[llvm-branch-commits] [clang] release/21.x: [C] Fix issue with -Wimplicit-void-ptr-cast (#154351) (PR #154386)

[Aaron Ballman via llvm-branch-commits]

https://github.com/AaronBallman updated https://github.com/llvm/llvm-project/pull/154386

>From b20f2405709969b6004119ce0846e1548b5498e8 Mon Sep 17 00:00:00 2001
From: Aaron Ballman <aaron at aaronballman.com>
Date: Tue, 19 Aug 2025 12:55:03 -0400
Subject: [PATCH] [C] Fix issue with -Wimplicit-void-ptr-cast (#154351)

The changes from https://github.com/llvm/llvm-project/pull/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
(cherry picked from commit ae434cdd0ba572ab1b11629c8a10073dea7d2f3f)
---
 clang/lib/Sema/SemaExpr.cpp              |  8 ++++----
 clang/test/Sema/implicit-void-ptr-cast.c | 12 ++++++++++++
 2 files changed, 16 insertions(+), 4 deletions(-)

diff --git a/clang/lib/Sema/SemaExpr.cpp b/clang/lib/Sema/SemaExpr.cpp
index 728ada33e2e63..5421e9562c8b2 100644
--- a/clang/lib/Sema/SemaExpr.cpp
+++ b/clang/lib/Sema/SemaExpr.cpp
@@ -9309,14 +9309,14 @@ 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..d5e9497191446 100644
--- a/clang/test/Sema/implicit-void-ptr-cast.c
+++ b/clang/test/Sema/implicit-void-ptr-cast.c
@@ -82,3 +82,15 @@ 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 *'}}
+  static T_Ref const y = ATOMIC_VAR_INIT((void*)NULL);   // c-warning {{implicit conversion when initializing 'const T_Ref' (aka 'const struct T *const') with an expression of type 'void *' is not permitted in C++}} \
+                                                            cxx-error {{cannot initialize a variable of type 'const T_Ref' (aka 'const T *const') with an rvalue of type 'void *'}}
+  static T_Ref z = ATOMIC_VAR_INIT((void*)NULL);         // c-warning {{implicit conversion when initializing 'T_Ref' (aka 'const struct T *') with an expression of type 'void *' is not permitted in C++}} \
+                                                            cxx-error {{cannot initialize a variable of type 'T_Ref' (aka 'const T *') with an rvalue of type 'void *'}}
+}