blob: 5b5d48bf6fe535bf807fbffa5c24eaae12194f06 [file] [log] [blame]
//===- LazyValueInfo.cpp - Value constraint analysis ------------*- C++ -*-===//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
// This file defines the interface for lazy computation of value constraint
// information.
#include "llvm/Analysis/LazyValueInfo.h"
#include "llvm/ADT/DenseSet.h"
#include "llvm/ADT/Optional.h"
#include "llvm/ADT/STLExtras.h"
#include "llvm/Analysis/AssumptionCache.h"
#include "llvm/Analysis/ConstantFolding.h"
#include "llvm/Analysis/InstructionSimplify.h"
#include "llvm/Analysis/TargetLibraryInfo.h"
#include "llvm/Analysis/ValueLattice.h"
#include "llvm/Analysis/ValueTracking.h"
#include "llvm/IR/AssemblyAnnotationWriter.h"
#include "llvm/IR/CFG.h"
#include "llvm/IR/ConstantRange.h"
#include "llvm/IR/Constants.h"
#include "llvm/IR/DataLayout.h"
#include "llvm/IR/Dominators.h"
#include "llvm/IR/Instructions.h"
#include "llvm/IR/IntrinsicInst.h"
#include "llvm/IR/Intrinsics.h"
#include "llvm/IR/LLVMContext.h"
#include "llvm/IR/PatternMatch.h"
#include "llvm/IR/ValueHandle.h"
#include "llvm/InitializePasses.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/FormattedStream.h"
#include "llvm/Support/KnownBits.h"
#include "llvm/Support/raw_ostream.h"
#include <map>
using namespace llvm;
using namespace PatternMatch;
#define DEBUG_TYPE "lazy-value-info"
// This is the number of worklist items we will process to try to discover an
// answer for a given value.
static const unsigned MaxProcessedPerValue = 500;
char LazyValueInfoWrapperPass::ID = 0;
LazyValueInfoWrapperPass::LazyValueInfoWrapperPass() : FunctionPass(ID) {
INITIALIZE_PASS_BEGIN(LazyValueInfoWrapperPass, "lazy-value-info",
"Lazy Value Information Analysis", false, true)
INITIALIZE_PASS_END(LazyValueInfoWrapperPass, "lazy-value-info",
"Lazy Value Information Analysis", false, true)
namespace llvm {
FunctionPass *createLazyValueInfoPass() { return new LazyValueInfoWrapperPass(); }
AnalysisKey LazyValueAnalysis::Key;
/// Returns true if this lattice value represents at most one possible value.
/// This is as precise as any lattice value can get while still representing
/// reachable code.
static bool hasSingleValue(const ValueLatticeElement &Val) {
if (Val.isConstantRange() &&
// Integer constants are single element ranges
return true;
if (Val.isConstant())
// Non integer constants
return true;
return false;
/// Combine two sets of facts about the same value into a single set of
/// facts. Note that this method is not suitable for merging facts along
/// different paths in a CFG; that's what the mergeIn function is for. This
/// is for merging facts gathered about the same value at the same location
/// through two independent means.
/// Notes:
/// * This method does not promise to return the most precise possible lattice
/// value implied by A and B. It is allowed to return any lattice element
/// which is at least as strong as *either* A or B (unless our facts
/// conflict, see below).
/// * Due to unreachable code, the intersection of two lattice values could be
/// contradictory. If this happens, we return some valid lattice value so as
/// not confuse the rest of LVI. Ideally, we'd always return Undefined, but
/// we do not make this guarantee. TODO: This would be a useful enhancement.
static ValueLatticeElement intersect(const ValueLatticeElement &A,
const ValueLatticeElement &B) {
// Undefined is the strongest state. It means the value is known to be along
// an unreachable path.
if (A.isUnknown())
return A;
if (B.isUnknown())
return B;
// If we gave up for one, but got a useable fact from the other, use it.
if (A.isOverdefined())
return B;
if (B.isOverdefined())
return A;
// Can't get any more precise than constants.
if (hasSingleValue(A))
return A;
if (hasSingleValue(B))
return B;
// Could be either constant range or not constant here.
if (!A.isConstantRange() || !B.isConstantRange()) {
// TODO: Arbitrary choice, could be improved
return A;
// Intersect two constant ranges
ConstantRange Range =
// Note: An empty range is implicitly converted to unknown or undef depending
// on MayIncludeUndef internally.
return ValueLatticeElement::getRange(
std::move(Range), /*MayIncludeUndef=*/A.isConstantRangeIncludingUndef() ||
// LazyValueInfoCache Decl
namespace {
/// A callback value handle updates the cache when values are erased.
class LazyValueInfoCache;
struct LVIValueHandle final : public CallbackVH {
LazyValueInfoCache *Parent;
LVIValueHandle(Value *V, LazyValueInfoCache *P = nullptr)
: CallbackVH(V), Parent(P) { }
void deleted() override;
void allUsesReplacedWith(Value *V) override {
} // end anonymous namespace
namespace {
using NonNullPointerSet = SmallDenseSet<AssertingVH<Value>, 2>;
/// This is the cache kept by LazyValueInfo which
/// maintains information about queries across the clients' queries.
class LazyValueInfoCache {
/// This is all of the cached information for one basic block. It contains
/// the per-value lattice elements, as well as a separate set for
/// overdefined values to reduce memory usage. Additionally pointers
/// dereferenced in the block are cached for nullability queries.
struct BlockCacheEntry {
SmallDenseMap<AssertingVH<Value>, ValueLatticeElement, 4> LatticeElements;
SmallDenseSet<AssertingVH<Value>, 4> OverDefined;
// None indicates that the nonnull pointers for this basic block
// block have not been computed yet.
Optional<NonNullPointerSet> NonNullPointers;
/// Cached information per basic block.
DenseMap<PoisoningVH<BasicBlock>, std::unique_ptr<BlockCacheEntry>>
/// Set of value handles used to erase values from the cache on deletion.
DenseSet<LVIValueHandle, DenseMapInfo<Value *>> ValueHandles;
const BlockCacheEntry *getBlockEntry(BasicBlock *BB) const {
auto It = BlockCache.find_as(BB);
if (It == BlockCache.end())
return nullptr;
return It->second.get();
BlockCacheEntry *getOrCreateBlockEntry(BasicBlock *BB) {
auto It = BlockCache.find_as(BB);
if (It == BlockCache.end())
It = BlockCache.insert({ BB, std::make_unique<BlockCacheEntry>() })
return It->second.get();
void addValueHandle(Value *Val) {
auto HandleIt = ValueHandles.find_as(Val);
if (HandleIt == ValueHandles.end())
ValueHandles.insert({ Val, this });
void insertResult(Value *Val, BasicBlock *BB,
const ValueLatticeElement &Result) {
BlockCacheEntry *Entry = getOrCreateBlockEntry(BB);
// Insert over-defined values into their own cache to reduce memory
// overhead.
if (Result.isOverdefined())
Entry->LatticeElements.insert({ Val, Result });
Optional<ValueLatticeElement> getCachedValueInfo(Value *V,
BasicBlock *BB) const {
const BlockCacheEntry *Entry = getBlockEntry(BB);
if (!Entry)
return None;
if (Entry->OverDefined.count(V))
return ValueLatticeElement::getOverdefined();
auto LatticeIt = Entry->LatticeElements.find_as(V);
if (LatticeIt == Entry->LatticeElements.end())
return None;
return LatticeIt->second;
bool isNonNullAtEndOfBlock(
Value *V, BasicBlock *BB,
function_ref<NonNullPointerSet(BasicBlock *)> InitFn) {
BlockCacheEntry *Entry = getOrCreateBlockEntry(BB);
if (!Entry->NonNullPointers) {
Entry->NonNullPointers = InitFn(BB);
for (Value *V : *Entry->NonNullPointers)
return Entry->NonNullPointers->count(V);
/// clear - Empty the cache.
void clear() {
/// Inform the cache that a given value has been deleted.
void eraseValue(Value *V);
/// This is part of the update interface to inform the cache
/// that a block has been deleted.
void eraseBlock(BasicBlock *BB);
/// Updates the cache to remove any influence an overdefined value in
/// OldSucc might have (unless also overdefined in NewSucc). This just
/// flushes elements from the cache and does not add any.
void threadEdgeImpl(BasicBlock *OldSucc,BasicBlock *NewSucc);
void LazyValueInfoCache::eraseValue(Value *V) {
for (auto &Pair : BlockCache) {
if (Pair.second->NonNullPointers)
auto HandleIt = ValueHandles.find_as(V);
if (HandleIt != ValueHandles.end())
void LVIValueHandle::deleted() {
// This erasure deallocates *this, so it MUST happen after we're done
// using any and all members of *this.
void LazyValueInfoCache::eraseBlock(BasicBlock *BB) {
void LazyValueInfoCache::threadEdgeImpl(BasicBlock *OldSucc,
BasicBlock *NewSucc) {
// When an edge in the graph has been threaded, values that we could not
// determine a value for before (i.e. were marked overdefined) may be
// possible to solve now. We do NOT try to proactively update these values.
// Instead, we clear their entries from the cache, and allow lazy updating to
// recompute them when needed.
// The updating process is fairly simple: we need to drop cached info
// for all values that were marked overdefined in OldSucc, and for those same
// values in any successor of OldSucc (except NewSucc) in which they were
// also marked overdefined.
std::vector<BasicBlock*> worklist;
const BlockCacheEntry *Entry = getBlockEntry(OldSucc);
if (!Entry || Entry->OverDefined.empty())
return; // Nothing to process here.
SmallVector<Value *, 4> ValsToClear(Entry->OverDefined.begin(),
// Use a worklist to perform a depth-first search of OldSucc's successors.
// NOTE: We do not need a visited list since any blocks we have already
// visited will have had their overdefined markers cleared already, and we
// thus won't loop to their successors.
while (!worklist.empty()) {
BasicBlock *ToUpdate = worklist.back();
// Skip blocks only accessible through NewSucc.
if (ToUpdate == NewSucc) continue;
// If a value was marked overdefined in OldSucc, and is here too...
auto OI = BlockCache.find_as(ToUpdate);
if (OI == BlockCache.end() || OI->second->OverDefined.empty())
auto &ValueSet = OI->second->OverDefined;
bool changed = false;
for (Value *V : ValsToClear) {
if (!ValueSet.erase(V))
// If we removed anything, then we potentially need to update
// blocks successors too.
changed = true;
if (!changed) continue;
llvm::append_range(worklist, successors(ToUpdate));
namespace {
/// An assembly annotator class to print LazyValueCache information in
/// comments.
class LazyValueInfoImpl;
class LazyValueInfoAnnotatedWriter : public AssemblyAnnotationWriter {
LazyValueInfoImpl *LVIImpl;
// While analyzing which blocks we can solve values for, we need the dominator
// information.
DominatorTree &DT;
LazyValueInfoAnnotatedWriter(LazyValueInfoImpl *L, DominatorTree &DTree)
: LVIImpl(L), DT(DTree) {}
void emitBasicBlockStartAnnot(const BasicBlock *BB,
formatted_raw_ostream &OS) override;
void emitInstructionAnnot(const Instruction *I,
formatted_raw_ostream &OS) override;
namespace {
// The actual implementation of the lazy analysis and update. Note that the
// inheritance from LazyValueInfoCache is intended to be temporary while
// splitting the code and then transitioning to a has-a relationship.
class LazyValueInfoImpl {
/// Cached results from previous queries
LazyValueInfoCache TheCache;
/// This stack holds the state of the value solver during a query.
/// It basically emulates the callstack of the naive
/// recursive value lookup process.
SmallVector<std::pair<BasicBlock*, Value*>, 8> BlockValueStack;
/// Keeps track of which block-value pairs are in BlockValueStack.
DenseSet<std::pair<BasicBlock*, Value*> > BlockValueSet;
/// Push BV onto BlockValueStack unless it's already in there.
/// Returns true on success.
bool pushBlockValue(const std::pair<BasicBlock *, Value *> &BV) {
if (!BlockValueSet.insert(BV).second)
return false; // It's already in the stack.
LLVM_DEBUG(dbgs() << "PUSH: " << *BV.second << " in "
<< BV.first->getName() << "\n");
return true;
AssumptionCache *AC; ///< A pointer to the cache of @llvm.assume calls.
const DataLayout &DL; ///< A mandatory DataLayout
/// Declaration of the llvm.experimental.guard() intrinsic,
/// if it exists in the module.
Function *GuardDecl;
Optional<ValueLatticeElement> getBlockValue(Value *Val, BasicBlock *BB);
Optional<ValueLatticeElement> getEdgeValue(Value *V, BasicBlock *F,
BasicBlock *T, Instruction *CxtI = nullptr);
// These methods process one work item and may add more. A false value
// returned means that the work item was not completely processed and must
// be revisited after going through the new items.
bool solveBlockValue(Value *Val, BasicBlock *BB);
Optional<ValueLatticeElement> solveBlockValueImpl(Value *Val, BasicBlock *BB);
Optional<ValueLatticeElement> solveBlockValueNonLocal(Value *Val,
BasicBlock *BB);
Optional<ValueLatticeElement> solveBlockValuePHINode(PHINode *PN,
BasicBlock *BB);
Optional<ValueLatticeElement> solveBlockValueSelect(SelectInst *S,
BasicBlock *BB);
Optional<ConstantRange> getRangeFor(Value *V, Instruction *CxtI,
BasicBlock *BB);
Optional<ValueLatticeElement> solveBlockValueBinaryOpImpl(
Instruction *I, BasicBlock *BB,
std::function<ConstantRange(const ConstantRange &,
const ConstantRange &)> OpFn);
Optional<ValueLatticeElement> solveBlockValueBinaryOp(BinaryOperator *BBI,
BasicBlock *BB);
Optional<ValueLatticeElement> solveBlockValueCast(CastInst *CI,
BasicBlock *BB);
Optional<ValueLatticeElement> solveBlockValueOverflowIntrinsic(
WithOverflowInst *WO, BasicBlock *BB);
Optional<ValueLatticeElement> solveBlockValueIntrinsic(IntrinsicInst *II,
BasicBlock *BB);
Optional<ValueLatticeElement> solveBlockValueExtractValue(
ExtractValueInst *EVI, BasicBlock *BB);
bool isNonNullAtEndOfBlock(Value *Val, BasicBlock *BB);
void intersectAssumeOrGuardBlockValueConstantRange(Value *Val,
ValueLatticeElement &BBLV,
Instruction *BBI);
void solve();
/// This is the query interface to determine the lattice value for the
/// specified Value* at the context instruction (if specified) or at the
/// start of the block.
ValueLatticeElement getValueInBlock(Value *V, BasicBlock *BB,
Instruction *CxtI = nullptr);
/// This is the query interface to determine the lattice value for the
/// specified Value* at the specified instruction using only information
/// from assumes/guards and range metadata. Unlike getValueInBlock(), no
/// recursive query is performed.
ValueLatticeElement getValueAt(Value *V, Instruction *CxtI);
/// This is the query interface to determine the lattice
/// value for the specified Value* that is true on the specified edge.
ValueLatticeElement getValueOnEdge(Value *V, BasicBlock *FromBB,
BasicBlock *ToBB,
Instruction *CxtI = nullptr);
/// Complete flush all previously computed values
void clear() {
/// Printing the LazyValueInfo Analysis.
void printLVI(Function &F, DominatorTree &DTree, raw_ostream &OS) {
LazyValueInfoAnnotatedWriter Writer(this, DTree);
F.print(OS, &Writer);
/// This is part of the update interface to inform the cache
/// that a block has been deleted.
void eraseBlock(BasicBlock *BB) {
/// This is the update interface to inform the cache that an edge from
/// PredBB to OldSucc has been threaded to be from PredBB to NewSucc.
void threadEdge(BasicBlock *PredBB,BasicBlock *OldSucc,BasicBlock *NewSucc);
LazyValueInfoImpl(AssumptionCache *AC, const DataLayout &DL,
Function *GuardDecl)
: AC(AC), DL(DL), GuardDecl(GuardDecl) {}
} // end anonymous namespace
void LazyValueInfoImpl::solve() {
SmallVector<std::pair<BasicBlock *, Value *>, 8> StartingStack(
BlockValueStack.begin(), BlockValueStack.end());
unsigned processedCount = 0;
while (!BlockValueStack.empty()) {
// Abort if we have to process too many values to get a result for this one.
// Because of the design of the overdefined cache currently being per-block
// to avoid naming-related issues (IE it wants to try to give different
// results for the same name in different blocks), overdefined results don't
// get cached globally, which in turn means we will often try to rediscover
// the same overdefined result again and again. Once something like
// PredicateInfo is used in LVI or CVP, we should be able to make the
// overdefined cache global, and remove this throttle.
if (processedCount > MaxProcessedPerValue) {
dbgs() << "Giving up on stack because we are getting too deep\n");
// Fill in the original values
while (!StartingStack.empty()) {
std::pair<BasicBlock *, Value *> &e = StartingStack.back();
TheCache.insertResult(e.second, e.first,
std::pair<BasicBlock *, Value *> e = BlockValueStack.back();
assert(BlockValueSet.count(e) && "Stack value should be in BlockValueSet!");
if (solveBlockValue(e.second, e.first)) {
// The work item was completely processed.
assert(BlockValueStack.back() == e && "Nothing should have been pushed!");
#ifndef NDEBUG
Optional<ValueLatticeElement> BBLV =
TheCache.getCachedValueInfo(e.second, e.first);
assert(BBLV && "Result should be in cache!");
dbgs() << "POP " << *e.second << " in " << e.first->getName() << " = "
<< *BBLV << "\n");
} else {
// More work needs to be done before revisiting.
assert(BlockValueStack.back() != e && "Stack should have been pushed!");
Optional<ValueLatticeElement> LazyValueInfoImpl::getBlockValue(Value *Val,
BasicBlock *BB) {
// If already a constant, there is nothing to compute.
if (Constant *VC = dyn_cast<Constant>(Val))
return ValueLatticeElement::get(VC);
if (Optional<ValueLatticeElement> OptLatticeVal =
TheCache.getCachedValueInfo(Val, BB))
return OptLatticeVal;
// We have hit a cycle, assume overdefined.
if (!pushBlockValue({ BB, Val }))
return ValueLatticeElement::getOverdefined();
// Yet to be resolved.
return None;
static ValueLatticeElement getFromRangeMetadata(Instruction *BBI) {
switch (BBI->getOpcode()) {
default: break;
case Instruction::Load:
case Instruction::Call:
case Instruction::Invoke:
if (MDNode *Ranges = BBI->getMetadata(LLVMContext::MD_range))
if (isa<IntegerType>(BBI->getType())) {
return ValueLatticeElement::getRange(
// Nothing known - will be intersected with other facts
return ValueLatticeElement::getOverdefined();
bool LazyValueInfoImpl::solveBlockValue(Value *Val, BasicBlock *BB) {
assert(!isa<Constant>(Val) && "Value should not be constant");
assert(!TheCache.getCachedValueInfo(Val, BB) &&
"Value should not be in cache");
// Hold off inserting this value into the Cache in case we have to return
// false and come back later.
Optional<ValueLatticeElement> Res = solveBlockValueImpl(Val, BB);
if (!Res)
// Work pushed, will revisit
return false;
TheCache.insertResult(Val, BB, *Res);
return true;
Optional<ValueLatticeElement> LazyValueInfoImpl::solveBlockValueImpl(
Value *Val, BasicBlock *BB) {
Instruction *BBI = dyn_cast<Instruction>(Val);
if (!BBI || BBI->getParent() != BB)
return solveBlockValueNonLocal(Val, BB);
if (PHINode *PN = dyn_cast<PHINode>(BBI))
return solveBlockValuePHINode(PN, BB);
if (auto *SI = dyn_cast<SelectInst>(BBI))
return solveBlockValueSelect(SI, BB);
// If this value is a nonnull pointer, record it's range and bailout. Note
// that for all other pointer typed values, we terminate the search at the
// definition. We could easily extend this to look through geps, bitcasts,
// and the like to prove non-nullness, but it's not clear that's worth it
// compile time wise. The context-insensitive value walk done inside
// isKnownNonZero gets most of the profitable cases at much less expense.
// This does mean that we have a sensitivity to where the defining
// instruction is placed, even if it could legally be hoisted much higher.
// That is unfortunate.
PointerType *PT = dyn_cast<PointerType>(BBI->getType());
if (PT && isKnownNonZero(BBI, DL))
return ValueLatticeElement::getNot(ConstantPointerNull::get(PT));
if (BBI->getType()->isIntegerTy()) {
if (auto *CI = dyn_cast<CastInst>(BBI))
return solveBlockValueCast(CI, BB);
if (BinaryOperator *BO = dyn_cast<BinaryOperator>(BBI))
return solveBlockValueBinaryOp(BO, BB);
if (auto *EVI = dyn_cast<ExtractValueInst>(BBI))
return solveBlockValueExtractValue(EVI, BB);
if (auto *II = dyn_cast<IntrinsicInst>(BBI))
return solveBlockValueIntrinsic(II, BB);
LLVM_DEBUG(dbgs() << " compute BB '" << BB->getName()
<< "' - unknown inst def found.\n");
return getFromRangeMetadata(BBI);
static void AddNonNullPointer(Value *Ptr, NonNullPointerSet &PtrSet) {
// TODO: Use NullPointerIsDefined instead.
if (Ptr->getType()->getPointerAddressSpace() == 0)
static void AddNonNullPointersByInstruction(
Instruction *I, NonNullPointerSet &PtrSet) {
if (LoadInst *L = dyn_cast<LoadInst>(I)) {
AddNonNullPointer(L->getPointerOperand(), PtrSet);
} else if (StoreInst *S = dyn_cast<StoreInst>(I)) {
AddNonNullPointer(S->getPointerOperand(), PtrSet);
} else if (MemIntrinsic *MI = dyn_cast<MemIntrinsic>(I)) {
if (MI->isVolatile()) return;
// FIXME: check whether it has a valuerange that excludes zero?
ConstantInt *Len = dyn_cast<ConstantInt>(MI->getLength());
if (!Len || Len->isZero()) return;
AddNonNullPointer(MI->getRawDest(), PtrSet);
if (MemTransferInst *MTI = dyn_cast<MemTransferInst>(MI))
AddNonNullPointer(MTI->getRawSource(), PtrSet);
bool LazyValueInfoImpl::isNonNullAtEndOfBlock(Value *Val, BasicBlock *BB) {
if (NullPointerIsDefined(BB->getParent(),
return false;
Val = Val->stripInBoundsOffsets();
return TheCache.isNonNullAtEndOfBlock(Val, BB, [](BasicBlock *BB) {
NonNullPointerSet NonNullPointers;
for (Instruction &I : *BB)
AddNonNullPointersByInstruction(&I, NonNullPointers);
return NonNullPointers;
Optional<ValueLatticeElement> LazyValueInfoImpl::solveBlockValueNonLocal(
Value *Val, BasicBlock *BB) {
ValueLatticeElement Result; // Start Undefined.
// If this is the entry block, we must be asking about an argument. The
// value is overdefined.
if (BB->isEntryBlock()) {
assert(isa<Argument>(Val) && "Unknown live-in to the entry block");
return ValueLatticeElement::getOverdefined();
// Loop over all of our predecessors, merging what we know from them into
// result. If we encounter an unexplored predecessor, we eagerly explore it
// in a depth first manner. In practice, this has the effect of discovering
// paths we can't analyze eagerly without spending compile times analyzing
// other paths. This heuristic benefits from the fact that predecessors are
// frequently arranged such that dominating ones come first and we quickly
// find a path to function entry. TODO: We should consider explicitly
// canonicalizing to make this true rather than relying on this happy
// accident.
for (BasicBlock *Pred : predecessors(BB)) {
Optional<ValueLatticeElement> EdgeResult = getEdgeValue(Val, Pred, BB);
if (!EdgeResult)
// Explore that input, then return here
return None;
// If we hit overdefined, exit early. The BlockVals entry is already set
// to overdefined.
if (Result.isOverdefined()) {
LLVM_DEBUG(dbgs() << " compute BB '" << BB->getName()
<< "' - overdefined because of pred (non local).\n");
return Result;
// Return the merged value, which is more precise than 'overdefined'.
return Result;
Optional<ValueLatticeElement> LazyValueInfoImpl::solveBlockValuePHINode(
PHINode *PN, BasicBlock *BB) {
ValueLatticeElement Result; // Start Undefined.
// Loop over all of our predecessors, merging what we know from them into
// result. See the comment about the chosen traversal order in
// solveBlockValueNonLocal; the same reasoning applies here.
for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
BasicBlock *PhiBB = PN->getIncomingBlock(i);
Value *PhiVal = PN->getIncomingValue(i);
// Note that we can provide PN as the context value to getEdgeValue, even
// though the results will be cached, because PN is the value being used as
// the cache key in the caller.
Optional<ValueLatticeElement> EdgeResult =
getEdgeValue(PhiVal, PhiBB, BB, PN);
if (!EdgeResult)
// Explore that input, then return here
return None;
// If we hit overdefined, exit early. The BlockVals entry is already set
// to overdefined.
if (Result.isOverdefined()) {
LLVM_DEBUG(dbgs() << " compute BB '" << BB->getName()
<< "' - overdefined because of pred (local).\n");
return Result;
// Return the merged value, which is more precise than 'overdefined'.
assert(!Result.isOverdefined() && "Possible PHI in entry block?");
return Result;
static ValueLatticeElement getValueFromCondition(Value *Val, Value *Cond,
bool isTrueDest = true);
// If we can determine a constraint on the value given conditions assumed by
// the program, intersect those constraints with BBLV
void LazyValueInfoImpl::intersectAssumeOrGuardBlockValueConstantRange(
Value *Val, ValueLatticeElement &BBLV, Instruction *BBI) {
BBI = BBI ? BBI : dyn_cast<Instruction>(Val);
if (!BBI)
BasicBlock *BB = BBI->getParent();
for (auto &AssumeVH : AC->assumptionsFor(Val)) {
if (!AssumeVH)
// Only check assumes in the block of the context instruction. Other
// assumes will have already been taken into account when the value was
// propagated from predecessor blocks.
auto *I = cast<CallInst>(AssumeVH);
if (I->getParent() != BB || !isValidAssumeForContext(I, BBI))
BBLV = intersect(BBLV, getValueFromCondition(Val, I->getArgOperand(0)));
// If guards are not used in the module, don't spend time looking for them
if (GuardDecl && !GuardDecl->use_empty() &&
BBI->getIterator() != BB->begin()) {
for (Instruction &I : make_range(std::next(BBI->getIterator().getReverse()),
BB->rend())) {
Value *Cond = nullptr;
if (match(&I, m_Intrinsic<Intrinsic::experimental_guard>(m_Value(Cond))))
BBLV = intersect(BBLV, getValueFromCondition(Val, Cond));
if (BBLV.isOverdefined()) {
// Check whether we're checking at the terminator, and the pointer has
// been dereferenced in this block.
PointerType *PTy = dyn_cast<PointerType>(Val->getType());
if (PTy && BB->getTerminator() == BBI &&
isNonNullAtEndOfBlock(Val, BB))
BBLV = ValueLatticeElement::getNot(ConstantPointerNull::get(PTy));
Optional<ValueLatticeElement> LazyValueInfoImpl::solveBlockValueSelect(
SelectInst *SI, BasicBlock *BB) {
// Recurse on our inputs if needed
Optional<ValueLatticeElement> OptTrueVal =
getBlockValue(SI->getTrueValue(), BB);
if (!OptTrueVal)
return None;
ValueLatticeElement &TrueVal = *OptTrueVal;
Optional<ValueLatticeElement> OptFalseVal =
getBlockValue(SI->getFalseValue(), BB);
if (!OptFalseVal)
return None;
ValueLatticeElement &FalseVal = *OptFalseVal;
if (TrueVal.isConstantRange() && FalseVal.isConstantRange()) {
const ConstantRange &TrueCR = TrueVal.getConstantRange();
const ConstantRange &FalseCR = FalseVal.getConstantRange();
Value *LHS = nullptr;
Value *RHS = nullptr;
SelectPatternResult SPR = matchSelectPattern(SI, LHS, RHS);
// Is this a min specifically of our two inputs? (Avoid the risk of
// ValueTracking getting smarter looking back past our immediate inputs.)
if (SelectPatternResult::isMinOrMax(SPR.Flavor) &&
LHS == SI->getTrueValue() && RHS == SI->getFalseValue()) {
ConstantRange ResultCR = [&]() {
switch (SPR.Flavor) {
llvm_unreachable("unexpected minmax type!");
case SPF_SMIN: /// Signed minimum
return TrueCR.smin(FalseCR);
case SPF_UMIN: /// Unsigned minimum
return TrueCR.umin(FalseCR);
case SPF_SMAX: /// Signed maximum
return TrueCR.smax(FalseCR);
case SPF_UMAX: /// Unsigned maximum
return TrueCR.umax(FalseCR);
return ValueLatticeElement::getRange(
ResultCR, TrueVal.isConstantRangeIncludingUndef() ||
if (SPR.Flavor == SPF_ABS) {
if (LHS == SI->getTrueValue())
return ValueLatticeElement::getRange(
TrueCR.abs(), TrueVal.isConstantRangeIncludingUndef());
if (LHS == SI->getFalseValue())
return ValueLatticeElement::getRange(
FalseCR.abs(), FalseVal.isConstantRangeIncludingUndef());
if (SPR.Flavor == SPF_NABS) {
ConstantRange Zero(APInt::getZero(TrueCR.getBitWidth()));
if (LHS == SI->getTrueValue())
return ValueLatticeElement::getRange(
Zero.sub(TrueCR.abs()), FalseVal.isConstantRangeIncludingUndef());
if (LHS == SI->getFalseValue())
return ValueLatticeElement::getRange(
Zero.sub(FalseCR.abs()), FalseVal.isConstantRangeIncludingUndef());
// Can we constrain the facts about the true and false values by using the
// condition itself? This shows up with idioms like e.g. select(a > 5, a, 5).
// TODO: We could potentially refine an overdefined true value above.
Value *Cond = SI->getCondition();
TrueVal = intersect(TrueVal,
getValueFromCondition(SI->getTrueValue(), Cond, true));
FalseVal = intersect(FalseVal,
getValueFromCondition(SI->getFalseValue(), Cond, false));
ValueLatticeElement Result = TrueVal;
return Result;
Optional<ConstantRange> LazyValueInfoImpl::getRangeFor(Value *V,
Instruction *CxtI,
BasicBlock *BB) {
Optional<ValueLatticeElement> OptVal = getBlockValue(V, BB);
if (!OptVal)
return None;
ValueLatticeElement &Val = *OptVal;
intersectAssumeOrGuardBlockValueConstantRange(V, Val, CxtI);
if (Val.isConstantRange())
return Val.getConstantRange();
const unsigned OperandBitWidth = DL.getTypeSizeInBits(V->getType());
return ConstantRange::getFull(OperandBitWidth);
Optional<ValueLatticeElement> LazyValueInfoImpl::solveBlockValueCast(
CastInst *CI, BasicBlock *BB) {
// Without knowing how wide the input is, we can't analyze it in any useful
// way.
if (!CI->getOperand(0)->getType()->isSized())
return ValueLatticeElement::getOverdefined();
// Filter out casts we don't know how to reason about before attempting to
// recurse on our operand. This can cut a long search short if we know we're
// not going to be able to get any useful information anways.
switch (CI->getOpcode()) {
case Instruction::Trunc:
case Instruction::SExt:
case Instruction::ZExt:
case Instruction::BitCast:
// Unhandled instructions are overdefined.
LLVM_DEBUG(dbgs() << " compute BB '" << BB->getName()
<< "' - overdefined (unknown cast).\n");
return ValueLatticeElement::getOverdefined();
// Figure out the range of the LHS. If that fails, we still apply the
// transfer rule on the full set since we may be able to locally infer
// interesting facts.
Optional<ConstantRange> LHSRes = getRangeFor(CI->getOperand(0), CI, BB);
if (!LHSRes.hasValue())
// More work to do before applying this transfer rule.
return None;
const ConstantRange &LHSRange = LHSRes.getValue();
const unsigned ResultBitWidth = CI->getType()->getIntegerBitWidth();
// NOTE: We're currently limited by the set of operations that ConstantRange
// can evaluate symbolically. Enhancing that set will allows us to analyze
// more definitions.
return ValueLatticeElement::getRange(LHSRange.castOp(CI->getOpcode(),
Optional<ValueLatticeElement> LazyValueInfoImpl::solveBlockValueBinaryOpImpl(
Instruction *I, BasicBlock *BB,
std::function<ConstantRange(const ConstantRange &,
const ConstantRange &)> OpFn) {
// Figure out the ranges of the operands. If that fails, use a
// conservative range, but apply the transfer rule anyways. This
// lets us pick up facts from expressions like "and i32 (call i32
// @foo()), 32"
Optional<ConstantRange> LHSRes = getRangeFor(I->getOperand(0), I, BB);
Optional<ConstantRange> RHSRes = getRangeFor(I->getOperand(1), I, BB);
if (!LHSRes.hasValue() || !RHSRes.hasValue())
// More work to do before applying this transfer rule.
return None;
const ConstantRange &LHSRange = LHSRes.getValue();
const ConstantRange &RHSRange = RHSRes.getValue();
return ValueLatticeElement::getRange(OpFn(LHSRange, RHSRange));
Optional<ValueLatticeElement> LazyValueInfoImpl::solveBlockValueBinaryOp(
BinaryOperator *BO, BasicBlock *BB) {
assert(BO->getOperand(0)->getType()->isSized() &&
"all operands to binary operators are sized");
if (BO->getOpcode() == Instruction::Xor) {
// Xor is the only operation not supported by ConstantRange::binaryOp().
LLVM_DEBUG(dbgs() << " compute BB '" << BB->getName()
<< "' - overdefined (unknown binary operator).\n");
return ValueLatticeElement::getOverdefined();
if (auto *OBO = dyn_cast<OverflowingBinaryOperator>(BO)) {
unsigned NoWrapKind = 0;
if (OBO->hasNoUnsignedWrap())
NoWrapKind |= OverflowingBinaryOperator::NoUnsignedWrap;
if (OBO->hasNoSignedWrap())
NoWrapKind |= OverflowingBinaryOperator::NoSignedWrap;
return solveBlockValueBinaryOpImpl(
[BO, NoWrapKind](const ConstantRange &CR1, const ConstantRange &CR2) {
return CR1.overflowingBinaryOp(BO->getOpcode(), CR2, NoWrapKind);
return solveBlockValueBinaryOpImpl(
BO, BB, [BO](const ConstantRange &CR1, const ConstantRange &CR2) {
return CR1.binaryOp(BO->getOpcode(), CR2);
LazyValueInfoImpl::solveBlockValueOverflowIntrinsic(WithOverflowInst *WO,
BasicBlock *BB) {
return solveBlockValueBinaryOpImpl(
WO, BB, [WO](const ConstantRange &CR1, const ConstantRange &CR2) {
return CR1.binaryOp(WO->getBinaryOp(), CR2);
Optional<ValueLatticeElement> LazyValueInfoImpl::solveBlockValueIntrinsic(
IntrinsicInst *II, BasicBlock *BB) {
if (!ConstantRange::isIntrinsicSupported(II->getIntrinsicID())) {
LLVM_DEBUG(dbgs() << " compute BB '" << BB->getName()
<< "' - unknown intrinsic.\n");
return getFromRangeMetadata(II);
SmallVector<ConstantRange, 2> OpRanges;
for (Value *Op : II->args()) {
Optional<ConstantRange> Range = getRangeFor(Op, II, BB);
if (!Range)
return None;
return ValueLatticeElement::getRange(
ConstantRange::intrinsic(II->getIntrinsicID(), OpRanges));
Optional<ValueLatticeElement> LazyValueInfoImpl::solveBlockValueExtractValue(
ExtractValueInst *EVI, BasicBlock *BB) {
if (auto *WO = dyn_cast<WithOverflowInst>(EVI->getAggregateOperand()))
if (EVI->getNumIndices() == 1 && *EVI->idx_begin() == 0)
return solveBlockValueOverflowIntrinsic(WO, BB);
// Handle extractvalue of insertvalue to allow further simplification
// based on replaced with.overflow intrinsics.
if (Value *V = SimplifyExtractValueInst(
EVI->getAggregateOperand(), EVI->getIndices(),
return getBlockValue(V, BB);
LLVM_DEBUG(dbgs() << " compute BB '" << BB->getName()
<< "' - overdefined (unknown extractvalue).\n");
return ValueLatticeElement::getOverdefined();
static bool matchICmpOperand(APInt &Offset, Value *LHS, Value *Val,
ICmpInst::Predicate Pred) {
if (LHS == Val)
return true;
// Handle range checking idiom produced by InstCombine. We will subtract the
// offset from the allowed range for RHS in this case.
const APInt *C;
if (match(LHS, m_Add(m_Specific(Val), m_APInt(C)))) {
Offset = *C;
return true;
// Handle the symmetric case. This appears in saturation patterns like
// (x == 16) ? 16 : (x + 1).
if (match(Val, m_Add(m_Specific(LHS), m_APInt(C)))) {
Offset = -*C;
return true;
// If (x | y) < C, then (x < C) && (y < C).
if (match(LHS, m_c_Or(m_Specific(Val), m_Value())) &&
(Pred == ICmpInst::ICMP_ULT || Pred == ICmpInst::ICMP_ULE))
return true;
// If (x & y) > C, then (x > C) && (y > C).
if (match(LHS, m_c_And(m_Specific(Val), m_Value())) &&
(Pred == ICmpInst::ICMP_UGT || Pred == ICmpInst::ICMP_UGE))
return true;
return false;
/// Get value range for a "(Val + Offset) Pred RHS" condition.
static ValueLatticeElement getValueFromSimpleICmpCondition(
CmpInst::Predicate Pred, Value *RHS, const APInt &Offset) {
ConstantRange RHSRange(RHS->getType()->getIntegerBitWidth(),
if (ConstantInt *CI = dyn_cast<ConstantInt>(RHS))
RHSRange = ConstantRange(CI->getValue());
else if (Instruction *I = dyn_cast<Instruction>(RHS))
if (auto *Ranges = I->getMetadata(LLVMContext::MD_range))
RHSRange = getConstantRangeFromMetadata(*Ranges);
ConstantRange TrueValues =
ConstantRange::makeAllowedICmpRegion(Pred, RHSRange);
return ValueLatticeElement::getRange(TrueValues.subtract(Offset));
static ValueLatticeElement getValueFromICmpCondition(Value *Val, ICmpInst *ICI,
bool isTrueDest) {
Value *LHS = ICI->getOperand(0);
Value *RHS = ICI->getOperand(1);
// Get the predicate that must hold along the considered edge.
CmpInst::Predicate EdgePred =
isTrueDest ? ICI->getPredicate() : ICI->getInversePredicate();
if (isa<Constant>(RHS)) {
if (ICI->isEquality() && LHS == Val) {
if (EdgePred == ICmpInst::ICMP_EQ)
return ValueLatticeElement::get(cast<Constant>(RHS));
else if (!isa<UndefValue>(RHS))
return ValueLatticeElement::getNot(cast<Constant>(RHS));
Type *Ty = Val->getType();
if (!Ty->isIntegerTy())
return ValueLatticeElement::getOverdefined();
unsigned BitWidth = Ty->getScalarSizeInBits();
APInt Offset(BitWidth, 0);
if (matchICmpOperand(Offset, LHS, Val, EdgePred))
return getValueFromSimpleICmpCondition(EdgePred, RHS, Offset);
CmpInst::Predicate SwappedPred = CmpInst::getSwappedPredicate(EdgePred);
if (matchICmpOperand(Offset, RHS, Val, SwappedPred))
return getValueFromSimpleICmpCondition(SwappedPred, LHS, Offset);
const APInt *Mask, *C;
if (match(LHS, m_And(m_Specific(Val), m_APInt(Mask))) &&
match(RHS, m_APInt(C))) {
// If (Val & Mask) == C then all the masked bits are known and we can
// compute a value range based on that.
if (EdgePred == ICmpInst::ICMP_EQ) {
KnownBits Known;
Known.Zero = ~*C & *Mask;
Known.One = *C & *Mask;
return ValueLatticeElement::getRange(
ConstantRange::fromKnownBits(Known, /*IsSigned*/ false));
// If (Val & Mask) != 0 then the value must be larger than the lowest set
// bit of Mask.
if (EdgePred == ICmpInst::ICMP_NE && !Mask->isZero() && C->isZero()) {
return ValueLatticeElement::getRange(ConstantRange::getNonEmpty(
APInt::getOneBitSet(BitWidth, Mask->countTrailingZeros()),
// If (X urem Modulus) >= C, then X >= C.
// TODO: An upper bound could be computed as well.
if (match(LHS, m_URem(m_Specific(Val), m_Value())) &&
match(RHS, m_APInt(C))) {
// Use the icmp region so we don't have to deal with different predicates.
ConstantRange CR = ConstantRange::makeExactICmpRegion(EdgePred, *C);
if (!CR.isEmptySet())
return ValueLatticeElement::getRange(ConstantRange::getNonEmpty(
CR.getUnsignedMin(), APInt(BitWidth, 0)));
return ValueLatticeElement::getOverdefined();
// Handle conditions of the form
// extractvalue(op.with.overflow(%x, C), 1).
static ValueLatticeElement getValueFromOverflowCondition(
Value *Val, WithOverflowInst *WO, bool IsTrueDest) {
// TODO: This only works with a constant RHS for now. We could also compute
// the range of the RHS, but this doesn't fit into the current structure of
// the edge value calculation.
const APInt *C;
if (WO->getLHS() != Val || !match(WO->getRHS(), m_APInt(C)))
return ValueLatticeElement::getOverdefined();
// Calculate the possible values of %x for which no overflow occurs.
ConstantRange NWR = ConstantRange::makeExactNoWrapRegion(
WO->getBinaryOp(), *C, WO->getNoWrapKind());
// If overflow is false, %x is constrained to NWR. If overflow is true, %x is
// constrained to it's inverse (all values that might cause overflow).
if (IsTrueDest)
NWR = NWR.inverse();
return ValueLatticeElement::getRange(NWR);
static Optional<ValueLatticeElement>
getValueFromConditionImpl(Value *Val, Value *Cond, bool isTrueDest,
bool isRevisit,
SmallDenseMap<Value *, ValueLatticeElement> &Visited,
SmallVectorImpl<Value *> &Worklist) {
if (!isRevisit) {
if (ICmpInst *ICI = dyn_cast<ICmpInst>(Cond))
return getValueFromICmpCondition(Val, ICI, isTrueDest);
if (auto *EVI = dyn_cast<ExtractValueInst>(Cond))
if (auto *WO = dyn_cast<WithOverflowInst>(EVI->getAggregateOperand()))
if (EVI->getNumIndices() == 1 && *EVI->idx_begin() == 1)
return getValueFromOverflowCondition(Val, WO, isTrueDest);
Value *L, *R;
bool IsAnd;
if (match(Cond, m_LogicalAnd(m_Value(L), m_Value(R))))
IsAnd = true;
else if (match(Cond, m_LogicalOr(m_Value(L), m_Value(R))))
IsAnd = false;
return ValueLatticeElement::getOverdefined();
auto LV = Visited.find(L);
auto RV = Visited.find(R);
// if (L && R) -> intersect L and R
// if (!(L || R)) -> intersect L and R
// if (L || R) -> union L and R
// if (!(L && R)) -> union L and R
if ((isTrueDest ^ IsAnd) && (LV != Visited.end())) {
ValueLatticeElement V = LV->second;
if (V.isOverdefined())
return V;
if (RV != Visited.end()) {
return V;
if (LV == Visited.end() || RV == Visited.end()) {
if (LV == Visited.end())
if (RV == Visited.end())
return None;
return intersect(LV->second, RV->second);
ValueLatticeElement getValueFromCondition(Value *Val, Value *Cond,
bool isTrueDest) {
assert(Cond && "precondition");
SmallDenseMap<Value*, ValueLatticeElement> Visited;
SmallVector<Value *> Worklist;
do {
Value *CurrentCond = Worklist.back();
// Insert an Overdefined placeholder into the set to prevent
// infinite recursion if there exists IRs that use not
// dominated by its def as in this example:
// "%tmp3 = or i1 undef, %tmp4"
// "%tmp4 = or i1 undef, %tmp3"
auto Iter =
Visited.try_emplace(CurrentCond, ValueLatticeElement::getOverdefined());
bool isRevisit = !Iter.second;
Optional<ValueLatticeElement> Result = getValueFromConditionImpl(
Val, CurrentCond, isTrueDest, isRevisit, Visited, Worklist);
if (Result) {
Visited[CurrentCond] = *Result;
} while (!Worklist.empty());
auto Result = Visited.find(Cond);
assert(Result != Visited.end());
return Result->second;
// Return true if Usr has Op as an operand, otherwise false.
static bool usesOperand(User *Usr, Value *Op) {
return is_contained(Usr->operands(), Op);
// Return true if the instruction type of Val is supported by
// constantFoldUser(). Currently CastInst, BinaryOperator and FreezeInst only.
// Call this before calling constantFoldUser() to find out if it's even worth
// attempting to call it.
static bool isOperationFoldable(User *Usr) {
return isa<CastInst>(Usr) || isa<BinaryOperator>(Usr) || isa<FreezeInst>(Usr);
// Check if Usr can be simplified to an integer constant when the value of one
// of its operands Op is an integer constant OpConstVal. If so, return it as an
// lattice value range with a single element or otherwise return an overdefined
// lattice value.
static ValueLatticeElement constantFoldUser(User *Usr, Value *Op,
const APInt &OpConstVal,
const DataLayout &DL) {
assert(isOperationFoldable(Usr) && "Precondition");
Constant* OpConst = Constant::getIntegerValue(Op->getType(), OpConstVal);
// Check if Usr can be simplified to a constant.
if (auto *CI = dyn_cast<CastInst>(Usr)) {
assert(CI->getOperand(0) == Op && "Operand 0 isn't Op");
if (auto *C = dyn_cast_or_null<ConstantInt>(
SimplifyCastInst(CI->getOpcode(), OpConst,
CI->getDestTy(), DL))) {
return ValueLatticeElement::getRange(ConstantRange(C->getValue()));
} else if (auto *BO = dyn_cast<BinaryOperator>(Usr)) {
bool Op0Match = BO->getOperand(0) == Op;
bool Op1Match = BO->getOperand(1) == Op;
assert((Op0Match || Op1Match) &&
"Operand 0 nor Operand 1 isn't a match");
Value *LHS = Op0Match ? OpConst : BO->getOperand(0);
Value *RHS = Op1Match ? OpConst : BO->getOperand(1);
if (auto *C = dyn_cast_or_null<ConstantInt>(
SimplifyBinOp(BO->getOpcode(), LHS, RHS, DL))) {
return ValueLatticeElement::getRange(ConstantRange(C->getValue()));
} else if (isa<FreezeInst>(Usr)) {
assert(cast<FreezeInst>(Usr)->getOperand(0) == Op && "Operand 0 isn't Op");
return ValueLatticeElement::getRange(ConstantRange(OpConstVal));
return ValueLatticeElement::getOverdefined();
/// Compute the value of Val on the edge BBFrom -> BBTo. Returns false if
/// Val is not constrained on the edge. Result is unspecified if return value
/// is false.
static Optional<ValueLatticeElement> getEdgeValueLocal(Value *Val,
BasicBlock *BBFrom,
BasicBlock *BBTo) {
// TODO: Handle more complex conditionals. If (v == 0 || v2 < 1) is false, we
// know that v != 0.
if (BranchInst *BI = dyn_cast<BranchInst>(BBFrom->getTerminator())) {
// If this is a conditional branch and only one successor goes to BBTo, then
// we may be able to infer something from the condition.
if (BI->isConditional() &&
BI->getSuccessor(0) != BI->getSuccessor(1)) {
bool isTrueDest = BI->getSuccessor(0) == BBTo;
assert(BI->getSuccessor(!isTrueDest) == BBTo &&
"BBTo isn't a successor of BBFrom");
Value *Condition = BI->getCondition();
// If V is the condition of the branch itself, then we know exactly what
// it is.
if (Condition == Val)
return ValueLatticeElement::get(ConstantInt::get(
Type::getInt1Ty(Val->getContext()), isTrueDest));
// If the condition of the branch is an equality comparison, we may be
// able to infer the value.
ValueLatticeElement Result = getValueFromCondition(Val, Condition,
if (!Result.isOverdefined())
return Result;
if (User *Usr = dyn_cast<User>(Val)) {
assert(Result.isOverdefined() && "Result isn't overdefined");
// Check with isOperationFoldable() first to avoid linearly iterating
// over the operands unnecessarily which can be expensive for
// instructions with many operands.
if (isa<IntegerType>(Usr->getType()) && isOperationFoldable(Usr)) {
const DataLayout &DL = BBTo->getModule()->getDataLayout();
if (usesOperand(Usr, Condition)) {
// If Val has Condition as an operand and Val can be folded into a
// constant with either Condition == true or Condition == false,
// propagate the constant.
// eg.
// ; %Val is true on the edge to %then.
// %Val = and i1 %Condition, true.
// br %Condition, label %then, label %else
APInt ConditionVal(1, isTrueDest ? 1 : 0);
Result = constantFoldUser(Usr, Condition, ConditionVal, DL);
} else {
// If one of Val's operand has an inferred value, we may be able to
// infer the value of Val.
// eg.
// ; %Val is 94 on the edge to %then.
// %Val = add i8 %Op, 1
// %Condition = icmp eq i8 %Op, 93
// br i1 %Condition, label %then, label %else
for (unsigned i = 0; i < Usr->getNumOperands(); ++i) {
Value *Op = Usr->getOperand(i);
ValueLatticeElement OpLatticeVal =
getValueFromCondition(Op, Condition, isTrueDest);
if (Optional<APInt> OpConst = OpLatticeVal.asConstantInteger()) {
Result = constantFoldUser(Usr, Op, OpConst.getValue(), DL);
if (!Result.isOverdefined())
return Result;
// If the edge was formed by a switch on the value, then we may know exactly
// what it is.
if (SwitchInst *SI = dyn_cast<SwitchInst>(BBFrom->getTerminator())) {
Value *Condition = SI->getCondition();
if (!isa<IntegerType>(Val->getType()))
return None;
bool ValUsesConditionAndMayBeFoldable = false;
if (Condition != Val) {
// Check if Val has Condition as an operand.
if (User *Usr = dyn_cast<User>(Val))
ValUsesConditionAndMayBeFoldable = isOperationFoldable(Usr) &&
usesOperand(Usr, Condition);
if (!ValUsesConditionAndMayBeFoldable)
return None;
assert((Condition == Val || ValUsesConditionAndMayBeFoldable) &&
"Condition != Val nor Val doesn't use Condition");
bool DefaultCase = SI->getDefaultDest() == BBTo;
unsigned BitWidth = Val->getType()->getIntegerBitWidth();
ConstantRange EdgesVals(BitWidth, DefaultCase/*isFullSet*/);
for (auto Case : SI->cases()) {
APInt CaseValue = Case.getCaseValue()->getValue();
ConstantRange EdgeVal(CaseValue);
if (ValUsesConditionAndMayBeFoldable) {
User *Usr = cast<User>(Val);
const DataLayout &DL = BBTo->getModule()->getDataLayout();
ValueLatticeElement EdgeLatticeVal =
constantFoldUser(Usr, Condition, CaseValue, DL);
if (EdgeLatticeVal.isOverdefined())
return None;
EdgeVal = EdgeLatticeVal.getConstantRange();
if (DefaultCase) {
// It is possible that the default destination is the destination of
// some cases. We cannot perform difference for those cases.
// We know Condition != CaseValue in BBTo. In some cases we can use
// this to infer Val == f(Condition) is != f(CaseValue). For now, we
// only do this when f is identity (i.e. Val == Condition), but we
// should be able to do this for any injective f.
if (Case.getCaseSuccessor() != BBTo && Condition == Val)
EdgesVals = EdgesVals.difference(EdgeVal);
} else if (Case.getCaseSuccessor() == BBTo)
EdgesVals = EdgesVals.unionWith(EdgeVal);
return ValueLatticeElement::getRange(std::move(EdgesVals));
return None;
/// Compute the value of Val on the edge BBFrom -> BBTo or the value at
/// the basic block if the edge does not constrain Val.
Optional<ValueLatticeElement> LazyValueInfoImpl::getEdgeValue(
Value *Val, BasicBlock *BBFrom, BasicBlock *BBTo, Instruction *CxtI) {
// If already a constant, there is nothing to compute.
if (Constant *VC = dyn_cast<Constant>(Val))
return ValueLatticeElement::get(VC);
ValueLatticeElement LocalResult = getEdgeValueLocal(Val, BBFrom, BBTo)
if (hasSingleValue(LocalResult))
// Can't get any more precise here
return LocalResult;
Optional<ValueLatticeElement> OptInBlock = getBlockValue(Val, BBFrom);
if (!OptInBlock)
return None;
ValueLatticeElement &InBlock = *OptInBlock;
// Try to intersect ranges of the BB and the constraint on the edge.
intersectAssumeOrGuardBlockValueConstantRange(Val, InBlock,
// We can use the context instruction (generically the ultimate instruction
// the calling pass is trying to simplify) here, even though the result of
// this function is generally cached when called from the solve* functions
// (and that cached result might be used with queries using a different
// context instruction), because when this function is called from the solve*
// functions, the context instruction is not provided. When called from
// LazyValueInfoImpl::getValueOnEdge, the context instruction is provided,
// but then the result is not cached.
intersectAssumeOrGuardBlockValueConstantRange(Val, InBlock, CxtI);
return intersect(LocalResult, InBlock);
ValueLatticeElement LazyValueInfoImpl::getValueInBlock(Value *V, BasicBlock *BB,
Instruction *CxtI) {
LLVM_DEBUG(dbgs() << "LVI Getting block end value " << *V << " at '"
<< BB->getName() << "'\n");
assert(BlockValueStack.empty() && BlockValueSet.empty());
Optional<ValueLatticeElement> OptResult = getBlockValue(V, BB);
if (!OptResult) {
OptResult = getBlockValue(V, BB);
assert(OptResult && "Value not available after solving");
ValueLatticeElement Result = *OptResult;
intersectAssumeOrGuardBlockValueConstantRange(V, Result, CxtI);
LLVM_DEBUG(dbgs() << " Result = " << Result << "\n");
return Result;
ValueLatticeElement LazyValueInfoImpl::getValueAt(Value *V, Instruction *CxtI) {
LLVM_DEBUG(dbgs() << "LVI Getting value " << *V << " at '" << CxtI->getName()
<< "'\n");
if (auto *C = dyn_cast<Constant>(V))
return ValueLatticeElement::get(C);
ValueLatticeElement Result = ValueLatticeElement::getOverdefined();
if (auto *I = dyn_cast<Instruction>(V))
Result = getFromRangeMetadata(I);
intersectAssumeOrGuardBlockValueConstantRange(V, Result, CxtI);
LLVM_DEBUG(dbgs() << " Result = " << Result << "\n");
return Result;
ValueLatticeElement LazyValueInfoImpl::
getValueOnEdge(Value *V, BasicBlock *FromBB, BasicBlock *ToBB,
Instruction *CxtI) {
LLVM_DEBUG(dbgs() << "LVI Getting edge value " << *V << " from '"
<< FromBB->getName() << "' to '" << ToBB->getName()
<< "'\n");
Optional<ValueLatticeElement> Result = getEdgeValue(V, FromBB, ToBB, CxtI);
if (!Result) {
Result = getEdgeValue(V, FromBB, ToBB, CxtI);
assert(Result && "More work to do after problem solved?");
LLVM_DEBUG(dbgs() << " Result = " << *Result << "\n");
return *Result;
void LazyValueInfoImpl::threadEdge(BasicBlock *PredBB, BasicBlock *OldSucc,
BasicBlock *NewSucc) {
TheCache.threadEdgeImpl(OldSucc, NewSucc);
// LazyValueInfo Impl
/// This lazily constructs the LazyValueInfoImpl.
static LazyValueInfoImpl &getImpl(void *&PImpl, AssumptionCache *AC,
const Module *M) {
if (!PImpl) {
assert(M && "getCache() called with a null Module");
const DataLayout &DL = M->getDataLayout();
Function *GuardDecl = M->getFunction(
PImpl = new LazyValueInfoImpl(AC, DL, GuardDecl);
return *static_cast<LazyValueInfoImpl*>(PImpl);
bool LazyValueInfoWrapperPass::runOnFunction(Function &F) {
Info.AC = &getAnalysis<AssumptionCacheTracker>().getAssumptionCache(F);
Info.TLI = &getAnalysis<TargetLibraryInfoWrapperPass>().getTLI(F);
if (Info.PImpl)
getImpl(Info.PImpl, Info.AC, F.getParent()).clear();
// Fully lazy.
return false;
void LazyValueInfoWrapperPass::getAnalysisUsage(AnalysisUsage &AU) const {
LazyValueInfo &LazyValueInfoWrapperPass::getLVI() { return Info; }
LazyValueInfo::~LazyValueInfo() { releaseMemory(); }
void LazyValueInfo::releaseMemory() {
// If the cache was allocated, free it.
if (PImpl) {
delete &getImpl(PImpl, AC, nullptr);
PImpl = nullptr;
bool LazyValueInfo::invalidate(Function &F, const PreservedAnalyses &PA,
FunctionAnalysisManager::Invalidator &Inv) {
// We need to invalidate if we have either failed to preserve this analyses
// result directly or if any of its dependencies have been invalidated.
auto PAC = PA.getChecker<LazyValueAnalysis>();
if (!(PAC.preserved() || PAC.preservedSet<AllAnalysesOn<Function>>()))
return true;
return false;
void LazyValueInfoWrapperPass::releaseMemory() { Info.releaseMemory(); }
LazyValueInfo LazyValueAnalysis::run(Function &F,
FunctionAnalysisManager &FAM) {
auto &AC = FAM.getResult<AssumptionAnalysis>(F);
auto &TLI = FAM.getResult<TargetLibraryAnalysis>(F);
return LazyValueInfo(&AC, &F.getParent()->getDataLayout(), &TLI);
/// Returns true if we can statically tell that this value will never be a
/// "useful" constant. In practice, this means we've got something like an
/// alloca or a malloc call for which a comparison against a constant can
/// only be guarding dead code. Note that we are potentially giving up some
/// precision in dead code (a constant result) in favour of avoiding a
/// expensive search for a easily answered common query.
static bool isKnownNonConstant(Value *V) {
V = V->stripPointerCasts();
// The return val of alloc cannot be a Constant.
if (isa<AllocaInst>(V))
return true;
return false;
Constant *LazyValueInfo::getConstant(Value *V, Instruction *CxtI) {
// Bail out early if V is known not to be a Constant.
if (isKnownNonConstant(V))
return nullptr;
BasicBlock *BB = CxtI->getParent();
ValueLatticeElement Result =
getImpl(PImpl, AC, BB->getModule()).getValueInBlock(V, BB, CxtI);
if (Result.isConstant())
return Result.getConstant();
if (Result.isConstantRange()) {
const ConstantRange &CR = Result.getConstantRange();
if (const APInt *SingleVal = CR.getSingleElement())
return ConstantInt::get(V->getContext(), *SingleVal);
return nullptr;
ConstantRange LazyValueInfo::getConstantRange(Value *V, Instruction *CxtI,
bool UndefAllowed) {
unsigned Width = V->getType()->getIntegerBitWidth();
BasicBlock *BB = CxtI->getParent();
ValueLatticeElement Result =
getImpl(PImpl, AC, BB->getModule()).getValueInBlock(V, BB, CxtI);
if (Result.isUnknown())
return ConstantRange::getEmpty(Width);
if (Result.isConstantRange(UndefAllowed))
return Result.getConstantRange(UndefAllowed);
// We represent ConstantInt constants as constant ranges but other kinds
// of integer constants, i.e. ConstantExpr will be tagged as constants
assert(!(Result.isConstant() && isa<ConstantInt>(Result.getConstant())) &&
"ConstantInt value must be represented as constantrange");
return ConstantRange::getFull(Width);
/// Determine whether the specified value is known to be a
/// constant on the specified edge. Return null if not.
Constant *LazyValueInfo::getConstantOnEdge(Value *V, BasicBlock *FromBB,
BasicBlock *ToBB,
Instruction *CxtI) {
Module *M = FromBB->getModule();
ValueLatticeElement Result =
getImpl(PImpl, AC, M).getValueOnEdge(V, FromBB, ToBB, CxtI);
if (Result.isConstant())
return Result.getConstant();
if (Result.isConstantRange()) {
const ConstantRange &CR = Result.getConstantRange();
if (const APInt *SingleVal = CR.getSingleElement())
return ConstantInt::get(V->getContext(), *SingleVal);
return nullptr;
ConstantRange LazyValueInfo::getConstantRangeOnEdge(Value *V,
BasicBlock *FromBB,
BasicBlock *ToBB,
Instruction *CxtI) {
unsigned Width = V->getType()->getIntegerBitWidth();
Module *M = FromBB->getModule();
ValueLatticeElement Result =
getImpl(PImpl, AC, M).getValueOnEdge(V, FromBB, ToBB, CxtI);
if (Result.isUnknown())
return ConstantRange::getEmpty(Width);
if (Result.isConstantRange())
return Result.getConstantRange();
// We represent ConstantInt constants as constant ranges but other kinds
// of integer constants, i.e. ConstantExpr will be tagged as constants
assert(!(Result.isConstant() && isa<ConstantInt>(Result.getConstant())) &&
"ConstantInt value must be represented as constantrange");
return ConstantRange::getFull(Width);
static LazyValueInfo::Tristate
getPredicateResult(unsigned Pred, Constant *C, const ValueLatticeElement &Val,
const DataLayout &DL, TargetLibraryInfo *TLI) {
// If we know the value is a constant, evaluate the conditional.
Constant *Res = nullptr;
if (Val.isConstant()) {
Res = ConstantFoldCompareInstOperands(Pred, Val.getConstant(), C, DL, TLI);
if (ConstantInt *ResCI = dyn_cast<ConstantInt>(Res))
return ResCI->isZero() ? LazyValueInfo::False : LazyValueInfo::True;
return LazyValueInfo::Unknown;
if (Val.isConstantRange()) {
ConstantInt *CI = dyn_cast<ConstantInt>(C);
if (!CI) return LazyValueInfo::Unknown;
const ConstantRange &CR = Val.getConstantRange();
if (Pred == ICmpInst::ICMP_EQ) {
if (!CR.contains(CI->getValue()))
return LazyValueInfo::False;
if (CR.isSingleElement())
return LazyValueInfo::True;
} else if (Pred == ICmpInst::ICMP_NE) {
if (!CR.contains(CI->getValue()))
return LazyValueInfo::True;
if (CR.isSingleElement())
return LazyValueInfo::False;
} else {
// Handle more complex predicates.
ConstantRange TrueValues = ConstantRange::makeExactICmpRegion(
(ICmpInst::Predicate)Pred, CI->getValue());
if (TrueValues.contains(CR))
return LazyValueInfo::True;
if (TrueValues.inverse().contains(CR))
return LazyValueInfo::False;
return LazyValueInfo::Unknown;
if (Val.isNotConstant()) {
// If this is an equality comparison, we can try to fold it knowing that
// "V != C1".
if (Pred == ICmpInst::ICMP_EQ) {
// !C1 == C -> false iff C1 == C.
Res = ConstantFoldCompareInstOperands(ICmpInst::ICMP_NE,
Val.getNotConstant(), C, DL,
if (Res->isNullValue())
return LazyValueInfo::False;
} else if (Pred == ICmpInst::ICMP_NE) {
// !C1 != C -> true iff C1 == C.
Res = ConstantFoldCompareInstOperands(ICmpInst::ICMP_NE,
Val.getNotConstant(), C, DL,
if (Res->isNullValue())
return LazyValueInfo::True;
return LazyValueInfo::Unknown;
return LazyValueInfo::Unknown;
/// Determine whether the specified value comparison with a constant is known to
/// be true or false on the specified CFG edge. Pred is a CmpInst predicate.
LazyValueInfo::getPredicateOnEdge(unsigned Pred, Value *V, Constant *C,
BasicBlock *FromBB, BasicBlock *ToBB,
Instruction *CxtI) {
Module *M = FromBB->getModule();
ValueLatticeElement Result =
getImpl(PImpl, AC, M).getValueOnEdge(V, FromBB, ToBB, CxtI);
return getPredicateResult(Pred, C, Result, M->getDataLayout(), TLI);
LazyValueInfo::getPredicateAt(unsigned Pred, Value *V, Constant *C,
Instruction *CxtI, bool UseBlockValue) {
// Is or is not NonNull are common predicates being queried. If
// isKnownNonZero can tell us the result of the predicate, we can
// return it quickly. But this is only a fastpath, and falling
// through would still be correct.
Module *M = CxtI->getModule();
const DataLayout &DL = M->getDataLayout();
if (V->getType()->isPointerTy() && C->isNullValue() &&
isKnownNonZero(V->stripPointerCastsSameRepresentation(), DL)) {
if (Pred == ICmpInst::ICMP_EQ)
return LazyValueInfo::False;
else if (Pred == ICmpInst::ICMP_NE)
return LazyValueInfo::True;
ValueLatticeElement Result = UseBlockValue
? getImpl(PImpl, AC, M).getValueInBlock(V, CxtI->getParent(), CxtI)
: getImpl(PImpl, AC, M).getValueAt(V, CxtI);
Tristate Ret = getPredicateResult(Pred, C, Result, DL, TLI);
if (Ret != Unknown)
return Ret;
// Note: The following bit of code is somewhat distinct from the rest of LVI;
// LVI as a whole tries to compute a lattice value which is conservatively
// correct at a given location. In this case, we have a predicate which we
// weren't able to prove about the merged result, and we're pushing that
// predicate back along each incoming edge to see if we can prove it
// separately for each input. As a motivating example, consider:
// bb1:
// %v1 = ... ; constantrange<1, 5>
// br label %merge
// bb2:
// %v2 = ... ; constantrange<10, 20>
// br label %merge
// merge:
// %phi = phi [%v1, %v2] ; constantrange<1,20>
// %pred = icmp eq i32 %phi, 8
// We can't tell from the lattice value for '%phi' that '%pred' is false
// along each path, but by checking the predicate over each input separately,
// we can.
// We limit the search to one step backwards from the current BB and value.
// We could consider extending this to search further backwards through the
// CFG and/or value graph, but there are non-obvious compile time vs quality
// tradeoffs.
BasicBlock *BB = CxtI->getParent();
// Function entry or an unreachable block. Bail to avoid confusing
// analysis below.
pred_iterator PI = pred_begin(BB), PE = pred_end(BB);
if (PI == PE)
return Unknown;
// If V is a PHI node in the same block as the context, we need to ask
// questions about the predicate as applied to the incoming value along
// each edge. This is useful for eliminating cases where the predicate is
// known along all incoming edges.
if (auto *PHI = dyn_cast<PHINode>(V))
if (PHI->getParent() == BB) {
Tristate Baseline = Unknown;
for (unsigned i = 0, e = PHI->getNumIncomingValues(); i < e; i++) {
Value *Incoming = PHI->getIncomingValue(i);
BasicBlock *PredBB = PHI->getIncomingBlock(i);
// Note that PredBB may be BB itself.
Tristate Result =
getPredicateOnEdge(Pred, Incoming, C, PredBB, BB, CxtI);
// Keep going as long as we've seen a consistent known result for
// all inputs.
Baseline = (i == 0) ? Result /* First iteration */
: (Baseline == Result ? Baseline
: Unknown); /* All others */
if (Baseline == Unknown)
if (Baseline != Unknown)
return Baseline;
// For a comparison where the V is outside this block, it's possible
// that we've branched on it before. Look to see if the value is known
// on all incoming edges.
if (!isa<Instruction>(V) || cast<Instruction>(V)->getParent() != BB) {
// For predecessor edge, determine if the comparison is true or false
// on that edge. If they're all true or all false, we can conclude
// the value of the comparison in this block.
Tristate Baseline = getPredicateOnEdge(Pred, V, C, *PI, BB, CxtI);
if (Baseline != Unknown) {
// Check that all remaining incoming values match the first one.
while (++PI != PE) {
Tristate Ret = getPredicateOnEdge(Pred, V, C, *PI, BB, CxtI);
if (Ret != Baseline)
// If we terminated early, then one of the values didn't match.
if (PI == PE) {
return Baseline;
return Unknown;
LazyValueInfo::Tristate LazyValueInfo::getPredicateAt(unsigned P, Value *LHS,
Value *RHS,
Instruction *CxtI,
bool UseBlockValue) {
CmpInst::Predicate Pred = (CmpInst::Predicate)P;
if (auto *C = dyn_cast<Constant>(RHS))
return getPredicateAt(P, LHS, C, CxtI, UseBlockValue);
if (auto *C = dyn_cast<Constant>(LHS))
return getPredicateAt(CmpInst::getSwappedPredicate(Pred), RHS, C, CxtI,
// Got two non-Constant values. While we could handle them somewhat,
// by getting their constant ranges, and applying ConstantRange::icmp(),
// so far it did not appear to be profitable.
return LazyValueInfo::Unknown;
void LazyValueInfo::threadEdge(BasicBlock *PredBB, BasicBlock *OldSucc,
BasicBlock *NewSucc) {
if (PImpl) {
getImpl(PImpl, AC, PredBB->getModule())
.threadEdge(PredBB, OldSucc, NewSucc);
void LazyValueInfo::eraseBlock(BasicBlock *BB) {
if (PImpl) {
getImpl(PImpl, AC, BB->getModule()).eraseBlock(BB);
void LazyValueInfo::printLVI(Function &F, DominatorTree &DTree, raw_ostream &OS) {
if (PImpl) {
getImpl(PImpl, AC, F.getParent()).printLVI(F, DTree, OS);
// Print the LVI for the function arguments at the start of each basic block.
void LazyValueInfoAnnotatedWriter::emitBasicBlockStartAnnot(
const BasicBlock *BB, formatted_raw_ostream &OS) {
// Find if there are latticevalues defined for arguments of the function.
auto *F = BB->getParent();
for (auto &Arg : F->args()) {
ValueLatticeElement Result = LVIImpl->getValueInBlock(
const_cast<Argument *>(&Arg), const_cast<BasicBlock *>(BB));
if (Result.isUnknown())
OS << "; LatticeVal for: '" << Arg << "' is: " << Result << "\n";
// This function prints the LVI analysis for the instruction I at the beginning
// of various basic blocks. It relies on calculated values that are stored in
// the LazyValueInfoCache, and in the absence of cached values, recalculate the
// LazyValueInfo for `I`, and print that info.
void LazyValueInfoAnnotatedWriter::emitInstructionAnnot(
const Instruction *I, formatted_raw_ostream &OS) {
auto *ParentBB = I->getParent();
SmallPtrSet<const BasicBlock*, 16> BlocksContainingLVI;
// We can generate (solve) LVI values only for blocks that are dominated by
// the I's parent. However, to avoid generating LVI for all dominating blocks,
// that contain redundant/uninteresting information, we print LVI for
// blocks that may use this LVI information (such as immediate successor
// blocks, and blocks that contain uses of `I`).
auto printResult = [&](const BasicBlock *BB) {
if (!BlocksContainingLVI.insert(BB).second)
ValueLatticeElement Result = LVIImpl->getValueInBlock(
const_cast<Instruction *>(I), const_cast<BasicBlock *>(BB));
OS << "; LatticeVal for: '" << *I << "' in BB: '";
BB->printAsOperand(OS, false);
OS << "' is: " << Result << "\n";
// Print the LVI analysis results for the immediate successor blocks, that
// are dominated by `ParentBB`.
for (auto *BBSucc : successors(ParentBB))
if (DT.dominates(ParentBB, BBSucc))
// Print LVI in blocks where `I` is used.
for (auto *U : I->users())
if (auto *UseI = dyn_cast<Instruction>(U))
if (!isa<PHINode>(UseI) || DT.dominates(ParentBB, UseI->getParent()))
namespace {
// Printer class for LazyValueInfo results.
class LazyValueInfoPrinter : public FunctionPass {
static char ID; // Pass identification, replacement for typeid
LazyValueInfoPrinter() : FunctionPass(ID) {
void getAnalysisUsage(AnalysisUsage &AU) const override {
// Get the mandatory dominator tree analysis and pass this in to the
// LVIPrinter. We cannot rely on the LVI's DT, since it's optional.
bool runOnFunction(Function &F) override {
dbgs() << "LVI for function '" << F.getName() << "':\n";
auto &LVI = getAnalysis<LazyValueInfoWrapperPass>().getLVI();
auto &DTree = getAnalysis<DominatorTreeWrapperPass>().getDomTree();
LVI.printLVI(F, DTree, dbgs());
return false;
char LazyValueInfoPrinter::ID = 0;
INITIALIZE_PASS_BEGIN(LazyValueInfoPrinter, "print-lazy-value-info",
"Lazy Value Info Printer Pass", false, false)
INITIALIZE_PASS_END(LazyValueInfoPrinter, "print-lazy-value-info",
"Lazy Value Info Printer Pass", false, false)