When converting a store into a memset, we currently insert the new
MemoryDef after the store MemoryDef, which requires all uses to be
renamed to the new def using a whole block scan. Instead, we can
insert the new MemoryDef before the store and not rename uses,
because we know that the location is immediately overwritten, so
all uses should still refer to the old MemoryDef. Those uses will
get renamed when the old MemoryDef is actually dropped, which is
efficient.
I expect something similar can be done for some of the other MSSA
updates in MemCpyOpt. This is an alternative to D107513, at least
for this particular case.
Differential Revision: https://reviews.llvm.org/D107702
The MemorySSA-based implementation has been enabled for a few months
(since D94376). This patch drops the old MDA-based implementation
entirely.
I've kept this to only the basic cleanup of dropping various
conditions -- the code could be further cleaned up now that there
is only one implementation.
Differential Revision: https://reviews.llvm.org/D102113
Attempt to enable MemCpyOpt unconditionally in D104801 uncovered the fact that
there are users that do not expect LLVM to materialize `memset` intrinsic.
While other passes can do that, too, MemCpyOpt triggers it more frequently and
breaks sanitizers and some downstream users.
For now introduce a flag to force-enable the flag and opt-in only CUDA
compilation with NVPTX back-end.
Differential Revision: https://reviews.llvm.org/D106401
- Loads from the constant memory (either explicit one or as the source
of memory transfer intrinsics) won't alias any stores.
Reviewed By: asbirlea, efriedma
Differential Revision: https://reviews.llvm.org/D107605
Rather than blocking the whole MemCpyOpt pass if the libcalls are
not available, only disable creation of new memset/memcpy intrinsics
where only load/stores were used previously. This only affects the
store merging and load-store conversion optimization. Other
optimizations are derived from existing intrinsics, which are
well-defined in the absence of libcalls -- not having the libcalls
just means that call simplification won't convert them to intrinsics.
This is a weaker variation of D104801, which dropped these checks
entirely. Ideally we would not couple emission of intrinsics to
libcall availability at all, but as the intrinsics may be legalized
to libcalls we need to be a bit careful right now.
Differential Revision: https://reviews.llvm.org/D106769
The patch does not depend on the availability of the library functions for
memcpy/memset as it operates on LLVM intrinsics. The optimizations are useful
on the targets that have these functions disabled (e.g. NVPTX & AMDGPU).
Differential Revision: https://reviews.llvm.org/D104801
Apparently, it is legal to use memcpy/memset with pointer types
other than i8*. Prior to 81fcdae68c
this case was silently miscompiled, as the i8 offset calculation
was performed on some other type. Now it would crash due to a
type mismatch. Fix this by inserting an explicit bitcast to i8*.
Currently all AA analyses marked as preserved are stateless, not taking
into account their dependent analyses. So there's no need to mark them
as preserved, they won't be invalidated unless their analyses are.
SCEVAAResults was the one exception to this, it was treated like a
typical analysis result. Make it like the others and don't invalidate
unless SCEV is invalidated.
Reviewed By: asbirlea
Differential Revision: https://reviews.llvm.org/D102032
As a follow-up to D95982, this patch continues unblocking optimizations that are blocked by pseudu probe instrumention.
The optimizations unblocked are:
- In-block load propagation.
- In-block dead store elimination
- Memory copy optimization that turns stores to consecutive memories into a memset.
These optimizations are local to a block, so they shouldn't affect the profile quality.
Reviewed By: wmi
Differential Revision: https://reviews.llvm.org/D100075
This makes the memcpy-memcpy and memcpy-memset optimizations work for
variable sizes as long as they are equal, relaxing the old restriction
that they are constant integers. If they're not equal, the old
requirement that they are constant integers with certain size
restrictions is used.
The implementation works by pushing the length tests further down in the
code, which reveals some places where it's enough that the lengths are
equal (but not necessarily constant).
Differential Revision: https://reviews.llvm.org/D100870
Add MemorySSAWrapperPass as a dependency to MemCpyOptLegacyPass,
since MemCpyOpt now uses MemorySSA by default.
Differential Revision: https://reviews.llvm.org/D98484
This fixes a regression from the MemDep-based implementation:
MemDep completely ignores lifetime.start intrinsics that aren't
MustAlias -- this is probably unsound, but it does mean that the
MemDep based implementation successfully eliminated memcpy's from
lifetime.start if the memcpy happens at an offset, rather than
the base address of the alloca.
Add a special case for the case where the lifetime.start spans the
whole alloca (which is pretty much the only kind of lifetime.start
that frontends ever emit), as we don't need to figure out our exact
aliasing relationship in that case, the whole alloca is dead prior
to the call.
If this doesn't cover all practically relevant cases, then it
would be possible to make use of the recently added PartialAlias
clobber offsets to make this more precise.
If a memset destination is overwritten by a memcpy and the sizes
are exactly the same, then the memset is simply dead. We can
directly drop it, instead of replacing it with a memset of zero
size, which is particularly ugly for the case of a dynamic size.
If the call is readnone, then there may not be any MemoryAccess
associated with the call. Bail out in that case.
This fixes the issue reported at
https://reviews.llvm.org/D94376#2578312.
This enables use of MemorySSA instead of MemDep in MemCpyOpt. To
allow this without significant compile-time impact, the MemCpyOpt
pass is moved directly before DSE (in the cases where this was not
already the case), which allows us to reuse the existing MemorySSA
analysis.
Unlike the MemDep-based implementation, the MemorySSA-based MemCpyOpt
can also perform simple optimizations across basic blocks.
Differential Revision: https://reviews.llvm.org/D94376
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
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
moveUp() moves instructions, so we should move the corresponding
memory accesses as well. We should also move the store instruction
itself: Even though we'll end up removing it later, this gives us
a correct MemoryDef to replace.
The implementation is somewhat more complicated than it should be,
because we also handle the case where P does not have a memory
access due to a degnerate AA pipeline. Hopefully, the need for this
will go away in the future, when the rest of the pass is based on
MSSA.
Differential Revision: https://reviews.llvm.org/D88778
If the memcpy operands are the same (which is allowed since D86815)
then the memcpy is effectively a no-op and the partially overlapping
memset is not dead.
Differential Revision: https://reviews.llvm.org/D89192
MemCpyOpt can shorten a memset if it is later partially overwritten
by a memcpy. It checks that the destination is not read in between,
but we also need to make sure that the destination cannot be observed
via unwinding.
Differential Revision: https://reviews.llvm.org/D89190
MemCpyOpt can hoist stores while load+store pairs into memcpy.
This hoisting can currently result in stores being executed that
weren't guaranteed to execute in the original problem.
Differential Revision: https://reviews.llvm.org/D89154
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
Next to erasing the instruction, we also always want to remove
it from MSSA and MD. Use a common function to do so.
This is a refactoring split out from D26739.
The removal of the cpy instruction is left to the caller of
performCallSlotOptzn(), including the invalidation of MD. Both
call-sites already do this.
Also handle incrementation of NumMemCpyInstr consistently at the
call-site. One of the call-site was already doing this, which
ended up incrementing the statistic twice.
This fix was part of D26739.
If we allow the non-integral pointers to become memset and memcpy, we loose the ability to reason about pointer propagation. This patch is modeled on changes we've carried downstream for a long time, figured it was worth being equally conservative for other users. There is room to refine the semantics and handling here if anyone is motivated.
This patch updates MemCpyOpt to preserve MemorySSA. It uses the
MemoryDef at the insertion point of the builder and inserts the new def
after that def.
In some cases, we just modify a memory instruction. In that case, get
the defining access, then remove the memory access and add a new one.
If the defining access is in a different block, insert a new def at the
beginning of the current block, otherwise after the defining access.
Reviewed By: asbirlea
Differential Revision: https://reviews.llvm.org/D86651
This is a followup to 1ccfb52a61, which made a number of changes
including the apparently innocuous reordering of required passes in
MemCpyOptimizer. This however altered the creation order of BasicAA vs
Phi Values analysis, meaning BasicAA did not pick up PhiValues as a
cached result. Instead if we require MemoryDependence first it will
require PhiValuesAnalysis allowing BasicAA to use it for better results.
I don't claim this is an excellent design, but it fixes a nasty little
regressions where a query later in JumpThreading was getting worse
results.
Differential Revision: https://reviews.llvm.org/D87027
Summary:
Analyses are preserved in MemCpyOptimizer.
Get analyses before running the pass and store the pointers, instead of
using lambdas and getting them every time on demand.
Reviewers: lenary, deadalnix, mehdi_amini, nikic, efriedma
Subscribers: hiraditya, llvm-commits
Tags: #llvm
Differential Revision: https://reviews.llvm.org/D74494
Previously these functions either returned a "changed" flag or a "repeat
instruction" flag, and could also modify an iterator to control which
instruction would be processed next.
Simplify this by always returning a "changed" flag, and handling all of
the "repeat instruction" functionality by modifying the iterator.
No functional change intended except in this case:
// If the source and destination of the memcpy are the same, then zap it.
... where the previous code failed to process the instruction after the
zapped memcpy.
Differential Revision: https://reviews.llvm.org/D81540
If the caller needs to reponsible for making sure the MaybeAlign
has a value, then we should just make the caller convert it to an Align
with operator*.
I explicitly deleted the relational comparison operators that
were being inherited from Optional. It's unclear what the meaning
of two MaybeAligns were one is defined and the other isn't
should be. So make the caller reponsible for defining the behavior.
I left the ==/!= operators from Optional. But now that exposed a
weird quirk that ==/!= between Align and MaybeAlign required the
MaybeAlign to be defined. But now we use the operator== from
Optional that takes an Optional and the Value.
Differential Revision: https://reviews.llvm.org/D80455
Now that load/store alignment is required, we no longer need most
of them. Also switch the getLoadStoreAlignment() helper to return
Align instead of MaybeAlign.
Along the lines of D77454 and D79968. Unlike loads and stores, the
default alignment is getPrefTypeAlign, to match the existing handling in
various places, including SelectionDAG and InstCombine.
Differential Revision: https://reviews.llvm.org/D80044
Nikita Popov