Compute 'isLet' from the VarDecl that is available when constructing
AccessedStorage so we don't need to recover the VarDecl for the base
later.
This generally makes more sense and is more efficient, but it will be
necessary when we look past class casts when finding the reference root.
This is important to do since otherwise, we may be implicitly reducing the
lifetime of a value which we can not do yet since we do not require all interior
pointer instructions to be guarded by borrows (yet). Once that constraint is in
place, we will not have this problem.
Consider a situation where one has a @owned switch_enum on an
indirect box case which is post-dominated by an unreachable that we want
to convert to @guaranteed:
enum MyEnum {
indirect case FirstCase(Int)
...
}
bb0(%in_guaranteed_addr : $*MyEnum):
...
%0 = load [copy] %in_guaranteed_addr : $*MyEnum
switch_enum %0 : $MyEnum, case #MyEnum.FirstCase: bb1, ...
bb1(%1 : @owned ${ var Int }):
%2 = project_box %1 : ${ var Int }, 0
%3 = load [trivial] %2 : $*Int
apply %log(%3) : $@convention(thin) (Int) -> ()
unreachable
In this case, we will not have a destroy_value on the box, but we may
have a project_box on the box. This is ok since we are going to leak the
value. But since we are using all consuming uses to determine the
lifetime, we will want to insert an end_borrow at the head of the
switch_enum dest block like follows:
bb0(%in_guaranteed_addr : $*MyEnum):
...
%0 = load_borrow %in_guaranteed_addr : $*MyEnum
switch_enum %0 : $MyEnum, case #MyEnum.FirstCase: bb1, ...
bb1(%1 : @guaranteed ${ var Int }):
end_borrow %1 : ${ var Int }
%2 = project_box %1 : ${ var Int }, 0
%3 = load [trivial] %2 : $*Int
apply %log(%3) : $@convention(thin) (Int) -> ()
unreachable
which would violate ownership invariants. Instead, we need to realize
that %1 is dominated by a dead end block so we may not have a
destroy_value upon it meaning we should just not insert the end_borrow
here. If we have a destroy_value upon it (since we did not get rid of a
destroy_value), then we will still get rid of the destroy_value if we are
going to optimize this, so we are still correct.
rdar://68096662
Just doing this quickly to prevent the bots from breaking. We still were using
the default instModCallbacks that do remove/RAUW/etc, but do not update data
structures.
SemanticARCOpts for maintainance reasons is becoming a series of small
optimization passes with a little pass manager that runs them. Given that, I
want to be able to be able to run subsets of these transforms for testing
reasons while normally running them in series.
This is in preparation for landing the coroutine lifetime extender and the
auto-coroutinizer.
This patch moves state from the main SemanticARCOptVisitor struct to instead be
on a context object. Sub-transformations should not need to know about the
visitor since how it processes things is orthogonal from the transformations
themselves.
This is so I can move individual sub-optimizations on SemanticARCOptVisitor into
their own files. So for instance, there will be one file containing the load
[copy] optimization and another containing the phi optimization, etc.
SemanticARCOpts keeps on growing with various optimizations attached to a single
"optimization" manager. Move it to its own folder in prepation for splitting it
into multiple different optimizations and utility files.
