[libcxx-commits] [clang] [libcxx] [clang] Add builtin to clear padding bytes (prework for P0528R3) (PR #75371)

[via libcxx-commits]

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@@ -2327,6 +2327,25 @@ Sema::CheckBuiltinFunctionCall(FunctionDecl *FDecl, unsigned BuiltinID,
   }
   case Builtin::BI__builtin_launder:
     return SemaBuiltinLaunder(*this, TheCall);
+  case Builtin::BI__builtin_clear_padding: {
+    const Expr *PtrArg = TheCall->getArg(0)->IgnoreParenImpCasts();
+    const QualType PtrArgType = PtrArg->getType();
+    if (!PtrArgType->isPointerType()) {
+      Diag(PtrArg->getBeginLoc(), diag::err_typecheck_convert_incompatible)
+          << PtrArgType << "pointer" << 1 << 0 << 3 << 1 << PtrArgType
+          << "pointer";
+      return ExprError();
+    }
+    if (PtrArgType->getPointeeType().isConstQualified()) {
+      Diag(PtrArg->getBeginLoc(), diag::err_typecheck_assign_const)
+          << TheCall->getSourceRange() << 5 /*ConstUnknown*/;
+      return ExprError();
+    }
+    if (RequireCompleteType(PtrArg->getBeginLoc(), PtrArgType->getPointeeType(),
+                            diag::err_typecheck_decl_incomplete_type))
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huixie90 wrote:

> Please define an error message that explains what's actually going wrong here, instead of reusing err_typecheck_decl_incomplete_type. (The other errors could also be improved a bit.)

hmm. the current error message looks like this

```
/tmp/a.cpp:5:29: error: variable has incomplete type 'A'
    5 |     __builtin_clear_padding(a);
      |                             ^
/tmp/a.cpp:1:8: note: forward declaration of 'A'
    1 | struct A;
```

In my opinion, the error is quite clear. It suggested the user that it does not work with incomplete type. 

https://github.com/llvm/llvm-project/pull/75371