)
<details>
<summary>Changes</summary>
A global on the `llvm.used`/`llvm.compiler.used` list can be deleted before the
module is released: CodeGen erases an unreferenced `GlobalValue` without RAUW
when the same mangled name is redefined with a different type
(`GetOrCreateLLVMGlobal`), which nulls the `WeakTrackingVH` on the used list —
value handles are not uses, so the `use_empty()` guard does not protect them.
In whole-TU compilation this is unobservable because the accompanying
`err_duplicate_mangled_name` suppresses `Release()`. The incremental
interpreter, however, clears the diagnostic state after the failed parse and
keeps building the same module, so the next successful parse runs `Release()`
and crashes in `emitUsed` dereferencing the dead handle:
```
clang-repl> __attribute__((used)) int a asm("sym") = 1; float b asm("sym") =
2.0f;
clang-repl> int ok = 0;
clang-repl: .../ValueHandle.h:95: llvm::Value&
llvm::ValueHandleBase::operator*() const: Assertion `V &&
"Dereferencing deleted ValueHandle"' failed.
```
Out-of-tree incremental clients hit the same crash through other routes that
delete an emitted used global before module release (e.g. CppInterOp's
force-emission of reflection queries, see compiler-research/CppInterOp#<!--
-->1068).
Fix: skip null handles when building the used array. The repro above is
included as a lit test; `clang/test/Interpreter`, `clang/test/CodeGen`, and
`clang/test/CodeGenCXX` pass locally.
🤖 Done with the help of [Claude Code](https://claude.com/claude-code) (Fable 5,
human in the loop)
---
Full diff: https://github.com/llvm/llvm-project/pull/210959.diff
2 Files Affected:
- (modified) clang/lib/CodeGen/CodeGenModule.cpp (+10-7)
- (added) clang/test/Interpreter/used-global-after-error.cpp (+15)
``````````diff
diff --git a/clang/lib/CodeGen/CodeGenModule.cpp
b/clang/lib/CodeGen/CodeGenModule.cpp
index 78627047b19ad..ead29559ced51 100644
--- a/clang/lib/CodeGen/CodeGenModule.cpp
+++ b/clang/lib/CodeGen/CodeGenModule.cpp
@@ -3701,13 +3701,16 @@ static void emitUsed(CodeGenModule &CGM, StringRef Name,
if (List.empty())
return;
- // Convert List to what ConstantArray needs.
- SmallVector<llvm::Constant*, 8> UsedArray;
- UsedArray.resize(List.size());
- for (unsigned i = 0, e = List.size(); i != e; ++i) {
- UsedArray[i] =
- llvm::ConstantExpr::getPointerBitCastOrAddrSpaceCast(
- cast<llvm::Constant>(&*List[i]), CGM.Int8PtrTy);
+ // Convert List to what ConstantArray needs. A used global may have been
+ // deleted after it was added to the list (e.g. when its home module keeps
+ // accumulating declarations after an erroneous incremental parse), leaving
+ // a null value handle behind; skip those entries.
+ SmallVector<llvm::Constant *, 8> UsedArray;
+ UsedArray.reserve(List.size());
+ for (const llvm::WeakTrackingVH &VH : List) {
+ if (llvm::Value *V = VH)
+ UsedArray.push_back(llvm::ConstantExpr::getPointerBitCastOrAddrSpaceCast(
+ cast<llvm::Constant>(V), CGM.Int8PtrTy));
}
if (UsedArray.empty())
diff --git a/clang/test/Interpreter/used-global-after-error.cpp
b/clang/test/Interpreter/used-global-after-error.cpp
new file mode 100644
index 0000000000000..fc1043042d5cc
--- /dev/null
+++ b/clang/test/Interpreter/used-global-after-error.cpp
@@ -0,0 +1,15 @@
+// REQUIRES: host-supports-jit
+// UNSUPPORTED: system-aix
+// RUN: cat %s | clang-repl | FileCheck %s
+
+// A cast<> of a null WeakTrackingVH used to crash emitUsed when a global on
+// the llvm.used list was deleted before the module was released: the
+// duplicate definition below is diagnosed by CodeGen, which then replaces the
+// used global's unreferenced GV with a differently-typed one; the failed
+// parse keeps the module alive, and the next successful parse finalizes it.
+extern "C" int printf(const char *, ...);
+__attribute__((used)) int a asm("sym") = 1; float b asm("sym") = 2.0f;
+auto r1 = printf("ok = %d\n", 42);
+// CHECK: ok = 42
+
+%quit
``````````
</details>
https://github.com/llvm/llvm-project/pull/210959
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