Currently the max alignment representable is 1GB, see D108661.
Setting the align of an object to 4GB is desirable in some cases to make sure the lower 32 bits are clear which can be used for some optimizations, e.g. https://crbug.com/1016945.
This uses an extra bit in instructions that carry an alignment. We can store 15 bits of "free" information, and with this change some instructions (e.g. AtomicCmpXchgInst) use 14 bits.
We can increase the max alignment representable above 4GB (up to 2^62) since we're only using 33 of the 64 values, but I've just limited it to 4GB for now.
The one place we have to update the bitcode format is for the alloca instruction. It stores its alignment into 5 bits of a 32 bit bitfield. I've added another field which is 8 bits and should be future proof for a while. For backward compatibility, we check if the old field has a value and use that, otherwise use the new field.
Updating clang's max allowed alignment will come in a future patch.
Reviewed By: hans
Differential Revision: https://reviews.llvm.org/D110451
Currently the max alignment representable is 1GB, see D108661.
Setting the align of an object to 4GB is desirable in some cases to make sure the lower 32 bits are clear which can be used for some optimizations, e.g. https://crbug.com/1016945.
This uses an extra bit in instructions that carry an alignment. We can store 15 bits of "free" information, and with this change some instructions (e.g. AtomicCmpXchgInst) use 14 bits.
We can increase the max alignment representable above 4GB (up to 2^62) since we're only using 33 of the 64 values, but I've just limited it to 4GB for now.
The one place we have to update the bitcode format is for the alloca instruction. It stores its alignment into 5 bits of a 32 bit bitfield. I've added another field which is 8 bits and should be future proof for a while. For backward compatibility, we check if the old field has a value and use that, otherwise use the new field.
Updating clang's max allowed alignment will come in a future patch.
Reviewed By: hans
Differential Revision: https://reviews.llvm.org/D110451
Currently the max alignment representable is 1GB, see D108661.
Setting the align of an object to 4GB is desirable in some cases to make sure the lower 32 bits are clear which can be used for some optimizations, e.g. https://crbug.com/1016945.
This uses an extra bit in instructions that carry an alignment. We can store 15 bits of "free" information, and with this change some instructions (e.g. AtomicCmpXchgInst) use 14 bits.
We can increase the max alignment representable above 4GB (up to 2^62) since we're only using 33 of the 64 values, but I've just limited it to 4GB for now.
The one place we have to update the bitcode format is for the alloca instruction. It stores its alignment into 5 bits of a 32 bit bitfield. I've added another field which is 8 bits and should be future proof for a while. For backward compatibility, we check if the old field has a value and use that, otherwise use the new field.
Updating clang's max allowed alignment will come in a future patch.
Reviewed By: hans
Differential Revision: https://reviews.llvm.org/D110451
For now we do should not treat byval arguments as local copies performed
on the call edge, though, in general we should. To make that happen we
need to teach various passes, e.g., DSE, about the copy effect of a
byval. That would also allow us to mark functions only accessing byval
arguments as readnone again, atguably their acceses have no effect
outside of the function, like accesses to allocas.
Reviewed By: kuter
Differential Revision: https://reviews.llvm.org/D108140
In LLVM IR, `AlignmentBitfieldElementT` is 5-bit wide
But that means that the maximal alignment exponent is `(1<<5)-2`,
which is `30`, not `29`. And indeed, alignment of `1073741824`
roundtrips IR serialization-deserialization.
While this doesn't seem all that important, this doubles
the maximal supported alignment from 512MiB to 1GiB,
and there's actually one noticeable use-case for that;
On X86, the huge pages can have sizes of 2MiB and 1GiB (!).
So while this doesn't add support for truly huge alignments,
which i think we can easily-ish do if wanted, i think this adds
zero-cost support for a not-trivially-dismissable case.
I don't believe we need any upgrade infrastructure,
and since we don't explicitly record the IR version,
we don't need to bump one either.
As @craig.topper speculates in D108661#2963519,
this might be an artificial limit imposed by the original implementation
of the `getAlignment()` functions.
Differential Revision: https://reviews.llvm.org/D108661
When we simplify at least one operand in the Attributor simplification
we can use the InstSimplify to work on the simplified operands. This
allows us to avoid duplication of the logic.
Depends on D106189
Differential Revision: https://reviews.llvm.org/D106190
D106185 allows us to determine if a store is needed easily. Using that
knowledge we can start to delete dead stores.
In AAIsDead we now track more state as an instruction can be dead (= the
old optimisitc state) or just "removable". A store instruction can be
removable while being very much alive, e.g., if it stores a constant
into an alloca or internal global. If we would pretend it was dead
instead of only removablewe we would ignore it when we determine what
values a load can see, so that is not what we want.
Differential Revision: https://reviews.llvm.org/D106188
This patch introduces `getPotentialCopiesOfStoredValue` which uses
AAPointerInfo to determine all "aliases" or "potential copies" of a
value that is stored into memory. This operation can fail but if it
succeeds it means we can visit all "uses" of a value even if it is
temporarily stored in memory.
There are two users for the function:
1) `Attributor::checkForAllUses` which will now ignore the value use
in a store if all "potential copies" can be identified and instead
be visited. This allows various AAs, including AAPointerInfo
itself, to look through memory.
2) `AANoCapture` which uses a custom use tracking through the
CaptureTracker interface and therefore needs to be thought
explicitly.
Differential Revision: https://reviews.llvm.org/D106185
We first simplify the operands of a compare and then reason on the
simplified versions, e.g., with AANonNull.
This does improve the simplification capabilities but also fixes a
potential problem that has not yet been observed by simplifying the
operands first.
A byval argument is a different value in the caller and callee, we
cannot propagate the information as part of AAValueSimplify. Users that
want to deal with byval arguments need to specifically perform the
argument -> call site step. We do not do this for now.
When we talk to outside analyse, e.g., LVI and ScalarEvolution, we need
to be careful with the query. The particular error occurred because we
folded a PHI node before the LVI query but the context location was now
not dominated by the value anymore. This is not supported by LVI so we
have to filter these situations before we query the outside analyses.
We have to be careful when we replace values to not use a non-dominating
instruction. It makes sense that simplification offers those as
"simplified values" but we can't manifest them in the IR without PHI
nodes. In the future we should consider potentially adding those PHI
nodes.
We should use AAValueSimplify for all value simplification, however
there was some leftover logic that predates AAValueSimplify in
AAReturnedValues. This remove the AAReturnedValues part and provides a
replacement by making AAValueSimplifyReturned strong enough to handle
all previously covered cases. Further, this improve
AAValueSimplifyCallSiteReturned to handle returned arguments.
AAReturnedValues is now much easier and the collected returned
values/instructions are now from the associated function only, making it
much more sane. We also do not have the brittle logic anymore that looks
for unresolved calls. Instead, we use AAValueSimplify to handle
recursion.
Useful code has been split into helper functions, e.g., an Attributor
interface to get a simplified value.
Differential Revision: https://reviews.llvm.org/D103860
Not all attributes are able to handle the interprocedural step and
follow the uses into a call site. Let them be able to combine call site
uses instead. This might result in some unused values/arguments being
leftover but it removes problems where we misused "is dead" even though
it was actually "is simplified/replaced".
We explicitly check for dead values due to constant propagation in
`AAIsDeadValueImpl::areAllUsesAssumedDead` instead.
Differential Revision: https://reviews.llvm.org/D103858
Broke check-clang, see https://reviews.llvm.org/D102307#2869065
Ran `git revert -n ebbe149a6f08535ede848a531a601ae6591cfbc5..269416d41908bb670f67af689155d5ab8eea689a`
When we talk to outside analyse, e.g., LVI and ScalarEvolution, we need
to be careful with the query. The particular error occurred because we
folded a PHI node before the LVI query but the context location was now
not dominated by the value anymore. This is not supported by LVI so we
have to filter these situations before we query the outside analyses.
We have to be careful when we replace values to not use a non-dominating
instruction. It makes sense that simplification offers those as
"simplified values" but we can't manifest them in the IR without PHI
nodes. In the future we should consider potentially adding those PHI
nodes.
We should use AAValueSimplify for all value simplification, however
there was some leftover logic that predates AAValueSimplify in
AAReturnedValues. This remove the AAReturnedValues part and provides a
replacement by making AAValueSimplifyReturned strong enough to handle
all previously covered cases. Further, this improve
AAValueSimplifyCallSiteReturned to handle returned arguments.
AAReturnedValues is now much easier and the collected returned
values/instructions are now from the associated function only, making it
much more sane. We also do not have the brittle logic anymore that looks
for unresolved calls. Instead, we use AAValueSimplify to handle
recursion.
Useful code has been split into helper functions, e.g., an Attributor
interface to get a simplified value.
Differential Revision: https://reviews.llvm.org/D103860
Not all attributes are able to handle the interprocedural step and
follow the uses into a call site. Let them be able to combine call site
uses instead. This might result in some unused values/arguments being
leftover but it removes problems where we misused "is dead" even though
it was actually "is simplified/replaced".
We explicitly check for dead values due to constant propagation in
`AAIsDeadValueImpl::areAllUsesAssumedDead` instead.
Differential Revision: https://reviews.llvm.org/D103858
We often need to deal with the value lattice that contains none and
undef as special values. A simple helper makes this much nicer.
Differential Revision: https://reviews.llvm.org/D103857
When we do simplification via AAPotentialValues or AAValueConstantRange
we need to simplify the operands of an instruction we deconstruct first.
This does not only improve the result, see for example range.ll, but is
required as we allow outside AAs to provide simplification rules via
callbacks. If we do ignore the simplification rules and base other
simplifications on the IR instead we can create an inconsistent state.
This should fix PR50683. The wrong assumption was that we
could always know what the callee is when we replace a call site
argument with undef. We wanted to know that to remove the `noundef`
that might be attached to the argument. Since no callee means we
did the propagation on the caller site, there is no need to remove
an attribute. It is only needed if we replace all uses and therefore
pass `undef` instead of the value that was passed in otherwise.
Summary:
The current implementation of AANoFreeFloating will incorrectly list floating
point loads and stores as may-free. This prevents other attributor instances
like HeapToStack from pushing some allocations to the stack.
Reviewed By: jdoerfert
Differential Revision: https://reviews.llvm.org/D103975
If we simplify values we sometimes end up with type mismatches. If the
value is a constant we can often cast it though to still allow
propagation. The logic is now put into a helper and it replaces some
ad hoc things we did before.
This also introduces the AA namespace for abstract attribute related
functions and types.
We have seen various problems when the call graph was not updated or
the updated did not succeed because it involved functions outside the
SCC. This patch adds assertions and checks to avoid accidentally
changing something outside the SCC that would impact the call graph.
It also prevents us from reanalyzing functions outside the current
SCC which could cause problems on its own. Note that the transformations
we do might cause the CG to be "more precise" but the original one would
always be a super set of the most precise one. Since the call graph is
by nature an approximation, it is good enough to have a super set of all
call edges.
The constant value lattice looks like this
```
<None>
|
<undef>
/ | \
... <0> ...
\ | /
<unknown>
```
We did not account for the undef and assumed a value meant we could not
change anymore. Now we actually check if we have the same value as
before, which will signal CHANGED to the users when we go from undef to
a specific constant.
This fixes, among other things, the bug exposed by @ipccp4 in
`value-simplify.ll`.
The state of AAPotentialValues tracks if undef is contained. It should
fold undef into the first non-undef value. However we missed a case
before. There was also a shadowing definition of two variables that
caused trouble. The test exposes both problems.
I think byval/sret and the others are close to being able to rip out
the code to support the missing type case. A lot of this code is
shared with inalloca, so catch this up to the others so that can
happen.
Since D86233 we have `mustprogress` which, in combination with
`readonly`, implies `willreturn`. The idea is that every side-effect
has to be modeled as a "write". Consequently, `readonly` means there
is no side-effect, and `mustprogress` guarantees that we cannot "loop"
forever without side-effect.
Reviewed By: fhahn
Differential Revision: https://reviews.llvm.org/D94125
The update_test_checks script can now check for global symbols and is able
to handle them properly when they differ across prefixes, e.g.,
attribute #0 might be different in different runs.
This patch simply updates all the Attributor tests with the new script.
Reviewed By: sstefan1
Differential Revision: https://reviews.llvm.org/D97906
We don't need a bool and an enum to express the three options we
currently have. This makes the interface nicer and much easier to
use optional dependencies. Also avoids mistakes where the bool is
false and enum ignored.
This is a follow-up of D95238's LangRef update.
This patch updates `programUndefinedIfUndefOrPoison(V)` to return true if
`V` is used by any memory-accessing instruction.
Interestingly, this affected many tests in Attributors, mainly about adding noundefs.
The tests are updated using llvm/utils/update_test_checks.py. I checked that the diffs
are about updating noundefs.
Reviewed By: nikic
Differential Revision: https://reviews.llvm.org/D96642
D70365 allows us to make attributes default. This is a follow up to
actually make nosync, nofree and willreturn default. The approach we
chose, for now, is to opt-in to default attributes to avoid introducing
problems to target specific intrinsics. Intrinsics with default
attributes can be created using `DefaultAttrsIntrinsic` class.
Arthur Eubanks