Silence spurious -Wnontrivial-memcall warnings in C mode (#137429)

clang currently issues a warning when memset is used on a struct that
contains an address-discriminated pointer field, even though this is
entirely valid behavior.

For example:

```
struct S {
  int * __ptrauth(1, 1, 100) p;
} s;

memset(&s, 0, sizeof(struct S));
```

Only allow the warning to be emitted in C++ mode to silence the warning.

rdar://142495870

Author: ahatanak

clang/lib/Sema/SemaChecking.cpp

@@ -9735,9 +9735,9 @@ void Sema::CheckMemaccessArguments(const CallExpr *Call,
       // completed later. GCC does not diagnose such code, but we may want to
       // consider diagnosing it in the future, perhaps under a different, but
       // related, diagnostic group.
-      bool MayBeTriviallyCopyableCXXRecord =
-          RT->isIncompleteType() ||
-          RT->desugar().isTriviallyCopyableType(Context);
+      bool NonTriviallyCopyableCXXRecord =
+          getLangOpts().CPlusPlus && !RT->isIncompleteType() &&
+          !RT->desugar().isTriviallyCopyableType(Context);
 
       if ((BId == Builtin::BImemset || BId == Builtin::BIbzero) &&
           RT->getDecl()->isNonTrivialToPrimitiveDefaultInitialize()) {
@@ -9746,7 +9746,7 @@ void Sema::CheckMemaccessArguments(const CallExpr *Call,
                                 << ArgIdx << FnName << PointeeTy << 0);
         SearchNonTrivialToInitializeField::diag(PointeeTy, Dest, *this);
       } else if ((BId == Builtin::BImemset || BId == Builtin::BIbzero) &&
-                 !MayBeTriviallyCopyableCXXRecord && ArgIdx == 0) {
+                 NonTriviallyCopyableCXXRecord && ArgIdx == 0) {
         // FIXME: Limiting this warning to dest argument until we decide
         // whether it's valid for source argument too.
         DiagRuntimeBehavior(Dest->getExprLoc(), Dest,
@@ -9759,7 +9759,7 @@ void Sema::CheckMemaccessArguments(const CallExpr *Call,
                                 << ArgIdx << FnName << PointeeTy << 1);
         SearchNonTrivialToCopyField::diag(PointeeTy, Dest, *this);
       } else if ((BId == Builtin::BImemcpy || BId == Builtin::BImemmove) &&
-                 !MayBeTriviallyCopyableCXXRecord && ArgIdx == 0) {
+                 NonTriviallyCopyableCXXRecord && ArgIdx == 0) {
         // FIXME: Limiting this warning to dest argument until we decide
         // whether it's valid for source argument too.
         DiagRuntimeBehavior(Dest->getExprLoc(), Dest,

clang/test/Sema/warn-nontrivial-struct-memaccess-ptrauth.c

@@ -0,0 +1,60 @@
+// RUN: %clang_cc1 -triple arm64-apple-ios -fptrauth-calls -fptrauth-intrinsics -fsyntax-only -verify=c,expected %s
+// RUN: %clang_cc1 -triple aarch64-linux-gnu -fptrauth-calls -fptrauth-intrinsics -fsyntax-only -verify=c,expected %s
+// RUN: %clang_cc1 -triple arm64-apple-ios -fptrauth-calls -fptrauth-intrinsics -fsyntax-only -x c++ -verify=cxx,expected %s
+// RUN: %clang_cc1 -triple aarch64-linux-gnu -fptrauth-calls -fptrauth-intrinsics -fsyntax-only -x c++ -verify=cxx,expected %s
+
+#if defined __cplusplus
+extern "C" {
+#endif
+
+void *memset(void *, int, __SIZE_TYPE__);
+void bzero(void *, __SIZE_TYPE__);
+void *memcpy(void *, const void *, __SIZE_TYPE__);
+void *memmove(void *, const void *, __SIZE_TYPE__);
+
+#if defined __cplusplus
+}
+#endif
+
+#define AQ __ptrauth(1,1,50)
+#define IQ __ptrauth(1,0,50)
+
+struct PtrAuthTrivial {
+  int f0;
+  int * IQ f1;
+};
+
+struct PtrAuthNonTrivial0 {
+  int f0;
+  int * AQ f1; // c-note 2 {{non-trivial to copy}}
+  int f2;
+};
+
+struct PtrAuthNonTrivial1 {
+  int * AQ f0; // c-note 2 {{non-trivial to copy}}
+  int f1;
+  struct PtrAuthNonTrivial0 f2;
+};
+
+void testPtrAuthTrivial(struct PtrAuthTrivial *d, struct PtrAuthTrivial *s) {
+  memset(d, 0, sizeof(struct PtrAuthTrivial));
+  memset(d, 1, sizeof(struct PtrAuthTrivial));
+  bzero(d, sizeof(struct PtrAuthTrivial));
+  memcpy(d, s, sizeof(struct PtrAuthTrivial));
+  memmove(d, s, sizeof(struct PtrAuthTrivial));
+}
+
+void testPtrAuthNonTrivial1(struct PtrAuthNonTrivial1 *d,
+                            struct PtrAuthNonTrivial1 *s) {
+  memset(d, 0, sizeof(struct PtrAuthNonTrivial1)); // cxx-warning {{is a pointer to non-trivially copyable type 'struct PtrAuthNonTrivial1'}} // cxx-note {{explicitly cast the pointer to silence}}
+  memset(d, 1, sizeof(struct PtrAuthNonTrivial1)); // cxx-warning {{is a pointer to non-trivially copyable type 'struct PtrAuthNonTrivial1'}} // cxx-note {{explicitly cast the pointer to silence}}
+  bzero(d, sizeof(struct PtrAuthNonTrivial1)); // cxx-warning {{is a pointer to non-trivially copyable type 'struct PtrAuthNonTrivial1'}} // cxx-note {{explicitly cast the pointer to silence}}
+  memcpy(d, s, sizeof(struct PtrAuthNonTrivial1));
+  // c-warning@-1 {{that is not trivial to primitive-copy}}
+  // cxx-warning@-2 {{is a pointer to non-trivially copyable type 'struct PtrAuthNonTrivial1'}}
+  // expected-note@-3 {{explicitly cast the pointer to silence}}
+  memmove(d, s, sizeof(struct PtrAuthNonTrivial1));
+  // c-warning@-1 {{that is not trivial to primitive-copy}}
+  // cxx-warning@-2 {{is a pointer to non-trivially copyable type 'struct PtrAuthNonTrivial1'}}
+  // expected-note@-3 {{explicitly cast the pointer to silence}}
+}