This is not nice, but it's the best transient solution possible,
and is better than just duplicating the whole function.
The problem is, this function is widely used,
and it is not at all obvious that all the users
could be painlessly switched to operate on DomTreeUpdater,
and somehow i don't feel like porting all those users first.
This function is one of last three that not operate on DomTreeUpdater.
This is not nice, but it's the best transient solution possible,
and is better than just duplicating the whole function.
The problem is, this function is widely used,
and it is not at all obvious that all the users
could be painlessly switched to operate on DomTreeUpdater,
and somehow i don't feel like porting all those users first.
This function is one of last three that not operate on DomTreeUpdater.
When we are adding edges to the terminator and potentially turning it
into a switch (if it wasn't already), it is possible that the
case we're adding will share it's destination with one of the
preexisting cases, in which case there is no domtree edge to add.
Indeed, this change does not have a test coverage change.
This failure has been exposed in an existing test coverage
by a follow-up patch that switches to lazy domtreeupdater mode,
and removes domtree verification from
SimplifyCFGOpt::simplifyOnce()/SimplifyCFGOpt::run(),
IOW it does not appear feasible to add dedicated test coverage here.
BB was already always branching to EdgeBB, there is no edge to add.
Indeed, this change does not have a test coverage change.
This failure has been exposed in an existing test coverage
by a follow-up patch that switches to lazy domtreeupdater mode,
and removes domtree verification from
SimplifyCFGOpt::simplifyOnce()/SimplifyCFGOpt::run(),
IOW it does not appear feasible to add dedicated test coverage here.
SI is the terminator of BB, so the edge we are adding obviously already existed.
Indeed, this change does not have a test coverage change.
This failure has been exposed in an existing test coverage
by a follow-up patch that switches to lazy domtreeupdater mode,
and removes domtree verification from
SimplifyCFGOpt::simplifyOnce()/SimplifyCFGOpt::run(),
IOW it does not appear feasible to add dedicated test coverage here.
Currently SimplifyCFG drops the debug locations of 'bonus' instructions.
Such instructions are moved before the first branch. The reason for the
current behavior is that this could lead to surprising debug stepping,
if the block that's folded is dead.
In case the first branch and the instructions to be folded have the same
debug location, this shouldn't be an issue and we can keep the debug
location.
Reviewed By: vsk
Differential Revision: https://reviews.llvm.org/D93662
I have added it in d15d81c because it *seemed* correct, was holding
for all the tests so far, and was validating the fix added in the same
commit, but as David Major is pointing out (with a reproducer),
the assertion isn't really correct after all. So remove it.
Note that the d15d81c still fine.
If the predecessor is a switch, and BB is not the default destination,
multiple cases could have the same destination. and it doesn't
make sense to re-process the predecessor, because we won't make any changes,
once is enough.
I'm not sure this can be really tested, other than via the assertion
being added here, which fires without the fix.
One would hope that it would have been already canonicalized into an
unconditional branch, but that isn't really guaranteed to happen
with SimplifyCFG's visitation order.
... which requires not removing a DomTree edge if the switch's default
still points at that destination, because it can't be removed;
... and not processing the same predecessor more than once.
... which requires not deleting an edge that just got deleted,
because we could be dealing with a block that didn't go through
ConstantFoldTerminator() yet, and thus has a degenerate cond br
with matching true/false destinations.
Notably, this doesn't switch *every* case, remaining cases
don't actually pass sanity checks in non-permissve mode,
and therefore require further analysis.
Note that SimplifyCFG still defaults to not preserving DomTree by default,
so this is effectively a NFC change.
This is NFC since SimplifyCFG still currently defaults to not preserving DomTree.
SimplifyCFGOpt::simplifyOnce() is only be called from SimplifyCFGOpt::run(),
and can not be called externally, since SimplifyCFGOpt is defined in .cpp
This avoids some needless verifications, and is thus a bit faster
without sacrificing precision.
We only need to remove non-TrueBB/non-FalseBB successors,
and we only need to do that once. We don't need to insert
any new edges, because no new successors will be added.
There is a number of transforms in SimplifyCFG that take DomTree out of
DomTreeUpdater, and do updates manually. Until they are fixed,
user passes are unable to claim that PDT is preserved.
Note that the default for SimplifyCFG is still not to preserve DomTree,
so this is still effectively NFC.
This pretty much concludes patch series for updating SimplifyCFG
to preserve DomTree. All 318 dedicated `-simplifycfg` tests now pass
with `-simplifycfg-require-and-preserve-domtree=1`.
There are a few leftovers that apparently don't have good test coverage.
I do not yet know what gaps in test coverage will the wider-scale testing
reveal, but the default flip might be close.
