This fits the name of the check better. The reason I am doing this renaming is
b/c I am going to add a nonconsumable but assignable check for
global_addr/ref_element_addr/captures with var semantics.
Specifically, previously if we emitted an error we just dumped all of the
consuming uses. Now instead for each consuming use that needs a copy, we perform
a search for a specific boundary use (consuming or non-consuming) that is
reachable from the former and emit a specialized error for it. Thus we emit for
the two consuming case the normal consumed twice error, and now for
non-consuming errors we emit the "use after consume" error.
For those who are unaware, CanonicalizeOSSALifetime::canonicalizeValueLifetime()
is really a high level driver routine for the functionality of
CanonicalizeOSSALifetime that computes liveness and then rewrites copies using
boundary information. This change introduces splits the implementation of
canonicalizeValueLifetime into two parts: a first part called computeLiveness
and a second part called rewriteLifetimes. Internally canonicalizeValueLifetime
still just calls these two methods.
The reason why I am doing this is that it lets the move only object checker use
the raw liveness information computed before the rewriting mucks with the
analysis information. This information is used by the checker to compute the raw
liveness boundary of a value and use that information to determine the list of
consuming uses not on the boundary, consuming uses on the boundary, and
non-consuming uses on the boundary. This is then used by later parts of the
checker to emit our errors.
Some additional benefits of doing this are:
1. I was able to eliminate callbacks in the rewriting stage of
CanonicalOSSALifetimes which previously gave the checker this information.
2. Previously the move checker did not have access to the non-consuming boundary
uses causing us to always fail appropriately, but sadly not emit a note showing
the non-consuming use. I am going to wire this up in a subsequent commit.
The other change to the implementation of the move checker that this caused is
that I needed to add an extra diagnostic check for instructions that consume the
value twice or consume the value and use the value. The reason why this must be
done is that liveness does not distinguish in between different operands on the
same instruction meaning such an error would be lost.
NOTE: The additional errors that are occuring in the move only object checker is
b/c I tweaked checkDestructureUsesOnBoundary so that when it detects an error it
continues instead of returns. This ensures that we get more that we emit errors
for multiple violations instead of just the first one.
rdar://104900171
This enables us to emit the appropriate error for consuming uses of fields and
also causes us to eliminate copies exposed by using fields of a move only type
in a non-consuming way.
rdar://103271138
