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llvm/lib/Analysis/LazyValueInfo.cpp
Vitaly Buka 82afb7ea06 LVI: Fix use-of-uninitialized-value after r294463 
BlockValueStack can be reallocated making reference e invalid.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@294572 91177308-0d34-0410-b5e6-96231b3b80d8
2017-02-09 09:28:05 +00:00

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//===- LazyValueInfo.cpp - Value constraint analysis ------------*- C++ -*-===//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// 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/STLExtras.h"
#include "llvm/Analysis/AssumptionCache.h"
#include "llvm/Analysis/ConstantFolding.h"
#include "llvm/Analysis/TargetLibraryInfo.h"
#include "llvm/Analysis/ValueTracking.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/Support/Debug.h"
#include "llvm/Support/raw_ostream.h"
#include <map>
#include <stack>
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;
INITIALIZE_PASS_BEGIN(LazyValueInfoWrapperPass, "lazy-value-info",
"Lazy Value Information Analysis", false, true)
INITIALIZE_PASS_DEPENDENCY(AssumptionCacheTracker)
INITIALIZE_PASS_DEPENDENCY(TargetLibraryInfoWrapperPass)
INITIALIZE_PASS_END(LazyValueInfoWrapperPass, "lazy-value-info",
"Lazy Value Information Analysis", false, true)
namespace llvm {
FunctionPass *createLazyValueInfoPass() { return new LazyValueInfoWrapperPass(); }
}
AnalysisKey LazyValueAnalysis::Key;
//===----------------------------------------------------------------------===//
// LVILatticeVal
//===----------------------------------------------------------------------===//
/// This is the information tracked by LazyValueInfo for each value.
///
/// FIXME: This is basically just for bringup, this can be made a lot more rich
/// in the future.
///
namespace {
class LVILatticeVal {
enum LatticeValueTy {
/// This Value has no known value yet. As a result, this implies the
/// producing instruction is dead. Caution: We use this as the starting
/// state in our local meet rules. In this usage, it's taken to mean
/// "nothing known yet".
undefined,
/// This Value has a specific constant value. (For constant integers,
/// constantrange is used instead. Integer typed constantexprs can appear
/// as constant.)
constant,
/// This Value is known to not have the specified value. (For constant
/// integers, constantrange is used instead. As above, integer typed
/// constantexprs can appear here.)
notconstant,
/// The Value falls within this range. (Used only for integer typed values.)
constantrange,
/// We can not precisely model the dynamic values this value might take.
overdefined
};
/// Val: This stores the current lattice value along with the Constant* for
/// the constant if this is a 'constant' or 'notconstant' value.
LatticeValueTy Tag;
Constant *Val;
ConstantRange Range;
public:
LVILatticeVal() : Tag(undefined), Val(nullptr), Range(1, true) {}
static LVILatticeVal get(Constant *C) {
LVILatticeVal Res;
if (!isa<UndefValue>(C))
Res.markConstant(C);
return Res;
}
static LVILatticeVal getNot(Constant *C) {
LVILatticeVal Res;
if (!isa<UndefValue>(C))
Res.markNotConstant(C);
return Res;
}
static LVILatticeVal getRange(ConstantRange CR) {
LVILatticeVal Res;
Res.markConstantRange(std::move(CR));
return Res;
}
static LVILatticeVal getOverdefined() {
LVILatticeVal Res;
Res.markOverdefined();
return Res;
}
bool isUndefined() const { return Tag == undefined; }
bool isConstant() const { return Tag == constant; }
bool isNotConstant() const { return Tag == notconstant; }
bool isConstantRange() const { return Tag == constantrange; }
bool isOverdefined() const { return Tag == overdefined; }
Constant *getConstant() const {
assert(isConstant() && "Cannot get the constant of a non-constant!");
return Val;
}
Constant *getNotConstant() const {
assert(isNotConstant() && "Cannot get the constant of a non-notconstant!");
return Val;
}
ConstantRange getConstantRange() const {
assert(isConstantRange() &&
"Cannot get the constant-range of a non-constant-range!");
return Range;
}
private:
void markOverdefined() {
if (isOverdefined())
return;
Tag = overdefined;
}
void markConstant(Constant *V) {
assert(V && "Marking constant with NULL");
if (ConstantInt *CI = dyn_cast<ConstantInt>(V)) {
markConstantRange(ConstantRange(CI->getValue()));
return;
}
if (isa<UndefValue>(V))
return;
assert((!isConstant() || getConstant() == V) &&
"Marking constant with different value");
assert(isUndefined());
Tag = constant;
Val = V;
}
void markNotConstant(Constant *V) {
assert(V && "Marking constant with NULL");
if (ConstantInt *CI = dyn_cast<ConstantInt>(V)) {
markConstantRange(ConstantRange(CI->getValue()+1, CI->getValue()));
return;
}
if (isa<UndefValue>(V))
return;
assert((!isConstant() || getConstant() != V) &&
"Marking constant !constant with same value");
assert((!isNotConstant() || getNotConstant() == V) &&
"Marking !constant with different value");
assert(isUndefined() || isConstant());
Tag = notconstant;
Val = V;
}
void markConstantRange(ConstantRange NewR) {
if (isConstantRange()) {
if (NewR.isEmptySet())
markOverdefined();
else {
Range = std::move(NewR);
}
return;
}
assert(isUndefined());
if (NewR.isEmptySet())
markOverdefined();
else {
Tag = constantrange;
Range = std::move(NewR);
}
}
public:
/// Merge the specified lattice value into this one, updating this
/// one and returning true if anything changed.
void mergeIn(const LVILatticeVal &RHS, const DataLayout &DL) {
if (RHS.isUndefined() || isOverdefined())
return;
if (RHS.isOverdefined()) {
markOverdefined();
return;
}
if (isUndefined()) {
*this = RHS;
return;
}
if (isConstant()) {
if (RHS.isConstant() && Val == RHS.Val)
return;
markOverdefined();
return;
}
if (isNotConstant()) {
if (RHS.isNotConstant() && Val == RHS.Val)
return;
markOverdefined();
return;
}
assert(isConstantRange() && "New LVILattice type?");
if (!RHS.isConstantRange()) {
// We can get here if we've encountered a constantexpr of integer type
// and merge it with a constantrange.
markOverdefined();
return;
}
ConstantRange NewR = Range.unionWith(RHS.getConstantRange());
if (NewR.isFullSet())
markOverdefined();
else
markConstantRange(NewR);
}
};
} // end anonymous namespace.
namespace llvm {
raw_ostream &operator<<(raw_ostream &OS, const LVILatticeVal &Val)
LLVM_ATTRIBUTE_USED;
raw_ostream &operator<<(raw_ostream &OS, const LVILatticeVal &Val) {
if (Val.isUndefined())
return OS << "undefined";
if (Val.isOverdefined())
return OS << "overdefined";
if (Val.isNotConstant())
return OS << "notconstant<" << *Val.getNotConstant() << '>';
if (Val.isConstantRange())
return OS << "constantrange<" << Val.getConstantRange().getLower() << ", "
<< Val.getConstantRange().getUpper() << '>';
return OS << "constant<" << *Val.getConstant() << '>';
}
}
/// 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 LVILatticeVal &Val) {
if (Val.isConstantRange() &&
Val.getConstantRange().isSingleElement())
// 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 LVILatticeVal intersect(LVILatticeVal A, LVILatticeVal B) {
// Undefined is the strongest state. It means the value is known to be along
// an unreachable path.
if (A.isUndefined())
return A;
if (B.isUndefined())
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 =
A.getConstantRange().intersectWith(B.getConstantRange());
// Note: An empty range is implicitly converted to overdefined internally.
// TODO: We could instead use Undefined here since we've proven a conflict
// and thus know this path must be unreachable.
return LVILatticeVal::getRange(std::move(Range));
}
//===----------------------------------------------------------------------===//
// LazyValueInfoCache Decl
//===----------------------------------------------------------------------===//
namespace {
/// A callback value handle updates the cache when values are erased.
class LazyValueInfoCache;
struct LVIValueHandle final : public CallbackVH {
// Needs to access getValPtr(), which is protected.
friend struct DenseMapInfo<LVIValueHandle>;
LazyValueInfoCache *Parent;
LVIValueHandle(Value *V, LazyValueInfoCache *P)
: CallbackVH(V), Parent(P) { }
void deleted() override;
void allUsesReplacedWith(Value *V) override {
deleted();
}
};
} // end anonymous namespace
namespace {
/// This is the cache kept by LazyValueInfo which
/// maintains information about queries across the clients' queries.
class LazyValueInfoCache {
/// This is all of the cached block information for exactly one Value*.
/// The entries are sorted by the BasicBlock* of the
/// entries, allowing us to do a lookup with a binary search.
/// Over-defined lattice values are recorded in OverDefinedCache to reduce
/// memory overhead.
struct ValueCacheEntryTy {
ValueCacheEntryTy(Value *V, LazyValueInfoCache *P) : Handle(V, P) {}
LVIValueHandle Handle;
SmallDenseMap<PoisoningVH<BasicBlock>, LVILatticeVal, 4> BlockVals;
};
/// This is all of the cached information for all values,
/// mapped from Value* to key information.
DenseMap<Value *, std::unique_ptr<ValueCacheEntryTy>> ValueCache;
/// This tracks, on a per-block basis, the set of values that are
/// over-defined at the end of that block.
typedef DenseMap<PoisoningVH<BasicBlock>, SmallPtrSet<Value *, 4>>
OverDefinedCacheTy;
OverDefinedCacheTy OverDefinedCache;
/// Keep track of all blocks that we have ever seen, so we
/// don't spend time removing unused blocks from our caches.
DenseSet<PoisoningVH<BasicBlock> > SeenBlocks;
public:
void insertResult(Value *Val, BasicBlock *BB, const LVILatticeVal &Result) {
SeenBlocks.insert(BB);
// Insert over-defined values into their own cache to reduce memory
// overhead.
if (Result.isOverdefined())
OverDefinedCache[BB].insert(Val);
else {
auto It = ValueCache.find_as(Val);
if (It == ValueCache.end()) {
ValueCache[Val] = make_unique<ValueCacheEntryTy>(Val, this);
It = ValueCache.find_as(Val);
assert(It != ValueCache.end() && "Val was just added to the map!");
}
It->second->BlockVals[BB] = Result;
}
}
bool isOverdefined(Value *V, BasicBlock *BB) const {
auto ODI = OverDefinedCache.find(BB);
if (ODI == OverDefinedCache.end())
return false;
return ODI->second.count(V);
}
bool hasCachedValueInfo(Value *V, BasicBlock *BB) const {
if (isOverdefined(V, BB))
return true;
auto I = ValueCache.find_as(V);
if (I == ValueCache.end())
return false;
return I->second->BlockVals.count(BB);
}
LVILatticeVal getCachedValueInfo(Value *V, BasicBlock *BB) const {
if (isOverdefined(V, BB))
return LVILatticeVal::getOverdefined();
auto I = ValueCache.find_as(V);
if (I == ValueCache.end())
return LVILatticeVal();
auto BBI = I->second->BlockVals.find(BB);
if (BBI == I->second->BlockVals.end())
return LVILatticeVal();
return BBI->second;
}
/// clear - Empty the cache.
void clear() {
SeenBlocks.clear();
ValueCache.clear();
OverDefinedCache.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);
friend struct LVIValueHandle;
};
}
void LazyValueInfoCache::eraseValue(Value *V) {
for (auto I = OverDefinedCache.begin(), E = OverDefinedCache.end(); I != E;) {
// Copy and increment the iterator immediately so we can erase behind
// ourselves.
auto Iter = I++;
SmallPtrSetImpl<Value *> &ValueSet = Iter->second;
ValueSet.erase(V);
if (ValueSet.empty())
OverDefinedCache.erase(Iter);
}
ValueCache.erase(V);
}
void LVIValueHandle::deleted() {
// This erasure deallocates *this, so it MUST happen after we're done
// using any and all members of *this.
Parent->eraseValue(*this);
}
void LazyValueInfoCache::eraseBlock(BasicBlock *BB) {
// Shortcut if we have never seen this block.
DenseSet<PoisoningVH<BasicBlock> >::iterator I = SeenBlocks.find(BB);
if (I == SeenBlocks.end())
return;
SeenBlocks.erase(I);
auto ODI = OverDefinedCache.find(BB);
if (ODI != OverDefinedCache.end())
OverDefinedCache.erase(ODI);
for (auto &I : ValueCache)
I.second->BlockVals.erase(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;
worklist.push_back(OldSucc);
auto I = OverDefinedCache.find(OldSucc);
if (I == OverDefinedCache.end())
return; // Nothing to process here.
SmallVector<Value *, 4> ValsToClear(I->second.begin(), I->second.end());
// 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();
worklist.pop_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 = OverDefinedCache.find(ToUpdate);
if (OI == OverDefinedCache.end())
continue;
SmallPtrSetImpl<Value *> &ValueSet = OI->second;
bool changed = false;
for (Value *V : ValsToClear) {
if (!ValueSet.erase(V))
continue;
// If we removed anything, then we potentially need to update
// blocks successors too.
changed = true;
if (ValueSet.empty()) {
OverDefinedCache.erase(OI);
break;
}
}
if (!changed) continue;
worklist.insert(worklist.end(), succ_begin(ToUpdate), succ_end(ToUpdate));
}
}
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.
DEBUG(dbgs() << "PUSH: " << *BV.second << " in " << BV.first->getName()
<< "\n");
BlockValueStack.push_back(BV);
return true;
}
AssumptionCache *AC; ///< A pointer to the cache of @llvm.assume calls.
const DataLayout &DL; ///< A mandatory DataLayout
DominatorTree *DT; ///< An optional DT pointer.
LVILatticeVal getBlockValue(Value *Val, BasicBlock *BB);
bool getEdgeValue(Value *V, BasicBlock *F, BasicBlock *T,
LVILatticeVal &Result, Instruction *CxtI = nullptr);
bool hasBlockValue(Value *Val, BasicBlock *BB);
// 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);
bool solveBlockValueImpl(LVILatticeVal &Res, Value *Val, BasicBlock *BB);
bool solveBlockValueNonLocal(LVILatticeVal &BBLV, Value *Val, BasicBlock *BB);
bool solveBlockValuePHINode(LVILatticeVal &BBLV, PHINode *PN, BasicBlock *BB);
bool solveBlockValueSelect(LVILatticeVal &BBLV, SelectInst *S,
BasicBlock *BB);
bool solveBlockValueBinaryOp(LVILatticeVal &BBLV, Instruction *BBI,
BasicBlock *BB);
bool solveBlockValueCast(LVILatticeVal &BBLV, Instruction *BBI,
BasicBlock *BB);
void intersectAssumeOrGuardBlockValueConstantRange(Value *Val,
LVILatticeVal &BBLV,
Instruction *BBI);
void solve();
public:
/// This is the query interface to determine the lattice
/// value for the specified Value* at the end of the specified block.
LVILatticeVal 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 (generally
/// from an assume intrinsic).
LVILatticeVal 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.
LVILatticeVal getValueOnEdge(Value *V, BasicBlock *FromBB,BasicBlock *ToBB,
Instruction *CxtI = nullptr);
/// Complete flush all previously computed values
void clear() {
TheCache.clear();
}
/// This is part of the update interface to inform the cache
/// that a block has been deleted.
void eraseBlock(BasicBlock *BB) {
TheCache.eraseBlock(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,
DominatorTree *DT = nullptr)
: AC(AC), DL(DL), DT(DT) {}
};
} // end anonymous namespace
void LazyValueInfoImpl::solve() {
SmallVector<std::pair<BasicBlock *, Value *>, 8> StartingStack(
BlockValueStack.begin(), BlockValueStack.end());
unsigned processedCount = 0;
while (!BlockValueStack.empty()) {
processedCount++;
// 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) {
DEBUG(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,
LVILatticeVal::getOverdefined());
StartingStack.pop_back();
}
BlockValueSet.clear();
BlockValueStack.clear();
return;
}
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!");
assert(TheCache.hasCachedValueInfo(e.second, e.first) &&
"Result should be in cache!");
DEBUG(dbgs() << "POP " << *e.second << " in " << e.first->getName()
<< " = " << TheCache.getCachedValueInfo(e.second, e.first) << "\n");
BlockValueStack.pop_back();
BlockValueSet.erase(e);
} else {
// More work needs to be done before revisiting.
assert(BlockValueStack.back() != e && "Stack should have been pushed!");
}
}
}
bool LazyValueInfoImpl::hasBlockValue(Value *Val, BasicBlock *BB) {
// If already a constant, there is nothing to compute.
if (isa<Constant>(Val))
return true;
return TheCache.hasCachedValueInfo(Val, BB);
}
LVILatticeVal LazyValueInfoImpl::getBlockValue(Value *Val, BasicBlock *BB) {
// If already a constant, there is nothing to compute.
if (Constant *VC = dyn_cast<Constant>(Val))
return LVILatticeVal::get(VC);
return TheCache.getCachedValueInfo(Val, BB);
}
static LVILatticeVal 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 LVILatticeVal::getRange(getConstantRangeFromMetadata(*Ranges));
}
break;
};
// Nothing known - will be intersected with other facts
return LVILatticeVal::getOverdefined();
}
bool LazyValueInfoImpl::solveBlockValue(Value *Val, BasicBlock *BB) {
if (isa<Constant>(Val))
return true;
if (TheCache.hasCachedValueInfo(Val, BB)) {
// If we have a cached value, use that.
DEBUG(dbgs() << " reuse BB '" << BB->getName()
<< "' val=" << TheCache.getCachedValueInfo(Val, BB) << '\n');
// Since we're reusing a cached value, we don't need to update the
// OverDefinedCache. The cache will have been properly updated whenever the
// cached value was inserted.
return true;
}
// Hold off inserting this value into the Cache in case we have to return
// false and come back later.
LVILatticeVal Res;
if (!solveBlockValueImpl(Res, Val, BB))
// Work pushed, will revisit
return false;
TheCache.insertResult(Val, BB, Res);
return true;
}
bool LazyValueInfoImpl::solveBlockValueImpl(LVILatticeVal &Res,
Value *Val, BasicBlock *BB) {
Instruction *BBI = dyn_cast<Instruction>(Val);
if (!BBI || BBI->getParent() != BB)
return solveBlockValueNonLocal(Res, Val, BB);
if (PHINode *PN = dyn_cast<PHINode>(BBI))
return solveBlockValuePHINode(Res, PN, BB);
if (auto *SI = dyn_cast<SelectInst>(BBI))
return solveBlockValueSelect(Res, 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-insensative value walk done inside
// isKnownNonNull gets most of the profitable cases at much less expense.
// This does mean that we have a sensativity 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 && isKnownNonNull(BBI)) {
Res = LVILatticeVal::getNot(ConstantPointerNull::get(PT));
return true;
}
if (BBI->getType()->isIntegerTy()) {
if (isa<CastInst>(BBI))
return solveBlockValueCast(Res, BBI, BB);
BinaryOperator *BO = dyn_cast<BinaryOperator>(BBI);
if (BO && isa<ConstantInt>(BO->getOperand(1)))
return solveBlockValueBinaryOp(Res, BBI, BB);
}
DEBUG(dbgs() << " compute BB '" << BB->getName()
<< "' - unknown inst def found.\n");
Res = getFromRangeMetadata(BBI);
return true;
}
static bool InstructionDereferencesPointer(Instruction *I, Value *Ptr) {
if (LoadInst *L = dyn_cast<LoadInst>(I)) {
return L->getPointerAddressSpace() == 0 &&
GetUnderlyingObject(L->getPointerOperand(),
L->getModule()->getDataLayout()) == Ptr;
}
if (StoreInst *S = dyn_cast<StoreInst>(I)) {
return S->getPointerAddressSpace() == 0 &&
GetUnderlyingObject(S->getPointerOperand(),
S->getModule()->getDataLayout()) == Ptr;
}
if (MemIntrinsic *MI = dyn_cast<MemIntrinsic>(I)) {
if (MI->isVolatile()) return false;
// FIXME: check whether it has a valuerange that excludes zero?
ConstantInt *Len = dyn_cast<ConstantInt>(MI->getLength());
if (!Len || Len->isZero()) return false;
if (MI->getDestAddressSpace() == 0)
if (GetUnderlyingObject(MI->getRawDest(),
MI->getModule()->getDataLayout()) == Ptr)
return true;
if (MemTransferInst *MTI = dyn_cast<MemTransferInst>(MI))
if (MTI->getSourceAddressSpace() == 0)
if (GetUnderlyingObject(MTI->getRawSource(),
MTI->getModule()->getDataLayout()) == Ptr)
return true;
}
return false;
}
/// Return true if the allocation associated with Val is ever dereferenced
/// within the given basic block. This establishes the fact Val is not null,
/// but does not imply that the memory at Val is dereferenceable. (Val may
/// point off the end of the dereferenceable part of the object.)
static bool isObjectDereferencedInBlock(Value *Val, BasicBlock *BB) {
assert(Val->getType()->isPointerTy());
const DataLayout &DL = BB->getModule()->getDataLayout();
Value *UnderlyingVal = GetUnderlyingObject(Val, DL);
// If 'GetUnderlyingObject' didn't converge, skip it. It won't converge
// inside InstructionDereferencesPointer either.
if (UnderlyingVal == GetUnderlyingObject(UnderlyingVal, DL, 1))
for (Instruction &I : *BB)
if (InstructionDereferencesPointer(&I, UnderlyingVal))
return true;
return false;
}
bool LazyValueInfoImpl::solveBlockValueNonLocal(LVILatticeVal &BBLV,
Value *Val, BasicBlock *BB) {
LVILatticeVal Result; // Start Undefined.
// If this is the entry block, we must be asking about an argument. The
// value is overdefined.
if (BB == &BB->getParent()->getEntryBlock()) {
assert(isa<Argument>(Val) && "Unknown live-in to the entry block");
// Bofore giving up, see if we can prove the pointer non-null local to
// this particular block.
if (Val->getType()->isPointerTy() &&
(isKnownNonNull(Val) || isObjectDereferencedInBlock(Val, BB))) {
PointerType *PTy = cast<PointerType>(Val->getType());
Result = LVILatticeVal::getNot(ConstantPointerNull::get(PTy));
} else {
Result = LVILatticeVal::getOverdefined();
}
BBLV = Result;
return true;
}
// 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 (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) {
LVILatticeVal EdgeResult;
if (!getEdgeValue(Val, *PI, BB, EdgeResult))
// Explore that input, then return here
return false;
Result.mergeIn(EdgeResult, DL);
// If we hit overdefined, exit early. The BlockVals entry is already set
// to overdefined.
if (Result.isOverdefined()) {
DEBUG(dbgs() << " compute BB '" << BB->getName()
<< "' - overdefined because of pred (non local).\n");
// Before giving up, see if we can prove the pointer non-null local to
// this particular block.
if (Val->getType()->isPointerTy() &&
isObjectDereferencedInBlock(Val, BB)) {
PointerType *PTy = cast<PointerType>(Val->getType());
Result = LVILatticeVal::getNot(ConstantPointerNull::get(PTy));
}
BBLV = Result;
return true;
}
}
// Return the merged value, which is more precise than 'overdefined'.
assert(!Result.isOverdefined());
BBLV = Result;
return true;
}
bool LazyValueInfoImpl::solveBlockValuePHINode(LVILatticeVal &BBLV,
PHINode *PN, BasicBlock *BB) {
LVILatticeVal 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);
LVILatticeVal EdgeResult;
// 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.
if (!getEdgeValue(PhiVal, PhiBB, BB, EdgeResult, PN))
// Explore that input, then return here
return false;
Result.mergeIn(EdgeResult, DL);
// If we hit overdefined, exit early. The BlockVals entry is already set
// to overdefined.
if (Result.isOverdefined()) {
DEBUG(dbgs() << " compute BB '" << BB->getName()
<< "' - overdefined because of pred (local).\n");
BBLV = Result;
return true;
}
}
// Return the merged value, which is more precise than 'overdefined'.
assert(!Result.isOverdefined() && "Possible PHI in entry block?");
BBLV = Result;
return true;
}
static LVILatticeVal 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, LVILatticeVal &BBLV, Instruction *BBI) {
BBI = BBI ? BBI : dyn_cast<Instruction>(Val);
if (!BBI)
return;
for (auto &AssumeVH : AC->assumptionsFor(Val)) {
if (!AssumeVH)
continue;
auto *I = cast<CallInst>(AssumeVH);
if (!isValidAssumeForContext(I, BBI, DT))
continue;
BBLV = intersect(BBLV, getValueFromCondition(Val, I->getArgOperand(0)));
}
// If guards are not used in the module, don't spend time looking for them
auto *GuardDecl = BBI->getModule()->getFunction(
Intrinsic::getName(Intrinsic::experimental_guard));
if (!GuardDecl || GuardDecl->use_empty())
return;
for (Instruction &I : make_range(BBI->getIterator().getReverse(),
BBI->getParent()->rend())) {
Value *Cond = nullptr;
if (match(&I, m_Intrinsic<Intrinsic::experimental_guard>(m_Value(Cond))))
BBLV = intersect(BBLV, getValueFromCondition(Val, Cond));
}
}
bool LazyValueInfoImpl::solveBlockValueSelect(LVILatticeVal &BBLV,
SelectInst *SI, BasicBlock *BB) {
// Recurse on our inputs if needed
if (!hasBlockValue(SI->getTrueValue(), BB)) {
if (pushBlockValue(std::make_pair(BB, SI->getTrueValue())))
return false;
BBLV = LVILatticeVal::getOverdefined();
return true;
}
LVILatticeVal TrueVal = getBlockValue(SI->getTrueValue(), BB);
// If we hit overdefined, don't ask more queries. We want to avoid poisoning
// extra slots in the table if we can.
if (TrueVal.isOverdefined()) {
BBLV = LVILatticeVal::getOverdefined();
return true;
}
if (!hasBlockValue(SI->getFalseValue(), BB)) {
if (pushBlockValue(std::make_pair(BB, SI->getFalseValue())))
return false;
BBLV = LVILatticeVal::getOverdefined();
return true;
}
LVILatticeVal FalseVal = getBlockValue(SI->getFalseValue(), BB);
// If we hit overdefined, don't ask more queries. We want to avoid poisoning
// extra slots in the table if we can.
if (FalseVal.isOverdefined()) {
BBLV = LVILatticeVal::getOverdefined();
return true;
}
if (TrueVal.isConstantRange() && FalseVal.isConstantRange()) {
ConstantRange TrueCR = TrueVal.getConstantRange();
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) {
default:
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);
};
}();
BBLV = LVILatticeVal::getRange(ResultCR);
return true;
}
// TODO: ABS, NABS from the SelectPatternResult
}
// 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));
// Handle clamp idioms such as:
// %24 = constantrange<0, 17>
// %39 = icmp eq i32 %24, 0
// %40 = add i32 %24, -1
// %siv.next = select i1 %39, i32 16, i32 %40
// %siv.next = constantrange<0, 17> not <-1, 17>
// In general, this can handle any clamp idiom which tests the edge
// condition via an equality or inequality.
if (auto *ICI = dyn_cast<ICmpInst>(Cond)) {
ICmpInst::Predicate Pred = ICI->getPredicate();
Value *A = ICI->getOperand(0);
if (ConstantInt *CIBase = dyn_cast<ConstantInt>(ICI->getOperand(1))) {
auto addConstants = [](ConstantInt *A, ConstantInt *B) {
assert(A->getType() == B->getType());
return ConstantInt::get(A->getType(), A->getValue() + B->getValue());
};
// See if either input is A + C2, subject to the constraint from the
// condition that A != C when that input is used. We can assume that
// that input doesn't include C + C2.
ConstantInt *CIAdded;
switch (Pred) {
default: break;
case ICmpInst::ICMP_EQ:
if (match(SI->getFalseValue(), m_Add(m_Specific(A),
m_ConstantInt(CIAdded)))) {
auto ResNot = addConstants(CIBase, CIAdded);
FalseVal = intersect(FalseVal,
LVILatticeVal::getNot(ResNot));
}
break;
case ICmpInst::ICMP_NE:
if (match(SI->getTrueValue(), m_Add(m_Specific(A),
m_ConstantInt(CIAdded)))) {
auto ResNot = addConstants(CIBase, CIAdded);
TrueVal = intersect(TrueVal,
LVILatticeVal::getNot(ResNot));
}
break;
};
}
}
LVILatticeVal Result; // Start Undefined.
Result.mergeIn(TrueVal, DL);
Result.mergeIn(FalseVal, DL);
BBLV = Result;
return true;
}
bool LazyValueInfoImpl::solveBlockValueCast(LVILatticeVal &BBLV,
Instruction *BBI,
BasicBlock *BB) {
if (!BBI->getOperand(0)->getType()->isSized()) {
// Without knowing how wide the input is, we can't analyze it in any useful
// way.
BBLV = LVILatticeVal::getOverdefined();
return true;
}
// 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 (BBI->getOpcode()) {
case Instruction::Trunc:
case Instruction::SExt:
case Instruction::ZExt:
case Instruction::BitCast:
break;
default:
// Unhandled instructions are overdefined.
DEBUG(dbgs() << " compute BB '" << BB->getName()
<< "' - overdefined (unknown cast).\n");
BBLV = LVILatticeVal::getOverdefined();
return true;
}
// 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.
if (!hasBlockValue(BBI->getOperand(0), BB))
if (pushBlockValue(std::make_pair(BB, BBI->getOperand(0))))
// More work to do before applying this transfer rule.
return false;
const unsigned OperandBitWidth =
DL.getTypeSizeInBits(BBI->getOperand(0)->getType());
ConstantRange LHSRange = ConstantRange(OperandBitWidth);
if (hasBlockValue(BBI->getOperand(0), BB)) {
LVILatticeVal LHSVal = getBlockValue(BBI->getOperand(0), BB);
intersectAssumeOrGuardBlockValueConstantRange(BBI->getOperand(0), LHSVal,
BBI);
if (LHSVal.isConstantRange())
LHSRange = LHSVal.getConstantRange();
}
const unsigned ResultBitWidth =
cast<IntegerType>(BBI->getType())->getBitWidth();
// 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.
auto CastOp = (Instruction::CastOps) BBI->getOpcode();
BBLV = LVILatticeVal::getRange(LHSRange.castOp(CastOp, ResultBitWidth));
return true;
}
bool LazyValueInfoImpl::solveBlockValueBinaryOp(LVILatticeVal &BBLV,
Instruction *BBI,
BasicBlock *BB) {
assert(BBI->getOperand(0)->getType()->isSized() &&
"all operands to binary operators are sized");
// Filter out operators we don't know how to reason about before attempting to
// recurse on our operand(s). This can cut a long search short if we know
// we're not going to be able to get any useful information anways.
switch (BBI->getOpcode()) {
case Instruction::Add:
case Instruction::Sub:
case Instruction::Mul:
case Instruction::UDiv:
case Instruction::Shl:
case Instruction::LShr:
case Instruction::And:
case Instruction::Or:
// continue into the code below
break;
default:
// Unhandled instructions are overdefined.
DEBUG(dbgs() << " compute BB '" << BB->getName()
<< "' - overdefined (unknown binary operator).\n");
BBLV = LVILatticeVal::getOverdefined();
return true;
};
// Figure out the range of the LHS. 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"
if (!hasBlockValue(BBI->getOperand(0), BB))
if (pushBlockValue(std::make_pair(BB, BBI->getOperand(0))))
// More work to do before applying this transfer rule.
return false;
const unsigned OperandBitWidth =
DL.getTypeSizeInBits(BBI->getOperand(0)->getType());
ConstantRange LHSRange = ConstantRange(OperandBitWidth);
if (hasBlockValue(BBI->getOperand(0), BB)) {
LVILatticeVal LHSVal = getBlockValue(BBI->getOperand(0), BB);
intersectAssumeOrGuardBlockValueConstantRange(BBI->getOperand(0), LHSVal,
BBI);
if (LHSVal.isConstantRange())
LHSRange = LHSVal.getConstantRange();
}
ConstantInt *RHS = cast<ConstantInt>(BBI->getOperand(1));
ConstantRange RHSRange = ConstantRange(RHS->getValue());
// 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.
auto BinOp = (Instruction::BinaryOps) BBI->getOpcode();
BBLV = LVILatticeVal::getRange(LHSRange.binaryOp(BinOp, RHSRange));
return true;
}
static LVILatticeVal getValueFromICmpCondition(Value *Val, ICmpInst *ICI,
bool isTrueDest) {
Value *LHS = ICI->getOperand(0);
Value *RHS = ICI->getOperand(1);
CmpInst::Predicate Predicate = ICI->getPredicate();
if (isa<Constant>(RHS)) {
if (ICI->isEquality() && LHS == Val) {
// We know that V has the RHS constant if this is a true SETEQ or
// false SETNE.
if (isTrueDest == (Predicate == ICmpInst::ICMP_EQ))
return LVILatticeVal::get(cast<Constant>(RHS));
else
return LVILatticeVal::getNot(cast<Constant>(RHS));
}
}
if (!Val->getType()->isIntegerTy())
return LVILatticeVal::getOverdefined();
// Use ConstantRange::makeAllowedICmpRegion in order to determine the possible
// range of Val guaranteed by the condition. Recognize comparisons in the from
// of:
// icmp <pred> Val, ...
// icmp <pred> (add Val, Offset), ...
// The latter is the range checking idiom that InstCombine produces. Subtract
// the offset from the allowed range for RHS in this case.
// Val or (add Val, Offset) can be on either hand of the comparison
if (LHS != Val && !match(LHS, m_Add(m_Specific(Val), m_ConstantInt()))) {
std::swap(LHS, RHS);
Predicate = CmpInst::getSwappedPredicate(Predicate);
}
ConstantInt *Offset = nullptr;
if (LHS != Val)
match(LHS, m_Add(m_Specific(Val), m_ConstantInt(Offset)));
if (LHS == Val || Offset) {
// Calculate the range of values that are allowed by the comparison
ConstantRange RHSRange(RHS->getType()->getIntegerBitWidth(),
/*isFullSet=*/true);
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);
// If we're interested in the false dest, invert the condition
CmpInst::Predicate Pred =
isTrueDest ? Predicate : CmpInst::getInversePredicate(Predicate);
ConstantRange TrueValues =
ConstantRange::makeAllowedICmpRegion(Pred, RHSRange);
if (Offset) // Apply the offset from above.
TrueValues = TrueValues.subtract(Offset->getValue());
return LVILatticeVal::getRange(std::move(TrueValues));
}
return LVILatticeVal::getOverdefined();
}
static LVILatticeVal
getValueFromCondition(Value *Val, Value *Cond, bool isTrueDest,
DenseMap<Value*, LVILatticeVal> &Visited);
static LVILatticeVal
getValueFromConditionImpl(Value *Val, Value *Cond, bool isTrueDest,
DenseMap<Value*, LVILatticeVal> &Visited) {
if (ICmpInst *ICI = dyn_cast<ICmpInst>(Cond))
return getValueFromICmpCondition(Val, ICI, isTrueDest);
// Handle conditions in the form of (cond1 && cond2), we know that on the
// true dest path both of the conditions hold.
if (!isTrueDest)
return LVILatticeVal::getOverdefined();
BinaryOperator *BO = dyn_cast<BinaryOperator>(Cond);
if (!BO || BO->getOpcode() != BinaryOperator::And)
return LVILatticeVal::getOverdefined();
auto RHS = getValueFromCondition(Val, BO->getOperand(0), isTrueDest, Visited);
auto LHS = getValueFromCondition(Val, BO->getOperand(1), isTrueDest, Visited);
return intersect(RHS, LHS);
}
static LVILatticeVal
getValueFromCondition(Value *Val, Value *Cond, bool isTrueDest,
DenseMap<Value*, LVILatticeVal> &Visited) {
auto I = Visited.find(Cond);
if (I != Visited.end())
return I->second;
auto Result = getValueFromConditionImpl(Val, Cond, isTrueDest, Visited);
Visited[Cond] = Result;
return Result;
}
LVILatticeVal getValueFromCondition(Value *Val, Value *Cond, bool isTrueDest) {
assert(Cond && "precondition");
DenseMap<Value*, LVILatticeVal> Visited;
return getValueFromCondition(Val, Cond, isTrueDest, Visited);
}
/// \brief 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 bool getEdgeValueLocal(Value *Val, BasicBlock *BBFrom,
BasicBlock *BBTo, LVILatticeVal &Result) {
// 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");
// If V is the condition of the branch itself, then we know exactly what
// it is.
if (BI->getCondition() == Val) {
Result = LVILatticeVal::get(ConstantInt::get(
Type::getInt1Ty(Val->getContext()), isTrueDest));
return true;
}
// If the condition of the branch is an equality comparison, we may be
// able to infer the value.
Result = getValueFromCondition(Val, BI->getCondition(), isTrueDest);
if (!Result.isOverdefined())
return true;
}
}
// 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())) {
if (SI->getCondition() != Val)
return false;
bool DefaultCase = SI->getDefaultDest() == BBTo;
unsigned BitWidth = Val->getType()->getIntegerBitWidth();
ConstantRange EdgesVals(BitWidth, DefaultCase/*isFullSet*/);
for (SwitchInst::CaseIt i : SI->cases()) {
ConstantRange EdgeVal(i.getCaseValue()->getValue());
if (DefaultCase) {
// It is possible that the default destination is the destination of
// some cases. There is no need to perform difference for those cases.
if (i.getCaseSuccessor() != BBTo)
EdgesVals = EdgesVals.difference(EdgeVal);
} else if (i.getCaseSuccessor() == BBTo)
EdgesVals = EdgesVals.unionWith(EdgeVal);
}
Result = LVILatticeVal::getRange(std::move(EdgesVals));
return true;
}
return false;
}
/// \brief Compute the value of Val on the edge BBFrom -> BBTo or the value at
/// the basic block if the edge does not constrain Val.
bool LazyValueInfoImpl::getEdgeValue(Value *Val, BasicBlock *BBFrom,
BasicBlock *BBTo, LVILatticeVal &Result,
Instruction *CxtI) {
// If already a constant, there is nothing to compute.
if (Constant *VC = dyn_cast<Constant>(Val)) {
Result = LVILatticeVal::get(VC);
return true;
}
LVILatticeVal LocalResult;
if (!getEdgeValueLocal(Val, BBFrom, BBTo, LocalResult))
// If we couldn't constrain the value on the edge, LocalResult doesn't
// provide any information.
LocalResult = LVILatticeVal::getOverdefined();
if (hasSingleValue(LocalResult)) {
// Can't get any more precise here
Result = LocalResult;
return true;
}
if (!hasBlockValue(Val, BBFrom)) {
if (pushBlockValue(std::make_pair(BBFrom, Val)))
return false;
// No new information.
Result = LocalResult;
return true;
}
// Try to intersect ranges of the BB and the constraint on the edge.
LVILatticeVal InBlock = getBlockValue(Val, BBFrom);
intersectAssumeOrGuardBlockValueConstantRange(Val, InBlock,
BBFrom->getTerminator());
// 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);
Result = intersect(LocalResult, InBlock);
return true;
}
LVILatticeVal LazyValueInfoImpl::getValueInBlock(Value *V, BasicBlock *BB,
Instruction *CxtI) {
DEBUG(dbgs() << "LVI Getting block end value " << *V << " at '"
<< BB->getName() << "'\n");
assert(BlockValueStack.empty() && BlockValueSet.empty());
if (!hasBlockValue(V, BB)) {
pushBlockValue(std::make_pair(BB, V));
solve();
}
LVILatticeVal Result = getBlockValue(V, BB);
intersectAssumeOrGuardBlockValueConstantRange(V, Result, CxtI);
DEBUG(dbgs() << " Result = " << Result << "\n");
return Result;
}
LVILatticeVal LazyValueInfoImpl::getValueAt(Value *V, Instruction *CxtI) {
DEBUG(dbgs() << "LVI Getting value " << *V << " at '"
<< CxtI->getName() << "'\n");
if (auto *C = dyn_cast<Constant>(V))
return LVILatticeVal::get(C);
LVILatticeVal Result = LVILatticeVal::getOverdefined();
if (auto *I = dyn_cast<Instruction>(V))
Result = getFromRangeMetadata(I);
intersectAssumeOrGuardBlockValueConstantRange(V, Result, CxtI);
DEBUG(dbgs() << " Result = " << Result << "\n");
return Result;
}
LVILatticeVal LazyValueInfoImpl::
getValueOnEdge(Value *V, BasicBlock *FromBB, BasicBlock *ToBB,
Instruction *CxtI) {
DEBUG(dbgs() << "LVI Getting edge value " << *V << " from '"
<< FromBB->getName() << "' to '" << ToBB->getName() << "'\n");
LVILatticeVal Result;
if (!getEdgeValue(V, FromBB, ToBB, Result, CxtI)) {
solve();
bool WasFastQuery = getEdgeValue(V, FromBB, ToBB, Result, CxtI);
(void)WasFastQuery;
assert(WasFastQuery && "More work to do after problem solved?");
}
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 DataLayout *DL,
DominatorTree *DT = nullptr) {
if (!PImpl) {
assert(DL && "getCache() called with a null DataLayout");
PImpl = new LazyValueInfoImpl(AC, *DL, DT);
}
return *static_cast<LazyValueInfoImpl*>(PImpl);
}
bool LazyValueInfoWrapperPass::runOnFunction(Function &F) {
Info.AC = &getAnalysis<AssumptionCacheTracker>().getAssumptionCache(F);
const DataLayout &DL = F.getParent()->getDataLayout();
DominatorTreeWrapperPass *DTWP =
getAnalysisIfAvailable<DominatorTreeWrapperPass>();
Info.DT = DTWP ? &DTWP->getDomTree() : nullptr;
Info.TLI = &getAnalysis<TargetLibraryInfoWrapperPass>().getTLI();
if (Info.PImpl)
getImpl(Info.PImpl, Info.AC, &DL, Info.DT).clear();
// Fully lazy.
return false;
}
void LazyValueInfoWrapperPass::getAnalysisUsage(AnalysisUsage &AU) const {
AU.setPreservesAll();
AU.addRequired<AssumptionCacheTracker>();
AU.addRequired<TargetLibraryInfoWrapperPass>();
}
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>>()) ||
(DT && Inv.invalidate<DominatorTreeAnalysis>(F, PA)))
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);
auto *DT = FAM.getCachedResult<DominatorTreeAnalysis>(F);
return LazyValueInfo(&AC, &TLI, DT);
}
/// 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, BasicBlock *BB,
Instruction *CxtI) {
// Bail out early if V is known not to be a Constant.
if (isKnownNonConstant(V))
return nullptr;
const DataLayout &DL = BB->getModule()->getDataLayout();
LVILatticeVal Result =
getImpl(PImpl, AC, &DL, DT).getValueInBlock(V, BB, CxtI);
if (Result.isConstant())
return Result.getConstant();
if (Result.isConstantRange()) {
ConstantRange CR = Result.getConstantRange();
if (const APInt *SingleVal = CR.getSingleElement())
return ConstantInt::get(V->getContext(), *SingleVal);
}
return nullptr;
}
ConstantRange LazyValueInfo::getConstantRange(Value *V, BasicBlock *BB,
Instruction *CxtI) {
assert(V->getType()->isIntegerTy());
unsigned Width = V->getType()->getIntegerBitWidth();
const DataLayout &DL = BB->getModule()->getDataLayout();
LVILatticeVal Result =
getImpl(PImpl, AC, &DL, DT).getValueInBlock(V, BB, CxtI);
if (Result.isUndefined())
return ConstantRange(Width, /*isFullSet=*/false);
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(Width, /*isFullSet=*/true);
}
/// 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) {
const DataLayout &DL = FromBB->getModule()->getDataLayout();
LVILatticeVal Result =
getImpl(PImpl, AC, &DL, DT).getValueOnEdge(V, FromBB, ToBB, CxtI);
if (Result.isConstant())
return Result.getConstant();
if (Result.isConstantRange()) {
ConstantRange CR = Result.getConstantRange();
if (const APInt *SingleVal = CR.getSingleElement())
return ConstantInt::get(V->getContext(), *SingleVal);
}
return nullptr;
}
static LazyValueInfo::Tristate getPredicateResult(unsigned Pred, Constant *C,
LVILatticeVal &Result,
const DataLayout &DL,
TargetLibraryInfo *TLI) {
// If we know the value is a constant, evaluate the conditional.
Constant *Res = nullptr;
if (Result.isConstant()) {
Res = ConstantFoldCompareInstOperands(Pred, Result.getConstant(), C, DL,
TLI);
if (ConstantInt *ResCI = dyn_cast<ConstantInt>(Res))
return ResCI->isZero() ? LazyValueInfo::False : LazyValueInfo::True;
return LazyValueInfo::Unknown;
}
if (Result.isConstantRange()) {
ConstantInt *CI = dyn_cast<ConstantInt>(C);
if (!CI) return LazyValueInfo::Unknown;
ConstantRange CR = Result.getConstantRange();
if (Pred == ICmpInst::ICMP_EQ) {
if (!CR.contains(CI->getValue()))
return LazyValueInfo::False;
if (CR.isSingleElement() && CR.contains(CI->getValue()))
return LazyValueInfo::True;
} else if (Pred == ICmpInst::ICMP_NE) {
if (!CR.contains(CI->getValue()))
return LazyValueInfo::True;
if (CR.isSingleElement() && CR.contains(CI->getValue()))
return LazyValueInfo::False;
}
// 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 (Result.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,
Result.getNotConstant(), C, DL,
TLI);
if (Res->isNullValue())
return LazyValueInfo::False;
} else if (Pred == ICmpInst::ICMP_NE) {
// !C1 != C -> true iff C1 == C.
Res = ConstantFoldCompareInstOperands(ICmpInst::ICMP_NE,
Result.getNotConstant(), C, DL,
TLI);
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::Tristate
LazyValueInfo::getPredicateOnEdge(unsigned Pred, Value *V, Constant *C,
BasicBlock *FromBB, BasicBlock *ToBB,
Instruction *CxtI) {
const DataLayout &DL = FromBB->getModule()->getDataLayout();
LVILatticeVal Result =
getImpl(PImpl, AC, &DL, DT).getValueOnEdge(V, FromBB, ToBB, CxtI);
return getPredicateResult(Pred, C, Result, DL, TLI);
}
LazyValueInfo::Tristate
LazyValueInfo::getPredicateAt(unsigned Pred, Value *V, Constant *C,
Instruction *CxtI) {
// Is or is not NonNull are common predicates being queried. If
// isKnownNonNull 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.
if (V->getType()->isPointerTy() && C->isNullValue() &&
isKnownNonNull(V->stripPointerCasts())) {
if (Pred == ICmpInst::ICMP_EQ)
return LazyValueInfo::False;
else if (Pred == ICmpInst::ICMP_NE)
return LazyValueInfo::True;
}
const DataLayout &DL = CxtI->getModule()->getDataLayout();
LVILatticeVal Result = getImpl(PImpl, AC, &DL, DT).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.
if (CxtI) {
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)
break;
}
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) break;
}
// If we terminated early, then one of the values didn't match.
if (PI == PE) {
return Baseline;
}
}
}
}
return Unknown;
}
void LazyValueInfo::threadEdge(BasicBlock *PredBB, BasicBlock *OldSucc,
BasicBlock *NewSucc) {
if (PImpl) {
const DataLayout &DL = PredBB->getModule()->getDataLayout();
getImpl(PImpl, AC, &DL, DT).threadEdge(PredBB, OldSucc, NewSucc);
}
}
void LazyValueInfo::eraseBlock(BasicBlock *BB) {
if (PImpl) {
const DataLayout &DL = BB->getModule()->getDataLayout();
getImpl(PImpl, AC, &DL, DT).eraseBlock(BB);
}
}
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