This is a straightforward port of MemCpyOpt to MemorySSA following
the approach of D26739. MemDep queries are replaced with MSSA queries
without changing the overall structure of the pass. Some care has
to be taken to account for differences between these APIs
(MemDep also returns reads, MSSA doesn't).
Differential Revision: https://reviews.llvm.org/D89207
CapturesBefore tracker has an overly restrictive dominates check when
the `BeforeHere` and the capture point are in different basic blocks.
All we need to check is that there is no path from the capture point
to `BeforeHere` (which is less stricter than the dominates check).
See added testcase in one of the users of CapturesBefore.
Reviewed-By: jdoerfert
Differential Revision: https://reviews.llvm.org/D90688
When performing a call slot optimization to a GEP destination, it
will currently usually fail, because the GEP is directly before the
memcpy and as such does not dominate the call. We should move it
above the call if that satisfies the domination requirement.
I think that a constant-index GEP is the only useful thing to move
here, as otherwise isDereferenceablePointer couldn't look through
it anyway. As such I'm not trying to generalize this further.
Differential Revision: https://reviews.llvm.org/D89623
This adds an -enable-memcpyopt-memoryssa option that currently does
nothing apart from requiring MSSA as a dependency. The tests are
split to run both with the option disabled and enabled. I went with
this rather than the separate directory DSE uses, as I found it
convenient to have a direct side-by-side comparison of differences.
Differential Revision: https://reviews.llvm.org/D89206
The call slot optimization has some home-grown code for checking
whether the destination is dereferenceable. Replace this with the
generic isDereferenceableAndAlignedPointer() helper.
I'm not checking alignment here, because that is currently handled
separately and may be an enforced alignment for allocas. The clean
way of integrating that part would probably be to accept a callback
in isDereferenceableAndAlignedPointer() for the actual isAligned check,
which would then have a chance to use an enforced alignment instead.
This allows the destination to be a GEP (among other things), though
the two open TODOs may prevent it from working in practice.
Differential Revision: https://reviews.llvm.org/D88805
When performing call slot optimization for a non-local destination,
we need to check whether there may be throwing calls between the
call and the copy. Otherwise, the early write to the destination
may be observable by the caller.
This was already done for call slot optimization of load/store,
but not for memcpys. For the sake of clarity, I'm moving this check
into the common optimization function, even if that does need an
additional instruction scan for the load/store case.
As efriedma pointed out, this check is not sufficient due to
potential accesses from another thread. This case is left as a TODO.
Differential Revision: https://reviews.llvm.org/D88799
Apparently querying dereferenceability of array allocations is
being intentionally penalized (https://reviews.llvm.org/D41398),
so avoid using them in tests.
The case of a destination read between call and memcpy was not
covered anywhere (but is handled correctly).
However, a potentially throwing call between the call and the
memcpy appears to be miscompiled.
Nikita Popov