[clang] [libc++] Add builtin to clear padding bytes (prework for P0528R3) (PR #75371)

[Eli Friedman via cfe-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();
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efriedma-quic wrote:

Why IgnoreParenImpCasts()?

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