rsmith added inline comments.
================
Comment at: lib/CodeGen/CGBuiltin.cpp:1674
+ Value *Ptr = EmitScalarExpr(E->getArg(0));
+ Ptr = Builder.CreateInvariantGroupBarrier(Ptr);
+ return RValue::get(Ptr);
----------------
It would be nice to avoid this for types that contain no const subobjects /
reference subobjects / vptrs. I think we can also omit this entirely if
`-fstrict-vtable-ptrs` is disabled, since in that case we don't generate any
`invariant.group` metadata.
I'd be OK with the former being left to a future change, but the latter should
be part of this change so we don't generate unnecessarily-inefficient code in
the default mode for uses of `std::launder`.
================
Comment at: lib/Sema/SemaChecking.cpp:860-864
+ if (!ArgTy->isPointerType()) {
+ S.Diag(TheCall->getLocStart(), diag::err_builtin_launder_non_pointer_arg)
+ << TheCall->getSourceRange();
+ return ExprError();
+ }
----------------
Please also check that the pointee type is an object type -- per
[ptr.launder]p3, "the program is ill-formed if T is a function type or cv
void", and we don't want our builtin to need to deal with such cases.
https://reviews.llvm.org/D40218
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