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.
