For the longest time we used `AAValueSimplify` and
`genericValueTraversal` to determine "potential values". This was
problematic for many reasons:
- We recomputed the result a lot as there was no caching for the 9
locations calling `genericValueTraversal`.
- We added the idea of "intra" vs. "inter" procedural simplification
only as an afterthought. `genericValueTraversal` did offer an option
but `AAValueSimplify` did not. Thus, we might end up with "too much"
simplification in certain situations and then gave up on it.
- Because `genericValueTraversal` was not a real `AA` we ended up with
problems like the infinite recursion bug (#54981) as well as code
duplication.
This patch introduces `AAPotentialValues` and replaces the
`AAValueSimplify` uses with it. `genericValueTraversal` is folded into
`AAPotentialValues` as are the instruction simplifications performed in
`AAValueSimplify` before. We further distinguish "intra" and "inter"
procedural simplification now.
`AAValueSimplify` was not deleted as we haven't ported the
re-materialization of instructions yet. There are other differences over
the former handling, e.g., we may not fold trivially foldable
instructions right now, e.g., `add i32 1, 1` is not folded to `i32 2`
but if an operand would be simplified to `i32 1` we would fold it still.
We are also even more aware of function/SCC boundaries in CGSCC passes,
which is good.
Fixes: https://github.com/llvm/llvm-project/issues/54981
Clang-format InstructionSimplify and convert all "FunctionName"s to
"functionName". This patch does touch a lot of files but gets done with
the cleanup of InstructionSimplify in one commit.
This is the alternative to the less invasive clang-format only patch: D126783
Reviewed By: spatel, rengolin
Differential Revision: https://reviews.llvm.org/D126889
We can use constant to allow undef and there is no need to force
integers in the API anyway. The user can decide if a non integer
constant is fine or not.
We need to be careful replacing values as call site arguments
(IRPosition::IRP_CALL_SITE_ARGUMENT) is representing a use and not a
value. This patch replaces the interface to take a IR position instead
making it harder to misuse accidentally. It does not change our tests
right now but a follow up exposed the potential footgun.
We used to be very conservative when integer states were merged.
Instead of adding the known range (which is large due to uncertainty)
into the assumed range (which is hopefully small), we can also only
allow to merge in both at the same time into their respective
counterpart. This will ensure we keep the invariant that assumed is part
of known.
When we recreate instructions as part of simplification we need to take
care of debug metadata and replacing the value multiple times. For now,
we handle both conservatively.
When we run the CGSCC pass we should only invest time on the SCC. We can
initialize AAs with information from the module slice but we should not
update those AAs. We make an exception for are call site of the SCC as
they are helpful providing information for the SCC.
Minor modifications to pointer privatization allow us to perform it even
in the CGSCC pass, similar to ArgumentPromotion.
The Attributor, as many other parts in LLVM, uses pointer equivalence
for `llvm::Value`s. This only works as long as `llvm::Value`s are
dynamically unique, or, to be exact, we will never end up with the same
`llvm::Value` representing two dynamic instances. We already provided a
helper to check the former, namely `AA::isDynamicallyUnique`, however we
could not check the latter. In this patch we move the logic into a
separate AA which helps with the growing complexity and use cases. We
also extend the interface to answer the second question rather than the
first. So we do not determine dynamically uniqueness but if we might end
up with the `llvm::Value` describing a different dynamic instance. Note
that the latter is very much tied to the Attributor capabilities to look
through memory, recursion, etc. so we need to update the logic as we go.
We look through loads in the "generic value traversal" and we
consequently don't need to look through them again in AAValueSimplify*.
The test changes stem from the fact that we allowed any simplified
value, incl. non-dynamically unique ones, as long as the underlying
memory was an alloca. This doesn't seem to make sense as allocas do not
protect against dynamically non-unique values. We need to make the
unique check better rather than excluding allocas. That in mind, we can
remove a lot of code by simply relying on the generic value traversal
load look through.
To soften the blow some minor adjustments have been made that allow more
simplification through the now used scheme and some tests have been
given a `norecurse` for now.
With D106397 we ensured that `AAReachability` will not answer queries for
potentially recursive functions. This was necessary as we did not treat
recursion explicitly otherwise. Now that we have
`AA::isPotentiallyReachable` we can make `AAReachability` a purely
intra-procedural AA which does not care about recursion.
`AA::isPotentiallyReachable`, however, does already deal with "going
back" the call graph and can now do so for potentially recursive
functions.
If we ignore droppable users everything only used in llvm.assume (among
other things) is going to be deleted as dead. This is not helpful.
Instead we want to only delete things we actually don't need anymore. A
follow up will deal with loads in a smarter way.
When simplify values we might end up with an instruction from a
different scope or just one that does not dominate the use. If the
instruction can be reproduced without side-effect (incl. UB) we can
now do that. For now this is mostly used for speculatable (intrinsic)
calls but as we learn to make things like arguments or loads available
this will become more powerful.
This will also allow us to remove dead stores more easily in a follow
up.
I didn't dig into this very much because it appears to be totally valid
(especially once these properties can come from attributes instead
of only from hard-coded library functions) for TLI to not be defined,
and nothing broke when I added this check, including with all my other
patches applied.
Differential Revision: https://reviews.llvm.org/D122917
Inline assembly is scary but we need to support it for the OpenMP GPU
device runtime. The new assumption expresses the fact that it may not
have call semantics, that is, it will not call another function but
simply perform an operation or side-effect. This is important for
reachability in the presence of inline assembly.
Differential Revision: https://reviews.llvm.org/D109986
Most intrinsics, especially "default" ones, will not call back into the
IR module. `nocallback` encodes this nicely. As it was not used before,
this patch also makes use of `nocallback` in the Attributor which
results in many more `norecurse` deductions.
Tablegen part is mechanical, test updates by script.
Differential Revision: https://reviews.llvm.org/D118680
There is potential for endless recursion if we try to determine the
underlying objects of a load, just to end up with the load as underlying
object. A proper solution will require us to pass a visited set around.
This will happen as we cleanup genericValueTraversal soon.
Before we used the capture tracker to follow pointer uses, now we do it
explicitly ourselves through the Attributor API. There are multiple
benefits: For one, the boilerplate is cut down by a lot. The class,
potential copies vector, etc. is all not needed anymore. We also do
avoid explicitly looking through memory here, something that was
duplicated and should only live in the `checkForAllUses~ helper. More
importantly, as we do simplifications we need to make sure all parties
are in sync when they reason about uses. The old way did not allow us to
do this but the new one does as every use visiting AA goes through
`checkForAllUses` now..
As replacements will become more complex it is better to have a single
AA responsible for replacing a use. Before this patch AAValueSimplify*
and AAValueSimplifyReturned could both try to replace the returned
value. The latter was marginally better for the old pass manager
when a function was already carrying a `returned` attribute and when
the context of the return instruction was important. The second
shortcoming was resolved by looking for return attributes in the
AAValueSimplifyCallSiteReturned initialization. The old PM impact is
not concerning.
This is yet another step towards the removal of AAReturnedValues, the
very first AA we should now try to eliminate due to the overlapping
logic with value simplification.
There was some ad-hoc handling of liveness and manifest to avoid
breaking CGSCC guarantees. Things always slipped through though.
This cleanup will:
1) Prevent us from manifesting any "information" outside the CGSCC.
This might be too conservative but we need to opt-in to annotation
not try to avoid some problematic ones.
2) Avoid running any liveness analysis outside the CGSCC. We did have
some AAIsDeadFunction handling to this end but we need this for all
AAIsDead classes. The reason is that AAIsDead information is only
correct if we actually manifest it, since we don't (see point 1) we
cannot actually derive/use it at all. We are currently trying to
avoid running any AA updates outside the CGSCC but that seems to
impact things quite a bit.
3) Assert, don't check, that our modifications (during cleanup) modifies
only CGSCC functions.
In an attempt to remove the memory leak we introduced a double free.
The problem was that we allowed a plain copy of the state and it was
actually used. The use was useless, so it is gone now. The copy
constructor is gone as well. The move constructor ensures the Accesses
pointers are owned by a single state, I hope.
Reported by: https://lab.llvm.org/buildbot/#/builders/16/builds/25820
Dropping this restriction seems to work fine (there are no assertion
failures), so it appears that either the updater got smarter or the
problematic cases are restricted elsewhere.
If doing this still causes issues, then the place to address it
would probably be 8f5bdaf481/llvm/lib/Transforms/IPO/Attributor.cpp (L1856-L1859),
which already prevents replacement outside the SCC, so I'm not
quite sure what this check is intended to avoid.
Differential Revision: https://reviews.llvm.org/D120987
This check is not compatible with opaque pointers. We can avoid
it by adjusting the getPointerAlignment() implementation to avoid
creating unnecessary ptrtoint expressions for bitcasted pointers.
The code already uses OnlyIfReduced to not create an expression
if it does not simplify, and this makes sure that folding a
bitcast and ptrtoint into a ptrtoint doesn't count as a
simplification.
Differential Revision: https://reviews.llvm.org/D120904
We already look through memory to determine where a value that is stored
might pop up again (potential copies). This patch introduces the other
direction with similar logic. If a value is loaded, we can follow all
the accesses to the pointer (or better object) and try to determine what
value might have been stored.
Both `undef` and `nullptr` are maximally aligned. This is especially
important as we often see `undef` until a proper value has been
identified during simplification.
With D106397 we used CFG reasoning to filter out writes that will not
interfere with a given load instruction. With this patch we use the
same logic (modulo the reversal in reachability check order) for store
instructions. As an example, we can now proof stores to shared memory
are dead if all the loads of the shared memory are not reachable from
them.
Heap-2-stack and heap-2-shared can replace an allocation call with
something else. To avoid us deriving information from the allocator
implementation we register a simplification callback now that will
force us to stop at the call site. We probably should create the
replacement memory eagerly and return that instead though.
While we can use range information when we derive dereferenceability we
must make sure to pick he right end of the range. Before we always went
with the minimal offset, which is not correct if we want to combine
the base dereferenceability with some offset. In that case it's the
maximum that gives the correct result.
We already have a check for !InstQueries.empty(), so move the for-range over InstQueries inside to avoid the AAReachability uninitialized variable static analysis warnings.
Prior to this change, LLVM would attempt to optimize an
aligned_alloc(33, ...) call to the stack. This flunked an assertion when
trying to emit the alloca, which crashed LLVM. Avoid that with extra
checks.
Differential Revision: https://reviews.llvm.org/D119604
Prior to this change, LLVM would attempt to optimize an
aligned_alloc(33, ...) call to the stack. This flunked an assertion when
trying to emit the alloca, which crashed LLVM. Avoid that with extra
checks.
Differential Revision: https://reviews.llvm.org/D119604
With
668c5c688b
we introduced an ordering issue revealed by the reverse iteration
buildbot. Depending on the order of the map that tracks the AAIsDead AAs
we ended up with slightly different attributes. This is not totally
unexpected and can happen. We should however be deterministic in our
orderings to avoid such issues.
When we move an allocation from the heap to the stack we need to
allocate it in the alloca AS and then cast the result. This also
prevents us from inserting the alloca after the allocation call but
rather right before.
Fixes https://github.com/llvm/llvm-project/issues/53858
When we use liveness for edges during the `genericValueTraversal` we
need to make sure to use the AAIsDead of the correct function. This
patch adds the proper logic and some simple caching scheme. We also
add an assertion to the `isEdgeDead` call to make sure future misuse
is detected earlier.
Fixes https://github.com/llvm/llvm-project/issues/53872
`UsedAssumedInformation` is a return argument utilized to determine what
information is known. Most APIs used it already but
`genericValueTraversal` did not. This adds it to `genericValueTraversal`
and replaces `AllCallSitesKnown` of `checkForAllCallSites` with the
commonly used `UsedAssumedInformation`.
This was supposed to be a NFC commit, then the test change appeared.
Turns out, we had one user of `AllCallSitesKnown` (AANoReturn) and the
way we set `AllCallSitesKnown` was wrong as we ignored the fact some
call sites were optimistically assumed dead. Included a dedicated test
for this as well now.
Fixes https://github.com/llvm/llvm-project/issues/53884
New users might want to check bins without a load or store instruction
at hand. Since we use those instructions only to find the offset and
size of the access anyway, we can expose an offset and size interface
to the outside world as well.
This commit mainly moves code around and exposes a class (OffsetAndSize)
as well as a method forallInterferingAccesses in AAPointerInfo.
Differential Revision: https://reviews.llvm.org/D119249
The oversight caused us to ignore call sites that are effectively dead
when we computed reachability (or more precise the call edges of a
function). The problem is that loads in the readonly callee might depend
on stores prior to the callee. If we do not track the call edge we
mistakenly assumed the store before the call cannot reach the load.
The problem is nicely visible in:
`llvm/test/Transforms/Attributor/ArgumentPromotion/basictest.ll`
Caused by D118673.
Fixes https://github.com/llvm/llvm-project/issues/53726
When we privatize a pointer (~argument promotion) we introduce new
private allocas as replacement. These need to be placed in the alloca
address space as later passes cannot properly deal with them otherwise.
Fixes https://github.com/llvm/llvm-project/issues/53725
The helper `Attributor::checkForAllReturnedValuesAndReturnInsts`
simplifies the returned value optimistically. In `AAUndefinedBehavior`
we cannot use such optimistic values when deducing UB. As a result, we
assumed UB for the return value of a function because we initially
(=optimistically) thought the function return is `undef`. While we later
adjusted this properly, the `AAUndefinedBehavior` was under the
impression the return value is "known" (=fix) and could never change.
To correct this we use `Attributor::checkForAllInstructions` and then
manually to perform simplification of the return value, only allowing
known values to be used. This actually matches the other UB deductions.
Fixes#53647
Changes the remark to emit on the function call that captures the globalized
variable instead of the globalized variable itself. The user should be able to
see which variable it was in the argument list of the function.
Reviewed By: jdoerfert
Differential Revision: https://reviews.llvm.org/D106980
To make usage easier (compared to the many reachability related AAs),
this patch introduces a helper API, `AA::isPotentiallyReachable`, which
performs all the necessary steps. It also does the "backwards"
reachability (see D106720) as that simplifies the AA a lot (backwards
queries were somewhat different from the other query resolvers), and
ensures we use cached values in every stage.
To test inter-procedural reachability in a reasonable way this patch
includes an extension to `AAPointerInfo::forallInterferingWrites`.
Basically, we can exclude writes if they cannot reach a load "during the
lifetime" of the allocation. That is, we need to go up the call graph to
determine reachability until we can determine the allocation would be
dead in the caller. This leads to new constant propagations (through
memory) in `value-simplify-pointer-info-gpu.ll`.
Note: The new code contains plenty debug output to determine how
reachability queries are resolved.
Parts extracted from D110078.
Differential Revision: https://reviews.llvm.org/D118673
D106720 introduced features that did not work properly as we could add
new queries after a fixpoint was reached and which could not be answered
by the information gathered up to the fixpoint alone.
As an alternative to D110078, which forced eager computation where we
want to continue to be lazy, this patch fixes the problem.
QueryAAs are AAs that allow lazy queries during their lifetime. They are
never fixed if they have no outstanding dependences and always run as
part of the updates in an iteration. To determine if we are done, all
query AAs are asked if they received new queries, if not, we only need
to consider updated AAs, as before. If new queries are present we go for
another iteration.
Differential Revision: https://reviews.llvm.org/D118669
This patch implement instruction reachability for AAFunctionReachability
attribute. It is used to tell if a certain instruction can reach a function
transitively.
NOTE: I created a new commit based of D106720 and set the author back to
Kuter. Other metadata, etc. is wrong. I also addressed the
remaining review comments and fixed the unit test.
Differential Revision: https://reviews.llvm.org/D106720
We missed out on AANoRecurse in the module pass because we had no call
graph. With AAFunctionReachability we can simply ask if the function may
reach itself.
Differential Revision: https://reviews.llvm.org/D110099
genericValueTraversal can look through arguments and allow value
simplification across function boundaries. In fact, the latter already
happened unchecked. With this change we allow the user of
genericValueTraversal to opt-out of interprocedural traversal if
required. We explicitly look through arguments now which helps to do
various things, incl. the propagation of constants into OpenMP parallel
regions (on the host).
We have two attributes that can answer readnone queries. While there is
a dependence between them, it seems best to not force the users to know
what AA to ask. The helpers also allow to check for readonly nicely.
Test changes show where we now deduce readnone but haven't before,
mostly because we only asked AAMemoryBehavior and not AAMemoryLocation.
AANoAlias has not been ported to the new API yet.
Since D104432 we can look through memory by analyzing all writes that
might interfere with a load. This patch provides some logic to exclude
writes that cannot interfere with a location, due to CFG reasoning.
We make sure to avoid multi-thread write-read situations properly while
we ignore writes that cannot reach a load or writes that will be
overwritten before the load is reached.
Differential Revision: https://reviews.llvm.org/D106397
No-sync is a property that we need in more places as complex
transformations emerge. To simplify the query we provide an
`AA::isNoSyncInst` helper now and expose two existing helpers through
the `AANoSync` class.
This relies on existing APIs and avoids accessing the pointer
element type. The alternative would be to extend getPointerOperand()
to also return the accessed type, but I figured going through
MemoryLocation would be cleaner.
Differential Revision: https://reviews.llvm.org/D117868
The old method to avoid unconstrained expansion of the constant range in
a loop did not work as soon as there were multiple instructions in
between the phi and its input. We now take a generic approach and limit
the number of updates as a fallback. The old method is kept as it
catches "the common case" early.
AAPointerInfo currently bails on constant expression GEPs with
notional overindexing. I don't think this is necessary, as the
following code handling GEPOperator will deal with arbitrary
indices appropriately.
Differential Revision: https://reviews.llvm.org/D117203
This completes removal of the isXLike queries, and depends on a whole series of earlier patches which have already landed.
Differential Revision: https://reviews.llvm.org/D117242
The basic idea is that we can parameterize the getObjectSize implementation with a callback which lets us replace the operand before analysis if desired. This is what Attributor is doing during it's abstract interpretation, and allows us to have one copy of the code.
Note this is not NFC for two reasons:
* The existing attributor code is wrong. (Well, this is under-specified to be honest, but at least inconsistent.) The intermediate math needs to be done in the index type of the pointer space. Imagine e.g. i64 arguments in a 32 bit address space.
* I did not preserve the behavior in getAPInt where we return 0 for a partially analyzed value. This looks simply wrong in the original code, and nothing test wise contradicts that.
Differential Revision: https://reviews.llvm.org/D117241
The existing code duplicated the same concern in two places, and (weirdly) changed the inference of the allocation size based on whether we could meet the alignment requirement. Instead, just directly check the allocation requirement.
Rewrite the calloc specific handling in heap-to-stack to allow arbitrary init values. The basic problem being solved is that if an allocation is initilized to anything other than zero, this must be explicitly done for the formed alloca as well.
This covers the calloc case today, but once a couple of earlier guards are removed in this code, downstream allocators with other init values could also be handled.
Inspired by discussion on D116971
If we look at potentially interfering accesses we need to ensure the
"IsExact" flag is set appropriately. Accesses that have an "unknown"
size or offset cannot be exact matches and we missed to flag that.
Error and test reported by Serguei N. Dmitriev.
We currently have two similar implementations of this concept:
isNoAliasCall() only checks for the noalias return attribute.
isNoAliasFn() also checks for allocation functions.
We should switch to only checking the attribute. SLC is responsible
for inferring the noalias return attribute for non-new allocation
functions (with a missing case fixed in
348bc76e35).
For new, clang is responsible for setting the attribute,
if -fno-assume-sane-operator-new is not passed.
Differential Revision: https://reviews.llvm.org/D116800
If we have multiple references into a map we need to ensure the ones
created late do not invalidate the ones created early. To do that we
need to make sure all but the first are not modifying the map, hence
for them the keys have to be present already.
Fixes#52875.
AAPointerInfo, and thereby other places, can look already through
internal global and stack memory. This patch enables them to look
through heap memory returned by functions with a `noalias` return.
In the future we can look through `noalias` arguments as well but that
will require AAIsDead to learn that such memory can be inspected by the
caller later on. We also need teach AAPointerInfo about dominance to
actually deal with memory that might not be `null` or `undef`
initialized. D106397 is a first step in that direction already.
Reviewed By: kuter
Differential Revision: https://reviews.llvm.org/D109170
While we skipped uses in stores if we can find all copies of the value
when the memory is loaded, we did not correlate the use in the store
with the use in the load. So far this lead to less precise results in the
offset calculations which prevented deductions. With the new
EquivalentUseCB callback argument the user of checkForAllUses can be
informed of the correlation and act on it appropriately.
Differential Revision: https://reviews.llvm.org/D109662
This patch changes the HeapToStack optimization to attach the return alignment
attribute information to the created alloca instruction. This would cause
problems when replacing the heap allocation with an alloca did not respect the
alignment of the original heap allocation, which would typically be aligned on
an 8 or 16 byte boundary. Malloc calls now contain alignment attributes,
so we can use that information here.
Reviewed By: jdoerfert
Differential Revision: https://reviews.llvm.org/D115888
Instead of using the ArgumentPromotion implementation, we now walk
call sites using checkForAllCallSites() and directly call
areTypesABICompatible() using the replacement types. I believe
that resolves the TODO in the code.
Differential Revision: https://reviews.llvm.org/D116033
Johannes Doerfert