llvm-6502/lib/Analysis/LazyValueInfo.cpp

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//===- LazyValueInfo.cpp - Value constraint analysis ----------------------===//
//
// 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.
//
//===----------------------------------------------------------------------===//
#define DEBUG_TYPE "lazy-value-info"
#include "llvm/Analysis/LazyValueInfo.h"
#include "llvm/Constants.h"
#include "llvm/Instructions.h"
#include "llvm/Analysis/ConstantFolding.h"
#include "llvm/Target/TargetData.h"
#include "llvm/Support/CFG.h"
#include "llvm/Support/Debug.h"
#include "llvm/Support/raw_ostream.h"
#include "llvm/ADT/DenseMap.h"
#include "llvm/ADT/PointerIntPair.h"
#include "llvm/ADT/STLExtras.h"
using namespace llvm;
char LazyValueInfo::ID = 0;
static RegisterPass<LazyValueInfo>
X("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 LLVM Value has no known value yet.
undefined,
/// constant - This LLVM Value has a specific constant value.
constant,
/// notconstant - This LLVM value is known to not have the specified value.
notconstant,
/// overdefined - This instruction is not known to be constant, and we know
/// 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.
PointerIntPair<Constant *, 2, LatticeValueTy> Val;
public:
LVILatticeVal() : Val(0, undefined) {}
static LVILatticeVal get(Constant *C) {
LVILatticeVal Res;
Res.markConstant(C);
return Res;
}
static LVILatticeVal getNot(Constant *C) {
LVILatticeVal Res;
Res.markNotConstant(C);
return Res;
}
bool isUndefined() const { return Val.getInt() == undefined; }
bool isConstant() const { return Val.getInt() == constant; }
bool isNotConstant() const { return Val.getInt() == notconstant; }
bool isOverdefined() const { return Val.getInt() == overdefined; }
Constant *getConstant() const {
assert(isConstant() && "Cannot get the constant of a non-constant!");
return Val.getPointer();
}
Constant *getNotConstant() const {
assert(isNotConstant() && "Cannot get the constant of a non-notconstant!");
return Val.getPointer();
}
/// markOverdefined - Return true if this is a change in status.
bool markOverdefined() {
if (isOverdefined())
return false;
Val.setInt(overdefined);
return true;
}
/// markConstant - Return true if this is a change in status.
bool markConstant(Constant *V) {
if (isConstant()) {
assert(getConstant() == V && "Marking constant with different value");
return false;
}
assert(isUndefined());
Val.setInt(constant);
assert(V && "Marking constant with NULL");
Val.setPointer(V);
return true;
}
/// markNotConstant - Return true if this is a change in status.
bool markNotConstant(Constant *V) {
if (isNotConstant()) {
assert(getNotConstant() == V && "Marking !constant with different value");
return false;
}
if (isConstant())
assert(getConstant() != V && "Marking not constant with different value");
else
assert(isUndefined());
Val.setInt(notconstant);
assert(V && "Marking constant with NULL");
Val.setPointer(V);
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 (RHS.isNotConstant()) {
if (isNotConstant()) {
if (getNotConstant() != RHS.getNotConstant() ||
isa<ConstantExpr>(getNotConstant()) ||
isa<ConstantExpr>(RHS.getNotConstant()))
return markOverdefined();
return false;
}
if (isConstant()) {
if (getConstant() == RHS.getNotConstant() ||
isa<ConstantExpr>(RHS.getNotConstant()) ||
isa<ConstantExpr>(getConstant()))
return markOverdefined();
return markNotConstant(RHS.getNotConstant());
}
assert(isUndefined() && "Unexpected lattice");
return markNotConstant(RHS.getNotConstant());
}
// RHS must be a constant, we must be undef, constant, or notconstant.
if (isUndefined())
return markConstant(RHS.getConstant());
if (isConstant()) {
if (getConstant() != RHS.getConstant())
return markOverdefined();
return false;
}
// If we are known "!=4" and RHS is "==5", stay at "!=4".
if (getNotConstant() == RHS.getConstant() ||
isa<ConstantExpr>(getNotConstant()) ||
isa<ConstantExpr>(RHS.getConstant()))
return markOverdefined();
return false;
}
};
} // end anonymous namespace.
namespace llvm {
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() << '>';
return OS << "constant<" << *Val.getConstant() << '>';
}
}
//===----------------------------------------------------------------------===//
// LazyValueInfoCache Decl
//===----------------------------------------------------------------------===//
namespace {
/// LazyValueInfoCache - This is the cache kept by LazyValueInfo which
/// maintains information about queries across the clients' queries.
class LazyValueInfoCache {
public:
/// BlockCacheEntryTy - This is a computed lattice value at the end of the
/// specified basic block for a Value* that depends on context.
typedef std::pair<BasicBlock*, LVILatticeVal> BlockCacheEntryTy;
/// 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::vector<BlockCacheEntryTy> ValueCacheEntryTy;
private:
/// ValueCache - This is all of the cached information for all values,
/// mapped from Value* to key information.
DenseMap<Value*, ValueCacheEntryTy> ValueCache;
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);
/// 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);
};
} // end anonymous namespace
namespace {
struct BlockCacheEntryComparator {
static int Compare(const void *LHSv, const void *RHSv) {
const LazyValueInfoCache::BlockCacheEntryTy *LHS =
static_cast<const LazyValueInfoCache::BlockCacheEntryTy *>(LHSv);
const LazyValueInfoCache::BlockCacheEntryTy *RHS =
static_cast<const LazyValueInfoCache::BlockCacheEntryTy *>(RHSv);
if (LHS->first < RHS->first)
return -1;
if (LHS->first > RHS->first)
return 1;
return 0;
}
bool operator()(const LazyValueInfoCache::BlockCacheEntryTy &LHS,
const LazyValueInfoCache::BlockCacheEntryTy &RHS) const {
return LHS.first < RHS.first;
}
};
}
//===----------------------------------------------------------------------===//
// LVIQuery Impl
//===----------------------------------------------------------------------===//
namespace {
/// LVIQuery - This is a transient object that exists while a query is
/// being performed.
///
/// TODO: Reuse LVIQuery instead of recreating it for every query, this avoids
/// reallocation of the densemap on every query.
class LVIQuery {
typedef LazyValueInfoCache::BlockCacheEntryTy BlockCacheEntryTy;
typedef LazyValueInfoCache::ValueCacheEntryTy ValueCacheEntryTy;
/// This is the current value being queried for.
Value *Val;
/// This is all of the cached information about this value.
ValueCacheEntryTy &Cache;
/// NewBlocks - This is a mapping of the new BasicBlocks which have been
/// added to cache but that are not in sorted order.
DenseMap<BasicBlock*, LVILatticeVal> NewBlockInfo;
public:
LVIQuery(Value *V, ValueCacheEntryTy &VC) : Val(V), Cache(VC) {
}
~LVIQuery() {
// When the query is done, insert the newly discovered facts into the
// cache in sorted order.
if (NewBlockInfo.empty()) return;
// Grow the cache to exactly fit the new data.
Cache.reserve(Cache.size() + NewBlockInfo.size());
// If we only have one new entry, insert it instead of doing a full-on
// sort.
if (NewBlockInfo.size() == 1) {
BlockCacheEntryTy Entry = *NewBlockInfo.begin();
ValueCacheEntryTy::iterator I =
std::lower_bound(Cache.begin(), Cache.end(), Entry,
BlockCacheEntryComparator());
assert((I == Cache.end() || I->first != Entry.first) &&
"Entry already in map!");
Cache.insert(I, Entry);
return;
}
// TODO: If we only have two new elements, INSERT them both.
Cache.insert(Cache.end(), NewBlockInfo.begin(), NewBlockInfo.end());
array_pod_sort(Cache.begin(), Cache.end(),
BlockCacheEntryComparator::Compare);
}
LVILatticeVal getBlockValue(BasicBlock *BB);
LVILatticeVal getEdgeValue(BasicBlock *FromBB, BasicBlock *ToBB);
private:
LVILatticeVal &getCachedEntryForBlock(BasicBlock *BB);
};
} // end anonymous namespace
/// getCachedEntryForBlock - See if we already have a value for this block. If
/// so, return it, otherwise create a new entry in the NewBlockInfo map to use.
LVILatticeVal &LVIQuery::getCachedEntryForBlock(BasicBlock *BB) {
// Do a binary search to see if we already have an entry for this block in
// the cache set. If so, find it.
if (!Cache.empty()) {
ValueCacheEntryTy::iterator Entry =
std::lower_bound(Cache.begin(), Cache.end(),
BlockCacheEntryTy(BB, LVILatticeVal()),
BlockCacheEntryComparator());
if (Entry != Cache.end() && Entry->first == BB)
return Entry->second;
}
// Otherwise, check to see if it's in NewBlockInfo or create a new entry if
// not.
return NewBlockInfo[BB];
}
LVILatticeVal LVIQuery::getBlockValue(BasicBlock *BB) {
// See if we already have a value for this block.
LVILatticeVal &BBLV = getCachedEntryForBlock(BB);
// If we've already computed this block's value, return it.
if (!BBLV.isUndefined()) {
DEBUG(dbgs() << " reuse BB '" << BB->getName() << "' val=" << BBLV <<'\n');
return BBLV;
}
// Otherwise, this is the first time we're seeing this block. Reset the
// lattice value to overdefined, so that cycles will terminate and be
// conservatively correct.
BBLV.markOverdefined();
// If V is live into BB, see if our predecessors know anything about it.
Instruction *BBI = dyn_cast<Instruction>(Val);
if (BBI == 0 || BBI->getParent() != BB) {
LVILatticeVal Result; // Start Undefined.
unsigned NumPreds = 0;
// Loop over all of our predecessors, merging what we know from them into
// result.
for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) {
Result.mergeIn(getEdgeValue(*PI, BB));
// 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");
return Result;
}
++NumPreds;
}
// If this is the entry block, we must be asking about an argument. The
// value is overdefined.
if (NumPreds == 0 && BB == &BB->getParent()->front()) {
assert(isa<Argument>(Val) && "Unknown live-in to the entry block");
Result.markOverdefined();
return Result;
}
// Return the merged value, which is more precise than 'overdefined'.
assert(!Result.isOverdefined());
return getCachedEntryForBlock(BB) = Result;
}
// If this value is defined by an instruction in this block, we have to
// process it here somehow or return overdefined.
if (PHINode *PN = dyn_cast<PHINode>(BBI)) {
(void)PN;
// TODO: PHI Translation in preds.
} else {
}
DEBUG(dbgs() << " compute BB '" << BB->getName()
<< "' - overdefined because inst def found.\n");
LVILatticeVal Result;
Result.markOverdefined();
return getCachedEntryForBlock(BB) = Result;
}
/// getEdgeValue - This method attempts to infer more complex
LVILatticeVal LVIQuery::getEdgeValue(BasicBlock *BBFrom, BasicBlock *BBTo) {
// TODO: Handle more complex conditionals. If (v == 0 || v2 < 1) is false, we
// know that v != 0.
if (BranchInst *BI = dyn_cast<BranchInst>(BBFrom->getTerminator())) {
// If this is a conditional branch and only one successor goes to BBTo, then
// we 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)
return LVILatticeVal::get(ConstantInt::get(
Type::getInt1Ty(Val->getContext()), isTrueDest));
// If the condition of the branch is an equality comparison, we may be
// able to infer the value.
if (ICmpInst *ICI = dyn_cast<ICmpInst>(BI->getCondition()))
if (ICI->isEquality() && ICI->getOperand(0) == Val &&
isa<Constant>(ICI->getOperand(1))) {
// We know that V has the RHS constant if this is a true SETEQ or
// false SETNE.
if (isTrueDest == (ICI->getPredicate() == ICmpInst::ICMP_EQ))
return LVILatticeVal::get(cast<Constant>(ICI->getOperand(1)));
return LVILatticeVal::getNot(cast<Constant>(ICI->getOperand(1)));
}
}
}
// 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 BBTo is the default destination of the switch, we don't know anything.
// Given a more powerful range analysis we could know stuff.
if (SI->getCondition() == Val && SI->getDefaultDest() != BBTo) {
// We only know something if there is exactly one value that goes from
// BBFrom to BBTo.
unsigned NumEdges = 0;
ConstantInt *EdgeVal = 0;
for (unsigned i = 1, e = SI->getNumSuccessors(); i != e; ++i) {
if (SI->getSuccessor(i) != BBTo) continue;
if (NumEdges++) break;
EdgeVal = SI->getCaseValue(i);
}
assert(EdgeVal && "Missing successor?");
if (NumEdges == 1)
return LVILatticeVal::get(EdgeVal);
}
}
// Otherwise see if the value is known in the block.
return getBlockValue(BBFrom);
}
//===----------------------------------------------------------------------===//
// LazyValueInfoCache Impl
//===----------------------------------------------------------------------===//
LVILatticeVal LazyValueInfoCache::getValueInBlock(Value *V, BasicBlock *BB) {
// If already a constant, there is nothing to compute.
if (Constant *VC = dyn_cast<Constant>(V))
return LVILatticeVal::get(VC);
DEBUG(dbgs() << "LVI Getting block end value " << *V << " at '"
<< BB->getName() << "'\n");
LVILatticeVal Result = LVIQuery(V, ValueCache[V]).getBlockValue(BB);
DEBUG(dbgs() << " Result = " << Result << "\n");
return Result;
}
LVILatticeVal LazyValueInfoCache::
getValueOnEdge(Value *V, BasicBlock *FromBB, BasicBlock *ToBB) {
// If already a constant, there is nothing to compute.
if (Constant *VC = dyn_cast<Constant>(V))
return LVILatticeVal::get(VC);
DEBUG(dbgs() << "LVI Getting edge value " << *V << " from '"
<< FromBB->getName() << "' to '" << ToBB->getName() << "'\n");
LVILatticeVal Result =
LVIQuery(V, ValueCache[V]).getEdgeValue(FromBB, ToBB);
DEBUG(dbgs() << " Result = " << Result << "\n");
return Result;
}
//===----------------------------------------------------------------------===//
// LazyValueInfo Impl
//===----------------------------------------------------------------------===//
bool LazyValueInfo::runOnFunction(Function &F) {
TD = getAnalysisIfAvailable<TargetData>();
// Fully lazy.
return false;
}
/// getCache - This lazily constructs the LazyValueInfoCache.
static LazyValueInfoCache &getCache(void *&PImpl) {
if (!PImpl)
PImpl = new LazyValueInfoCache();
return *static_cast<LazyValueInfoCache*>(PImpl);
}
void LazyValueInfo::releaseMemory() {
// If the cache was allocated, free it.
if (PImpl) {
delete &getCache(PImpl);
PImpl = 0;
}
}
Constant *LazyValueInfo::getConstant(Value *V, BasicBlock *BB) {
LVILatticeVal Result = getCache(PImpl).getValueInBlock(V, BB);
if (Result.isConstant())
return Result.getConstant();
return 0;
}
/// 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) {
LVILatticeVal Result = getCache(PImpl).getValueOnEdge(V, FromBB, ToBB);
if (Result.isConstant())
return Result.getConstant();
return 0;
}
/// 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) {
LVILatticeVal Result = getCache(PImpl).getValueOnEdge(V, FromBB, ToBB);
// If we know the value is a constant, evaluate the conditional.
Constant *Res = 0;
if (Result.isConstant()) {
Res = ConstantFoldCompareInstOperands(Pred, Result.getConstant(), C, TD);
if (ConstantInt *ResCI = dyn_cast_or_null<ConstantInt>(Res))
return ResCI->isZero() ? False : True;
return 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, TD);
if (Res->isNullValue())
return False;
} else if (Pred == ICmpInst::ICMP_NE) {
// !C1 != C -> true iff C1 == C.
Res = ConstantFoldCompareInstOperands(ICmpInst::ICMP_NE,
Result.getNotConstant(), C, TD);
if (Res->isNullValue())
return True;
}
return Unknown;
}
return Unknown;
}