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//===- AssumeBundleBuilder.cpp - tools to preserve informations -*- 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
//
//===----------------------------------------------------------------------===//
#include "llvm/Transforms/Utils/AssumeBundleBuilder.h"
#include "llvm/Analysis/AssumeBundleQueries.h"
#include "llvm/ADT/DenseSet.h"
#include "llvm/IR/Function.h"
#include "llvm/IR/InstIterator.h"
#include "llvm/IR/IntrinsicInst.h"
#include "llvm/IR/Module.h"
#include "llvm/Support/CommandLine.h"
using namespace llvm;
cl::opt<bool> ShouldPreserveAllAttributes(
"assume-preserve-all", cl::init(false), cl::Hidden,
cl::desc("enable preservation of all attrbitues. even those that are "
"unlikely to be usefull"));
cl::opt<bool> EnableKnowledgeRetention(
"enable-knowledge-retention", cl::init(false), cl::Hidden,
cl::desc(
"enable preservation of attributes throughout code transformation"));
namespace {
struct AssumedKnowledge {
const char *Name;
Value *Argument;
enum {
None,
Empty,
Tombstone,
};
/// Contain the argument and a flag if needed.
llvm::PointerIntPair<Value *, 2> WasOn;
};
} // namespace
namespace llvm {
template <> struct DenseMapInfo<AssumedKnowledge> {
static AssumedKnowledge getEmptyKey() {
return {nullptr, nullptr, {nullptr, AssumedKnowledge::Empty}};
}
static AssumedKnowledge getTombstoneKey() {
return {nullptr, nullptr, {nullptr, AssumedKnowledge::Tombstone}};
}
static unsigned getHashValue(const AssumedKnowledge &AK) {
return hash_combine(AK.Name, AK.Argument, AK.WasOn.getPointer());
}
static bool isEqual(const AssumedKnowledge &LHS,
const AssumedKnowledge &RHS) {
return LHS.WasOn == RHS.WasOn && LHS.Name == RHS.Name &&
LHS.Argument == RHS.Argument;
}
};
} // namespace llvm
namespace {
/// Deterministically compare OperandBundleDef.
/// The ordering is:
/// - by the attribute's name aka operand bundle tag, (doesn't change)
/// - then by the numeric Value of the argument, (doesn't change)
/// - lastly by the Name of the current Value it WasOn. (may change)
/// This order is deterministic and allows looking for the right kind of
/// attribute with binary search. However finding the right WasOn needs to be
/// done via linear search because values can get replaced.
bool isLowerOpBundle(const OperandBundleDef &LHS, const OperandBundleDef &RHS) {
auto getTuple = [](const OperandBundleDef &Op) {
return std::make_tuple(
Op.getTag(),
Op.input_size() <= ABA_Argument
? 0
: cast<ConstantInt>(*(Op.input_begin() + ABA_Argument))
->getZExtValue(),
Op.input_size() <= ABA_WasOn
? StringRef("")
: (*(Op.input_begin() + ABA_WasOn))->getName());
};
return getTuple(LHS) < getTuple(RHS);
}
bool isUsefullToPreserve(Attribute::AttrKind Kind) {
switch (Kind) {
case Attribute::NonNull:
case Attribute::Alignment:
case Attribute::Dereferenceable:
case Attribute::DereferenceableOrNull:
case Attribute::Cold:
return true;
default:
return false;
}
}
/// This class contain all knowledge that have been gather while building an
/// llvm.assume and the function to manipulate it.
struct AssumeBuilderState {
Module *M;
SmallDenseSet<AssumedKnowledge, 8> AssumedKnowledgeSet;
AssumeBuilderState(Module *M) : M(M) {}
void addAttribute(Attribute Attr, Value *WasOn) {
if (!ShouldPreserveAllAttributes &&
(Attr.isTypeAttribute() || Attr.isStringAttribute() ||
!isUsefullToPreserve(Attr.getKindAsEnum())))
return;
StringRef Name;
Value *AttrArg = nullptr;
if (Attr.isStringAttribute())
Name = Attr.getKindAsString();
else
Name = Attribute::getNameFromAttrKind(Attr.getKindAsEnum());
if (Attr.isIntAttribute())
AttrArg = ConstantInt::get(Type::getInt64Ty(M->getContext()),
Attr.getValueAsInt());
AssumedKnowledgeSet.insert(
{Name.data(), AttrArg, {WasOn, AssumedKnowledge::None}});
}
void addCall(const CallBase *Call) {
auto addAttrList = [&](AttributeList AttrList) {
for (unsigned Idx = AttributeList::FirstArgIndex;
Idx < AttrList.getNumAttrSets(); Idx++)
for (Attribute Attr : AttrList.getAttributes(Idx))
addAttribute(Attr, Call->getArgOperand(Idx - 1));
for (Attribute Attr : AttrList.getFnAttributes())
addAttribute(Attr, nullptr);
};
addAttrList(Call->getAttributes());
if (Function *Fn = Call->getCalledFunction())
addAttrList(Fn->getAttributes());
}
IntrinsicInst *build() {
if (AssumedKnowledgeSet.empty())
return nullptr;
Function *FnAssume = Intrinsic::getDeclaration(M, Intrinsic::assume);
LLVMContext &C = M->getContext();
SmallVector<OperandBundleDef, 8> OpBundle;
for (const AssumedKnowledge &Elem : AssumedKnowledgeSet) {
SmallVector<Value *, 2> Args;
assert(Attribute::getAttrKindFromName(Elem.Name) ==
Attribute::AttrKind::None ||
static_cast<bool>(Elem.Argument) ==
Attribute::doesAttrKindHaveArgument(
Attribute::getAttrKindFromName(Elem.Name)));
if (Elem.WasOn.getPointer())
Args.push_back(Elem.WasOn.getPointer());
if (Elem.Argument)
Args.push_back(Elem.Argument);
OpBundle.push_back(OperandBundleDefT<Value *>(Elem.Name, Args));
}
llvm::sort(OpBundle, isLowerOpBundle);
return cast<IntrinsicInst>(CallInst::Create(
FnAssume, ArrayRef<Value *>({ConstantInt::getTrue(C)}), OpBundle));
}
void addAttr(Attribute::AttrKind Kind, Value *Val, unsigned Argument = 0) {
AssumedKnowledge AK;
AK.Name = Attribute::getNameFromAttrKind(Kind).data();
AK.WasOn.setPointer(Val);
if (Attribute::doesAttrKindHaveArgument(Kind)) {
AK.Argument =
ConstantInt::get(Type::getInt64Ty(M->getContext()), Argument);
} else {
AK.Argument = nullptr;
assert(Argument == 0 && "there should be no argument");
}
AssumedKnowledgeSet.insert(AK);
};
void addAccessedPtr(Instruction *MemInst, Value *Pointer, Type *AccType,
MaybeAlign MA) {
uint64_t DerefSize = MemInst->getModule()
->getDataLayout()
.getTypeStoreSize(AccType)
.getKnownMinSize();
if (DerefSize != 0) {
addAttr(Attribute::Dereferenceable, Pointer, DerefSize);
if (!NullPointerIsDefined(MemInst->getFunction(),
Pointer->getType()->getPointerAddressSpace()))
addAttr(Attribute::NonNull, Pointer);
}
if (MA.valueOrOne() > 1)
addAttr(Attribute::Alignment, Pointer, MA.valueOrOne().value());
}
void addInstruction(Instruction *I) {
if (auto *Call = dyn_cast<CallBase>(I))
return addCall(Call);
if (auto *Load = dyn_cast<LoadInst>(I))
return addAccessedPtr(I, Load->getPointerOperand(), Load->getType(),
Load->getAlign());
if (auto *Store = dyn_cast<StoreInst>(I))
return addAccessedPtr(I, Store->getPointerOperand(),
Store->getValueOperand()->getType(),
Store->getAlign());
// TODO: Add support for the other Instructions.
// TODO: Maybe we should look around and merge with other llvm.assume.
}
};
} // namespace
IntrinsicInst *llvm::buildAssumeFromInst(Instruction *I) {
if (!EnableKnowledgeRetention)
return nullptr;
AssumeBuilderState Builder(I->getModule());
Builder.addInstruction(I);
return Builder.build();
}
void llvm::salvageKnowledge(Instruction *I) {
if (Instruction *Intr = buildAssumeFromInst(I))
Intr->insertBefore(I);
}
PreservedAnalyses AssumeBuilderPass::run(Function &F,
FunctionAnalysisManager &AM) {
for (Instruction &I : instructions(F))
if (Instruction *Assume = buildAssumeFromInst(&I))
Assume->insertBefore(&I);
return PreservedAnalyses::all();
}
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