This is phase-1 of switching from llvm::Optional to std::optional in the
next rebranch. llvm::Optional was removed from upstream LLVM, so we need
to migrate off rather soon. On Darwin, std::optional, and llvm::Optional
have the same layout, so we don't need to be as concerned about ABI
beyond the name mangling. `llvm::Optional` is only returned from one
function in
```
getStandardTypeSubst(StringRef TypeName,
bool allowConcurrencyManglings);
```
It's the return value, so it should not impact the mangling of the
function, and the layout is the same as `std::optional`, so it should be
mostly okay. This function doesn't appear to have users, and the ABI was
already broken 2 years ago for concurrency and no one seemed to notice
so this should be "okay".
I'm doing the migration incrementally so that folks working on main can
cherry-pick back to the release/5.9 branch. Once 5.9 is done and locked
away, then we can go through and finish the replacement. Since `None`
and `Optional` show up in contexts where they are not `llvm::None` and
`llvm::Optional`, I'm preparing the work now by going through and
removing the namespace unwrapping and making the `llvm` namespace
explicit. This should make it fairly mechanical to go through and
replace llvm::Optional with std::optional, and llvm::None with
std::nullopt. It's also a change that can be brought onto the
release/5.9 with minimal impact. This should be an NFC change.
This updates how we model reborrow's lifetimes for ownership verification.
Today we follow and combine a borrow's lifetime through phi args as well.
Owned values lifetimes end at a phi arg. This discrepency in modeling
lifetimes leads to the OwnershipVerifier raising errors incorrectly for
cases such as this, where the borrow and the base value do not dominate
the end_borrow:
bb0:
cond_br undef, bb1, bb2
bb1:
%copy0 = copy_value %0
%borrow0 = begin_borrow %copy0
br bb3(%borrow0, %copy0)
bb2:
%copy1 = copy_value %1
%borrow1 = begin_borrow %copy1
br bb3(%borrow1, %copy1)
bb3(%borrow, %baseVal):
end_borrow %borrow
destroy_value %baseVal
This PR adds a new ReborrowVerifier. The ownership verifier collects borrow's
lifetime ending users and populates the worklist of the ReborrowVerifier
with reborrows and the corresponding base value.
ReborrowVerifier then verifies that the lifetime of the reborrow is
within the lifetime of the base value.
This is doing a few things with a simple change to use a builder:
1. It cleans up how we emit errors so we have a builder object that constructs
errors. The errors then just become dumb POD data that the builder vends to
callers that via the boolean values describe what errors were found.
2. Now that we have one place where we are actually emitting these errors, I
cleaned up how we emit the errors by normalizing the output so function names
are quoted the same.
3. I changed our error emission so that we emit a unique count of the errors as
we emit them. This makes it so that our pattern matching is much more robust
against weird pattern match errors that can be difficult to debug due to the
errors having unrelated test cases/file check patterns bleed
together. Before/end checks eliminate this problem. I updated all of the
relevant test cases.
The reason /why/ I am doing this though is that I am going to be adding support
to the LinearLifetimeChecker for flagging objects that are outside of the
lifetime that we are verifying (meaning either before or after). This is going
to cause me to need to track /all/ non consuming uses when performing linear
lifetime checks and thus most likely emit more errors. I was finding it to be
difficult to update the current tests given the state of the world before this
patch, so I was inspired to clean this up to satisfy practical as well as debt
concerns.
HOW THIS WAS DONE: I did this by refactoring the last usages of checkValue into
a higher level API that uses checkValue as an implementation detail:
completeConsumingUseSet(...). All of these places in
MandatoryInlining/PredictableMemOpts all wanted behavior where we complete a set
of consuming uses for a value, detecting if the consuming use is in a different
loop nest from the value.
WHY DO THIS: The reason why I wanted to do this is that checkValue is a lower
level API that drives the actual low level computation. We shouldn't expose its
interface to the LinearLifetimeChecker's users since it is our own private
implementation detail that also has some sharp edges.
AN ADDITIONAL BENEFIT: Additionally by hiding the declaration of checkValue, the
last public use of LinearLifetimeError and ErrorBehaviorKind was not
private. This allowed me to then move the declarations of those two to a private
header (./lib/SIL/LinearLifetimeCheckerPrivate.h) and make their declarations
private to LinearLifetimeChecker as well. As such, I renamed them to
LinearLifetimeChecker::Error and LinearLifetimeChecker::ErrorBehaviorKind.
The only reason why BranchPropagatedUser existed was because early on in SIL, we
weren't sure if cond_br should be able to handle non-trivial values in
ossa. Now, we have reached the point where we have enough experience to make the
judgement that it is not worth having in the representation due to it not
holding its weight.
Now that in ToT we have banned cond_br from having non-trivial operands in ossa,
I can just eliminate BranchPropagatedUser and replace it with the operands that
we used to construct them!
A few notes:
1. Part of my motiviation in doing this is that I want to change LiveRange to
store operands instead of instructions. This is because we are interested in
being able to understand the LiveRange at a use granularity in cases where we
have multiple operands. While doing this, I discovered that I needed
SILInstructions to use the Linear Lifetime Checker. Then I realized that now was
the time to just unwind BranchPropagatedUser.
2. In certain places in SemanticARCOpts, I had to do add some extra copies to
transform arrays of instructions from LiveRange into their operand form. I am
going to remove them in a subsequent commit when I change LiveRange to work on
operands. I am doing this split to be incremental.
3. I changed isSingleInitAllocStack to have an out array of Operand *. The only
user of this code is today in SemanticARCOpts and this information is fed to the
Linear Lifetime Checker, so I needed to do it.
OwnershipUtils.h is growing a bit and I want to use it to store abstract higher
level utilities for working with ossa. LinearLifetimeChecker is just a low level
detail of that, so it makes sense to move it out now.
