erichkeane updated this revision to Diff 465725.
erichkeane marked 2 inline comments as done.
erichkeane added a comment.

Fix based on Aaron's comments.


CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D135287/new/

https://reviews.llvm.org/D135287

Files:
  clang/docs/ReleaseNotes.rst
  clang/include/clang/Basic/DiagnosticGroups.td
  clang/include/clang/Basic/DiagnosticSemaKinds.td
  clang/lib/Sema/SemaExpr.cpp
  clang/test/CXX/temp/temp.decls/temp.class/temp.mem.func/p1inst.cpp
  clang/test/SemaCXX/disallow_void_deref.cpp
  clang/test/SemaCXX/reinterpret-cast.cpp

Index: clang/test/SemaCXX/reinterpret-cast.cpp
===================================================================
--- clang/test/SemaCXX/reinterpret-cast.cpp
+++ clang/test/SemaCXX/reinterpret-cast.cpp
@@ -214,11 +214,11 @@
   (void)*reinterpret_cast<float*>(v_ptr);
 
   // Casting to void pointer
-  (void)*reinterpret_cast<void*>(&a); // expected-warning {{ISO C++ does not allow}}
-  (void)*reinterpret_cast<void*>(&b); // expected-warning {{ISO C++ does not allow}}
-  (void)*reinterpret_cast<void*>(&l); // expected-warning {{ISO C++ does not allow}}
-  (void)*reinterpret_cast<void*>(&d); // expected-warning {{ISO C++ does not allow}}
-  (void)*reinterpret_cast<void*>(&f); // expected-warning {{ISO C++ does not allow}}
+  (void)*reinterpret_cast<void*>(&a); // expected-error {{ISO C++ does not allow}}
+  (void)*reinterpret_cast<void*>(&b); // expected-error {{ISO C++ does not allow}}
+  (void)*reinterpret_cast<void*>(&l); // expected-error {{ISO C++ does not allow}}
+  (void)*reinterpret_cast<void*>(&d); // expected-error {{ISO C++ does not allow}}
+  (void)*reinterpret_cast<void*>(&f); // expected-error {{ISO C++ does not allow}}
 }
 
 void reinterpret_cast_allowlist () {
Index: clang/test/SemaCXX/disallow_void_deref.cpp
===================================================================
--- /dev/null
+++ clang/test/SemaCXX/disallow_void_deref.cpp
@@ -0,0 +1,16 @@
+// RUN: %clang_cc1 -fsyntax-only -verify=enabled,sfinae -std=c++20 %s
+// RUN: %clang_cc1 -fsyntax-only -verify=sfinae -std=c++20 -Wno-void-ptr-dereference %s
+
+void f(void* p) {
+  (void)*p; // enabled-error{{ISO C++ does not allow indirection on operand of type 'void *'}}
+}
+
+template<class T>
+concept deref = requires (T& t) {
+      { *t }; // #FAILED_REQ
+};
+
+static_assert(deref<void*>);
+// sfinae-error@-1{{static assertion failed}}
+// sfinae-note@-2{{because 'void *' does not satisfy 'deref'}}
+// sfinae-note@#FAILED_REQ{{because '*t' would be invalid: ISO C++ does not allow indirection on operand of type 'void *'}}
Index: clang/test/CXX/temp/temp.decls/temp.class/temp.mem.func/p1inst.cpp
===================================================================
--- clang/test/CXX/temp/temp.decls/temp.class/temp.mem.func/p1inst.cpp
+++ clang/test/CXX/temp/temp.decls/temp.class/temp.mem.func/p1inst.cpp
@@ -8,7 +8,7 @@
 
 template<typename T, typename U>
 void X0<T, U>::f(T *t, const U &u) {
-  *t = u; // expected-warning{{indirection on operand of type 'void *'}} expected-error{{not assignable}}
+  *t = u; // expected-error{{indirection on operand of type 'void *'}} expected-error{{not assignable}}
 }
 
 void test_f(X0<float, int> xfi, X0<void, int> xvi, float *fp, void *vp, int i) {
Index: clang/lib/Sema/SemaExpr.cpp
===================================================================
--- clang/lib/Sema/SemaExpr.cpp
+++ clang/lib/Sema/SemaExpr.cpp
@@ -14536,9 +14536,12 @@
     //   [...] the expression to which [the unary * operator] is applied shall
     //   be a pointer to an object type, or a pointer to a function type
     LangOptions LO = S.getLangOpts();
-    if (LO.CPlusPlus || !(LO.C99 && (IsAfterAmp || S.isUnevaluatedContext())))
+    if (LO.CPlusPlus)
+      S.Diag(OpLoc, diag::ext_typecheck_indirection_through_void_pointer_cpp)
+          << OpTy << Op->getSourceRange();
+    else if (!(LO.C99 && (IsAfterAmp || S.isUnevaluatedContext())))
       S.Diag(OpLoc, diag::ext_typecheck_indirection_through_void_pointer)
-          << LO.CPlusPlus << OpTy << Op->getSourceRange();
+          << OpTy << Op->getSourceRange();
   }
 
   // Dereferences are usually l-values...
Index: clang/include/clang/Basic/DiagnosticSemaKinds.td
===================================================================
--- clang/include/clang/Basic/DiagnosticSemaKinds.td
+++ clang/include/clang/Basic/DiagnosticSemaKinds.td
@@ -6932,8 +6932,11 @@
 def err_typecheck_indirection_requires_pointer : Error<
   "indirection requires pointer operand (%0 invalid)">;
 def ext_typecheck_indirection_through_void_pointer : ExtWarn<
-  "ISO %select{C|C++}0 does not allow indirection on operand of type %1">,
-  InGroup<DiagGroup<"void-ptr-dereference">>;
+  "ISO C does not allow indirection on operand of type %0">,
+  InGroup<VoidPointerDeref>;
+def ext_typecheck_indirection_through_void_pointer_cpp
+    : ExtWarn<"ISO C++ does not allow indirection on operand of type %0">,
+      InGroup<VoidPointerDeref>, DefaultError, SFINAEFailure;
 def warn_indirection_through_null : Warning<
   "indirection of non-volatile null pointer will be deleted, not trap">,
   InGroup<NullDereference>;
Index: clang/include/clang/Basic/DiagnosticGroups.td
===================================================================
--- clang/include/clang/Basic/DiagnosticGroups.td
+++ clang/include/clang/Basic/DiagnosticGroups.td
@@ -961,6 +961,7 @@
                                   [VoidPointerToEnumCast]>;
 def PointerToIntCast : DiagGroup<"pointer-to-int-cast",
                                  [PointerToEnumCast, VoidPointerToIntCast]>;
+def VoidPointerDeref : DiagGroup<"void-ptr-dereference">;
 
 def FUseLdPath : DiagGroup<"fuse-ld-path">;
 
Index: clang/docs/ReleaseNotes.rst
===================================================================
--- clang/docs/ReleaseNotes.rst
+++ clang/docs/ReleaseNotes.rst
@@ -86,6 +86,17 @@
   typedef char int8_a16 __attribute__((aligned(16)));
   int8_a16 array[4]; // Now diagnosed as the element size not being a multiple of the array alignment.
 
+- Clang now diagnoses indirection of ``void *`` in C++ mode as a warning which
+  defaults to an error. This is compatible with ISO C++, GCC, ICC, and MSVC. This
+  is also now a SFINAE error so constraint checking and SFINAE checking can be
+  compatible with other compilers. It is expected that this will be upgraded to
+  an error-only diagnostic in the next Clang release.
+
+  .. code-block:: c++
+
+  void func(void *p) {
+    *p; // Now diagnosed as a warning-as-error.
+  }
 
 What's New in Clang |release|?
 ==============================
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