Owned lifetime canonicalization bails on move-only values.
Previously, though, every value that was fed to canonicalization was
then attempted to be deleted. For dead move-only values, the result
could be to shorten move-only lifetimes, which is illegal per language
rules.
Here, this is fixed by not attempting to delete owned values for which
canonicalization bailed.
rdar://114323803
To eliminate copies which become newly spurious, Mem2Reg canonicalizes
the lifetimes of values that are stored and of newly introduced phis
after rewriting.
It's possible, however, for the values that are stored to be deleted
during canonicalization if a value and its copy are both stored to the
address. Such values must not be canonicalized. So check whether
values have been erased before canonicalizing them.
rdar://113762355
There is no implementation to handle insertion of compensating releases of the non-trivial store's src for this case.
This never really happens, because destructor analysis is very limited and we end up banning alloc_ref with ref count instructions.
It is necessary for opaque values where for casts that will newly start
out as checked_cast_brs and be lowered to checked_cast_addr_brs, since
the latter has the source formal type, IRGen relies on being able to
access it, and there's no way in general to obtain the source formal
type from the source lowered type.
Corrected the comments describing what the
`promoteSingleBlockAllocation` and `promoteMultiBlockAllocation`
functions do since they were no longer accurate.
Previously there were the functions `promoteSingleAllocation` and
`removeSingleBlockAllocation`. The distinction between these based on
the name alone is a bit subtle. Shortened the name of
`promoteSingleAllocation` to `promoteAllocation`.
`std::optional` doesn't have `hasValue` or `getPointer`. Using the
implicit decay to boolean, and grabbing the pointer to the element by
expanding the optional and grabbing the reference address.
llvm::SmallSetVector changed semantics
(https://reviews.llvm.org/D152497) resulting in build failures in Swift.
The old semantics allowed usage of types that did not have an
`operator==` because `SmallDenseSet` uses `DenseSetInfo<T>::isEqual` to
determine equality. The new implementation switched to using
`std::find`, which internally uses `operator==`. This type is used
pretty frequently with `swift::Type`, which intentionally deletes
`operator==` as it is not the canonical type and therefore cannot be
compared in normal circumstances.
This patch adds a new type-alias to the Swift namespace that provides
the old semantic behavior for `SmallSetVector`. I've also gone through
and replaced usages of `llvm::SmallSetVector` with the
`Swift::SmallSetVector` in places where we're storing a type that
doesn't implement or explicitly deletes `operator==`. The changes to
`llvm::SmallSetVector` should improve compile-time performance, so I
left the `llvm::SmallSetVector` where possible.
The new implementation has several benefits compared to the old C++ implementation:
* It is significantly simpler. It optimizes each load separately instead of all at once with bit-field based dataflow.
* It's using alias analysis more accurately which enables more loads to be optimized
* It avoids inserting additional copies in OSSA
The algorithm is a data flow analysis which starts at the original load and searches for preceding stores or loads by following the control flow in backward direction.
The preceding stores and loads provide the "available values" with which the original load can be replaced.
This patch migrates the compiler off of the deprecated LLVM APIs where I
can.
- APInt::getAllOnesValue -> APInt::getAllOnes
- APInt::getNullValue -> APInt::getZero
- APInt::isNullValue -> APInt::isZero
- APInt::getMinSignedBits -> APInt::getSignificantBits
- clang::Module::submodule_{begin,end} -> clang::Module::submodules
When determining where to destroy a captured alloc_box, the frontier of
the capturing partial_apply is computed. Previously, that computation
just used the uses of the partial_apply. If the partial_apply were
moved and the original destroyed before the apply, however, the result
would be a miscompile where the destroy_addr/dealloc_stack for the
alloc_stack to which the alloc_box was promoted was destroyed before the
apply of the closure which used the address.
When determining where to destroy a captured alloc_box, the frontier of
the capturing partial_apply is computed. Previously, that computation
just used the uses of the partial_apply. If the partial_apply were
copied and the original destroyed before the apply, however, the result
would be a miscompile where the destroy_addr/dealloc_stack for the
alloc_stack to which the alloc_box was promoted was destroyed before the
apply of the closure which used the address.
This is an improvement of #67031 which avoids deleting the closure function
body during AllocBoxToStack, which still breaks pass invariants by modifying
functions other than the currently-analyzed function. As a function pass,
AllocBoxToStack also doesn't really know with certainty whether the original
closure function is unused after stack promotion or not. We still want to
eliminate the original when it may contain invalid SIL for move-only values
that rely on the escape analysis for correct semantics, so rather than mark the
original function to be *ignored* during move-only checking, mark it to be
*deleted* by move-only checking if the function is in fact unused at that
point.
If the marked function is still used, we let it pass through move-only
checking normally, which may cause redundant diagnostics but is the right
thing to do since code is still potentially using the closure with escaping
semantics. We should rearrange things to make this situation impossible in
the future.
rdar://110675352
The old C++ pass didn't catch a few cases.
Also:
* The new pass is significantly simpler: it doesn't perform dataflow for _all_ memory locations at once using bitfields, but handles each store separately. (In both implementations there is a complexity limit in place to avoid quadratic complexity)
* The new pass works with OSSA
