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Attributor.h
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Attributor.h
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//===- Attributor.h --- Module-wide attribute deduction ---------*- C++ -*-===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
//
// Attributor: An inter procedural (abstract) "attribute" deduction framework.
//
// The Attributor framework is an inter procedural abstract analysis (fixpoint
// iteration analysis). The goal is to allow easy deduction of new attributes as
// well as information exchange between abstract attributes in-flight.
//
// The Attributor class is the driver and the link between the various abstract
// attributes. The Attributor will iterate until a fixpoint state is reached by
// all abstract attributes in-flight, or until it will enforce a pessimistic fix
// point because an iteration limit is reached.
//
// Abstract attributes, derived from the AbstractAttribute class, actually
// describe properties of the code. They can correspond to actual LLVM-IR
// attributes, or they can be more general, ultimately unrelated to LLVM-IR
// attributes. The latter is useful when an abstract attributes provides
// information to other abstract attributes in-flight but we might not want to
// manifest the information. The Attributor allows to query in-flight abstract
// attributes through the `Attributor::getAAFor` method (see the method
// description for an example). If the method is used by an abstract attribute
// P, and it results in an abstract attribute Q, the Attributor will
// automatically capture a potential dependence from Q to P. This dependence
// will cause P to be reevaluated whenever Q changes in the future.
//
// The Attributor will only reevaluated abstract attributes that might have
// changed since the last iteration. That means that the Attribute will not
// revisit all instructions/blocks/functions in the module but only query
// an update from a subset of the abstract attributes.
//
// The update method `AbstractAttribute::updateImpl` is implemented by the
// specific "abstract attribute" subclasses. The method is invoked whenever the
// currently assumed state (see the AbstractState class) might not be valid
// anymore. This can, for example, happen if the state was dependent on another
// abstract attribute that changed. In every invocation, the update method has
// to adjust the internal state of an abstract attribute to a point that is
// justifiable by the underlying IR and the current state of abstract attributes
// in-flight. Since the IR is given and assumed to be valid, the information
// derived from it can be assumed to hold. However, information derived from
// other abstract attributes is conditional on various things. If the justifying
// state changed, the `updateImpl` has to revisit the situation and potentially
// find another justification or limit the optimistic assumes made.
//
// Change is the key in this framework. Until a state of no-change, thus a
// fixpoint, is reached, the Attributor will query the abstract attributes
// in-flight to re-evaluate their state. If the (current) state is too
// optimistic, hence it cannot be justified anymore through other abstract
// attributes or the state of the IR, the state of the abstract attribute will
// have to change. Generally, we assume abstract attribute state to be a finite
// height lattice and the update function to be monotone. However, these
// conditions are not enforced because the iteration limit will guarantee
// termination. If an optimistic fixpoint is reached, or a pessimistic fix
// point is enforced after a timeout, the abstract attributes are tasked to
// manifest their result in the IR for passes to come.
//
// Attribute manifestation is not mandatory. If desired, there is support to
// generate a single or multiple LLVM-IR attributes already in the helper struct
// IRAttribute. In the simplest case, a subclass inherits from IRAttribute with
// a proper Attribute::AttrKind as template parameter. The Attributor
// manifestation framework will then create and place a new attribute if it is
// allowed to do so (based on the abstract state). Other use cases can be
// achieved by overloading AbstractAttribute or IRAttribute methods.
//
//
// The "mechanics" of adding a new "abstract attribute":
// - Define a class (transitively) inheriting from AbstractAttribute and one
// (which could be the same) that (transitively) inherits from AbstractState.
// For the latter, consider the already available BooleanState and
// IntegerState if they fit your needs, e.g., you require only a bit-encoding.
// - Implement all pure methods. Also use overloading if the attribute is not
// conforming with the "default" behavior: A (set of) LLVM-IR attribute(s) for
// an argument, call site argument, function return value, or function. See
// the class and method descriptions for more information on the two
// "Abstract" classes and their respective methods.
// - Register opportunities for the new abstract attribute in the
// `Attributor::identifyDefaultAbstractAttributes` method if it should be
// counted as a 'default' attribute.
// - Add sufficient tests.
// - Add a Statistics object for bookkeeping. If it is a simple (set of)
// attribute(s) manifested through the Attributor manifestation framework, see
// the bookkeeping function in Attributor.cpp.
// - If instructions with a certain opcode are interesting to the attribute, add
// that opcode to the switch in `Attributor::identifyAbstractAttributes`. This
// will make it possible to query all those instructions through the
// `InformationCache::getOpcodeInstMapForFunction` interface and eliminate the
// need to traverse the IR repeatedly.
//
//===----------------------------------------------------------------------===//
#ifndef LLVM_TRANSFORMS_IPO_ATTRIBUTOR_H
#define LLVM_TRANSFORMS_IPO_ATTRIBUTOR_H
#include "llvm/ADT/SetVector.h"
#include "llvm/ADT/MapVector.h"
#include "llvm/IR/CallSite.h"
#include "llvm/IR/PassManager.h"
namespace llvm {
struct AbstractAttribute;
struct InformationCache;
struct AAIsDead;
class Function;
/// Simple enum class that forces the status to be spelled out explicitly.
///
///{
enum class ChangeStatus {
CHANGED,
UNCHANGED,
};
ChangeStatus operator|(ChangeStatus l, ChangeStatus r);
ChangeStatus operator&(ChangeStatus l, ChangeStatus r);
///}
/// Helper to describe and deal with positions in the LLVM-IR.
///
/// A position in the IR is described by an anchor value and an "offset" that
/// could be the argument number, for call sites and arguments, or an indicator
/// of the "position kind". The kinds, specified in the Kind enum below, include
/// the locations in the attribute list, i.a., function scope and return value,
/// as well as a distinction between call sites and functions. Finally, there
/// are floating values that do not have a corresponding attribute list
/// position.
struct IRPosition {
virtual ~IRPosition() {}
/// The positions we distinguish in the IR.
///
/// The values are chosen such that the KindOrArgNo member has a value >= 1
/// if it is an argument or call site argument while a value < 1 indicates the
/// respective kind of that value.
enum Kind : int {
IRP_INVALID = -6, ///< An invalid position.
IRP_FLOAT = -5, ///< A position that is not associated with a spot suitable
///< for attributes. This could be any value or instruction.
IRP_RETURNED = -4, ///< An attribute for the function return value.
IRP_CALL_SITE_RETURNED = -3, ///< An attribute for a call site return value.
IRP_FUNCTION = -2, ///< An attribute for a function (scope).
IRP_CALL_SITE = -1, ///< An attribute for a call site (function scope).
IRP_ARGUMENT = 0, ///< An attribute for a function argument.
IRP_CALL_SITE_ARGUMENT = 1, ///< An attribute for a call site argument.
};
/// Default constructor available to create invalid positions implicitly. All
/// other positions need to be created explicitly through the appropriate
/// static member function.
IRPosition() : AnchorVal(nullptr), KindOrArgNo(IRP_INVALID) { verify(); }
/// Create a position describing the value of \p V.
static const IRPosition value(const Value &V) {
if (auto *Arg = dyn_cast<Argument>(&V))
return IRPosition::argument(*Arg);
if (auto *CB = dyn_cast<CallBase>(&V))
return IRPosition::callsite_returned(*CB);
return IRPosition(const_cast<Value &>(V), IRP_FLOAT);
}
/// Create a position describing the function scope of \p F.
static const IRPosition function(const Function &F) {
return IRPosition(const_cast<Function &>(F), IRP_FUNCTION);
}
/// Create a position describing the returned value of \p F.
static const IRPosition returned(const Function &F) {
return IRPosition(const_cast<Function &>(F), IRP_RETURNED);
}
/// Create a position describing the argument \p Arg.
static const IRPosition argument(const Argument &Arg) {
return IRPosition(const_cast<Argument &>(Arg), Kind(Arg.getArgNo()));
}
/// Create a position describing the function scope of \p CB.
static const IRPosition callsite_function(const CallBase &CB) {
return IRPosition(const_cast<CallBase &>(CB), IRP_CALL_SITE);
}
/// Create a position describing the returned value of \p CB.
static const IRPosition callsite_returned(const CallBase &CB) {
return IRPosition(const_cast<CallBase &>(CB), IRP_CALL_SITE_RETURNED);
}
/// Create a position describing the argument of \p CB at position \p ArgNo.
static const IRPosition callsite_argument(const CallBase &CB,
unsigned ArgNo) {
return IRPosition(const_cast<CallBase &>(CB), Kind(ArgNo));
}
/// Create a position describing the function scope of \p ICS.
static const IRPosition callsite_function(ImmutableCallSite ICS) {
return IRPosition::callsite_function(cast<CallBase>(*ICS.getInstruction()));
}
/// Create a position describing the returned value of \p ICS.
static const IRPosition callsite_returned(ImmutableCallSite ICS) {
return IRPosition::callsite_returned(cast<CallBase>(*ICS.getInstruction()));
}
/// Create a position describing the argument of \p ICS at position \p ArgNo.
static const IRPosition callsite_argument(ImmutableCallSite ICS,
unsigned ArgNo) {
return IRPosition::callsite_argument(cast<CallBase>(*ICS.getInstruction()),
ArgNo);
}
/// Create a position with function scope matching the "context" of \p IRP.
/// If \p IRP is a call site (see isAnyCallSitePosition()) then the result
/// will be a call site position, otherwise the function position of the
/// associated function.
static const IRPosition function_scope(const IRPosition &IRP) {
if (IRP.isAnyCallSitePosition()) {
return IRPosition::callsite_function(
cast<CallBase>(IRP.getAnchorValue()));
}
assert(IRP.getAssociatedFunction());
return IRPosition::function(*IRP.getAssociatedFunction());
}
bool operator==(const IRPosition &RHS) const {
return (AnchorVal == RHS.AnchorVal) && (KindOrArgNo == RHS.KindOrArgNo);
}
bool operator!=(const IRPosition &RHS) const { return !(*this == RHS); }
/// Return the value this abstract attribute is anchored with.
///
/// The anchor value might not be the associated value if the latter is not
/// sufficient to determine where arguments will be manifested. This is, so
/// far, only the case for call site arguments as the value is not sufficient
/// to pinpoint them. Instead, we can use the call site as an anchor.
///
///{
Value &getAnchorValue() {
assert(KindOrArgNo != IRP_INVALID &&
"Invalid position does not have an anchor value!");
return *AnchorVal;
}
const Value &getAnchorValue() const {
return const_cast<IRPosition *>(this)->getAnchorValue();
}
///}
/// Return the associated function, if any.
///
///{
Function *getAssociatedFunction() {
if (auto *CB = dyn_cast<CallBase>(AnchorVal))
return CB->getCalledFunction();
assert(KindOrArgNo != IRP_INVALID &&
"Invalid position does not have an anchor scope!");
Value &V = getAnchorValue();
if (isa<Function>(V))
return &cast<Function>(V);
if (isa<Argument>(V))
return cast<Argument>(V).getParent();
if (isa<Instruction>(V))
return cast<Instruction>(V).getFunction();
return nullptr;
}
const Function *getAssociatedFunction() const {
return const_cast<IRPosition *>(this)->getAssociatedFunction();
}
///}
/// Return the associated argument, if any.
///
///{
Argument *getAssociatedArgument() {
if (auto *Arg = dyn_cast<Argument>(&getAnchorValue()))
return Arg;
int ArgNo = getArgNo();
if (ArgNo < 0)
return nullptr;
Function *AssociatedFn = getAssociatedFunction();
if (!AssociatedFn || AssociatedFn->arg_size() <= unsigned(ArgNo))
return nullptr;
return AssociatedFn->arg_begin() + ArgNo;
}
const Argument *getAssociatedArgument() const {
return const_cast<IRPosition *>(this)->getAssociatedArgument();
}
///}
/// Return true if the position refers to a function interface, that is the
/// function scope, the function return, or an argumnt.
bool isFnInterfaceKind() const {
switch (getPositionKind()) {
case IRPosition::IRP_FUNCTION:
case IRPosition::IRP_RETURNED:
case IRPosition::IRP_ARGUMENT:
return true;
default:
return false;
}
}
/// Return the Function surrounding the anchor value.
///
///{
Function *getAnchorScope() {
Value &V = getAnchorValue();
if (isa<Function>(V))
return &cast<Function>(V);
if (isa<Argument>(V))
return cast<Argument>(V).getParent();
if (isa<Instruction>(V))
return cast<Instruction>(V).getFunction();
return nullptr;
}
const Function *getAnchorScope() const {
return const_cast<IRPosition *>(this)->getAnchorScope();
}
///}
/// Return the context instruction, if any.
///
///{
Instruction *getCtxI() {
Value &V = getAnchorValue();
if (auto *I = dyn_cast<Instruction>(&V))
return I;
if (auto *Arg = dyn_cast<Argument>(&V))
if (!Arg->getParent()->isDeclaration())
return &Arg->getParent()->getEntryBlock().front();
if (auto *F = dyn_cast<Function>(&V))
if (!F->isDeclaration())
return &(F->getEntryBlock().front());
return nullptr;
}
const Instruction *getCtxI() const {
return const_cast<IRPosition *>(this)->getCtxI();
}
///}
/// Return the value this abstract attribute is associated with.
///
///{
Value &getAssociatedValue() {
assert(KindOrArgNo != IRP_INVALID &&
"Invalid position does not have an associated value!");
if (getArgNo() < 0 || isa<Argument>(AnchorVal))
return *AnchorVal;
assert(isa<CallBase>(AnchorVal) && "Expected a call base!");
return *cast<CallBase>(AnchorVal)->getArgOperand(getArgNo());
}
const Value &getAssociatedValue() const {
return const_cast<IRPosition *>(this)->getAssociatedValue();
}
///}
/// Return the argument number of the associated value if it is an argument or
/// call site argument, otherwise a negative value.
int getArgNo() const { return KindOrArgNo; }
/// Return the index in the attribute list for this position.
unsigned getAttrIdx() const {
switch (getPositionKind()) {
case IRPosition::IRP_INVALID:
case IRPosition::IRP_FLOAT:
break;
case IRPosition::IRP_FUNCTION:
case IRPosition::IRP_CALL_SITE:
return AttributeList::FunctionIndex;
case IRPosition::IRP_RETURNED:
case IRPosition::IRP_CALL_SITE_RETURNED:
return AttributeList::ReturnIndex;
case IRPosition::IRP_ARGUMENT:
case IRPosition::IRP_CALL_SITE_ARGUMENT:
return KindOrArgNo + AttributeList::FirstArgIndex;
}
llvm_unreachable(
"There is no attribute index for a floating or invalid position!");
}
/// Return the associated position kind.
Kind getPositionKind() const {
if (getArgNo() >= 0) {
assert(((isa<Argument>(getAnchorValue()) &&
isa<Argument>(getAssociatedValue())) ||
isa<CallBase>(getAnchorValue())) &&
"Expected argument or call base due to argument number!");
if (isa<CallBase>(getAnchorValue()))
return IRP_CALL_SITE_ARGUMENT;
return IRP_ARGUMENT;
}
assert(KindOrArgNo < 0 &&
"Expected (call site) arguments to never reach this point!");
assert(!isa<Argument>(getAnchorValue()) &&
"Expected arguments to have an associated argument position!");
return Kind(KindOrArgNo);
}
/// TODO: Figure out if the attribute related helper functions should live
/// here or somewhere else.
/// Return true if any kind in \p AKs existing in the IR at a position that
/// will affect this one. See also getAttrs(...).
bool hasAttr(ArrayRef<Attribute::AttrKind> AKs) const;
/// Return the attributes of any kind in \p AKs existing in the IR at a
/// position that will affect this one. While each position can only have a
/// single attribute of any kind in \p AKs, there are "subsuming" positions
/// that could have an attribute as well. This method returns all attributes
/// found in \p Attrs.
void getAttrs(ArrayRef<Attribute::AttrKind> AKs,
SmallVectorImpl<Attribute> &Attrs) const;
/// Return the attribute of kind \p AK existing in the IR at this position.
Attribute getAttr(Attribute::AttrKind AK) const {
if (getPositionKind() == IRP_INVALID || getPositionKind() == IRP_FLOAT)
return Attribute();
AttributeList AttrList;
if (ImmutableCallSite ICS = ImmutableCallSite(&getAnchorValue()))
AttrList = ICS.getAttributes();
else
AttrList = getAssociatedFunction()->getAttributes();
if (AttrList.hasAttribute(getAttrIdx(), AK))
return AttrList.getAttribute(getAttrIdx(), AK);
return Attribute();
}
bool isAnyCallSitePosition() const {
switch (getPositionKind()) {
case IRPosition::IRP_CALL_SITE:
case IRPosition::IRP_CALL_SITE_RETURNED:
case IRPosition::IRP_CALL_SITE_ARGUMENT:
return true;
default:
return false;
}
}
/// Special DenseMap key values.
///
///{
static const IRPosition EmptyKey;
static const IRPosition TombstoneKey;
///}
private:
/// Private constructor for special values only!
explicit IRPosition(int KindOrArgNo)
: AnchorVal(0), KindOrArgNo(KindOrArgNo) {}
/// IRPosition anchored at \p AnchorVal with kind/argument numbet \p PK.
explicit IRPosition(Value &AnchorVal, Kind PK)
: AnchorVal(&AnchorVal), KindOrArgNo(PK) {
verify();
}
/// Verify internal invariants.
void verify();
/// The value this position is anchored at.
Value *AnchorVal;
/// The argument number, if non-negative, or the position "kind".
int KindOrArgNo;
};
/// Helper that allows IRPosition as a key in a DenseMap.
template <> struct DenseMapInfo<IRPosition> {
static inline IRPosition getEmptyKey() { return IRPosition::EmptyKey; }
static inline IRPosition getTombstoneKey() {
return IRPosition::TombstoneKey;
}
static unsigned getHashValue(const IRPosition &IRP) {
return (DenseMapInfo<Value *>::getHashValue(&IRP.getAnchorValue()) << 4) ^
(unsigned(IRP.getArgNo()));
}
static bool isEqual(const IRPosition &LHS, const IRPosition &RHS) {
return LHS == RHS;
}
};
/// A visitor class for IR positions.
///
/// Given a position P, the SubsumingPositionIterator allows to visit "subsuming
/// positions" wrt. attributes/information. Thus, if a piece of information
/// holds for a subsuming position, it also holds for the position P.
///
/// The subsuming positions always include the initial position and then,
/// depending on the position kind, additionally the following ones:
/// - for IRP_RETURNED:
/// - the function (IRP_FUNCTION)
/// - for IRP_ARGUMENT:
/// - the function (IRP_FUNCTION)
/// - for IRP_CALL_SITE:
/// - the callee (IRP_FUNCTION), if known
/// - for IRP_CALL_SITE_RETURNED:
/// - the callee (IRP_RETURNED), if known
/// - the call site (IRP_FUNCTION)
/// - the callee (IRP_FUNCTION), if known
/// - for IRP_CALL_SITE_ARGUMENT:
/// - the argument of the callee (IRP_ARGUMENT), if known
/// - the callee (IRP_FUNCTION), if known
/// - the position the call site argument is associated with if it is not
/// anchored to the call site, e.g., if it is an arugment then the argument
/// (IRP_ARGUMENT)
class SubsumingPositionIterator {
SmallVector<IRPosition, 4> IRPositions;
using iterator = decltype(IRPositions)::iterator;
public:
SubsumingPositionIterator(const IRPosition &IRP);
iterator begin() { return IRPositions.begin(); }
iterator end() { return IRPositions.end(); }
};
/// Data structure to hold cached (LLVM-IR) information.
///
/// All attributes are given an InformationCache object at creation time to
/// avoid inspection of the IR by all of them individually. This default
/// InformationCache will hold information required by 'default' attributes,
/// thus the ones deduced when Attributor::identifyDefaultAbstractAttributes(..)
/// is called.
///
/// If custom abstract attributes, registered manually through
/// Attributor::registerAA(...), need more information, especially if it is not
/// reusable, it is advised to inherit from the InformationCache and cast the
/// instance down in the abstract attributes.
struct InformationCache {
InformationCache(const DataLayout &DL) : DL(DL) {}
/// A map type from opcodes to instructions with this opcode.
using OpcodeInstMapTy = DenseMap<unsigned, SmallVector<Instruction *, 32>>;
/// Return the map that relates "interesting" opcodes with all instructions
/// with that opcode in \p F.
OpcodeInstMapTy &getOpcodeInstMapForFunction(const Function &F) {
return FuncInstOpcodeMap[&F];
}
/// A vector type to hold instructions.
using InstructionVectorTy = std::vector<Instruction *>;
/// Return the instructions in \p F that may read or write memory.
InstructionVectorTy &getReadOrWriteInstsForFunction(const Function &F) {
return FuncRWInstsMap[&F];
}
private:
/// A map type from functions to opcode to instruction maps.
using FuncInstOpcodeMapTy = DenseMap<const Function *, OpcodeInstMapTy>;
/// A map type from functions to their read or write instructions.
using FuncRWInstsMapTy = DenseMap<const Function *, InstructionVectorTy>;
/// A nested map that remembers all instructions in a function with a certain
/// instruction opcode (Instruction::getOpcode()).
FuncInstOpcodeMapTy FuncInstOpcodeMap;
/// A map from functions to their instructions that may read or write memory.
FuncRWInstsMapTy FuncRWInstsMap;
/// The datalayout used in the module.
const DataLayout &DL;
/// Give the Attributor access to the members so
/// Attributor::identifyDefaultAbstractAttributes(...) can initialize them.
friend struct Attributor;
};
/// The fixpoint analysis framework that orchestrates the attribute deduction.
///
/// The Attributor provides a general abstract analysis framework (guided
/// fixpoint iteration) as well as helper functions for the deduction of
/// (LLVM-IR) attributes. However, also other code properties can be deduced,
/// propagated, and ultimately manifested through the Attributor framework. This
/// is particularly useful if these properties interact with attributes and a
/// co-scheduled deduction allows to improve the solution. Even if not, thus if
/// attributes/properties are completely isolated, they should use the
/// Attributor framework to reduce the number of fixpoint iteration frameworks
/// in the code base. Note that the Attributor design makes sure that isolated
/// attributes are not impacted, in any way, by others derived at the same time
/// if there is no cross-reasoning performed.
///
/// The public facing interface of the Attributor is kept simple and basically
/// allows abstract attributes to one thing, query abstract attributes
/// in-flight. There are two reasons to do this:
/// a) The optimistic state of one abstract attribute can justify an
/// optimistic state of another, allowing to framework to end up with an
/// optimistic (=best possible) fixpoint instead of one based solely on
/// information in the IR.
/// b) This avoids reimplementing various kinds of lookups, e.g., to check
/// for existing IR attributes, in favor of a single lookups interface
/// provided by an abstract attribute subclass.
///
/// NOTE: The mechanics of adding a new "concrete" abstract attribute are
/// described in the file comment.
struct Attributor {
/// Constructor
///
/// \param InfoCache Cache to hold various information accessible for
/// the abstract attributes.
/// \param DepRecomputeInterval Number of iterations until the dependences
/// between abstract attributes are recomputed.
/// \param Whitelist If not null, a set limiting the attribute opportunities.
Attributor(InformationCache &InfoCache, unsigned DepRecomputeInterval,
DenseSet<const char *> *Whitelist = nullptr)
: InfoCache(InfoCache), DepRecomputeInterval(DepRecomputeInterval),
Whitelist(Whitelist) {}
~Attributor() { DeleteContainerPointers(AllAbstractAttributes); }
/// Run the analyses until a fixpoint is reached or enforced (timeout).
///
/// The attributes registered with this Attributor can be used after as long
/// as the Attributor is not destroyed (it owns the attributes now).
///
/// \Returns CHANGED if the IR was changed, otherwise UNCHANGED.
ChangeStatus run();
/// Lookup an abstract attribute of type \p AAType at position \p IRP. While
/// no abstract attribute is found equivalent positions are checked, see
/// SubsumingPositionIterator. Thus, the returned abstract attribute
/// might be anchored at a different position, e.g., the callee if \p IRP is a
/// call base.
///
/// This method is the only (supported) way an abstract attribute can retrieve
/// information from another abstract attribute. As an example, take an
/// abstract attribute that determines the memory access behavior for a
/// argument (readnone, readonly, ...). It should use `getAAFor` to get the
/// most optimistic information for other abstract attributes in-flight, e.g.
/// the one reasoning about the "captured" state for the argument or the one
/// reasoning on the memory access behavior of the function as a whole.
///
/// If the flag \p TrackDependence is set to false the dependence from
/// \p QueryingAA to the return abstract attribute is not automatically
/// recorded. This should only be used if the caller will record the
/// dependence explicitly if necessary, thus if it the returned abstract
/// attribute is used for reasoning. To record the dependences explicitly use
/// the `Attributor::recordDependence` method.
template <typename AAType>
const AAType &getAAFor(const AbstractAttribute &QueryingAA,
const IRPosition &IRP, bool TrackDependence = true) {
return getOrCreateAAFor<AAType>(IRP, &QueryingAA, TrackDependence);
}
/// Explicitly record a dependence from \p FromAA to \p ToAA, that is if
/// \p FromAA changes \p ToAA should be updated as well.
///
/// This method should be used in conjunction with the `getAAFor` method and
/// with the TrackDependence flag passed to the method set to false. This can
/// be beneficial to avoid false dependences but it requires the users of
/// `getAAFor` to explicitly record true dependences through this method.
void recordDependence(const AbstractAttribute &FromAA,
const AbstractAttribute &ToAA) {
QueryMap[&FromAA].insert(const_cast<AbstractAttribute *>(&ToAA));
}
/// Introduce a new abstract attribute into the fixpoint analysis.
///
/// Note that ownership of the attribute is given to the Attributor. It will
/// invoke delete for the Attributor on destruction of the Attributor.
///
/// Attributes are identified by their IR position (AAType::getIRPosition())
/// and the address of their static member (see AAType::ID).
template <typename AAType> AAType ®isterAA(AAType &AA) {
static_assert(std::is_base_of<AbstractAttribute, AAType>::value,
"Cannot register an attribute with a type not derived from "
"'AbstractAttribute'!");
// Put the attribute in the lookup map structure and the container we use to
// keep track of all attributes.
IRPosition &IRP = AA.getIRPosition();
AAMap[IRP][&AAType::ID] = &AA;
AllAbstractAttributes.push_back(&AA);
return AA;
}
/// Return the internal information cache.
InformationCache &getInfoCache() { return InfoCache; }
/// Determine opportunities to derive 'default' attributes in \p F and create
/// abstract attribute objects for them.
///
/// \param F The function that is checked for attribute opportunities.
///
/// Note that abstract attribute instances are generally created even if the
/// IR already contains the information they would deduce. The most important
/// reason for this is the single interface, the one of the abstract attribute
/// instance, which can be queried without the need to look at the IR in
/// various places.
void identifyDefaultAbstractAttributes(Function &F);
/// Record that \p I is deleted after information was manifested.
void deleteAfterManifest(Instruction &I) { ToBeDeletedInsts.insert(&I); }
/// Record that \p BB is deleted after information was manifested.
void deleteAfterManifest(BasicBlock &BB) { ToBeDeletedBlocks.insert(&BB); }
/// Record that \p F is deleted after information was manifested.
void deleteAfterManifest(Function &F) { ToBeDeletedFunctions.insert(&F); }
/// Return true if \p AA (or its context instruction) is assumed dead.
///
/// If \p LivenessAA is not provided it is queried.
bool isAssumedDead(const AbstractAttribute &AA, const AAIsDead *LivenessAA);
/// Check \p Pred on all function call sites.
///
/// This method will evaluate \p Pred on call sites and return
/// true if \p Pred holds in every call sites. However, this is only possible
/// all call sites are known, hence the function has internal linkage.
bool checkForAllCallSites(const function_ref<bool(CallSite)> &Pred,
const AbstractAttribute &QueryingAA,
bool RequireAllCallSites);
/// Check \p Pred on all values potentially returned by \p F.
///
/// This method will evaluate \p Pred on all values potentially returned by
/// the function associated with \p QueryingAA. The returned values are
/// matched with their respective return instructions. Returns true if \p Pred
/// holds on all of them.
bool checkForAllReturnedValuesAndReturnInsts(
const function_ref<bool(Value &, const SmallSetVector<ReturnInst *, 4> &)>
&Pred,
const AbstractAttribute &QueryingAA);
/// Check \p Pred on all values potentially returned by the function
/// associated with \p QueryingAA.
///
/// This is the context insensitive version of the method above.
bool checkForAllReturnedValues(const function_ref<bool(Value &)> &Pred,
const AbstractAttribute &QueryingAA);
/// Check \p Pred on all instructions with an opcode present in \p Opcodes.
///
/// This method will evaluate \p Pred on all instructions with an opcode
/// present in \p Opcode and return true if \p Pred holds on all of them.
bool checkForAllInstructions(const function_ref<bool(Instruction &)> &Pred,
const AbstractAttribute &QueryingAA,
const ArrayRef<unsigned> &Opcodes);
/// Check \p Pred on all call-like instructions (=CallBased derived).
///
/// See checkForAllCallLikeInstructions(...) for more information.
bool
checkForAllCallLikeInstructions(const function_ref<bool(Instruction &)> &Pred,
const AbstractAttribute &QueryingAA) {
return checkForAllInstructions(Pred, QueryingAA,
{(unsigned)Instruction::Invoke,
(unsigned)Instruction::CallBr,
(unsigned)Instruction::Call});
}
/// Check \p Pred on all Read/Write instructions.
///
/// This method will evaluate \p Pred on all instructions that read or write
/// to memory present in the information cache and return true if \p Pred
/// holds on all of them.
bool checkForAllReadWriteInstructions(
const llvm::function_ref<bool(Instruction &)> &Pred,
AbstractAttribute &QueryingAA);
/// Return the data layout associated with the anchor scope.
const DataLayout &getDataLayout() const { return InfoCache.DL; }
private:
/// The private version of getAAFor that allows to omit a querying abstract
/// attribute. See also the public getAAFor method.
template <typename AAType>
const AAType &getOrCreateAAFor(const IRPosition &IRP,
const AbstractAttribute *QueryingAA = nullptr,
bool TrackDependence = false) {
if (const AAType *AAPtr =
lookupAAFor<AAType>(IRP, QueryingAA, TrackDependence))
return *AAPtr;
// No matching attribute found, create one.
// Use the static create method.
auto &AA = AAType::createForPosition(IRP, *this);
registerAA(AA);
AA.initialize(*this);
// Bootstrap the new attribute with an initial update to propagate
// information, e.g., function -> call site. If it is not on a given
// whitelist we will not perform updates at all.
if (Whitelist && !Whitelist->count(&AAType::ID))
AA.getState().indicatePessimisticFixpoint();
else
AA.update(*this);
if (TrackDependence && AA.getState().isValidState())
QueryMap[&AA].insert(const_cast<AbstractAttribute *>(QueryingAA));
return AA;
}
/// Return the attribute of \p AAType for \p IRP if existing.
template <typename AAType>
const AAType *lookupAAFor(const IRPosition &IRP,
const AbstractAttribute *QueryingAA = nullptr,
bool TrackDependence = false) {
static_assert(std::is_base_of<AbstractAttribute, AAType>::value,
"Cannot query an attribute with a type not derived from "
"'AbstractAttribute'!");
assert((QueryingAA || !TrackDependence) &&
"Cannot track dependences without a QueryingAA!");
// Lookup the abstract attribute of type AAType. If found, return it after
// registering a dependence of QueryingAA on the one returned attribute.
const auto &KindToAbstractAttributeMap =
AAMap.lookup(const_cast<IRPosition &>(IRP));
if (AAType *AA = static_cast<AAType *>(
KindToAbstractAttributeMap.lookup(&AAType::ID))) {
// Do not register a dependence on an attribute with an invalid state.
if (TrackDependence && AA->getState().isValidState())
QueryMap[AA].insert(const_cast<AbstractAttribute *>(QueryingAA));
return AA;
}
return nullptr;
}
/// The set of all abstract attributes.
///{
using AAVector = SmallVector<AbstractAttribute *, 64>;
AAVector AllAbstractAttributes;
///}
/// A nested map to lookup abstract attributes based on the argument position
/// on the outer level, and the addresses of the static member (AAType::ID) on
/// the inner level.
///{
using KindToAbstractAttributeMap =
DenseMap<const char *, AbstractAttribute *>;
DenseMap<IRPosition, KindToAbstractAttributeMap> AAMap;
///}
/// A map from abstract attributes to the ones that queried them through calls
/// to the getAAFor<...>(...) method.
///{
using QueryMapTy =
MapVector<const AbstractAttribute *, SetVector<AbstractAttribute *>>;
QueryMapTy QueryMap;
///}
/// The information cache that holds pre-processed (LLVM-IR) information.
InformationCache &InfoCache;
/// Number of iterations until the dependences between abstract attributes are
/// recomputed.
const unsigned DepRecomputeInterval;
/// If not null, a set limiting the attribute opportunities.
const DenseSet<const char *> *Whitelist;
/// Functions, blocks, and instructions we delete after manifest is done.
///
///{
SmallPtrSet<Function *, 8> ToBeDeletedFunctions;
SmallPtrSet<BasicBlock *, 8> ToBeDeletedBlocks;
SmallPtrSet<Instruction *, 8> ToBeDeletedInsts;
///}
};
/// An interface to query the internal state of an abstract attribute.
///
/// The abstract state is a minimal interface that allows the Attributor to
/// communicate with the abstract attributes about their internal state without
/// enforcing or exposing implementation details, e.g., the (existence of an)
/// underlying lattice.
///
/// It is sufficient to be able to query if a state is (1) valid or invalid, (2)
/// at a fixpoint, and to indicate to the state that (3) an optimistic fixpoint
/// was reached or (4) a pessimistic fixpoint was enforced.
///
/// All methods need to be implemented by the subclass. For the common use case,
/// a single boolean state or a bit-encoded state, the BooleanState and
/// IntegerState classes are already provided. An abstract attribute can inherit
/// from them to get the abstract state interface and additional methods to
/// directly modify the state based if needed. See the class comments for help.
struct AbstractState {
virtual ~AbstractState() {}
/// Return if this abstract state is in a valid state. If false, no
/// information provided should be used.
virtual bool isValidState() const = 0;
/// Return if this abstract state is fixed, thus does not need to be updated
/// if information changes as it cannot change itself.
virtual bool isAtFixpoint() const = 0;
/// Indicate that the abstract state should converge to the optimistic state.
///
/// This will usually make the optimistically assumed state the known to be
/// true state.
///
/// \returns ChangeStatus::UNCHANGED as the assumed value should not change.
virtual ChangeStatus indicateOptimisticFixpoint() = 0;
/// Indicate that the abstract state should converge to the pessimistic state.
///
/// This will usually revert the optimistically assumed state to the known to
/// be true state.
///
/// \returns ChangeStatus::CHANGED as the assumed value may change.
virtual ChangeStatus indicatePessimisticFixpoint() = 0;
};
/// Simple state with integers encoding.
///
/// The interface ensures that the assumed bits are always a subset of the known
/// bits. Users can only add known bits and, except through adding known bits,
/// they can only remove assumed bits. This should guarantee monotoniticy and
/// thereby the existence of a fixpoint (if used corretly). The fixpoint is
/// reached when the assumed and known state/bits are equal. Users can
/// force/inidicate a fixpoint. If an optimistic one is indicated, the known
/// state will catch up with the assumed one, for a pessimistic fixpoint it is
/// the other way around.
struct IntegerState : public AbstractState {
/// Underlying integer type, we assume 32 bits to be enough.
using base_t = uint32_t;
/// Initialize the (best) state.
IntegerState(base_t BestState = ~0) : Assumed(BestState) {}
/// Return the worst possible representable state.
static constexpr base_t getWorstState() { return 0; }
/// See AbstractState::isValidState()
/// NOTE: For now we simply pretend that the worst possible state is invalid.
bool isValidState() const override { return Assumed != getWorstState(); }
/// See AbstractState::isAtFixpoint()
bool isAtFixpoint() const override { return Assumed == Known; }
/// See AbstractState::indicateOptimisticFixpoint(...)
ChangeStatus indicateOptimisticFixpoint() override {
Known = Assumed;
return ChangeStatus::UNCHANGED;
}
/// See AbstractState::indicatePessimisticFixpoint(...)
ChangeStatus indicatePessimisticFixpoint() override {
Assumed = Known;
return ChangeStatus::CHANGED;
}
/// Return the known state encoding
base_t getKnown() const { return Known; }
/// Return the assumed state encoding.
base_t getAssumed() const { return Assumed; }
/// Return true if the bits set in \p BitsEncoding are "known bits".
bool isKnown(base_t BitsEncoding) const {
return (Known & BitsEncoding) == BitsEncoding;
}
/// Return true if the bits set in \p BitsEncoding are "assumed bits".
bool isAssumed(base_t BitsEncoding) const {
return (Assumed & BitsEncoding) == BitsEncoding;
}
/// Add the bits in \p BitsEncoding to the "known bits".
IntegerState &addKnownBits(base_t Bits) {
// Make sure we never miss any "known bits".
Assumed |= Bits;
Known |= Bits;
return *this;
}
/// Remove the bits in \p BitsEncoding from the "assumed bits" if not known.
IntegerState &removeAssumedBits(base_t BitsEncoding) {
// Make sure we never loose any "known bits".
Assumed = (Assumed & ~BitsEncoding) | Known;
return *this;
}
/// Keep only "assumed bits" also set in \p BitsEncoding but all known ones.
IntegerState &intersectAssumedBits(base_t BitsEncoding) {
// Make sure we never loose any "known bits".
Assumed = (Assumed & BitsEncoding) | Known;
return *this;
}
/// Take minimum of assumed and \p Value.
IntegerState &takeAssumedMinimum(base_t Value) {
// Make sure we never loose "known value".
Assumed = std::max(std::min(Assumed, Value), Known);
return *this;
}
/// Take maximum of known and \p Value.
IntegerState &takeKnownMaximum(base_t Value) {
// Make sure we never loose "known value".
Assumed = std::max(Value, Assumed);
Known = std::max(Value, Known);