> Interesting distinction, but once the object is replaced by scalars, those scalars are placed on the stack.
No, they become data flow edges, so could be in a register, or part of an addressing operation, or value-numbered, or nothing at all if they’re never used, so only on the stack as a worst-case fallback.
> Do I understand it correctly that you are saying real stack allocation would involve allocating the whole object, including the header, on the stack
Yes, which is useful in some cases, but generally a lot weaker than full scalar replacement.
No, they become data flow edges, so could be in a register, or part of an addressing operation, or value-numbered, or nothing at all if they’re never used, so only on the stack as a worst-case fallback.
> Do I understand it correctly that you are saying real stack allocation would involve allocating the whole object, including the header, on the stack
Yes, which is useful in some cases, but generally a lot weaker than full scalar replacement.