[clang] [clang] Add __builtin_start_object_lifetime builtin. (PR #82776)

[Sam McCall via cfe-commits]

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@@ -4386,6 +4386,7 @@ RValue CodeGenFunction::EmitBuiltinExpr(const GlobalDecl GD, unsigned BuiltinID,
 
     return RValue::get(nullptr);
   }
+  case Builtin::BI__builtin_start_object_lifetime:
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sam-mccall wrote:

is there something to be commented here about why what we do here is sufficient?
It seems surprising to my very-untrained eye that start_lifetime is the same as launder, and we don't need any extra TBAA metadata or so...

https://github.com/llvm/llvm-project/pull/82776