[C] Fix issue with -Wimplicit-void-ptr-cast

[AaronBallman]

The changes from #136855 missed a change with atomic assignment constraints. This fixes a bug where we'd accidentally drop a non-atomic-to-atomic conversion step.

Fixes #154157

co-authored-by: @ahatanak

[AaronBallman]

Because this is fixing an issue introduced in Clang 21, there's no release note because I plan to backport the fix to the release branch.

[llvmbot]

@llvm/pr-subscribers-clang

Author: Aaron Ballman (AaronBallman)

Changes

The changes from #136855 missed a change with atomic assignment constraints. This fixes a bug where we'd accidentally drop a non-atomic-to-atomic conversion step.

Fixes #154157

co-authored-by: @ahatanak

---

Full diff: https://github.com/llvm/llvm-project/pull/154351.diff

2 Files Affected:

• (modified) clang/lib/Sema/SemaExpr.cpp (+4-4)
• (modified) clang/test/Sema/implicit-void-ptr-cast.c (+8)

diff --git a/clang/lib/Sema/SemaExpr.cpp b/clang/lib/Sema/SemaExpr.cpp
index 237c068f59283..265cd799373a5 100644
--- a/clang/lib/Sema/SemaExpr.cpp
+++ b/clang/lib/Sema/SemaExpr.cpp
@@ -9317,14 +9317,14 @@ AssignConvertType Sema::CheckAssignmentConstraints(QualType LHSType,
   // If we have an atomic type, try a non-atomic assignment, then just add an
   // atomic qualification step.
   if (const AtomicType *AtomicTy = dyn_cast<AtomicType>(LHSType)) {
-    AssignConvertType result =
+    AssignConvertType Result =
         CheckAssignmentConstraints(AtomicTy->getValueType(), RHS, Kind);
-    if (result != AssignConvertType::Compatible)
-      return result;
+    if (!IsAssignConvertCompatible(Result))
+      return Result;
     if (Kind != CK_NoOp && ConvertRHS)
       RHS = ImpCastExprToType(RHS.get(), AtomicTy->getValueType(), Kind);
     Kind = CK_NonAtomicToAtomic;
-    return AssignConvertType::Compatible;
+    return Result;
   }
 
   // If the left-hand side is a reference type, then we are in a
diff --git a/clang/test/Sema/implicit-void-ptr-cast.c b/clang/test/Sema/implicit-void-ptr-cast.c
index 3c3e153d1dbda..1a8e1574907d4 100644
--- a/clang/test/Sema/implicit-void-ptr-cast.c
+++ b/clang/test/Sema/implicit-void-ptr-cast.c
@@ -82,3 +82,11 @@ void more(void) {
   ptr3 = SOMETHING_THAT_IS_NOT_NULL; // c-warning {{implicit conversion when assigning to 'char *' from type 'void *' is not permitted in C++}} \
                                         cxx-error {{assigning to 'char *' from incompatible type 'void *'}}
 }
+
+void gh154157(void) {
+  #define ATOMIC_VAR_INIT(value) (value)
+
+  typedef const struct T * T_Ref;
+  static T_Ref _Atomic x = ATOMIC_VAR_INIT((void*)NULL); // c-warning {{implicit conversion when initializing '_Atomic(T_Ref)' with an expression of type 'void *' is not permitted in C++}} \
+                                                            cxx-error {{cannot initialize a variable of type '_Atomic(T_Ref)' with an rvalue of type 'void *'}}
+}

[AaronBallman]

I believe the Windows failure is unrelated, but we'll see what precommit CI comes back with this time. I wasn't able to reproduce the crash locally on my Windows machine, though.

[AaronBallman]

Windows failures are unrelated, other PRs are having the same issue:
#154342
#154347

[AaronBallman]

/cherry-pick ae434cd

[llvmbot]

/pull-request #154386