[move-function] Add support for loadable vars #40478
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… mark_unresolved_move_addr.
To give a bit more information, currently the way the move function is
implemented is that:
1. SILGen emits a builtin "move" that is called within the function _move in the
stdlib.
2. Mandatory Inlining today if the final inlined type is address only, inlines
builtin "move" as mark_unresolved_move_addr. Otherwise, if the inlined type
is loadable, it performs a load [take] + move [diagnostic] + store [init].
3. In the diagnostic pipeline before any mem optimizations have run, we run the
move checker for addresses. This eliminates /all/ mark_unresolved_move_addr
as part of emitting diagnostics. In order to make this work, we perform a
small optimization before the checker runs that moves the
mark_unresolved_move_addr from being on temporary alloc_stacks to the true
base underlying address we are trying to move. This optimization is necessary
since _move is generic and often times SILGen will emit this temporary that
we do not want.
4. Then after we have run the guaranteed mem optimizations, we run the object
based move checker emitting diagnostics.
This PR changes the scheme above to the following:
1. SILGen emits a builtin "move" that is called within the function _move in the
stdlib.
2. Mandatory Inlining inlines builtin "move" as mark_unresolved_move_addr.
3. In the diagnostic pipeline before we have run any mem optimizations and
before we have run the actual move address checker, we massage the IR as we
do above but in a separate pass where in addition we try to match this pattern:
```
%temporary = alloc_stack $LoadableType
store %1 to [init] %temporary : $*LoadableType
mark_unresolved_move_addr %temporary to %otherAddr : $*LoadableType
destroy_addr %temporary : $*LoadableType
```
and transform it to:
```
%temporary = alloc_stack $LoadableType
%2 = move_value [allows_diagnostics] %1 : $*LoadableType
store %2 to [init] %temporary : $*LoadableType
destroy_addr %temporary : $*LoadableType
```
ensuring that the object move checker will handle this.
4. Then after we have run the guaranteed mem optimizations, we run the object
based move checker emitting diagnostics.
This is done by extending the support in the previous PR for
a. If we see the following pattern:
```
%0 = alloc_stack [lexical] $LoadableType, var
... *init of %0* ...
%1 = load [copy] %0 : $*LoadableType
%temporary = alloc_stack $LoadableType
store %1 to [init] %temporary : $*LoadableType
mark_unresolved_move_addr %temporary to %otherAddr : $*LoadableType
destroy_addr %temporary : $*LoadableType
```
we transform it to:
```
%0 = alloc_stack [lexical] $LoadableType, var
... *init of %0* ...
%1 = load [copy] %0 : $*LoadableType
%temporary = alloc_stack $LoadableType
store %2 to [init] %temporary : $*LoadableType
mark_unresolved_move_addr %0 to %otherAddr : $*LoadableType
destroy_addr %temporary : $*LoadableType
```
For safety reasons, we always make sure that %0 isn't destroyed in between
the load [copy] and the mark_unresolved_move_addr. After this runs, we can
use the address verifier on these types of vars with some additional work
that I am doing in a subsequent commit.
…ical borrows. A lexical borrow is creating a new entity that should be checked separately from the operand of the lexical borrow.
This is safe to do since: 1. _move is already an always emit into client transparent function, so no ABI impact comes from it. 2. _move is underscored so it is a non-stable stdlib API meaning we aren't providing any guarantees here. 3. Code that doesn't use _move will not be effected by this so there isn't an impact on other code.
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I had to make two changes to do this: