The utility was computing the boundary of the `copy_value` with the
`end_borrow`s as users. But there may not be any `end_borrow`s thanks
to dead-ends. Instead, consider both guaranteed users and any
`end_borrow`s.
Fixes a miscompile in CSE.
rdar://158353230
CSE "looks through" ownership operations, which can lead to problematic substitutions. This fix cleans up owned operands even when the newly substituted value has no ownership.
For example:
%0 = enum $Optional<Interface>, #Optional.none!enumelt
%1 = move_value [lexical] %0
%2 = enum $Optional<Interface>, #Optional.none!enumelt
%3 = struct $EndpointCommon (%2)
%4 = struct $EndpointCommon (%1)
CSE combines the two .none enums:
%0 = enum $Optional<Interface>, #Optional.none!enumelt
%2 = enum $Optional<Interface>, #Optional.none!enumelt
Then combines the two structs:
%3 = struct $EndpointCommon (%2)
%4 = struct $EndpointCommon (%1)
Leaving a dead move_value:
%1 = move_value [lexical] %0
which is invalid OSSA. Now, when replacing the owned struct, we add destroys for its operands.
Fixes rdar://156431548 Error! Found a leaked owned value that was never consumed.
To handle borrowing operands that produce a dependence value but do not create a
nested borrow scope. This includes non-reborrow borrowed-from and guaranteed
mark_dependence [nonescaping].
CSE uses OSSA rauw which creates copies and copies that are created to optimize
across borrow scopes are unoptimizable. This PR avoids this situation for now.
To find if all the uses are within a guaranteed value, we should find all borrow introducers.
swift::findOwnershipReferenceAggregate looks only through forwarding operations with single operands.
For simplicity, continue using swift::findOwnershipReferenceAggregate, but return false when it does
not find a borrow introducer.
This is needed after running the SSAUpdater for an existing OSSA value, because the updater can
insert unnecessary phis in the middle of the original liverange which breaks up the original
liverange into smaller ones:
```
%1 = def_of_owned_value
%2 = begin_borrow %1
...
br bb2(%1)
bb2(%3 : @owned $T): // inserted by SSAUpdater
...
end_borrow %2 // use after end-of-lifetime!
destroy_value %3
```
It's not needed to run this utility if SSAUpdater is used to create a _new_ OSSA liverange.
Compute, update and handle borrowed-from instruction in various utilities and passes.
Also, used borrowed-from to simplify `gatherBorrowIntroducers` and `gatherEnclosingValues`.
Replace those utilities by `Value.getBorrowIntroducers` and `Value.getEnclosingValues`, which return a lazily computed Sequence of borrowed/enclosing values.
For years, optimizer engineers have been hitting a common bug caused by passes
assuming all SILValues have a parent function only to be surprised by SILUndef.
Generally we see SILUndef not that often so we see this come up later in
testing. This patch eliminates that problem by making SILUndef uniqued at the
function level instead of the module level. This ensures that it makes sense for
SILUndef to have a parent function, eliminating this possibility since we can
define an API to get its parent function.
rdar://123484595
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.
Add TermInst::forwardedOperand.
Add SILArgument::forwardedTerminatorResultOperand. This API will be
moved into a proper TerminatorResult abstraction.
Remove getSingleTerminatorOperand, which could be misused because it's
not necessarilly forwarding ownership.
Remove the isTransformationTerminator API, which is not useful or well
defined.
Rewrite several instances of complex logic to handle block arguments
with the simple terminator result API. This defines away potential
bugs where we don't detect casts that perform implicit conversion.
Replace uses of the SILPhiArgument type and code that explicitly
handle block arguments. Control flow is irrelevant in these
situations. SILPhiArgument needs to be deleted ASAP. Instead, use
simple APIs like SILArgument::isTerminatorResult(). Eventually this
will be replaced by a TerminatorResult type.
First restore the basic PrunedLiveness abstraction to its original
intention. Move code outside of the basic abstraction that polutes the
abstraction and is fundamentally wrong from the perspective of the
liveness abstraction.
Most clients need to reason about live ranges, including the def
points, not just liveness based on use points. Add a PrunedLiveRange
layer of types that understand where the live range is
defined. Knowing where the live range is defined (the kill set) helps
reliably check that arbitrary points are within the boundary. This
way, the client doesn't need to be manage this on its own. We can also
support holes in the live range for non-SSA liveness. This makes it
safe and correct for the way liveness is now being used. This layer
safety handles:
- multiple defs
- instructions that are both uses and defs
- dead values
- unreachable code
- self-loops
So it's no longer the client's responsibility to check these things!
Add SSAPrunedLiveness and MultiDefPrunedLiveness to safely handle each
situation.
Split code that I can't figure out into
DiagnosticPrunedLiveness. Hopefully it will be deleted soon.
Andy some time ago already created the new API but didn't go through and update
the old occurences. I did that in this PR and then deprecated the old API. The
tree is clean, so I could just remove it, but I decided to be nicer to
downstream people by deprecating it first.
This fix unblocks unrelated optimizer commits. A unit test will be
introduced with those commits.
The RAUW utility does not correctly handle reborrows. It is in the
middle of being rewritten. For now, simply bail out since this isn't
an important case to optimize.
RAUWing a lexical value with a non-lexical value is illegal because it
would result in the value's lifetime being shortened without regard to
deinit barriers. RAUWing _with_ a lexical value is LEGAL so long as
doing so doesn't extend its lifetime.
Replacing all uses of a lexical value with another value, even another
lexical value, may change the lifetime of the value in ways that aren't
permitted for a lexical lifetime.
SemanticARCOptVisitor::performGuaranteedCopyValueOptimization was
converting this SIL
%borrow = begin_borrow %copiedValue
%copy = copy_value %borrow
%borrowCopy = begin_borrow %copy
end_borrow %borrow
end_borrow %borrowCopy
destroy_value %copy
// something something
unreachable
into
%borrow = begin_borrow %copiedValue
%innerBorrow = begin_borrow %borrow
end_borrow %borrow
end_borrow %innerBorrow
// something something
unreachable
Dead-end blocks are simply irrelevant for this
optimization. Unfortunately, there were multiple layers of attempted
workarounds that were hiding the real problem, except in rare cases.
Thanks Nate Chandler for reducing the test.
This cleans up 90 instances of this warning and reduces the build spew
when building on Linux. This helps identify actual issues when
building which can get lost in the stream of warning messages. It also
helps restore the ability to build the compiler with gcc.
The InstructionDeleter needs to move the callbacks during construction
to prevent the client code from using the old callbacks.
Fixes iterator invalidation bugs.
Call findOwnershipReferenceRoot when checking for guaranteed values
from SILFunctionArgument.
TODO: We need to add a component path to a reference root abstraction
to handle references that come from a struct_extract or tuple_extract.
Required to fix SILCombine.
Divide the logic into smaller pieces. This allows passes to check for
replaceability before generating the replacement value.
Preparation for simplifying OSSA utilities into smaller logical
components making them flexibile and allowing improvements to be
staged in.
Preparation for rewriting non-trivial terminators and generalizing
support for guaranteed phis.
Add guaranteedUsePoints to the RAUW context. This will replace ALL
existing context book-keeping once the old code is deleted.
Introduce a borrowCopyOverScope entry point to handle extending
lifetime over a BorrowedValue. This simply uses the
BorrowedLifetimeExtender.
Introduce higher-level APIs:
- borrowOverValue to extened over a guaranteedValue
- borrowOverSingleUse to extened over a single guaranteed use
These replace both createPlusZeroBorrow and createPlusOneBorrow.
Update RAUW-ctor, RAUW::handleUnowned, and replaceAddressUses to use
the new API.
Restructure RAUW::canFixUpOwnershipForRAUW. Simply use
findInnerTransitiveGuaranteedUses.
Replace RAUW::handleGuaranteed and rewriteReborrows with
OLE::borrowOverValue.
Use the BorrowedLifetimeExtender utility to handle all situations
correctly.
TODO: createPlusOneBorrow can be completely removed, and a massive
amount of confusing/incomplete code can be deleted in a follow-up
commit.
Without introducing any new borrow scopes or owned lifetimes.
Top-level APIs:
- extendOwnedLifetime()
- extendLocalBorrow()
New utilitiy: GuaranteedOwnershipExtension.
This is a simple utility to determine whether new uses can be added to
an existing guaranteed value. It reports the kind of transformation
needed and performs the transformation if requested. If transformation
is needed, it simply calls one of the two top-level APIs.
