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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/Analysis/AssumptionCache.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 {
/// 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;
using MapKey = std::pair<Value *, Attribute::AttrKind>;
SmallDenseMap<MapKey, unsigned, 8> AssumedKnowledgeMap;
Instruction *InsertBeforeInstruction = nullptr;
AssumeBuilderState(Module *M) : M(M) {}
void addKnowledge(RetainedKnowledge RK) {
MapKey Key{RK.WasOn, RK.AttrKind};
auto Lookup = AssumedKnowledgeMap.find(Key);
if (Lookup == AssumedKnowledgeMap.end()) {
AssumedKnowledgeMap[Key] = RK.ArgValue;
return;
}
assert(((Lookup->second == 0 && RK.ArgValue == 0) ||
(Lookup->second != 0 && RK.ArgValue != 0)) &&
"inconsistent argument value");
/// This is only desirable because for all attributes taking an argument
/// higher is better.
Lookup->second = std::max(Lookup->second, RK.ArgValue);
}
void addAttribute(Attribute Attr, Value *WasOn) {
if (Attr.isTypeAttribute() || Attr.isStringAttribute() ||
(!ShouldPreserveAllAttributes &&
!isUsefullToPreserve(Attr.getKindAsEnum())))
return;
unsigned AttrArg = 0;
if (Attr.isIntAttribute())
AttrArg = Attr.getValueAsInt();
addKnowledge({Attr.getKindAsEnum(), AttrArg, WasOn});
}
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 (AssumedKnowledgeMap.empty())
return nullptr;
Function *FnAssume = Intrinsic::getDeclaration(M, Intrinsic::assume);
LLVMContext &C = M->getContext();
SmallVector<OperandBundleDef, 8> OpBundle;
for (auto &MapElem : AssumedKnowledgeMap) {
SmallVector<Value *, 2> Args;
if (MapElem.first.first)
Args.push_back(MapElem.first.first);
/// This is only valid because for all attribute that currently exist a
/// value of 0 is useless. and should not be preserved.
if (MapElem.second)
Args.push_back(ConstantInt::get(Type::getInt64Ty(M->getContext()),
MapElem.second));
OpBundle.push_back(OperandBundleDefT<Value *>(
std::string(Attribute::getNameFromAttrKind(MapElem.first.second)),
Args));
}
llvm::sort(OpBundle, isLowerOpBundle);
return cast<IntrinsicInst>(CallInst::Create(
FnAssume, ArrayRef<Value *>({ConstantInt::getTrue(C)}), OpBundle));
}
void addAccessedPtr(Instruction *MemInst, Value *Pointer, Type *AccType,
MaybeAlign MA) {
unsigned DerefSize = MemInst->getModule()
->getDataLayout()
.getTypeStoreSize(AccType)
.getKnownMinSize();
if (DerefSize != 0) {
addKnowledge({Attribute::Dereferenceable, DerefSize, Pointer});
if (!NullPointerIsDefined(MemInst->getFunction(),
Pointer->getType()->getPointerAddressSpace()))
addKnowledge({Attribute::NonNull, 0u, Pointer});
}
if (MA.valueOrOne() > 1)
addKnowledge(
{Attribute::Alignment, unsigned(MA.valueOrOne().value()), Pointer});
}
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, AssumptionCache *AC) {
if (!EnableKnowledgeRetention)
return;
AssumeBuilderState Builder(I->getModule());
Builder.InsertBeforeInstruction = I;
Builder.addInstruction(I);
if (IntrinsicInst *Intr = Builder.build()) {
Intr->insertBefore(I);
if (AC)
AC->registerAssumption(Intr);
}
}
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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