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llvm-project/llvm/lib/Transforms/Utils/AssumeBundleBuilder.cpp

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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
//
//===----------------------------------------------------------------------===//
#define DEBUG_TYPE "assume-builder"
#include "llvm/Transforms/Utils/AssumeBundleBuilder.h"
#include "llvm/ADT/DepthFirstIterator.h"
#include "llvm/ADT/MapVector.h"
#include "llvm/ADT/Statistic.h"
#include "llvm/Analysis/AssumeBundleQueries.h"
#include "llvm/Analysis/AssumptionCache.h"
#include "llvm/Analysis/ValueTracking.h"
#include "llvm/IR/Dominators.h"
#include "llvm/IR/Function.h"
#include "llvm/IR/InstIterator.h"
#include "llvm/IR/IntrinsicInst.h"
#include "llvm/IR/Module.h"
#include "llvm/InitializePasses.h"
#include "llvm/Support/CommandLine.h"
#include "llvm/Support/DebugCounter.h"
#include "llvm/Transforms/Utils/Local.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"));
STATISTIC(NumAssumeBuilt, "Number of assume built by the assume builder");
STATISTIC(NumBundlesInAssumes, "Total number of Bundles in the assume built");
STATISTIC(NumAssumesMerged,
"Number of assume merged by the assume simplify pass");
STATISTIC(NumAssumesRemoved,
"Number of assume removed by the assume simplify pass");
DEBUG_COUNTER(BuildAssumeCounter, "assume-builder-counter",
"Controls which assumes gets created");
namespace {
bool isUsefullToPreserve(Attribute::AttrKind Kind) {
switch (Kind) {
case Attribute::NonNull:
case Attribute::NoUndef:
case Attribute::Alignment:
case Attribute::Dereferenceable:
case Attribute::DereferenceableOrNull:
case Attribute::Cold:
return true;
default:
return false;
}
}
/// This function will try to transform the given knowledge into a more
/// canonical one. the canonical knowledge maybe the given one.
RetainedKnowledge canonicalizedKnowledge(RetainedKnowledge RK, Module *M) {
switch (RK.AttrKind) {
default:
return RK;
case Attribute::NonNull:
RK.WasOn = getUnderlyingObject(RK.WasOn);
return RK;
case Attribute::Alignment: {
Value *V = RK.WasOn->stripInBoundsOffsets([&](const Value *Strip) {
if (auto *GEP = dyn_cast<GEPOperator>(Strip))
RK.ArgValue =
MinAlign(RK.ArgValue,
GEP->getMaxPreservedAlignment(M->getDataLayout()).value());
});
RK.WasOn = V;
return RK;
}
case Attribute::Dereferenceable:
case Attribute::DereferenceableOrNull: {
int64_t Offset = 0;
Value *V = GetPointerBaseWithConstantOffset(
RK.WasOn, Offset, M->getDataLayout(), /*AllowNonInBounds*/ false);
if (Offset < 0)
return RK;
RK.ArgValue = RK.ArgValue + Offset;
RK.WasOn = V;
}
}
return RK;
}
/// 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>;
SmallMapVector<MapKey, unsigned, 8> AssumedKnowledgeMap;
Instruction *InstBeingRemoved = nullptr;
AssumptionCache* AC = nullptr;
DominatorTree* DT = nullptr;
AssumeBuilderState(Module *M, Instruction *I = nullptr,
AssumptionCache *AC = nullptr, DominatorTree *DT = nullptr)
: M(M), InstBeingRemoved(I), AC(AC), DT(DT) {}
bool tryToPreserveWithoutAddingAssume(RetainedKnowledge RK) {
if (!InstBeingRemoved || !RK.WasOn)
return false;
bool HasBeenPreserved = false;
Use* ToUpdate = nullptr;
getKnowledgeForValue(
RK.WasOn, {RK.AttrKind}, AC,
[&](RetainedKnowledge RKOther, Instruction *Assume,
const CallInst::BundleOpInfo *Bundle) {
if (!isValidAssumeForContext(Assume, InstBeingRemoved, DT))
return false;
if (RKOther.ArgValue >= RK.ArgValue) {
HasBeenPreserved = true;
return true;
} else if (isValidAssumeForContext(InstBeingRemoved, Assume,
DT)) {
HasBeenPreserved = true;
IntrinsicInst *Intr = cast<IntrinsicInst>(Assume);
ToUpdate = &Intr->op_begin()[Bundle->Begin + ABA_Argument];
return true;
}
return false;
});
if (ToUpdate)
ToUpdate->set(
ConstantInt::get(Type::getInt64Ty(M->getContext()), RK.ArgValue));
return HasBeenPreserved;
}
bool isKnowledgeWorthPreserving(RetainedKnowledge RK) {
if (!RK)
return false;
if (!RK.WasOn)
return true;
if (RK.WasOn->getType()->isPointerTy()) {
Value *UnderlyingPtr = getUnderlyingObject(RK.WasOn);
if (isa<AllocaInst>(UnderlyingPtr) || isa<GlobalValue>(UnderlyingPtr))
return false;
}
if (auto *Arg = dyn_cast<Argument>(RK.WasOn)) {
if (Arg->hasAttribute(RK.AttrKind) &&
(!Attribute::doesAttrKindHaveArgument(RK.AttrKind) ||
Arg->getAttribute(RK.AttrKind).getValueAsInt() >= RK.ArgValue))
return false;
return true;
}
if (auto *Inst = dyn_cast<Instruction>(RK.WasOn))
if (wouldInstructionBeTriviallyDead(Inst)) {
if (RK.WasOn->use_empty())
return false;
Use *SingleUse = RK.WasOn->getSingleUndroppableUse();
if (SingleUse && SingleUse->getUser() == InstBeingRemoved)
return false;
}
return true;
}
void addKnowledge(RetainedKnowledge RK) {
RK = canonicalizedKnowledge(RK, M);
if (!isKnowledgeWorthPreserving(RK))
return;
if (tryToPreserveWithoutAddingAssume(RK))
return;
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;
if (!DebugCounter::shouldExecute(BuildAssumeCounter))
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));
NumBundlesInAssumes++;
}
NumAssumeBuilt++;
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,
DominatorTree *DT) {
if (!EnableKnowledgeRetention || I->isTerminator())
return;
AssumeBuilderState Builder(I->getModule(), I, AC, DT);
Builder.addInstruction(I);
if (IntrinsicInst *Intr = Builder.build()) {
Intr->insertBefore(I);
if (AC)
AC->registerAssumption(Intr);
}
}
namespace {
struct AssumeSimplify {
Function &F;
AssumptionCache &AC;
DominatorTree *DT;
LLVMContext &C;
SmallDenseSet<IntrinsicInst *> CleanupToDo;
StringMapEntry<uint32_t> *IgnoreTag;
SmallDenseMap<BasicBlock *, SmallVector<IntrinsicInst *, 4>, 8> BBToAssume;
bool MadeChange = false;
AssumeSimplify(Function &F, AssumptionCache &AC, DominatorTree *DT,
LLVMContext &C)
: F(F), AC(AC), DT(DT), C(C),
IgnoreTag(C.getOrInsertBundleTag(IgnoreBundleTag)) {}
void buildMapping(bool FilterBooleanArgument) {
BBToAssume.clear();
for (Value *V : AC.assumptions()) {
if (!V)
continue;
IntrinsicInst *Assume = cast<IntrinsicInst>(V);
if (FilterBooleanArgument) {
auto *Arg = dyn_cast<ConstantInt>(Assume->getOperand(0));
if (!Arg || Arg->isZero())
continue;
}
BBToAssume[Assume->getParent()].push_back(Assume);
}
for (auto &Elem : BBToAssume) {
llvm::sort(Elem.second,
[](const IntrinsicInst *LHS, const IntrinsicInst *RHS) {
return LHS->comesBefore(RHS);
});
}
}
/// Remove all asumes in CleanupToDo if there boolean argument is true and
/// ForceCleanup is set or the assume doesn't hold valuable knowledge.
void RunCleanup(bool ForceCleanup) {
for (IntrinsicInst *Assume : CleanupToDo) {
auto *Arg = dyn_cast<ConstantInt>(Assume->getOperand(0));
if (!Arg || Arg->isZero() ||
(!ForceCleanup && !isAssumeWithEmptyBundle(*Assume)))
continue;
MadeChange = true;
if (ForceCleanup)
NumAssumesMerged++;
else
NumAssumesRemoved++;
Assume->eraseFromParent();
}
CleanupToDo.clear();
}
/// Remove knowledge stored in assume when it is already know by an attribute
/// or an other assume. This can when valid update an existing knowledge in an
/// attribute or an other assume.
void dropRedundantKnowledge() {
struct MapValue {
IntrinsicInst *Assume;
unsigned ArgValue;
CallInst::BundleOpInfo *BOI;
};
buildMapping(false);
SmallDenseMap<std::pair<Value *, Attribute::AttrKind>,
SmallVector<MapValue, 2>, 16>
Knowledge;
for (BasicBlock *BB : depth_first(&F))
for (Value *V : BBToAssume[BB]) {
if (!V)
continue;
IntrinsicInst *Assume = cast<IntrinsicInst>(V);
for (CallInst::BundleOpInfo &BOI : Assume->bundle_op_infos()) {
auto RemoveFromAssume = [&]() {
CleanupToDo.insert(Assume);
if (BOI.Begin != BOI.End) {
Use *U = &Assume->op_begin()[BOI.Begin + ABA_WasOn];
U->set(UndefValue::get(U->get()->getType()));
}
BOI.Tag = IgnoreTag;
};
if (BOI.Tag == IgnoreTag) {
CleanupToDo.insert(Assume);
continue;
}
RetainedKnowledge RK = getKnowledgeFromBundle(*Assume, BOI);
if (auto *Arg = dyn_cast_or_null<Argument>(RK.WasOn)) {
bool HasSameKindAttr = Arg->hasAttribute(RK.AttrKind);
if (HasSameKindAttr)
if (!Attribute::doesAttrKindHaveArgument(RK.AttrKind) ||
Arg->getAttribute(RK.AttrKind).getValueAsInt() >=
RK.ArgValue) {
RemoveFromAssume();
continue;
}
if (isValidAssumeForContext(
Assume, &*F.getEntryBlock().getFirstInsertionPt()) ||
Assume == &*F.getEntryBlock().getFirstInsertionPt()) {
if (HasSameKindAttr)
Arg->removeAttr(RK.AttrKind);
Arg->addAttr(Attribute::get(C, RK.AttrKind, RK.ArgValue));
MadeChange = true;
RemoveFromAssume();
continue;
}
}
auto &Lookup = Knowledge[{RK.WasOn, RK.AttrKind}];
for (MapValue &Elem : Lookup) {
if (!isValidAssumeForContext(Elem.Assume, Assume, DT))
continue;
if (Elem.ArgValue >= RK.ArgValue) {
RemoveFromAssume();
continue;
} else if (isValidAssumeForContext(Assume, Elem.Assume, DT)) {
Elem.Assume->op_begin()[Elem.BOI->Begin + ABA_Argument].set(
ConstantInt::get(Type::getInt64Ty(C), RK.ArgValue));
MadeChange = true;
RemoveFromAssume();
continue;
}
}
Lookup.push_back({Assume, RK.ArgValue, &BOI});
}
}
}
using MergeIterator = SmallVectorImpl<IntrinsicInst *>::iterator;
/// Merge all Assumes from Begin to End in and insert the resulting assume as
/// high as possible in the basicblock.
void mergeRange(BasicBlock *BB, MergeIterator Begin, MergeIterator End) {
if (Begin == End || std::next(Begin) == End)
return;
/// Provide no additional information so that AssumeBuilderState doesn't
/// try to do any punning since it already has been done better.
AssumeBuilderState Builder(F.getParent());
/// For now it is initialized to the best value it could have
Instruction *InsertPt = BB->getFirstNonPHI();
if (isa<LandingPadInst>(InsertPt))
InsertPt = InsertPt->getNextNode();
for (IntrinsicInst *I : make_range(Begin, End)) {
CleanupToDo.insert(I);
for (CallInst::BundleOpInfo &BOI : I->bundle_op_infos()) {
RetainedKnowledge RK = getKnowledgeFromBundle(*I, BOI);
if (!RK)
continue;
Builder.addKnowledge(RK);
if (auto *I = dyn_cast_or_null<Instruction>(RK.WasOn))
if (I->getParent() == InsertPt->getParent() &&
(InsertPt->comesBefore(I) || InsertPt == I))
InsertPt = I->getNextNode();
}
}
/// Adjust InsertPt if it is before Begin, since mergeAssumes only
/// guarantees we can place the resulting assume between Begin and End.
if (InsertPt->comesBefore(*Begin))
for (auto It = (*Begin)->getIterator(), E = InsertPt->getIterator();
It != E; --It)
if (!isGuaranteedToTransferExecutionToSuccessor(&*It)) {
InsertPt = It->getNextNode();
break;
}
IntrinsicInst *MergedAssume = Builder.build();
if (!MergedAssume)
return;
MadeChange = true;
MergedAssume->insertBefore(InsertPt);
AC.registerAssumption(MergedAssume);
}
/// Merge assume when they are in the same BasicBlock and for all instruction
/// between them isGuaranteedToTransferExecutionToSuccessor returns true.
void mergeAssumes() {
buildMapping(true);
SmallVector<MergeIterator, 4> SplitPoints;
for (auto &Elem : BBToAssume) {
SmallVectorImpl<IntrinsicInst *> &AssumesInBB = Elem.second;
if (AssumesInBB.size() < 2)
continue;
/// AssumesInBB is already sorted by order in the block.
BasicBlock::iterator It = AssumesInBB.front()->getIterator();
BasicBlock::iterator E = AssumesInBB.back()->getIterator();
SplitPoints.push_back(AssumesInBB.begin());
MergeIterator LastSplit = AssumesInBB.begin();
for (; It != E; ++It)
if (!isGuaranteedToTransferExecutionToSuccessor(&*It)) {
for (; (*LastSplit)->comesBefore(&*It); ++LastSplit)
;
if (SplitPoints.back() != LastSplit)
SplitPoints.push_back(LastSplit);
}
SplitPoints.push_back(AssumesInBB.end());
for (auto SplitIt = SplitPoints.begin();
SplitIt != std::prev(SplitPoints.end()); SplitIt++) {
mergeRange(Elem.first, *SplitIt, *(SplitIt + 1));
}
SplitPoints.clear();
}
}
};
bool simplifyAssumes(Function &F, AssumptionCache *AC, DominatorTree *DT) {
AssumeSimplify AS(F, *AC, DT, F.getContext());
/// Remove knowledge that is already known by a dominating other assume or an
/// attribute.
AS.dropRedundantKnowledge();
/// Remove assume that are empty.
AS.RunCleanup(false);
/// Merge assume in the same basicblock when possible.
AS.mergeAssumes();
/// Remove assume that were merged.
AS.RunCleanup(true);
return AS.MadeChange;
}
} // namespace
PreservedAnalyses AssumeSimplifyPass::run(Function &F,
FunctionAnalysisManager &AM) {
if (!EnableKnowledgeRetention)
return PreservedAnalyses::all();
simplifyAssumes(F, &AM.getResult<AssumptionAnalysis>(F),
AM.getCachedResult<DominatorTreeAnalysis>(F));
return PreservedAnalyses::all();
}
namespace {
class AssumeSimplifyPassLegacyPass : public FunctionPass {
public:
static char ID;
AssumeSimplifyPassLegacyPass() : FunctionPass(ID) {
initializeAssumeSimplifyPassLegacyPassPass(
*PassRegistry::getPassRegistry());
}
bool runOnFunction(Function &F) override {
if (skipFunction(F) || !EnableKnowledgeRetention)
return false;
AssumptionCache &AC =
getAnalysis<AssumptionCacheTracker>().getAssumptionCache(F);
DominatorTreeWrapperPass *DTWP =
getAnalysisIfAvailable<DominatorTreeWrapperPass>();
return simplifyAssumes(F, &AC, DTWP ? &DTWP->getDomTree() : nullptr);
}
void getAnalysisUsage(AnalysisUsage &AU) const override {
AU.addRequired<AssumptionCacheTracker>();
AU.setPreservesAll();
}
};
} // namespace
char AssumeSimplifyPassLegacyPass::ID = 0;
INITIALIZE_PASS_BEGIN(AssumeSimplifyPassLegacyPass, "assume-simplify",
"Assume Simplify", false, false)
INITIALIZE_PASS_DEPENDENCY(AssumptionCacheTracker)
INITIALIZE_PASS_END(AssumeSimplifyPassLegacyPass, "assume-simplify",
"Assume Simplify", false, false)
FunctionPass *llvm::createAssumeSimplifyPass() {
return new AssumeSimplifyPassLegacyPass();
}
PreservedAnalyses AssumeBuilderPass::run(Function &F,
FunctionAnalysisManager &AM) {
AssumptionCache *AC = &AM.getResult<AssumptionAnalysis>(F);
DominatorTree* DT = AM.getCachedResult<DominatorTreeAnalysis>(F);
for (Instruction &I : instructions(F))
salvageKnowledge(&I, AC, DT);
return PreservedAnalyses::all();
}
namespace {
class AssumeBuilderPassLegacyPass : public FunctionPass {
public:
static char ID;
AssumeBuilderPassLegacyPass() : FunctionPass(ID) {
initializeAssumeBuilderPassLegacyPassPass(*PassRegistry::getPassRegistry());
}
bool runOnFunction(Function &F) override {
AssumptionCache &AC =
getAnalysis<AssumptionCacheTracker>().getAssumptionCache(F);
DominatorTreeWrapperPass *DTWP =
getAnalysisIfAvailable<DominatorTreeWrapperPass>();
for (Instruction &I : instructions(F))
salvageKnowledge(&I, &AC, DTWP ? &DTWP->getDomTree() : nullptr);
return true;
}
void getAnalysisUsage(AnalysisUsage &AU) const override {
AU.addRequired<AssumptionCacheTracker>();
AU.setPreservesAll();
}
};
} // namespace
char AssumeBuilderPassLegacyPass::ID = 0;
INITIALIZE_PASS_BEGIN(AssumeBuilderPassLegacyPass, "assume-builder",
"Assume Builder", false, false)
INITIALIZE_PASS_DEPENDENCY(AssumptionCacheTracker)
INITIALIZE_PASS_END(AssumeBuilderPassLegacyPass, "assume-builder",
"Assume Builder", false, false)
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