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llvm/lib/Analysis/LazyValueInfo.cpp
Hans Wennborg 4d48c3f1aa LazyValueInfo: Actually re-visit partially solved block-values in solveBlockValue() 
If solveBlockValue() needs results from predecessors that are not already
computed, it returns false with the intention of resuming when the dependencies
have been resolved. However, the computation would never be resumed since an
'overdefined' result had been placed in the cache, preventing any further
computation.

The point of placing the 'overdefined' result in the cache seems to have been
to break cycles, but we can check for that when inserting work items in the
BlockValue stack instead. This makes the "stop and resume" mechanism of
solveBlockValue() work as intended, unlocking more analysis.

Using this patch shaves 120 KB off a 64-bit Chromium build on Linux.

I benchmarked compiling bzip2.c at -O2 but couldn't measure any difference in
compile time.

Tests by Jiangning Liu from r215343 / PR21238, Pete Cooper, and me.

Differential Revision: http://reviews.llvm.org/D6397

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@222768 91177308-0d34-0410-b5e6-96231b3b80d8
2014-11-25 17:23:05 +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/AssumptionTracker.h"
#include "llvm/Analysis/ConstantFolding.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/PatternMatch.h"
#include "llvm/IR/ValueHandle.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/raw_ostream.h"
#include "llvm/Target/TargetLibraryInfo.h"
#include <map>
#include <stack>
using namespace llvm;
using namespace PatternMatch;
#define DEBUG_TYPE "lazy-value-info"
char LazyValueInfo::ID = 0;
INITIALIZE_PASS_BEGIN(LazyValueInfo, "lazy-value-info",
"Lazy Value Information Analysis", false, true)
INITIALIZE_PASS_DEPENDENCY(AssumptionTracker)
INITIALIZE_PASS_DEPENDENCY(TargetLibraryInfo)
INITIALIZE_PASS_END(LazyValueInfo, "lazy-value-info",
"Lazy Value Information Analysis", false, true)
namespace llvm {
FunctionPass *createLazyValueInfoPass() { return new LazyValueInfo(); }
}
//===----------------------------------------------------------------------===//
// LVILatticeVal
//===----------------------------------------------------------------------===//
/// 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 {
/// undefined - This Value has no known value yet.
undefined,
/// constant - This Value has a specific constant value.
constant,
/// notconstant - This Value is known to not have the specified value.
notconstant,
/// constantrange - The Value falls within this range.
constantrange,
/// overdefined - This value is not known to be constant, and we know that
/// it has a value.
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(CR);
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;
}
/// markOverdefined - Return true if this is a change in status.
bool markOverdefined() {
if (isOverdefined())
return false;
Tag = overdefined;
return true;
}
/// markConstant - Return true if this is a change in status.
bool markConstant(Constant *V) {
assert(V && "Marking constant with NULL");
if (ConstantInt *CI = dyn_cast<ConstantInt>(V))
return markConstantRange(ConstantRange(CI->getValue()));
if (isa<UndefValue>(V))
return false;
assert((!isConstant() || getConstant() == V) &&
"Marking constant with different value");
assert(isUndefined());
Tag = constant;
Val = V;
return true;
}
/// markNotConstant - Return true if this is a change in status.
bool markNotConstant(Constant *V) {
assert(V && "Marking constant with NULL");
if (ConstantInt *CI = dyn_cast<ConstantInt>(V))
return markConstantRange(ConstantRange(CI->getValue()+1, CI->getValue()));
if (isa<UndefValue>(V))
return false;
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;
return true;
}
/// markConstantRange - Return true if this is a change in status.
bool markConstantRange(const ConstantRange NewR) {
if (isConstantRange()) {
if (NewR.isEmptySet())
return markOverdefined();
bool changed = Range != NewR;
Range = NewR;
return changed;
}
assert(isUndefined());
if (NewR.isEmptySet())
return markOverdefined();
Tag = constantrange;
Range = NewR;
return true;
}
/// mergeIn - Merge the specified lattice value into this one, updating this
/// one and returning true if anything changed.
bool mergeIn(const LVILatticeVal &RHS) {
if (RHS.isUndefined() || isOverdefined()) return false;
if (RHS.isOverdefined()) return markOverdefined();
if (isUndefined()) {
Tag = RHS.Tag;
Val = RHS.Val;
Range = RHS.Range;
return true;
}
if (isConstant()) {
if (RHS.isConstant()) {
if (Val == RHS.Val)
return false;
return markOverdefined();
}
if (RHS.isNotConstant()) {
if (Val == RHS.Val)
return markOverdefined();
// Unless we can prove that the two Constants are different, we must
// move to overdefined.
// FIXME: use DataLayout/TargetLibraryInfo for smarter constant folding.
if (ConstantInt *Res = dyn_cast<ConstantInt>(
ConstantFoldCompareInstOperands(CmpInst::ICMP_NE,
getConstant(),
RHS.getNotConstant())))
if (Res->isOne())
return markNotConstant(RHS.getNotConstant());
return markOverdefined();
}
// RHS is a ConstantRange, LHS is a non-integer Constant.
// FIXME: consider the case where RHS is a range [1, 0) and LHS is
// a function. The correct result is to pick up RHS.
return markOverdefined();
}
if (isNotConstant()) {
if (RHS.isConstant()) {
if (Val == RHS.Val)
return markOverdefined();
// Unless we can prove that the two Constants are different, we must
// move to overdefined.
// FIXME: use DataLayout/TargetLibraryInfo for smarter constant folding.
if (ConstantInt *Res = dyn_cast<ConstantInt>(
ConstantFoldCompareInstOperands(CmpInst::ICMP_NE,
getNotConstant(),
RHS.getConstant())))
if (Res->isOne())
return false;
return markOverdefined();
}
if (RHS.isNotConstant()) {
if (Val == RHS.Val)
return false;
return markOverdefined();
}
return markOverdefined();
}
assert(isConstantRange() && "New LVILattice type?");
if (!RHS.isConstantRange())
return markOverdefined();
ConstantRange NewR = Range.unionWith(RHS.getConstantRange());
if (NewR.isFullSet())
return markOverdefined();
return 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() << '>';
else if (Val.isConstantRange())
return OS << "constantrange<" << Val.getConstantRange().getLower() << ", "
<< Val.getConstantRange().getUpper() << '>';
return OS << "constant<" << *Val.getConstant() << '>';
}
}
//===----------------------------------------------------------------------===//
// LazyValueInfoCache Decl
//===----------------------------------------------------------------------===//
namespace {
/// LVIValueHandle - A callback value handle updates the cache when
/// values are erased.
class LazyValueInfoCache;
struct LVIValueHandle : public CallbackVH {
LazyValueInfoCache *Parent;
LVIValueHandle(Value *V, LazyValueInfoCache *P)
: CallbackVH(V), Parent(P) { }
void deleted() override;
void allUsesReplacedWith(Value *V) override {
deleted();
}
};
}
namespace {
/// LazyValueInfoCache - This is the cache kept by LazyValueInfo which
/// maintains information about queries across the clients' queries.
class LazyValueInfoCache {
/// ValueCacheEntryTy - 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.
typedef std::map<AssertingVH<BasicBlock>, LVILatticeVal> ValueCacheEntryTy;
/// ValueCache - This is all of the cached information for all values,
/// mapped from Value* to key information.
std::map<LVIValueHandle, ValueCacheEntryTy> ValueCache;
/// OverDefinedCache - This tracks, on a per-block basis, the set of
/// values that are over-defined at the end of that block. This is required
/// for cache updating.
typedef std::pair<AssertingVH<BasicBlock>, Value*> OverDefinedPairTy;
DenseSet<OverDefinedPairTy> OverDefinedCache;
/// SeenBlocks - Keep track of all blocks that we have ever seen, so we
/// don't spend time removing unused blocks from our caches.
DenseSet<AssertingVH<BasicBlock> > SeenBlocks;
/// BlockValueStack - This stack holds the state of the value solver
/// during a query. It basically emulates the callstack of the naive
/// recursive value lookup process.
std::stack<std::pair<BasicBlock*, Value*> > BlockValueStack;
/// BlockValueSet - Keeps track of which block-value pairs are in
/// BlockValueStack.
DenseSet<std::pair<BasicBlock*, Value*> > BlockValueSet;
/// pushBlockValue - Push BV onto BlockValueStack unless it's already in
/// there. Returns true on success.
bool pushBlockValue(const std::pair<BasicBlock *, Value *> &BV) {
if (BlockValueSet.count(BV))
return false; // It's already in the stack.
BlockValueStack.push(BV);
BlockValueSet.insert(BV);
return true;
}
/// A pointer to the cache of @llvm.assume calls.
AssumptionTracker *AT;
/// An optional DL pointer.
const DataLayout *DL;
/// An optional DT pointer.
DominatorTree *DT;
friend struct LVIValueHandle;
void insertResult(Value *Val, BasicBlock *BB, const LVILatticeVal &Result) {
SeenBlocks.insert(BB);
lookup(Val)[BB] = Result;
if (Result.isOverdefined())
OverDefinedCache.insert(std::make_pair(BB, Val));
}
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 solveBlockValueNonLocal(LVILatticeVal &BBLV,
Value *Val, BasicBlock *BB);
bool solveBlockValuePHINode(LVILatticeVal &BBLV,
PHINode *PN, BasicBlock *BB);
bool solveBlockValueConstantRange(LVILatticeVal &BBLV,
Instruction *BBI, BasicBlock *BB);
void mergeAssumeBlockValueConstantRange(Value *Val, LVILatticeVal &BBLV,
Instruction *BBI);
void solve();
ValueCacheEntryTy &lookup(Value *V) {
return ValueCache[LVIValueHandle(V, this)];
}
public:
/// getValueInBlock - 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);
/// getValueAt - 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);
/// getValueOnEdge - 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);
/// threadEdge - 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);
/// eraseBlock - This is part of the update interface to inform the cache
/// that a block has been deleted.
void eraseBlock(BasicBlock *BB);
/// clear - Empty the cache.
void clear() {
SeenBlocks.clear();
ValueCache.clear();
OverDefinedCache.clear();
}
LazyValueInfoCache(AssumptionTracker *AT,
const DataLayout *DL = nullptr,
DominatorTree *DT = nullptr) : AT(AT), DL(DL), DT(DT) {}
};
} // end anonymous namespace
void LVIValueHandle::deleted() {
typedef std::pair<AssertingVH<BasicBlock>, Value*> OverDefinedPairTy;
SmallVector<OverDefinedPairTy, 4> ToErase;
for (const OverDefinedPairTy &P : Parent->OverDefinedCache)
if (P.second == getValPtr())
ToErase.push_back(P);
for (const OverDefinedPairTy &P : ToErase)
Parent->OverDefinedCache.erase(P);
// This erasure deallocates *this, so it MUST happen after we're done
// using any and all members of *this.
Parent->ValueCache.erase(*this);
}
void LazyValueInfoCache::eraseBlock(BasicBlock *BB) {
// Shortcut if we have never seen this block.
DenseSet<AssertingVH<BasicBlock> >::iterator I = SeenBlocks.find(BB);
if (I == SeenBlocks.end())
return;
SeenBlocks.erase(I);
SmallVector<OverDefinedPairTy, 4> ToErase;
for (const OverDefinedPairTy& P : OverDefinedCache)
if (P.first == BB)
ToErase.push_back(P);
for (const OverDefinedPairTy &P : ToErase)
OverDefinedCache.erase(P);
for (std::map<LVIValueHandle, ValueCacheEntryTy>::iterator
I = ValueCache.begin(), E = ValueCache.end(); I != E; ++I)
I->second.erase(BB);
}
void LazyValueInfoCache::solve() {
while (!BlockValueStack.empty()) {
std::pair<BasicBlock*, Value*> &e = BlockValueStack.top();
assert(BlockValueSet.count(e) && "Stack value should be in BlockValueSet!");
if (solveBlockValue(e.second, e.first)) {
// The work item was completely processed.
assert(BlockValueStack.top() == e && "Nothing should have been pushed!");
assert(lookup(e.second).count(e.first) && "Result should be in cache!");
BlockValueStack.pop();
BlockValueSet.erase(e);
} else {
// More work needs to be done before revisiting.
assert(BlockValueStack.top() != e && "Stack should have been pushed!");
}
}
}
bool LazyValueInfoCache::hasBlockValue(Value *Val, BasicBlock *BB) {
// If already a constant, there is nothing to compute.
if (isa<Constant>(Val))
return true;
LVIValueHandle ValHandle(Val, this);
std::map<LVIValueHandle, ValueCacheEntryTy>::iterator I =
ValueCache.find(ValHandle);
if (I == ValueCache.end()) return false;
return I->second.count(BB);
}
LVILatticeVal LazyValueInfoCache::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);
SeenBlocks.insert(BB);
return lookup(Val)[BB];
}
bool LazyValueInfoCache::solveBlockValue(Value *Val, BasicBlock *BB) {
if (isa<Constant>(Val))
return true;
if (lookup(Val).count(BB)) {
// If we have a cached value, use that.
DEBUG(dbgs() << " reuse BB '" << BB->getName()
<< "' val=" << lookup(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;
Instruction *BBI = dyn_cast<Instruction>(Val);
if (!BBI || BBI->getParent() != BB) {
if (!solveBlockValueNonLocal(Res, Val, BB))
return false;
insertResult(Val, BB, Res);
return true;
}
if (PHINode *PN = dyn_cast<PHINode>(BBI)) {
if (!solveBlockValuePHINode(Res, PN, BB))
return false;
insertResult(Val, BB, Res);
return true;
}
if (AllocaInst *AI = dyn_cast<AllocaInst>(BBI)) {
Res = LVILatticeVal::getNot(ConstantPointerNull::get(AI->getType()));
insertResult(Val, BB, Res);
return true;
}
// We can only analyze the definitions of certain classes of instructions
// (integral binops and casts at the moment), so bail if this isn't one.
LVILatticeVal Result;
if ((!isa<BinaryOperator>(BBI) && !isa<CastInst>(BBI)) ||
!BBI->getType()->isIntegerTy()) {
DEBUG(dbgs() << " compute BB '" << BB->getName()
<< "' - overdefined because inst def found.\n");
Res.markOverdefined();
insertResult(Val, BB, Res);
return true;
}
// FIXME: We're currently limited to binops with a constant RHS. This should
// be improved.
BinaryOperator *BO = dyn_cast<BinaryOperator>(BBI);
if (BO && !isa<ConstantInt>(BO->getOperand(1))) {
DEBUG(dbgs() << " compute BB '" << BB->getName()
<< "' - overdefined because inst def found.\n");
Res.markOverdefined();
insertResult(Val, BB, Res);
return true;
}
if (!solveBlockValueConstantRange(Res, BBI, BB))
return false;
insertResult(Val, BB, Res);
return true;
}
static bool InstructionDereferencesPointer(Instruction *I, Value *Ptr) {
if (LoadInst *L = dyn_cast<LoadInst>(I)) {
return L->getPointerAddressSpace() == 0 &&
GetUnderlyingObject(L->getPointerOperand()) == Ptr;
}
if (StoreInst *S = dyn_cast<StoreInst>(I)) {
return S->getPointerAddressSpace() == 0 &&
GetUnderlyingObject(S->getPointerOperand()) == 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()) == Ptr)
return true;
if (MemTransferInst *MTI = dyn_cast<MemTransferInst>(MI))
if (MTI->getSourceAddressSpace() == 0)
if (GetUnderlyingObject(MTI->getRawSource()) == Ptr)
return true;
}
return false;
}
bool LazyValueInfoCache::solveBlockValueNonLocal(LVILatticeVal &BBLV,
Value *Val, BasicBlock *BB) {
LVILatticeVal Result; // Start Undefined.
// If this is a pointer, and there's a load from that pointer in this BB,
// then we know that the pointer can't be NULL.
bool NotNull = false;
if (Val->getType()->isPointerTy()) {
if (isKnownNonNull(Val)) {
NotNull = true;
} else {
Value *UnderlyingVal = GetUnderlyingObject(Val);
// If 'GetUnderlyingObject' didn't converge, skip it. It won't converge
// inside InstructionDereferencesPointer either.
if (UnderlyingVal == GetUnderlyingObject(UnderlyingVal, nullptr, 1)) {
for (Instruction &I : *BB) {
if (InstructionDereferencesPointer(&I, UnderlyingVal)) {
NotNull = true;
break;
}
}
}
}
}
// 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");
if (NotNull) {
PointerType *PTy = cast<PointerType>(Val->getType());
Result = LVILatticeVal::getNot(ConstantPointerNull::get(PTy));
} else {
Result.markOverdefined();
}
BBLV = Result;
return true;
}
// Loop over all of our predecessors, merging what we know from them into
// result.
bool EdgesMissing = false;
for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) {
LVILatticeVal EdgeResult;
EdgesMissing |= !getEdgeValue(Val, *PI, BB, EdgeResult);
if (EdgesMissing)
continue;
Result.mergeIn(EdgeResult);
// 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.\n");
// If we previously determined that this is a pointer that can't be null
// then return that rather than giving up entirely.
if (NotNull) {
PointerType *PTy = cast<PointerType>(Val->getType());
Result = LVILatticeVal::getNot(ConstantPointerNull::get(PTy));
}
BBLV = Result;
return true;
}
}
if (EdgesMissing)
return false;
// Return the merged value, which is more precise than 'overdefined'.
assert(!Result.isOverdefined());
BBLV = Result;
return true;
}
bool LazyValueInfoCache::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.
bool EdgesMissing = false;
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.
EdgesMissing |= !getEdgeValue(PhiVal, PhiBB, BB, EdgeResult, PN);
if (EdgesMissing)
continue;
Result.mergeIn(EdgeResult);
// 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.\n");
BBLV = Result;
return true;
}
}
if (EdgesMissing)
return false;
// Return the merged value, which is more precise than 'overdefined'.
assert(!Result.isOverdefined() && "Possible PHI in entry block?");
BBLV = Result;
return true;
}
static bool getValueFromFromCondition(Value *Val, ICmpInst *ICI,
LVILatticeVal &Result,
bool isTrueDest = true);
// If we can determine a constant range for the value Val in the context
// provided by the instruction BBI, then merge it into BBLV. If we did find a
// constant range, return true.
void LazyValueInfoCache::mergeAssumeBlockValueConstantRange(Value *Val,
LVILatticeVal &BBLV,
Instruction *BBI) {
BBI = BBI ? BBI : dyn_cast<Instruction>(Val);
if (!BBI)
return;
for (auto &I : AT->assumptions(BBI->getParent()->getParent())) {
if (!isValidAssumeForContext(I, BBI, DL, DT))
continue;
Value *C = I->getArgOperand(0);
if (ICmpInst *ICI = dyn_cast<ICmpInst>(C)) {
LVILatticeVal Result;
if (getValueFromFromCondition(Val, ICI, Result)) {
if (BBLV.isOverdefined())
BBLV = Result;
else
BBLV.mergeIn(Result);
}
}
}
}
bool LazyValueInfoCache::solveBlockValueConstantRange(LVILatticeVal &BBLV,
Instruction *BBI,
BasicBlock *BB) {
// Figure out the range of the LHS. If that fails, bail.
if (!hasBlockValue(BBI->getOperand(0), BB)) {
if (pushBlockValue(std::make_pair(BB, BBI->getOperand(0))))
return false;
BBLV.markOverdefined();
return true;
}
LVILatticeVal LHSVal = getBlockValue(BBI->getOperand(0), BB);
mergeAssumeBlockValueConstantRange(BBI->getOperand(0), LHSVal, BBI);
if (!LHSVal.isConstantRange()) {
BBLV.markOverdefined();
return true;
}
ConstantRange LHSRange = LHSVal.getConstantRange();
ConstantRange RHSRange(1);
IntegerType *ResultTy = cast<IntegerType>(BBI->getType());
if (isa<BinaryOperator>(BBI)) {
if (ConstantInt *RHS = dyn_cast<ConstantInt>(BBI->getOperand(1))) {
RHSRange = ConstantRange(RHS->getValue());
} else {
BBLV.markOverdefined();
return true;
}
}
// 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.
LVILatticeVal Result;
switch (BBI->getOpcode()) {
case Instruction::Add:
Result.markConstantRange(LHSRange.add(RHSRange));
break;
case Instruction::Sub:
Result.markConstantRange(LHSRange.sub(RHSRange));
break;
case Instruction::Mul:
Result.markConstantRange(LHSRange.multiply(RHSRange));
break;
case Instruction::UDiv:
Result.markConstantRange(LHSRange.udiv(RHSRange));
break;
case Instruction::Shl:
Result.markConstantRange(LHSRange.shl(RHSRange));
break;
case Instruction::LShr:
Result.markConstantRange(LHSRange.lshr(RHSRange));
break;
case Instruction::Trunc:
Result.markConstantRange(LHSRange.truncate(ResultTy->getBitWidth()));
break;
case Instruction::SExt:
Result.markConstantRange(LHSRange.signExtend(ResultTy->getBitWidth()));
break;
case Instruction::ZExt:
Result.markConstantRange(LHSRange.zeroExtend(ResultTy->getBitWidth()));
break;
case Instruction::BitCast:
Result.markConstantRange(LHSRange);
break;
case Instruction::And:
Result.markConstantRange(LHSRange.binaryAnd(RHSRange));
break;
case Instruction::Or:
Result.markConstantRange(LHSRange.binaryOr(RHSRange));
break;
// Unhandled instructions are overdefined.
default:
DEBUG(dbgs() << " compute BB '" << BB->getName()
<< "' - overdefined because inst def found.\n");
Result.markOverdefined();
break;
}
BBLV = Result;
return true;
}
bool getValueFromFromCondition(Value *Val, ICmpInst *ICI,
LVILatticeVal &Result, bool isTrueDest) {
if (ICI && isa<Constant>(ICI->getOperand(1))) {
if (ICI->isEquality() && ICI->getOperand(0) == Val) {
// We know that V has the RHS constant if this is a true SETEQ or
// false SETNE.
if (isTrueDest == (ICI->getPredicate() == ICmpInst::ICMP_EQ))
Result = LVILatticeVal::get(cast<Constant>(ICI->getOperand(1)));
else
Result = LVILatticeVal::getNot(cast<Constant>(ICI->getOperand(1)));
return true;
}
// Recognize the range checking idiom that InstCombine produces.
// (X-C1) u< C2 --> [C1, C1+C2)
ConstantInt *NegOffset = nullptr;
if (ICI->getPredicate() == ICmpInst::ICMP_ULT)
match(ICI->getOperand(0), m_Add(m_Specific(Val),
m_ConstantInt(NegOffset)));
ConstantInt *CI = dyn_cast<ConstantInt>(ICI->getOperand(1));
if (CI && (ICI->getOperand(0) == Val || NegOffset)) {
// Calculate the range of values that would satisfy the comparison.
ConstantRange CmpRange(CI->getValue());
ConstantRange TrueValues =
ConstantRange::makeICmpRegion(ICI->getPredicate(), CmpRange);
if (NegOffset) // Apply the offset from above.
TrueValues = TrueValues.subtract(NegOffset->getValue());
// If we're interested in the false dest, invert the condition.
if (!isTrueDest) TrueValues = TrueValues.inverse();
Result = LVILatticeVal::getRange(TrueValues);
return true;
}
}
return false;
}
/// \brief Compute the value of Val on the edge BBFrom -> BBTo. Returns false if
/// Val is not constrained on the edge.
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 maybe 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.
ICmpInst *ICI = dyn_cast<ICmpInst>(BI->getCondition());
if (getValueFromFromCondition(Val, ICI, Result, isTrueDest))
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(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 constraint Val.
bool LazyValueInfoCache::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;
}
if (getEdgeValueLocal(Val, BBFrom, BBTo, Result)) {
if (!Result.isConstantRange() ||
Result.getConstantRange().getSingleElement())
return true;
// FIXME: this check should be moved to the beginning of the function when
// LVI better supports recursive values. Even for the single value case, we
// can intersect to detect dead code (an empty range).
if (!hasBlockValue(Val, BBFrom)) {
if (pushBlockValue(std::make_pair(BBFrom, Val)))
return false;
Result.markOverdefined();
return true;
}
// Try to intersect ranges of the BB and the constraint on the edge.
LVILatticeVal InBlock = getBlockValue(Val, BBFrom);
mergeAssumeBlockValueConstantRange(Val, InBlock, BBFrom->getTerminator());
// See note on the use of the CxtI with mergeAssumeBlockValueConstantRange,
// and caching, below.
mergeAssumeBlockValueConstantRange(Val, InBlock, CxtI);
if (!InBlock.isConstantRange())
return true;
ConstantRange Range =
Result.getConstantRange().intersectWith(InBlock.getConstantRange());
Result = LVILatticeVal::getRange(Range);
return true;
}
if (!hasBlockValue(Val, BBFrom)) {
if (pushBlockValue(std::make_pair(BBFrom, Val)))
return false;
Result.markOverdefined();
return true;
}
// If we couldn't compute the value on the edge, use the value from the BB.
Result = getBlockValue(Val, BBFrom);
mergeAssumeBlockValueConstantRange(Val, Result, 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
// LazyValueInfoCache::getValueOnEdge, the context instruction is provided,
// but then the result is not cached.
mergeAssumeBlockValueConstantRange(Val, Result, CxtI);
return true;
}
LVILatticeVal LazyValueInfoCache::getValueInBlock(Value *V, BasicBlock *BB,
Instruction *CxtI) {
DEBUG(dbgs() << "LVI Getting block end value " << *V << " at '"
<< BB->getName() << "'\n");
assert(BlockValueStack.empty() && BlockValueSet.empty());
pushBlockValue(std::make_pair(BB, V));
solve();
LVILatticeVal Result = getBlockValue(V, BB);
mergeAssumeBlockValueConstantRange(V, Result, CxtI);
DEBUG(dbgs() << " Result = " << Result << "\n");
return Result;
}
LVILatticeVal LazyValueInfoCache::getValueAt(Value *V, Instruction *CxtI) {
DEBUG(dbgs() << "LVI Getting value " << *V << " at '"
<< CxtI->getName() << "'\n");
LVILatticeVal Result;
mergeAssumeBlockValueConstantRange(V, Result, CxtI);
DEBUG(dbgs() << " Result = " << Result << "\n");
return Result;
}
LVILatticeVal LazyValueInfoCache::
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 LazyValueInfoCache::threadEdge(BasicBlock *PredBB, 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);
DenseSet<Value*> ClearSet;
for (OverDefinedPairTy &P : OverDefinedCache)
if (P.first == OldSucc)
ClearSet.insert(P.second);
// 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;
bool changed = false;
for (Value *V : ClearSet) {
// If a value was marked overdefined in OldSucc, and is here too...
DenseSet<OverDefinedPairTy>::iterator OI =
OverDefinedCache.find(std::make_pair(ToUpdate, V));
if (OI == OverDefinedCache.end()) continue;
// Remove it from the caches.
ValueCacheEntryTy &Entry = ValueCache[LVIValueHandle(V, this)];
ValueCacheEntryTy::iterator CI = Entry.find(ToUpdate);
assert(CI != Entry.end() && "Couldn't find entry to update?");
Entry.erase(CI);
OverDefinedCache.erase(OI);
// If we removed anything, then we potentially need to update
// blocks successors too.
changed = true;
}
if (!changed) continue;
worklist.insert(worklist.end(), succ_begin(ToUpdate), succ_end(ToUpdate));
}
}
//===----------------------------------------------------------------------===//
// LazyValueInfo Impl
//===----------------------------------------------------------------------===//
/// getCache - This lazily constructs the LazyValueInfoCache.
static LazyValueInfoCache &getCache(void *&PImpl,
AssumptionTracker *AT,
const DataLayout *DL = nullptr,
DominatorTree *DT = nullptr) {
if (!PImpl)
PImpl = new LazyValueInfoCache(AT, DL, DT);
return *static_cast<LazyValueInfoCache*>(PImpl);
}
bool LazyValueInfo::runOnFunction(Function &F) {
AT = &getAnalysis<AssumptionTracker>();
DominatorTreeWrapperPass *DTWP =
getAnalysisIfAvailable<DominatorTreeWrapperPass>();
DT = DTWP ? &DTWP->getDomTree() : nullptr;
DataLayoutPass *DLP = getAnalysisIfAvailable<DataLayoutPass>();
DL = DLP ? &DLP->getDataLayout() : nullptr;
TLI = &getAnalysis<TargetLibraryInfo>();
if (PImpl)
getCache(PImpl, AT, DL, DT).clear();
// Fully lazy.
return false;
}
void LazyValueInfo::getAnalysisUsage(AnalysisUsage &AU) const {
AU.setPreservesAll();
AU.addRequired<AssumptionTracker>();
AU.addRequired<TargetLibraryInfo>();
}
void LazyValueInfo::releaseMemory() {
// If the cache was allocated, free it.
if (PImpl) {
delete &getCache(PImpl, AT);
PImpl = nullptr;
}
}
Constant *LazyValueInfo::getConstant(Value *V, BasicBlock *BB,
Instruction *CxtI) {
LVILatticeVal Result =
getCache(PImpl, AT, 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;
}
/// getConstantOnEdge - 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) {
LVILatticeVal Result =
getCache(PImpl, AT, 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 =
ICmpInst::makeConstantRange((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;
}
/// getPredicateOnEdge - 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) {
LVILatticeVal Result =
getCache(PImpl, AT, 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) {
LVILatticeVal Result =
getCache(PImpl, AT, DL, DT).getValueAt(V, CxtI);
return getPredicateResult(Pred, C, Result, DL, TLI);
}
void LazyValueInfo::threadEdge(BasicBlock *PredBB, BasicBlock *OldSucc,
BasicBlock *NewSucc) {
if (PImpl) getCache(PImpl, AT, DL, DT).threadEdge(PredBB, OldSucc, NewSucc);
}
void LazyValueInfo::eraseBlock(BasicBlock *BB) {
if (PImpl) getCache(PImpl, AT, DL, DT).eraseBlock(BB);
}
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