commit 2a41b31fcdfcb67ab7038fc2ffb606fd50b83a84
Author: Nathan Chancellor <natechancellor@gmail.com>
Date:   Sat Mar 7 16:37:44 2020 -0800

    [Sema] Add -Wpointer-to-enum-cast and -Wvoid-pointer-to-enum-cast
    
    GCC does not warn on casts from pointers to enumerators, while clang
    currently does: https://godbolt.org/z/3DFDVG
    
    This causes a bunch of extra warnings in the Linux kernel, where
    certain structs contain a void pointer to avoid using a gigantic
    union for all of the various types of driver data, such as
    versions.
    
    Add a diagnostic that allows certain projects like the kernel to
    disable the warning just for enums, which allows those projects to
    keep full compatibility with GCC but keeps the intention of treating
    casts to integers and enumerators the same by default so that other
    projects have the opportunity to catch issues not noticed before (or
    follow suite and disable the warning).
    
    Link: https://github.com/ClangBuiltLinux/linux/issues/887
    
    Reviewed By: rjmccall
    
    Differential Revision: https://reviews.llvm.org/D75758

diff --git a/clang/include/clang/Basic/DiagnosticGroups.td b/clang/include/clang/Basic/DiagnosticGroups.td
index 6c79ea59173..ae3f882dd91 100644
--- a/clang/include/clang/Basic/DiagnosticGroups.td
+++ b/clang/include/clang/Basic/DiagnosticGroups.td
@@ -838,9 +838,13 @@ def IncompatibleExceptionSpec : DiagGroup<"incompatible-exception-spec">;
 def IntToVoidPointerCast : DiagGroup<"int-to-void-pointer-cast">;
 def IntToPointerCast : DiagGroup<"int-to-pointer-cast",
                                  [IntToVoidPointerCast]>;
-def VoidPointerToIntCast : DiagGroup<"void-pointer-to-int-cast">;
+def VoidPointerToEnumCast : DiagGroup<"void-pointer-to-enum-cast">;
+def VoidPointerToIntCast : DiagGroup<"void-pointer-to-int-cast",
+                                     [VoidPointerToEnumCast]>;
+def PointerToEnumCast : DiagGroup<"pointer-to-enum-cast",
+                                  [VoidPointerToEnumCast]>;
 def PointerToIntCast : DiagGroup<"pointer-to-int-cast",
-                                 [VoidPointerToIntCast]>;
+                                 [PointerToEnumCast, VoidPointerToIntCast]>;
 
 def Move : DiagGroup<"move", [
     PessimizingMove,
diff --git a/clang/include/clang/Basic/DiagnosticSemaKinds.td b/clang/include/clang/Basic/DiagnosticSemaKinds.td
index 181341fed78..b0338c44cca 100644
--- a/clang/include/clang/Basic/DiagnosticSemaKinds.td
+++ b/clang/include/clang/Basic/DiagnosticSemaKinds.td
@@ -3668,9 +3668,15 @@ def warn_int_to_void_pointer_cast : Warning<
 def warn_pointer_to_int_cast : Warning<
   "cast to smaller integer type %1 from %0">,
   InGroup<PointerToIntCast>;
+def warn_pointer_to_enum_cast : Warning<
+  warn_pointer_to_int_cast.Text>,
+  InGroup<PointerToEnumCast>;
 def warn_void_pointer_to_int_cast : Warning<
   "cast to smaller integer type %1 from %0">,
   InGroup<VoidPointerToIntCast>;
+def warn_void_pointer_to_enum_cast : Warning<
+  warn_void_pointer_to_int_cast.Text>,
+  InGroup<VoidPointerToEnumCast>;
 def ext_ms_pointer_to_int_cast : ExtWarn<
   "cast to smaller integer type %1 from %0 is a Microsoft extension">,
 InGroup<MicrosoftCast>;
diff --git a/clang/lib/Sema/SemaCast.cpp b/clang/lib/Sema/SemaCast.cpp
index 17d07c57a41..8edff2439e0 100644
--- a/clang/lib/Sema/SemaCast.cpp
+++ b/clang/lib/Sema/SemaCast.cpp
@@ -2777,11 +2777,16 @@ void CastOperation::CheckCStyleCast() {
       // If the result cannot be represented in the integer type, the behavior
       // is undefined. The result need not be in the range of values of any
       // integer type.
-      unsigned Diag = Self.getLangOpts().MicrosoftExt
-                          ? diag::ext_ms_pointer_to_int_cast
-                          : SrcType->isVoidPointerType()
-                                ? diag::warn_void_pointer_to_int_cast
-                                : diag::warn_pointer_to_int_cast;
+      unsigned Diag;
+      if (Self.getLangOpts().MicrosoftExt)
+        Diag = diag::ext_ms_pointer_to_int_cast;
+      else if (SrcType->isVoidPointerType())
+        Diag = DestType->isEnumeralType() ? diag::warn_void_pointer_to_enum_cast
+                                          : diag::warn_void_pointer_to_int_cast;
+      else if (DestType->isEnumeralType())
+        Diag = diag::warn_pointer_to_enum_cast;
+      else
+        Diag = diag::warn_pointer_to_int_cast;
       Self.Diag(OpRange.getBegin(), Diag) << SrcType << DestType << OpRange;
     }
   }
diff --git a/clang/test/Sema/cast.c b/clang/test/Sema/cast.c
index 0c4fc7d129f..2335f219807 100644
--- a/clang/test/Sema/cast.c
+++ b/clang/test/Sema/cast.c
@@ -186,3 +186,23 @@ void *intToPointerCast2(X x) {
 void *intToPointerCast3() {
   return (void*)(1 + 3);
 }
+
+void voidPointerToEnumCast(VoidPtr v) {
+  (void)(X) v; // expected-warning{{cast to smaller integer type 'X' from 'VoidPtr' (aka 'void *')}}
+  // Test that casts to void* can be controlled separately
+  // from other -Wpointer-to-enum-cast warnings.
+#pragma clang diagnostic push
+#pragma clang diagnostic ignored "-Wvoid-pointer-to-enum-cast"
+  (void)(X) v; // no-warning
+#pragma clang diagnostic pop
+}
+
+void pointerToEnumCast(CharPtr v) {
+  (void)(X) v; // expected-warning{{cast to smaller integer type 'X' from 'CharPtr' (aka 'char *')}}
+  // Test that casts to void* can be controlled separately
+  // from other -Wpointer-to-enum-cast warnings.
+#pragma clang diagnostic push
+#pragma clang diagnostic ignored "-Wvoid-pointer-to-enum-cast"
+  (void)(X) v; // expected-warning{{cast to smaller integer type 'X' from 'CharPtr' (aka 'char *')}}
+#pragma clang diagnostic pop
+}