This matches the checks done at the beginning of isKnownNonEqual that this code is partially emulating.
Without this we can get assertion failures due to the bit widths of the KnownBits not matching.
llvm-svn: 306044
Using various methods, BasicAA tries to determine whether two
GetElementPtr memory locations alias when its base pointers are known
to be equal. When none of its heuristics are applicable, it falls back
to PartialAlias to, according to a comment, protect TBAA making a wrong
decision in case of unions and malloc. PartialAlias is not correct,
because a PartialAlias result implies that some, but not all, bytes
overlap which is not necessarily the case here.
AAResults returns the first analysis result that is not MayAlias.
BasicAA is always the first alias analysis. When it returns
PartialAlias, no other analysis is queried to give a more exact result
(which was the intention of returning PartialAlias instead of MayAlias).
For instance, ScopedAA could return a more accurate result.
The PartialAlias hack was introduced in r131781 (and re-applied in
r132632 after some reverts) to fix llvm.org/PR9971 where TBAA returns a
wrong NoAlias result due to a union. A test case for the malloc case
mentioned in the comment was not provided and I don't think it is
affected since it returns an omnipotent char anyway.
Since r303851 (https://reviews.llvm.org/D33328) clang does emit specific
TBAA for unions anymore (but "omnipotent char" instead). Hence, the
PartialAlias workaround is not required anymore.
This patch passes the test-suite and check-llvm/check-clang of a
self-hoisted build on x64.
Reviewed By: hfinkel
Differential Revision: https://reviews.llvm.org/D34318
llvm-svn: 305938
This is a fix for the test case in PR32314.
Basic Alias Analysis can ask if two nodes are known non-equal after looking through a phi node to find a GEP. isAddOfNonZero saw an add of a constant from the same phi and said that its output couldn't be equal. But Basic Alias Analysis was really asking about the value from the previous loop iteration.
This patch at least makes that case not happen anymore, I'm not sure if there were still other ways this can fail. As was discussed in the bug, it looks like fixing BasicAA would be difficult so this patch seemed like a possible workaround
Differential Revision: https://reviews.llvm.org/D33136
llvm-svn: 305481
Summary:
llvm.invariant.group.barrier returns pointer that mustalias
pointer it takes. It can't be marked with `returned` attribute,
because it would be remove easily. The other reason is that
only Alias Analysis can know about this, because if any other
pass would know it, then the result would be replaced with it's
argument, which would be invalid.
We can think about returned pointer as something that mustalias, but
it doesn't have to be bitwise the same as the argument.
Reviewers: dberlin, chandlerc, hfinkel, sanjoy
Subscribers: reames, nlewycky, rsmith, anna, amharc
Differential Revision: https://reviews.llvm.org/D31585
llvm-svn: 301227
BasicAA wants to know if a function is either a malloc or calloc like function. Currently we have to check both separately. This means both calls check if its an intrinsic, query TLI, check the nobuiltin attribute, scan the AllocationFnData, etc.
This patch adds a isMallocOrCallocLikeFn so we can go through all of the checks once per call.
This also changes the one other location I saw that called both together.
Differential Revision: https://reviews.llvm.org/D32188
llvm-svn: 300608
This avoids the confusing 'CS.paramHasAttr(ArgNo + 1, Foo)' pattern.
Previously we were testing return value attributes with index 0, so I
introduced hasReturnAttr() for that use case.
llvm-svn: 300367
This adds a parameter to @llvm.objectsize that makes it return
conservative values if it's given null.
This fixes PR23277.
Differential Revision: https://reviews.llvm.org/D28494
llvm-svn: 298430
This is fixing pr31761: BasicAA is deducing NoAlias
on the result of the GEP if the base pointer is itself NoAlias.
This is possible only if the NoAlias on the base pointer is
deduced with a non-sized query: this should guarantee that
the pointers are belonging to different memory allocation
and that the GEP can't legally jump from one to another.
Differential Revision: https://reviews.llvm.org/D29216
llvm-svn: 293293
Summary:
The LibFunc::Func enum holds enumerators named for libc functions.
Unfortunately, there are real situations, including libc implementations, where
function names are actually macros (musl uses "#define fopen64 fopen", for
example; any other transitively visible macro would have similar effects).
Strictly speaking, a conforming C++ Standard Library should provide any such
macros as functions instead (via <cstdio>). However, there are some "library"
functions which are not part of the standard, and thus not subject to this
rule (fopen64, for example). So, in order to be both portable and consistent,
the enum should not use the bare function names.
The old enum naming used a namespace LibFunc and an enum Func, with bare
enumerators. This patch changes LibFunc to be an enum with enumerators prefixed
with "LibFFunc_". (Unfortunately, a scoped enum is not sufficient to override
macros.)
There are additional changes required in clang.
Reviewers: rsmith
Subscribers: mehdi_amini, mzolotukhin, nemanjai, llvm-commits
Differential Revision: https://reviews.llvm.org/D28476
llvm-svn: 292848
There is no need to do this within an analysis. That method shouldn't
even be reached if this predicate holds as the actual useful
optimization is in the analysis manager itself.
llvm-svn: 290614
This requires custom handling because BasicAA caches handles to other
analyses and so it needs to trigger indirect invalidation.
This fixes one of the common crashes when using the new PM in real
pipelines. I've also tweaked a regression test to check that we are at
least handling the most immediate case.
I'm going to work at re-structuring this test some to both scale better
(rather than all being in one file) and check more invalidation paths in
a follow-up commit, but I wanted to get the basic bug fix in place.
llvm-svn: 290603
When iterating over data operands in AA, don't make argument-attribute-specific
queries on bundle operands. Trying to fix self hosting...
llvm-svn: 289765
After r289755, the AssumptionCache is no longer needed. Variables affected by
assumptions are now found by using the new operand-bundle-based scheme. This
new scheme is more computationally efficient, and also we need much less
code...
llvm-svn: 289756
Instead, expose whether the current type is an array or a struct, if an array
what the upper bound is, and if a struct the struct type itself. This is
in preparation for a later change which will make PointerType derive from
Type rather than SequentialType.
Differential Revision: https://reviews.llvm.org/D26594
llvm-svn: 288458
analyses to have a common type which is enforced rather than using
a char object and a `void *` type when used as an identifier.
This has a number of advantages. First, it at least helps some of the
confusion raised in Justin Lebar's code review of why `void *` was being
used everywhere by having a stronger type that connects to documentation
about this.
However, perhaps more importantly, it addresses a serious issue where
the alignment of these pointer-like identifiers was unknown. This made
it hard to use them in pointer-like data structures. We were already
dodging this in dangerous ways to create the "all analyses" entry. In
a subsequent patch I attempted to use these with TinyPtrVector and
things fell apart in a very bad way.
And it isn't just a compile time or type system issue. Worse than that,
the actual alignment of these pointer-like opaque identifiers wasn't
guaranteed to be a useful alignment as they were just characters.
This change introduces a type to use as the "key" object whose address
forms the opaque identifier. This both forces the objects to have proper
alignment, and provides type checking that we get it right everywhere.
It also makes the types somewhat less mysterious than `void *`.
We could go one step further and introduce a truly opaque pointer-like
type to return from the `ID()` static function rather than returning
`AnalysisKey *`, but that didn't seem to be a clear win so this is just
the initial change to get to a reliably typed and aligned object serving
is a key for all the analyses.
Thanks to Richard Smith and Justin Lebar for helping pick plausible
names and avoid making this refactoring many times. =] And thanks to
Sean for the super fast review!
While here, I've tried to move away from the "PassID" nomenclature
entirely as it wasn't really helping and is overloaded with old pass
manager constructs. Now we have IDs for analyses, and key objects whose
address can be used as IDs. Where possible and clear I've shortened this
to just "ID". In a few places I kept "AnalysisID" to make it clear what
was being identified.
Differential Revision: https://reviews.llvm.org/D27031
llvm-svn: 287783
In BasicAA GEP operand values get adjusted ("wrap-around") based on the
pointersize. Otherwise, in non-64b modes, AA could report false negatives.
However, a wrap-around is valid only for a fully evaluated expression.
It had been introduced to fix an alias problem in
http://lists.llvm.org/pipermail/llvm-commits/Week-of-Mon-20160118/326163.html.
This commit restricts the wrap-around to constant gep operands only where the
value is known at compile-time.
llvm-svn: 284908
Recursive calls to aliasCheck from alias[GEP|Select|PHI] may result in a second call to GetUnderlyingObject for a Value, whose underlying object is already computed. This patch ensures that in this situations, the underlying object is not computed again, and the result of the previous call is resued.
https://reviews.llvm.org/D22305
llvm-svn: 278519
Summary:
We teach alias analysis that invariant.start is readonly.
This helps with GVN and memcopy optimizations that currently treat.
invariant.start as a clobber.
We need to treat this as readonly, so that DSE does not incorrectly
remove stores prior to the invariant.start
Reviewers: sanjoy, reames, majnemer, dberlin
Subscribers: llvm-commits
Differential Revision: https://reviews.llvm.org/D23214
llvm-svn: 278138
Besides a general consistently benefit, the extra layer of indirection
allows the mechanical part of https://reviews.llvm.org/D23256 that
requires touching every transformation and analysis to be factored out
cleanly.
Thanks to David for the suggestion.
llvm-svn: 278077
Motivated by the work on the llvm.noalias intrinsic, teach BasicAA to look
through returned-argument functions when answering queries. This is essential
so that we don't loose all other AA information when supplementing with
llvm.noalias.
Differential Revision: http://reviews.llvm.org/D9383
llvm-svn: 275035
Summary:
This complements the earlier addition of IntrWriteMem and IntrWriteArgMem
LLVM intrinsic properties, see D18291.
Also start using the attribute for memset, memcpy, and memmove intrinsics,
and remove their special-casing in BasicAliasAnalysis.
Reviewers: reames, joker.eph
Subscribers: joker.eph, llvm-commits
Differential Revision: http://reviews.llvm.org/D18714
llvm-svn: 274485
Patch by Taewook Oh
Summary: Patch for Bug 27478. Make BasicAliasAnalysis claims NoAlias if two GEPs index different fields of the same structure.
Reviewers: hfinkel, dberlin
Subscribers: dberlin, mcrosier, llvm-commits
Differential Revision: http://reviews.llvm.org/D20665
llvm-svn: 271415
r270777 improved the precision of alloca vs. inbounbds GEP alias queries: if
we have (a) an inbounds GEP and (b) a pointer based on an alloca, and the
beginning of the object the GEP points to would have a negative offset with
respect to the alloca, then the GEP can not alias pointer (b).
This makes the same logic fire when (b) is based on a GlobalVariable instead
of an alloca.
Differential Revision: http://reviews.llvm.org/D20652
llvm-svn: 270893
It turns out that too many passes are relying on alias analysis results
for control dependencies. Until we fix that by introducing a more accurate
modelling of control dependencies, special case assume in MemorySSA instead.
Also introduce tests to ensure we don't regress the FunctionAttrs or LICM
passes.
Differential Revision: http://reviews.llvm.org/D20658
llvm-svn: 270823
If a we have (a) a GEP and (b) a pointer based on an alloca, and the
beginning of the object the GEP points would have a negative offset with
repsect to the alloca, then the GEP can not alias pointer (b).
For example, consider code like:
struct { int f0, int f1, ...} foo;
...
foo alloca;
foo *random = bar(alloca);
int *f0 = &alloca.f0
int *f1 = &random->f1;
Which is lowered, approximately, to:
%alloca = alloca %struct.foo
%random = call %struct.foo* @random(%struct.foo* %alloca)
%f0 = getelementptr inbounds %struct, %struct.foo* %alloca, i32 0, i32 0
%f1 = getelementptr inbounds %struct, %struct.foo* %random, i32 0, i32 1
Assume %f1 and %f0 alias. Then %f1 would point into the object allocated
by %alloca. Since the %f1 GEP is inbounds, that means %random must also
point into the same object. But since %f0 points to the beginning of %alloca,
the highest %f1 can be is (%alloca + 3). This means %random can not be higher
than (%alloca - 1), and so is not inbounds, a contradiction.
Differential Revision: http://reviews.llvm.org/D20495
llvm-svn: 270777
When it has a DataLayout, DecomposeGEPExpression() should return the same object
as GetUnderlyingObject(). Per the FIXME, it currently always has a DL, so the
runtime check is redundant and can become an assert.
llvm-svn: 270268
Equivalent GEP indices with different types are treated as different
indices altogether, leading to an incorrect AA result. Fix the issue
by comparing indices based on their values.
Thanks to Mikael Holmén for reporting the issue!
Differential Revision: http://reviews.llvm.org/D19935
llvm-svn: 269197
Summary:
The idea is very close to what we do for assume intrinsics: we mark the
guard intrinsics as writing to arbitrary memory to maintain control
dependence, but under the covers we teach AA that they do not mod any
particular memory location.
Reviewers: chandlerc, hfinkel, gbiv, reames
Subscribers: george.burgess.iv, mcrosier, llvm-commits
Differential Revision: http://reviews.llvm.org/D19575
llvm-svn: 269007
I tried to be as close as possible to the strongest check that
existed before; cleaning these up properly is left for future work.
Differential Revision: http://reviews.llvm.org/D19469
llvm-svn: 267758
Summary:
Fixes PR26774.
If you're aware of the issue, feel free to skip the "Motivation"
section and jump directly to "This patch".
Motivation:
I define "refinement" as discarding behaviors from a program that the
optimizer has license to discard. So transforming:
```
void f(unsigned x) {
unsigned t = 5 / x;
(void)t;
}
```
to
```
void f(unsigned x) { }
```
is refinement, since the behavior went from "if x == 0 then undefined
else nothing" to "nothing" (the optimizer has license to discard
undefined behavior).
Refinement is a fundamental aspect of many mid-level optimizations done
by LLVM. For instance, transforming `x == (x + 1)` to `false` also
involves refinement since the expression's value went from "if x is
`undef` then { `true` or `false` } else { `false` }" to "`false`" (by
definition, the optimizer has license to fold `undef` to any non-`undef`
value).
Unfortunately, refinement implies that the optimizer cannot assume
that the implementation of a function it can see has all of the
behavior an unoptimized or a differently optimized version of the same
function can have. This is a problem for functions with comdat
linkage, where a function can be replaced by an unoptimized or a
differently optimized version of the same source level function.
For instance, FunctionAttrs cannot assume a comdat function is
actually `readnone` even if it does not have any loads or stores in
it; since there may have been loads and stores in the "original
function" that were refined out in the currently visible variant, and
at the link step the linker may in fact choose an implementation with
a load or a store. As an example, consider a function that does two
atomic loads from the same memory location, and writes to memory only
if the two values are not equal. The optimizer is allowed to refine
this function by first CSE'ing the two loads, and the folding the
comparision to always report that the two values are equal. Such a
refined variant will look like it is `readonly`. However, the
unoptimized version of the function can still write to memory (since
the two loads //can// result in different values), and selecting the
unoptimized version at link time will retroactively invalidate
transforms we may have done under the assumption that the function
does not write to memory.
Note: this is not just a problem with atomics or with linking
differently optimized object files. See PR26774 for more realistic
examples that involved neither.
This patch:
This change introduces a new set of linkage types, predicated as
`GlobalValue::mayBeDerefined` that returns true if the linkage type
allows a function to be replaced by a differently optimized variant at
link time. It then changes a set of IPO passes to bail out if they see
such a function.
Reviewers: chandlerc, hfinkel, dexonsmith, joker.eph, rnk
Subscribers: mcrosier, llvm-commits
Differential Revision: http://reviews.llvm.org/D18634
llvm-svn: 265762
This doesn't change how many times we construct domtrees in the normal
pipeline, and it removes fragility and instability where basic-aa may
not be run in time to see domtrees because they happen to be constructed
afterward.
This isn't quite as clean as the change to memdep because there is
a mode where basic-aa specifically runs without domtrees -- in the
hacking version used by function-attrs with the legacy pass manager.
llvm-svn: 263234
This was originally a pointer to support pass managers which didn't use
AnalysisManagers. However, that doesn't realistically come up much and
the complexity of supporting it doesn't really make sense.
In fact, *many* parts of the pass manager were just assuming the pointer
was never null already. This at least makes it much more explicit and
clear.
llvm-svn: 263219
work in the face of the limitations of DLLs and templated static
variables.
This requires passes that use the AnalysisBase mixin provide a static
variable themselves. So as to keep their APIs clean, I've made these
private and befriended the CRTP base class (which is the common
practice).
I've added documentation to AnalysisBase for why this is necessary and
at what point we can go back to the much simpler system.
This is clearly a better pattern than the extern template as it caught
*numerous* places where the template magic hadn't been applied and
things were "just working" but would eventually have broken
mysteriously.
llvm-svn: 263216
MemoryDependenceAnalysis had a hard-coded exception to the general aliasing rules for malloc and calloc. The reasoning that applied there is equally valid in BasicAA and clarifies the remaining logic in MDA.
In principal, this can expose slightly more optimization opportunities, but since essentially all of our aliasing aware memory optimization passes go through MDA, this will likely be NFC in practice.
Differential Revision: http://reviews.llvm.org/D15912
llvm-svn: 263075
parts of the AA interface out of the base class of every single AA
result object.
Because this logic reformulates the query in terms of some other aspect
of the API, it would easily cause O(n^2) query patterns in alias
analysis. These could in turn be magnified further based on the number
of call arguments, and then further based on the number of AA queries
made for a particular call. This ended up causing problems for Rust that
were actually noticable enough to get a bug (PR26564) and probably other
places as well.
When originally re-working the AA infrastructure, the desire was to
regularize the pattern of refinement without losing any generality.
While I think it was successful, that is clearly proving to be too
costly. And the cost is needless: we gain no actual improvement for this
generality of making a direct query to tbaa actually be able to
re-use some other alias analysis's refinement logic for one of the other
APIs, or some such. In short, this is entirely wasted work.
To the extent possible, delegation to other API surfaces should be done
at the aggregation layer so that we can avoid re-walking the
aggregation. In fact, this significantly simplifies the logic as we no
longer need to smuggle the aggregation layer into each alias analysis
(or the TargetLibraryInfo into each alias analysis just so we can form
argument memory locations!).
However, we also have some delegation logic inside of BasicAA and some
of it even makes sense. When the delegation logic is baking in specific
knowledge of aliasing properties of the LLVM IR, as opposed to simply
reformulating the query to utilize a different alias analysis interface
entry point, it makes a lot of sense to restrict that logic to
a different layer such as BasicAA. So one aspect of the delegation that
was in every AA base class is that when we don't have operand bundles,
we re-use function AA results as a fallback for callsite alias results.
This relies on the IR properties of calls and functions w.r.t. aliasing,
and so seems a better fit to BasicAA. I've lifted the logic up to that
point where it seems to be a natural fit. This still does a bit of
redundant work (we query function attributes twice, once via the
callsite and once via the function AA query) but it is *exactly* twice
here, no more.
The end result is that all of the delegation logic is hoisted out of the
base class and into either the aggregation layer when it is a pure
retargeting to a different API surface, or into BasicAA when it relies
on the IR's aliasing properties. This should fix the quadratic query
pattern reported in PR26564, although I don't have a stand-alone test
case to reproduce it.
It also seems general goodness. Now the numerous AAs that don't need
target library info don't carry it around and depend on it. I think
I can even rip out the general access to the aggregation layer and only
expose that in BasicAA as it is the only place where we re-query in that
manner.
However, this is a non-trivial change to the AA infrastructure so I want
to get some additional eyes on this before it lands. Sadly, it can't
wait long because we should really cherry pick this into 3.8 if we're
going to go this route.
Differential Revision: http://reviews.llvm.org/D17329
llvm-svn: 262490
analyses in the new pass manager.
These just handle really basic stuff: turning a type name into a string
statically that is nice to print in logs, and getting a static unique ID
for each analysis.
Sadly, the format of passes in anonymous namespaces makes using their
names in tests really annoying so I've customized the names of the no-op
passes to keep tests sane to read.
This is the first of a few simplifying refactorings for the new pass
manager that should reduce boilerplate and confusion.
llvm-svn: 262004
Summary:
GEPOperator: provide getResultElementType alongside getSourceElementType.
This is made possible by adding a result element type field to GetElementPtrConstantExpr, which GetElementPtrInst already has.
GEP: replace get(Pointer)ElementType uses with get{Source,Result}ElementType.
Reviewers: mjacob, dblaikie
Subscribers: llvm-commits
Differential Revision: http://reviews.llvm.org/D16275
llvm-svn: 258145
Since writeonly is the only missing attribute and special case left for the memset/memcpy family of intrinsics, rearrange the code to make that much more clear.
llvm-svn: 256949
Most of the properties of memset_pattern16 can be now covered by the generic attributes and inferred by InferFunctionAttrs. The only exceptions are:
- We don't yet have a writeonly attribute for the first argument.
- We don't have an attribute for modeling the access size facts encoded in MemoryLocation.cpp.
Differential Revision: http://reviews.llvm.org/D15879
llvm-svn: 256911
We only need to describe the writeonly property of one of the arguments. All of the rest of the semantics are nicely described by existing attributes in Intrinsics.td.
Differential Revision: http://reviews.llvm.org/D15880
llvm-svn: 256910
In getArgModRefInfo we consider all arguments as having MRI_ModRef.
However for arguments marked with readonly attribute we can return
more precise answer - MRI_Ref.
Differential Revision: http://reviews.llvm.org/D13992
llvm-svn: 251525
Summary: This idiom is used elsewhere in LLVM, but was overlooked here.
Reviewers: chandlerc
Subscribers: llvm-commits
Differential Revision: http://reviews.llvm.org/D13628
llvm-svn: 251348
If the loaded type sizes don't match the element type of the sequential type, all bets are off and the addresses may, indeed, overlap.
Surprisingly, this just got caught in one test, on one builder, out of the 30+ builders testing this change. Congratulations go to http://lab.llvm.org:8011/builders/clang-aarch64-lnt/builds/5205.
llvm-svn: 251112
If the final indices of two GEPs can be proven to not be equal, and
the GEP is of a SequentialType (not a StructType), then the two GEPs
do not alias.
llvm-svn: 251016
Remove implicit ilist iterator conversions from LLVMAnalysis.
I came across something really scary in `llvm::isKnownNotFullPoison()`
which relied on `Instruction::getNextNode()` being completely broken
(not surprising, but scary nevertheless). This function is documented
(and coded to) return `nullptr` when it gets to the sentinel, but with
an `ilist_half_node` as a sentinel, the sentinel check looks into some
other memory and we don't recognize we've hit the end.
Rooting out these scary cases is the reason I'm removing the implicit
conversions before doing anything else with `ilist`; I'm not at all
surprised that clients rely on badness.
I found another scary case -- this time, not relying on badness, just
bad (but I guess getting lucky so far) -- in
`ObjectSizeOffsetEvaluator::compute_()`. Here, we save out the
insertion point, do some things, and then restore it. Previously, we
let the iterator auto-convert to `Instruction*`, and then set it back
using the `Instruction*` version:
Instruction *PrevInsertPoint = Builder.GetInsertPoint();
/* Logic that may change insert point */
if (PrevInsertPoint)
Builder.SetInsertPoint(PrevInsertPoint);
The check for `PrevInsertPoint` doesn't protect correctly against bad
accesses. If the insertion point has been set to the end of a basic
block (i.e., `SetInsertPoint(SomeBB)`), then `GetInsertPoint()` returns
an iterator pointing at the list sentinel. The version of
`SetInsertPoint()` that's getting called will then call
`PrevInsertPoint->getParent()`, which explodes horribly. The only
reason this hasn't blown up is that it's fairly unlikely the builder is
adding to the end of the block; usually, we're adding instructions
somewhere before the terminator.
llvm-svn: 249925
with the new pass manager, and no longer relying on analysis groups.
This builds essentially a ground-up new AA infrastructure stack for
LLVM. The core ideas are the same that are used throughout the new pass
manager: type erased polymorphism and direct composition. The design is
as follows:
- FunctionAAResults is a type-erasing alias analysis results aggregation
interface to walk a single query across a range of results from
different alias analyses. Currently this is function-specific as we
always assume that aliasing queries are *within* a function.
- AAResultBase is a CRTP utility providing stub implementations of
various parts of the alias analysis result concept, notably in several
cases in terms of other more general parts of the interface. This can
be used to implement only a narrow part of the interface rather than
the entire interface. This isn't really ideal, this logic should be
hoisted into FunctionAAResults as currently it will cause
a significant amount of redundant work, but it faithfully models the
behavior of the prior infrastructure.
- All the alias analysis passes are ported to be wrapper passes for the
legacy PM and new-style analysis passes for the new PM with a shared
result object. In some cases (most notably CFL), this is an extremely
naive approach that we should revisit when we can specialize for the
new pass manager.
- BasicAA has been restructured to reflect that it is much more
fundamentally a function analysis because it uses dominator trees and
loop info that need to be constructed for each function.
All of the references to getting alias analysis results have been
updated to use the new aggregation interface. All the preservation and
other pass management code has been updated accordingly.
The way the FunctionAAResultsWrapperPass works is to detect the
available alias analyses when run, and add them to the results object.
This means that we should be able to continue to respect when various
passes are added to the pipeline, for example adding CFL or adding TBAA
passes should just cause their results to be available and to get folded
into this. The exception to this rule is BasicAA which really needs to
be a function pass due to using dominator trees and loop info. As
a consequence, the FunctionAAResultsWrapperPass directly depends on
BasicAA and always includes it in the aggregation.
This has significant implications for preserving analyses. Generally,
most passes shouldn't bother preserving FunctionAAResultsWrapperPass
because rebuilding the results just updates the set of known AA passes.
The exception to this rule are LoopPass instances which need to preserve
all the function analyses that the loop pass manager will end up
needing. This means preserving both BasicAAWrapperPass and the
aggregating FunctionAAResultsWrapperPass.
Now, when preserving an alias analysis, you do so by directly preserving
that analysis. This is only necessary for non-immutable-pass-provided
alias analyses though, and there are only three of interest: BasicAA,
GlobalsAA (formerly GlobalsModRef), and SCEVAA. Usually BasicAA is
preserved when needed because it (like DominatorTree and LoopInfo) is
marked as a CFG-only pass. I've expanded GlobalsAA into the preserved
set everywhere we previously were preserving all of AliasAnalysis, and
I've added SCEVAA in the intersection of that with where we preserve
SCEV itself.
One significant challenge to all of this is that the CGSCC passes were
actually using the alias analysis implementations by taking advantage of
a pretty amazing set of loop holes in the old pass manager's analysis
management code which allowed analysis groups to slide through in many
cases. Moving away from analysis groups makes this problem much more
obvious. To fix it, I've leveraged the flexibility the design of the new
PM components provides to just directly construct the relevant alias
analyses for the relevant functions in the IPO passes that need them.
This is a bit hacky, but should go away with the new pass manager, and
is already in many ways cleaner than the prior state.
Another significant challenge is that various facilities of the old
alias analysis infrastructure just don't fit any more. The most
significant of these is the alias analysis 'counter' pass. That pass
relied on the ability to snoop on AA queries at different points in the
analysis group chain. Instead, I'm planning to build printing
functionality directly into the aggregation layer. I've not included
that in this patch merely to keep it smaller.
Note that all of this needs a nearly complete rewrite of the AA
documentation. I'm planning to do that, but I'd like to make sure the
new design settles, and to flesh out a bit more of what it looks like in
the new pass manager first.
Differential Revision: http://reviews.llvm.org/D12080
llvm-svn: 247167
Hopefully this will end the GEPs saga!
This commit reverts r245394, i.e., it reapplies r221876 while incorporating the
fixes from D11847.
r221876 was not reapplied alone because it was not safe and D11847 was not
applied alone because it needs r221876 to produce correct results.
This should fix PR24596.
Original commit message for r221876:
Let's try this again...
This reverts r219432, plus a bug fix.
Description of the bug in r219432 (by Nick):
The bug was using AllPositive to break out of the loop; if the loop break
condition i != e is changed to i != e && AllPositive then the
test_modulo_analysis_with_global test I've added will fail as the Modulo will
be calculated incorrectly (as the last loop iteration is skipped, so Modulo
isn't updated with its Scale).
Nick also adds this comment:
ComputeSignBit is safe to use in loops as it takes into account phi nodes, and
the == EK_ZeroEx check is safe in loops as, no matter how the variable changes
between iterations, zero-extensions will always guarantee a zero sign bit. The
isValueEqualInPotentialCycles check is therefore definitely not needed as all
the variable analysis holds no matter how the variables change between loop
iterations.
And this patch also adds another enhancement to GetLinearExpression - basically
to convert ConstantInts to Offsets (see test_const_eval and
test_const_eval_scaled for the situations this improves).
Original commit message:
This reverts r218944, which reverted r218714, plus a bug fix.
Description of the bug in r218714 (by Nick):
The original patch forgot to check if the Scale in VariableGEPIndex flipped the
sign of the variable. The BasicAA pass iterates over the instructions in the
order they appear in the function, and so BasicAliasAnalysis::aliasGEP is
called with the variable it first comes across as parameter GEP1. Adding a
%reorder label puts the definition of %a after %b so aliasGEP is called with %b
as the first parameter and %a as the second. aliasGEP later calculates that %a
== %b + 1 - %idxprom where %idxprom >= 0 (if %a was passed as the first
parameter it would calculate %b == %a - 1 + %idxprom where %idxprom >= 0) -
ignoring that %idxprom is scaled by -1 here lead the patch to incorrectly
conclude that %a > %b.
Revised patch by Nick White, thanks! Thanks to Lang to isolating the bug.
Slightly modified by me to add an early exit from the loop and avoid
unnecessary, but expensive, function calls.
Original commit message:
Two related things:
1. Fixes a bug when calculating the offset in GetLinearExpression. The code
previously used zext to extend the offset, so negative offsets were converted
to large positive ones.
2. Enhance aliasGEP to deduce that, if the difference between two GEP
allocations is positive and all the variables that govern the offset are also
positive (i.e. the offset is strictly after the higher base pointer), then
locations that fit in the gap between the two base pointers are NoAlias.
Patch by Nick White!
Message from D11847:
Un-revert of r241981 and fix for PR23626. The 'Or' case of GetLinearExpression
delegates to 'Add' if possible, and if not it returns an Opaque value.
Unfortunately the Scale and Offsets weren't being set (and so defaulted to 0) -
and a scale of zero effectively removes the variable from the GEP instruction.
This meant that BasicAA would return MustAliases when it should have been
returning PartialAliases (and PR23626 was an example of the GVN pass using an
incorrect MustAlias to merge loads from what should have been different
pointers).
Differential Revision: http://reviews.llvm.org/D11847
Patch by Nick White <n.j.white@gmail.com>!
llvm-svn: 246502
All possible ModRef behaviours can be completely represented using existing LLVM IR attributes.
Differential Revision: http://reviews.llvm.org/D12033
llvm-svn: 245224
This is the first mechanical step in preparation for making this and all
the other alias analysis passes available to the new pass manager. I'm
factoring out all the totally boring changes I can so I'm moving code
around here with no other changes. I've even minimized the formatting
churn.
I'll reformat and freshen comments on the interface now that its located
in the right place so that the substantive changes don't triger this.
llvm-svn: 244197
preparation for de-coupling the AA implementations.
In order to do this, they had to become fake-scoped using the
traditional LLVM pattern of a leading initialism. These can't be actual
scoped enumerations because they're bitfields and thus inherently we use
them as integers.
I've also renamed the behavior enums that are specific to reasoning
about the mod/ref behavior of functions when called. This makes it more
clear that they have a very narrow domain of applicability.
I think there is a significantly cleaner API for all of this, but
I don't want to try to do really substantive changes for now, I just
want to refactor the things away from analysis groups so I'm preserving
the exact original design and just cleaning up the names, style, and
lifting out of the class.
Differential Revision: http://reviews.llvm.org/D10564
llvm-svn: 242963
Summary:
This patch allows phi nodes like
%x = phi [ %incptr, ... ] [ %var, ... ]
%incptr = getelementptr %x, 1
to be analyzed by BasicAliasAnalysis.
In aliasPHI, we can detect incoming values that are recursive GEPs with a
constant offset. Instead of trying to analyze a recursive GEP (and failing),
we now ignore it and instead set the size of the memory referenced by
the PHINode to UnknownSize. This represents all the possible memory
locations the pointer represented by the PHINode could be advanced to
by the GEP.
For now, this new behavior is turned off by default to allow debugging of
performance degradations seen with SPEC/x86 and Hexagon benchmarks.
The flag -basicaa-recphi turns it on.
Reviewers: hfinkel, sanjoy
Subscribers: tobiasvk_caf, sanjoy, llvm-commits
Differential Revision: http://reviews.llvm.org/D10368
llvm-svn: 242320
r236894 caused PR23626 (Clang miscompiles webkit's base64 decoder), and was
reverted in r237984. This reapplies the patch with an additional test case for
PR23626 and the associated fix (both scales and offsets in the
BasicAliasAnalysis::constantOffsetHeuristic should initially be zero).
Patch by Nick White, thanks!
llvm-svn: 241981
This change adds new attribute called "argmemonly". Function marked with this attribute can only access memory through it's argument pointers. This attribute directly corresponds to the "OnlyAccessesArgumentPointees" ModRef behaviour in alias analysis.
Differential Revision: http://reviews.llvm.org/D10398
llvm-svn: 241979
This will allow classes to implement the AA interface without deriving
from the class or referencing an internal enum of some other class as
their return types.
Also, to a pretty fundamental extent, concepts such as 'NoAlias',
'MayAlias', and 'MustAlias' are first class concepts in LLVM and we
aren't saving anything by scoping them heavily.
My mild preference would have been to use a scoped enum, but that
feature is essentially completely broken AFAICT. I'm extremely
disappointed. For example, we cannot through any reasonable[1] means
construct an enum class (or analog) which has scoped names but converts
to a boolean in order to test for the possibility of aliasing.
[1]: Richard Smith came up with a "solution", but it requires class
templates, and lots of boilerplate setting up the enumeration multiple
times. Something like Boost.PP could potentially bundle this up, but
even that would be quite painful and it doesn't seem realistically worth
it. The enum class solution would probably work without the need for
a bool conversion.
Differential Revision: http://reviews.llvm.org/D10495
llvm-svn: 240255
The patch is generated using this command:
tools/clang/tools/extra/clang-tidy/tool/run-clang-tidy.py -fix \
-checks=-*,llvm-namespace-comment -header-filter='llvm/.*|clang/.*' \
llvm/lib/
Thanks to Eugene Kosov for the original patch!
llvm-svn: 240137
This is now living in MemoryLocation, which is what it pertains to. It
is also an enum there rather than a static data member which is left
never defined.
llvm-svn: 239886
that it is its own entity in the form of MemoryLocation, and update all
the callers.
This is an entirely mechanical change. References to "Location" within
AA subclases become "MemoryLocation", and elsewhere
"AliasAnalysis::Location" becomes "MemoryLocation". Hope that helps
out-of-tree folks update.
llvm-svn: 239885
virtual interface on AliasAnalysis only deals with ModRef information.
This interface was both computing memory locations by using TLI and
other tricks to estimate the size of memory referenced by an operand,
and computing ModRef information through similar investigations. This
change narrows the scope of the virtual interface on AliasAnalysis
slightly.
Note that all of this code could live in BasicAA, and be done with
a single investigation of the argument, if it weren't for the fact that
the generic code in AliasAnalysis::getModRefBehavior for a callsite
calls into the virtual aspect of (now) getArgModRefInfo. But this
patch's arrangement seems a not terrible way to go for now.
The other interesting wrinkle is how we could reasonably extend LLVM
with support for custom memory location sizes and mod/ref behavior for
library routines. After discussions with Hal on the review, the
conclusion is that this would be best done by fleshing out the much
desired support for extensions to TLI, and support these types of
queries in that interface where we would likely be doing other library
API recognition and analysis.
Differential Revision: http://reviews.llvm.org/D10259
llvm-svn: 239884
Now that Intrinsic::ID is a typed enum, we can forward declare it and so return it from this method.
This updates all users which were either using an unsigned to store it, or had a now unnecessary cast.
llvm-svn: 237810
We already had a method to iterate over all the incoming values of a PHI. This just changes all eligible code to use it.
Ineligible code included anything which cared about the index, or was also trying to get the i'th incoming BB.
llvm-svn: 237169
Summary:
There are several unhandled edge cases in BasicAA's GetLinearExpression
method. This changes fixes outstanding issues, including zext / sext of
a constant with the sign bit set, and the refusal to decompose zexts or
sexts of wrapping arithmetic.
Test Plan: Unit tests added in //q.ext.ll//.
Patch by Nick White.
Reviewers: hfinkel, sanjoy
Reviewed By: hfinkel, sanjoy
Subscribers: sanjoy, llvm-commits, hfinkel
Differential Revision: http://reviews.llvm.org/D6682
llvm-svn: 236894
It got this in some cases (if one of them was an identified object), but not in all cases.
This caused stores to undef to block load-forwarding in some cases, etc.
Added test to Transforms/GVN to verify optimization occurs as expected.
llvm-svn: 236511
This pushes the use of PointerType::getElementType up into several
callers - I'll essentially just have to keep pushing that up the stack
until I can eliminate every call to it...
llvm-svn: 233604
