Adding `move_value [lexical]` and `begin_borrow [lexical]` should happen
all the time at this point. Remove the ability to omit these
instructions and update the corresponding tests.
Mandatory copy propagation was primarily a stop-gap until lexcial
lifetimes were implemented. It supposedly made variables lifetimes
more consistent between -O and -Onone builds. Now that lexical
lifetimes are enabled, it is no longer needed for that purpose (and
will never satisfactorily meet that goal anyway).
Mandatory copy propagation may be enabled again later as a -Onone "
optimization. But that requires a more careful audit of the effect on
debug information.
For now, it should be disabled.
The effect of passing -enable-copy-propagation is both to enable the
CopyPropagation pass to shorten object lifetimes and also to enable
lexical lifetimes to ensure that object lifetimes aren't shortened while
a variable is still in scope and used.
Add a new flag, -enable-lexical-borrow-scopes=true to override
-enable-copy-propagation's effect (setting it to ::ExperimentalLate) on
SILOptions::LexicalLifetimes that sets it to ::Early even in the face of
-enable-copy-propagation. The old flag -disable-lexical-lifetimes is
renamed to -enable-lexical-borrow-scopes=false but continues to set that
option to ::Off even when -enable-copy-propagation is passed.
`willreturn`
This function attribute indicates that a call of this function will
either exhibit undefined behavior or comes back and continues execution
at a point in the existing call stack that includes the current
invocation. Annotated functions may still raise an exception, i.a.,
`nounwind` is not implied. If an invocation of an annotated function does
not return control back to a point in the call stack, the behavior is
undefined.
I conservatively did not assume that the deinit is willreturn therefore
release like operations are not marked `willreturn`.
rdar://73574236
Only relevant for -Xfrontend -enable-copy-propagation in debug builds.
It's only an experimental mode for now for shrinking lifetimes while
providing lldb an easy way to report a friendly error.
Goals:
- two repetitive digits that don't look like garbage
- less than a page, so it can never be a real pointer
- reserve as many low bits as possible so it can't be a tagged pointer
- not used by any other memory smashers
0x440 is 64-byte aligned which is plenty for any conceivable object
allocator.
