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