Needed to diagnose MutableSpan and OutputSpan.
For now, simply remove the bailout and TODO. The next change will introduce more
logic to force a diagnostic error in rare cases that can't be handled completely.
Fixes rdar://143584461 (Extended exclusive borrow issues with
MutableSpan and OutputSpan)
Functional changes:
Improved modeling of dependence on local variable scopes.
For nested modify->read accesses, only extend the read accesses.
Avoid making a read access dependent on an inout argument.
The following needs to be an error to prevent span storage from being modified:
@lifetime(owner)
foo(owner: inout Owner) -> Span {
owner.span
}
Improve usability of borrowing trivial values (UnsafePointer). Allow:
let span = Span(buffer.baseAddress)
Ignore access scopes for trivial values.
Structural changes:
Delete the LifetimeDependenceUseDefWalker.
Encapsulate all logic for variable introducers within the LifetimeDependenceInsertion pass. Once mark_dependence instructions are inserted, no subsequent pass needs to think about the "root" of a dependence.
Fixes: rdar://142451725 (Escape analysis fails with mutations)
If the base value of a mark_dependence is an address, that memory location must be initialized at the mark_dependence.
This requires that the mark_dependence is considered to read from the base address.
If the memory location depends on something, insert a dependency for the loaded value:
```
%2 = mark_dependence %1 on %0
%3 = load %2
```
->
```
%2 = mark_dependence %1 on %0 // not needed anymore, can be removed eventually
%3 = load %2
%4 = mark_dependence %3 on %0
// replace %3 with %4
```
Memory effects of begin_access are only defined to prevent the optimizer moving loads and stores across a begin_access.
But those memory effects are not relevant for RedundantLoadElimination
This is necessary to fix a recent OSSA bug that breaks common occurrences on
mark_dependence [nonescaping]. Rather than reverting that change above, we make
forward progress toward implicit borrows scopes, as was the original intention.
In the near future, all InteriorPointer instructions will create an implicit
borrow scope. This means we have the option of not emitting extraneous
begin/end_borrow instructions around intructions like ref_element_addr,
open_existential, and project_box. After that, we can also migrate
GuaranteedForwarding instructions like tuple_extract and struct_extract.
We use the formal source type do decide whether a checked_cast_br is
known to succeed/fail. If we don't update it we loose that optimization
That is:
```
checked_cast_br AnyObject in %2 : X to X, bb1, bb2
```
Will not be simplified even though the operand and the destintation type
matches.
The problem with `is_escaping_closure` was that it didn't consume its operand and therefore reference count checks were unreliable.
For example, copy-propagation could break it.
As this instruction was always used together with an immediately following `destroy_value` of the closure, it makes sense to combine both into a `destroy_not_escaped_closure`.
It
1. checks the reference count and returns true if it is 1
2. consumes and destroys the operand
When an optimization updates borrowed-from instruction it might be necessary to remove the old enclosing values from the borrowed-from instructions.
An optimization might transform the SIL in a way that an existing enclosing value is not valid anymore.
Fixes a compiler crash:
rdar://142991910
Global let-variables are immutable, except in functions which initialize them.
This brings back handling of global let-variables in alias analysis, which was removed in the previous commit.
Although a let-field can never be mutated, a release or consume of the class must be considered as writing to such a field.
This change removes the special handling of let-fields in two places, where they don't belong.
Class fields are handled by ImmutableScope anyway.
Handling of global let-variable is temporarily removed by this commit.
Fixes a miscompile.
rdar://142996449
Record a forwarding mark_dependence as a local access. This is necessary because
we now emit a mark_dependence for @out arguments, which will be the starting
point for diagnostics:
%out = alloc_stack
apply %f(%owned, %out) : $(Owner) -> @lifetime(borrow 0) @out View
%unused = mark_dependence [unresolved] %out on %owner
%dependentValue = load %out
This mark_dependence has no uses. Instead, it simply records the dependency of
the in-memory value on the owner. Consequently, simply walking the uses of
LifetimeDependence.dependentValue does fails to diagnose any escapes. Instead,
if the dependentValue is an address-type mark_dependence, treat it as a local
access to the address that it forwards. Then we find any reachable uses of that
local variable as a potential escape.
Fixes rdar://143040479
(Borrow diagnostics not triggered for @out return values)
Ignore marker instructions for the purpose of determining whether a store is a
full assignment:
%a = alloc_stack
%m = moveonlywrapper_to_copyable_addr %a
store %0 to [init] %m // <=== full assignemt
Unlike @in, treat @in_guaranteed like a caller-side dependence
scope because there is not need to look for the end of the lifetime in the
current function.
Completely fixes rdar://142847915 (Crash during lifetime checking
while building new swift standard library `Span`-related features)
For a lifetime dependent call that depends on a temporary store_borrow, the
generated mark_dependendence should be on the stored value, not the stack
location.
%temp = alloc_stack $AnyObject
%sb = store_borrow %arg to %temp
apply %10(%out, %sb)
mark_dependence [unresolved] %out on %arg
end_borrow %sb
Fixes rdar://142847915 (Crash during lifetime checking while
building new swift standard library `Span`-related features)
This encourages AccessPathWalker clients to handle enclosing mark_deps. In
some cases, it is necessary. The accessBaseWithScopes API now provides both
nested begin_access and mark_dependence.
A `unchecked_enum_data` which extracts a trivial payload out of a non-trivial enum ends the lifetime of its owned operand.
Fixes an ownership verification error
rdar://142644731
