If the pointer returned by a function is not "the base pointer" but has
an offset, we need to track the offset such that users can apply it to
their offset chain when they create accesses.
This was reported by @ye-luo and reduced test cases are included. The
OffsetInfo was moved and the container was replaced with a set to avoid
excessive growth. Otherwise, the patch just replaces the "returns
pointer" flag with the "returned offsets", and deals with the applying
to offsets at the call site.
---------
Co-authored-by: Johannes Doerfert <jdoerfert@llnl.gov>
Instead of visiting call sites in Attribute::checkForAllUses, we now
keep track of returns in AAPointerInfo and use the call site return
information as required. This way, the user of
AAPointerInfo(CallSite)Argument can determine if the call return should
be visited. We do not collect them as "may accesses" in the
AAPointerInfo(CallSite)Argument itself in case a return user is found.
Before, we kept the call site access kind (may/must) when we translated
the access. However, the pointer we access it through (by passing it to
the callee) might not be the underlying object. We have similar logic
when we add store and load accesses.
- Allocas and GlobalValues cannot be simplified, so we should not try.
- If we never used any assumed state, the AAUnderlyingObjects doesn't
require an additional update.
- If we have seen an object (or it's underlying object) before, we do
not need to inspect it anymore.
The original logic for "SeenObjects" was flawed and caused us to add
intermediate values to the underlying object list if a PHI or select
instruction referenced the same underlying object twice. The test
changes are all instances of this situation and we now correctly derive
`memory(none)` for the functions that only access stack memory.
---------
Co-authored-by: Shilei Tian <i@tianshilei.me>
It was `inaccessiblemem: readwrite` before, no need for the read.
No real benefit is expected but it can help debugging and other efforts.
Differential Revision: https://reviews.llvm.org/D156478
If the function is non-IPO amendable we do skip most attributes/AAs.
However, if an AA has a isImpliedByIR that can deduce the attribute from
other attributes, we can run those. For now, we manually enable them,
if we have more later we can use some automation/flag.
AANonNull is now the first AA that is always queried via the new APIs
and not created manually. Others will follow shortly to avoid trivial
AAs whenever possible.
This commit introduced some helper logic that will make it simpler to
port the next one. It also untangles AADereferenceable and AANonNull
such that the former does not keep a handle on the latter. Finally,
we stop deducing `nonnull` for `undef`, which was incorrect.
If an attribute is implied by the IR we do not (always) create an AA
anymore. To keep test coverage, and given the lack of a good heuristic
to decide otherwise, we will now also manifest such attributes.
We had some custom handling for existing MemoryEffects but we now move
it to the place we check other existing attributes before we manifest
new ones. If we later decide to curb duplication (of attributes on the
call site and callee), we can do that at a single location and for all
attributes.
The test changes basically add known `memory` callee information to the
call sites.
Instead of creating an AA for an IR attribute we can first check if it
is implied/known. If so, we can save the time to create the AA, figure
out it is implied, fix it, and later manifest it in the IR
(redundantly). Other IR attributes can be added to the list in
`AA::hasAssumedIRAttr` later on, for now we support 8 different ones.
It was never really useful to track #iterations, though it helped during
the initial development. What we should track, in a follow up, are
potentially #updates. That is also what we should restrict instead of
the #iterations.
Derive the mustprogress attribute based on the willreturn attribute
or the fact that all callers are mustprogress.
Differential Revision: https://reviews.llvm.org/D94740
Similar to loads, PHIs can be used to introduce non-dynamically unique
values into the simplification "algorithm". We need to check that PHIs
do not carry such a value from one iteration into the next as can cause
downstream reasoning to fail, e.g., downstream could think a comparison
is equal because the simplified values are equal while they are defined
in different loop iterations. Similarly, instructions in cycles are now
conservatively treated as non-dynamically unique. We could do better but
I'll leave that for the future.
The change in AAUnderlyingObjects allows us to ignore dynamically unique
when we simply look for underlying objects. The user of that AA should
be aware that the result might not be a dynamically unique value.
We improved our simplification and this exposed a bug in the store
elimination. A load that had dead uses and assume uses was thought to be
used by assumes only. Consequently we also deleted the "dead use users".
This was a problem because a dead use just means we will not use the
load there. The user might still be needed.
Exposed by OvO, reported by @ye-luo.
Check lines were regenerated for these.
The alignment changes in byval-2. look suspicious at first glance,
but actually only propagate pre-existing UB.
This patch introduces a new AA `AAUnderlyingObjects`. It is basically like a wrapper
AA of the function `AA::getAssumedUnderlyingObjects`, but it can recursively do
query if the underlying object is an indirect access, such as a phi node or a select
instruction.
Reviewed By: jdoerfert
Differential Revision: https://reviews.llvm.org/D141164
We were already treating branch on poison as UB, but branch on
undef is also UB. Move the checks into the correct function.
From LangRef for br:
> If ‘cond’ is poison or undef, this instruction has undefined behavior.
From LangRef for switch:
> If ‘value’ is poison or undef, this instruction has undefined behavior.
There is a minor regression in dont-distribute-phi.ll, apparently
we handle that pattern in logical but not bitwise form.
AAPotentialConstantValues now works for PHI and Load by simply examinig
AAPotentialValues for the instruction itself.
Reviewed By: jdoerfert
Differential Revision: https://reviews.llvm.org/D140371
We had two AAs for reachability but it was very cumbersome to extend
them. We also had some fallback to use LLVM-core mechanisms and cache
the result. The new design shares the query code and interface nicely
between AAIntraFnReachability and AAInterFnReachability.
As part of the rewrite we also added the ExclusionSet to the queries.
Even if a value is for sure written we need to visit the call sites as
they might end up inside the function that reads and writes the value.
In a follow up we can introduce correct reasoning to avoid the backwards
traversal in this case and instead check if any call site between the
write and the read might reach a potential write we want to exclude.
An expression of the form `gep(base, select(pred, const1, const2))` can result
in a set of offsets instead of just one. PointerInfo can now track these sets
instead of conservatively modeling them as Unknown. In general, AAPointerInfo
now uses AAPotentialConstantValues to examine the operands of the GEP.
Reviewed By: jdoerfert
Differential Revision: https://reviews.llvm.org/D138646
An expression of the form `gep(base, select(pred, const1, const2))` can result
in a set of offsets instead of just one. PointerInfo can now track these sets
instead of conservatively modeling them as Unknown. In general, AAPointerInfo
now uses AAPotentialConstantValues to examine the operands of the GEP.
Reviewed By: jdoerfert
Differential Revision: https://reviews.llvm.org/D138646
Similar to dominance reasoning, we cannot use CFG reachability if the
instructions might be executed by different threads. A follow up will
improve our sensitivity for situations when it is OK to use graph
reasoning.
This restores commit b756096b0cbef0918394851644649b3c28a886e2, which was
originally reverted in 00b09a7b18abb253d36b3d3e1c546007288f6e89.
AAPointerInfo now maintains a list of all Access objects that it owns, along
with the following maps:
- OffsetBins: OffsetAndSize -> { Access }
- InstTupleMap: RemoteI x LocalI -> Access
A RemoteI is any instruction that accesses memory. RemoteI is different from
LocalI if and only if LocalI is a call; then RemoteI is some instruction in the
callgraph starting from LocalI.
Motivation: When AAPointerInfo recomputes the offset for an instruction, it sets
the value to Unknown if the new offset is not the same as the old offset. The
instruction must now be moved from its current bin to the bin corresponding to
the new offset. This happens for example, when:
- A PHINode has operands that result in different offsets.
- The same remote inst is reachable from the same local inst via different paths
in the callgraph:
```
A (local inst)
|
B
/ \
C1 C2
\ /
D (remote inst)
```
This fixes a bug where a store is incorrectly eliminated in a lit test.
Reviewed By: jdoerfert, ye-luo
Differential Revision: https://reviews.llvm.org/D136526
This switches everything to use the memory attribute proposed in
https://discourse.llvm.org/t/rfc-unify-memory-effect-attributes/65579.
The old argmemonly, inaccessiblememonly and inaccessiblemem_or_argmemonly
attributes are dropped. The readnone, readonly and writeonly attributes
are restricted to parameters only.
The old attributes are auto-upgraded both in bitcode and IR.
The bitcode upgrade is a policy requirement that has to be retained
indefinitely. The IR upgrade is mainly there so it's not necessary
to update all tests using memory attributes in this patch, which
is already large enough. We could drop that part after migrating
tests, or retain it longer term, to make it easier to import IR
from older LLVM versions.
High-level Function/CallBase APIs like doesNotAccessMemory() or
setDoesNotAccessMemory() are mapped transparently to the memory
attribute. Code that directly manipulates attributes (e.g. via
AttributeList) on the other hand needs to switch to working with
the memory attribute instead.
Differential Revision: https://reviews.llvm.org/D135780
AAPointerInfo now maintains a list of all Access objects that it owns, along
with the following maps:
- OffsetBins: OffsetAndSize -> { Access }
- InstTupleMap: RemoteI x LocalI -> Access
A RemoteI is any instruction that accesses memory. RemoteI is different from
LocalI if and only if LocalI is a call; then RemoteI is some instruction in the
callgraph starting from LocalI.
Motivation: When AAPointerInfo recomputes the offset for an instruction, it sets
the value to Unknown if the new offset is not the same as the old offset. The
instruction must now be moved from its current bin to the bin corresponding to
the new offset. This happens for example, when:
- A PHINode has operands that result in different offsets.
- The same remote inst is reachable from the same local inst via different paths
in the callgraph:
```
A (local inst)
|
B
/ \
C1 C2
\ /
D (remote inst)
```
This fixes a bug where a store is incorrectly eliminated in a lit test.
Reviewed By: jdoerfert
Differential Revision: https://reviews.llvm.org/D136526
A User like the PHINode may be visited multiple times for the same pointer along
different def-use edges. The uninitialized state of OffsetInfo at the first
visit needs to be distinct from the Unknown value that may be assigned after
processing the PHINode. Without that, a PHINode with all inputs Unknown is never
followed to its uses. This results in incorrect optimization because some
interfering accessess are missed.
Differential Revision: https://reviews.llvm.org/D134704
Now that the legacy PM is no longer tested, the huge matrix of
test prefixes used by attributor tests is no longer needed and very
confusing for the casual reader. Reduce the prefixes down to just
CHECK, TUNIT and CGSCC.
This is the first patch in a series intended for removing flag
-enable-new-pm=0 from lit tests. This is part of a bigger
effort of completely removing legacy code related to legacy
pass manager in favor of currently default new pass manager.
In this patch flag has been removed only from tests where no significant
change has been required because checks has been duplicated for
both PMs.
Reviewed By: fhahn
Differential Revision: https://reviews.llvm.org/D134150
We no longer need specialized knowledge of these allocator functions in
this file since we have the correct attributes available now.
As far as I can tell the changes in the attributor tests are due to
things getting more consistent on alloc-family once we remove the static
list entries.
The two test changes in NewGVN merit extra scrutiny: NewGVN appears to
be _extremely_ sensitive to the inaccessiblememonly for reasons that
are beyond me. As a result, I had-enumerated all the attributes on
allocation functions in those two tests instead of using -inferattrs.
I assumed that the two -disable-simplify-libcalls tests there no
longer are sensible since the function declaration now includes all the
relevant attributes.
Differential Revision: https://reviews.llvm.org/D130107
If we look at a write, we should not enact the "has been written to"
logic introduced to avoid spurious write -> read dependences. Doing so
lead to elimination of stores we needed, which is obviously bad.
If a function is non-recursive we only performed intra-procedural
reasoning for reachability (via AA::isPotentiallyReachable). However,
if it is re-entrant that doesn't mean we can't reach. Instead of this
problematic logic in the reachability reasoning we utilize logic in
AAPointerInfo. If a location is for sure written by a function it can
be re-entrant or recursive we know only intra-procedural reasoning is
sufficient.
If we have a dominating must-write access we do not need to know the
initial value of some object to perform reasoning about the potential
values. The dominating must-write has overwritten the initial value.
We were quite conservative when it came to PHI node handling to avoid
recursive reasoning. Now we check more direct if we have seen a PHI
already or not. This allows non-recursive PHI chains to be handled.
This also exposed a bug as we did only model the effect of one loop
traversal. `phi_no_store_3` has been adapted to show how we would have
used `undef` instead of `1` before. With this patch we don't replace
it at all, which is expected as we do not argue about loop iterations
(or alignments).
