Nate Chandler 41877ae7b7 [Mem2Reg] Don't promote proj(unchecked_addr_cast). ...

In OSSA, the result of an `unchecked_bitwise_cast` must immediately be
copied or `unchecked_bitwise_cast`'d again.  In particular, it is not
permitted to borrow it.  For example, the result can't be borrowed for
the purpose of performinig additional projections (`struct_extract`,
`tuple_extract`) on the borrowed value.  Consequently, we cannot promote
an address if such a promotion would result in such a pattern.  That
means we can't promote an address `%addr` which is used like
`struct_element_addr(unchecked_addr_cast(%addr))` or
`tuple_element_addr(unchecked_addr_cast(%addr))`.  We can still promote
`unchecked_addr_cast(unchecked_addr_cast(%addr))`.

In ownership-lowered SIL, this doesn't apply and we can still promote
address with such projections.

rdar://153693915

2025-07-03 14:52:23 -07:00

86 KiB

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